From cf1ad350ffd9ead7e4a6a54a65929be6c085ed12 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Fri, 9 Feb 2024 13:36:31 -0700
Subject: [PATCH 01/22] Makes Time::isStrftimeFormat() public

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Time.php | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/Sources/Time.php b/Sources/Time.php
index ddc449eaea..f1ffc4c98f 100644
--- a/Sources/Time.php
+++ b/Sources/Time.php
@@ -987,6 +987,17 @@ public static function getDateOrTimeFormat(string $type = '', string $format = '
 		return self::datetimePartialFormat($type, $format);
 	}
 
+	/**
+	 * Figures out whether the passed format is a strftime format.
+	 *
+	 * @param string $format The format string.
+	 * @return bool Whether it is a strftime format.
+	 */
+	public static function isStrftimeFormat(string $format): bool
+	{
+		return (bool) preg_match('/' . self::REGEX_STRFTIME . '/', $format);
+	}
+
 	/**
 	 * Backward compatibility wrapper for the format method.
 	 *
@@ -1275,17 +1286,6 @@ protected static function datetimePartialFormat(string $type, string $format): s
 
 		return self::$formats[$orig_format][$type];
 	}
-
-	/**
-	 * Figures out whether the passed format is a strftime format.
-	 *
-	 * @param string $format The format string.
-	 * @return bool Whether it is a strftime format.
-	 */
-	protected static function isStrftimeFormat(string $format): bool
-	{
-		return (bool) preg_match('/' . self::REGEX_STRFTIME . '/', $format);
-	}
 }
 
 ?>
\ No newline at end of file

From 9627ad8b6afc3cc75480485e74f57d3f0b6dc4dc Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Wed, 27 Dec 2023 19:11:46 -0700
Subject: [PATCH 02/22] Implements SMF\TimeInterval

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/TimeInterval.php | 277 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 277 insertions(+)
 create mode 100644 Sources/TimeInterval.php

diff --git a/Sources/TimeInterval.php b/Sources/TimeInterval.php
new file mode 100644
index 0000000000..ed1442e634
--- /dev/null
+++ b/Sources/TimeInterval.php
@@ -0,0 +1,277 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF;
+
+/**
+ * Extends \DateInterval with some extra features for SMF.
+ */
+class TimeInterval extends \DateInterval implements \Stringable
+{
+	/****************
+	 * Public methods
+	 ****************/
+
+	/**
+	 * Constructor.
+	 *
+	 * Like \DateInterval::__construct(), except that it can accept fractional
+	 * values for whatever the smallest unit is. In other words, it supports the
+	 * complete spec for ISO 8601 durations, not just a subset of the spec.
+	 *
+	 * @param string $duration An ISO 8601 duration string.
+	 */
+	public function __construct(string $duration)
+	{
+		// First, check for duration string (e.g. 'P1DT2H').
+		// Matches could be just 'P' if alt format was used.
+		$valid = preg_match('/P(?:(?P<y>[\d\.]+)Y)?(?:(?P<m>[\d\.]+)M)?(?:(?P<w>[\d\.]+)W)?(?:(?P<d>[\d\.]+)D)?(?:T(?:(?P<h>[\d\.]+)H)?(?:(?P<i>[\d\.]+)M)?(?:(?P<s>[\d\.]+)S)?)?/', $duration, $matches) && $matches[0] !== 'P';
+
+		// Next, check for alt format (e.g. 'P0000-00-01T02:00:00').
+		if (!$valid) {
+			$valid = preg_match('/P(?P<y>\d+)-?(?P<m>\d+)-?(?P<w>\d+)-?(?P<d>\d+)T(?P<h>\d+):?(?P<i>\d+):?(?P<s>[\d\.]+)/', $duration, $matches);
+		}
+
+		if (!$valid) {
+			throw new \ValueError();
+		}
+
+		// Clean up $matches.
+		$matches = array_map(
+			// Quick way to cast to int or float without extra logic.
+			fn ($v) => $v + 0,
+			// Filter out the stuff we don't need.
+			array_filter(
+				$matches,
+				fn ($v, $k) => !is_int($k) && $v !== '',
+				ARRAY_FILTER_USE_BOTH,
+			),
+		);
+
+		// For simplicity, convert weeks to days.
+		if (!empty($matches['w'])) {
+			$matches['d'] = ($matches['d'] ?? 0) + $matches['w'] * 7;
+			unset($matches['w']);
+		}
+
+		// Figure out if we have any fractional values.
+		$frac = [
+			'prop' => null,
+			'value' => null,
+		];
+
+		$props = [
+			's' => [
+				'frac_prop' => 'f',
+				'multiplier' => 1,
+				'unit' => 'S',
+			],
+			'i' => [
+				'frac_prop' => 's',
+				'multiplier' => 60,
+				'unit' => 'M',
+			],
+			'h' => [
+				'frac_prop' => 'i',
+				'multiplier' => 60,
+				'unit' => 'H',
+			],
+			'd' => [
+				'frac_prop' => 'h',
+				'multiplier' => 24,
+				'unit' => 'D',
+			],
+			'm' => [
+				'frac_prop' => 'd',
+				// This is calibrated so that 'P0.5M' means 'P15D' but 'P0.99M' means 'P28D'.
+				'multiplier' => !isset($matches['m']) || fmod($matches['m'], 1.0) <= 0.5 ? 30 : 32 - (4 * fmod($matches['m'], 1.0)),
+				'unit' => 'M',
+			],
+			'y' => [
+				'frac_prop' => 'm',
+				'multiplier' => 12,
+				'unit' => 'Y',
+			],
+		];
+
+		$can_be_fractional = true;
+
+		foreach ($props as $prop => $info) {
+			if (!isset($matches[$prop])) {
+				continue;
+			}
+
+			if (is_float($matches[$prop])) {
+				if (!$can_be_fractional) {
+					throw new \ValueError();
+				}
+
+				$frac['prop'] = $info['frac_prop'];
+				$frac['value'] = round(($matches[$prop] - (int) $matches[$prop]) * $info['multiplier'], 6);
+
+				$matches[$prop] = (int) $matches[$prop];
+			}
+
+			// ISO 8601 only allows the smallest provided unit to be fractional.
+			$can_be_fractional = false;
+		}
+
+		if (!isset($frac['prop'])) {
+			// If we have no fractional values, construction is easy.
+			parent::__construct($duration);
+		} else {
+			// Rebuild $duration without the fractional value.
+			$duration = 'P';
+
+			foreach (array_reverse($props) as $prop => $info) {
+				if ($prop === 'h') {
+					$duration .= 'T';
+				}
+
+				if (!empty($matches[$prop])) {
+					$duration .= $matches[$prop] . $info['unit'];
+				}
+			}
+
+			// Construct.
+			parent::__construct(rtrim($duration, 'PT'));
+
+			// Finally, set the fractional value.
+			$this->{$frac['prop']} += $frac['value'];
+		}
+	}
+
+	/**
+	 * Formats the object as a string so it can be reconstructed later.
+	 *
+	 * @return string A ISO 8601 duration string suitable for reconstructing
+	 *    this object.
+	 */
+	public function __toString(): string
+	{
+		$format = 'P';
+
+		foreach (['y', 'm', 'd', 'h', 'i', 's'] as $prop) {
+			if ($prop === 'h') {
+				$format .= 'T';
+			}
+
+			if (!empty($this->{$prop}) || ($prop === 's' && !empty($this->f))) {
+				$format .= '%' . $prop . ($prop === 'i' ? 'M' : strtoupper($prop));
+			}
+		}
+
+		$string = rtrim($this->format($format), 'PT');
+
+		if ($string === '') {
+			$string = 'PT0S';
+		}
+
+		if (!empty($this->f)) {
+			$string = preg_replace_callback('/\d+(?=S)/', fn ($m) => $m[0] + $this->f, $string);
+		}
+
+		return $string;
+	}
+
+	/**
+	 * Formats the object as a string that can be parsed by strtotime().
+	 *
+	 * @return string A strtotime parsable string suitable for reconstructing
+	 *    this object.
+	 */
+	public function toParsable(): string
+	{
+		$result = [];
+
+		$props = [
+			'invert' => null,
+			'y' => 'years',
+			'm' => 'months',
+			'd' => 'days',
+			'h' => 'hours',
+			'i' => 'minutes',
+			's' => 'seconds',
+			'f' => 'microseconds',
+		];
+
+		foreach ($props as $prop => $string) {
+			if (empty($this->{$prop})) {
+				continue;
+			}
+
+			switch ($prop) {
+				case 'invert':
+					$result[] = '-';
+					break;
+
+				default:
+					$result[] = $this->format('%' . $prop) . ' ' . $string;
+					break;
+			}
+		}
+
+		if (empty($result)) {
+			$result[] = '0 seconds';
+		}
+
+		return implode(' ', $result);
+	}
+
+	/**
+	 * Converts this interval to a number of seconds.
+	 *
+	 * Because months have variable lengths, leap years exist, etc., it is
+	 * necessary to provide a reference date that the interval will measure
+	 * from in order to calculate the exact number of seconds.
+	 *
+	 * @param \DateTimeInterface $when Reference date that this interval will
+	 *    be added to in order to calculate the exact number of seconds.
+	 * @return int|float Number of seconds in this interval, counting from the
+	 *    reference date.
+	 */
+	public function toSeconds(\DateTimeInterface $when): int|float
+	{
+		$later = \DateTime::createFromInterface($when);
+		$later->add($this);
+
+		$fmt = !empty($this->f) ? 'U.u' : 'U';
+
+		return ($later->format($fmt) - $when->format($fmt));
+	}
+
+	/***********************
+	 * Public static methods
+	 ***********************/
+
+	/**
+	 * Convert a \DateInterval object into a TimeInterval object.
+	 *
+	 * @param string $object A \DateInterval object.
+	 * @return TimeInterval A TimeInterval object.
+	 */
+	public static function createFromDateInterval(\DateInterval $object): static
+	{
+		$new = new TimeInterval('P0D');
+
+		foreach (['y', 'm', 'd', 'h', 'i', 's', 'f', 'invert'] as $prop) {
+			$new->{$prop} = $object->{$prop};
+		}
+
+		return $new;
+	}
+}
+
+?>
\ No newline at end of file

From 7f48a4cf6bfeb3f4a6cf4d7a00acab3fb8f4ead5 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Thu, 7 Dec 2023 11:44:02 -0700
Subject: [PATCH 03/22] Kill off the deprecated 'span' event property

It's a relic from before the calendar supported times, it doesn't work reliably for events with times, and even for all-day events its behaviour can be somewhat odd.
Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Event.php | 80 +++++++++++------------------------------------
 1 file changed, 18 insertions(+), 62 deletions(-)

diff --git a/Sources/Event.php b/Sources/Event.php
index ce8361b54f..e0152ba320 100644
--- a/Sources/Event.php
+++ b/Sources/Event.php
@@ -570,11 +570,6 @@ public function __set(string $prop, mixed $value): void
 
 					break;
 
-				case 'span':
-				case 'num_days':
-					$this->setNumDays($value);
-					break;
-
 				// These computed properties are read-only.
 				case 'tz_abbrev':
 				case 'new':
@@ -722,11 +717,6 @@ public function __get(string $prop): mixed
 				$value = $this->start->tz_abbrev;
 				break;
 
-			case 'span':
-			case 'num_days':
-				$value = $this->getNumDays();
-				break;
-
 			case 'new':
 				$value = !isset($this->id) || $this->id < 1;
 				break;
@@ -833,10 +823,6 @@ public function __isset(string $prop): bool
 			case 'end_iso_gmdate':
 				return property_exists($this, 'end');
 
-			case 'span':
-			case 'num_days':
-				return property_exists($this, 'start') && property_exists($this, 'end');
-
 			case 'new':
 			case 'is_selected':
 			case 'href':
@@ -1087,48 +1073,6 @@ public static function remove(int $id): void
 	 * Internal methods
 	 ******************/
 
-	/**
-	 * Gets the number of days across which this event occurs.
-	 *
-	 * For example, if the event starts and ends on the same day, span is 1.
-	 * If the event starts Monday night and ends Wednesday morning, span is 3.
-	 *
-	 * @return int Number of days that this event spans, or 0 on error.
-	 */
-	protected function getNumDays(): int
-	{
-		if (!($this->start instanceof \DateTimeInterface) || !($this->end instanceof \DateTimeInterface) || $this->end->getTimestamp() < $this->start->getTimestamp()) {
-			return 0;
-		}
-
-		return ((int) $this->start->diff($this->end)->format('%a')) + ($this->end->format('H') < $this->start->format('H') ? 2 : 1);
-	}
-
-	/**
-	 * Adjusts the end date so that the number of days across which this event
-	 * occurs will be $num_days.
-	 *
-	 * @param int $num_days The target number of days the event should span.
-	 *    If $num_days is set to a value less than 1, no change will be made.
-	 *    This method imposes no upper limit on $num_days, but if $num_days
-	 *    exceeds the value of Config::$modSettings['cal_maxspan'], other parts
-	 *    of this class will impose that limit.
-	 */
-	protected function setNumDays(int $num_days): void
-	{
-		if (!($this->start instanceof \DateTimeInterface) || !($this->end instanceof \DateTimeInterface) || $num_days < 1) {
-			return;
-		}
-
-		$current_span = $this->getNumDays();
-
-		if ($current_span == $num_days) {
-			return;
-		}
-
-		$this->end->modify($current_span < $num_days ? '+' : '-' . ($num_days - $current_span) . ' days');
-	}
-
 	/**
 	 * Ensures that the start and end dates have a sane relationship.
 	 */
@@ -1145,8 +1089,8 @@ protected function fixEndDate(): void
 		}
 
 		// If the event is too long, cap it at the max.
-		if (!empty(Config::$modSettings['cal_maxspan']) && $this->getNumDays() > Config::$modSettings['cal_maxspan']) {
-			$this->setNumDays(Config::$modSettings['cal_maxspan']);
+		if (!empty(Config::$modSettings['cal_maxspan']) && $this->start->diff($this->end)->format('%a') > Config::$modSettings['cal_maxspan']) {
+			$this->end = (clone $this->start)->modify('+' . Config::$modSettings['cal_maxspan'] . ' days');
 		}
 	}
 
@@ -1432,15 +1376,27 @@ function ($key) {
 		}
 
 		// Make sure we use valid values for everything
-		if (!isset($input['end_date'])) {
-			$input['end_date'] = $input['start_date'];
-		}
-
 		if ($input['allday'] || !isset($input['start_time'])) {
 			$input['allday'] = true;
 			$input['start_time'] = '00:00:00';
 		}
 
+		if (!isset($input['end_date'])) {
+			if (isset($input['span'])) {
+				$start = new \DateTimeImmutable($input['start_date'] . (empty($input['allday']) ? ' ' . $input['start_time'] . ' ' .  $input['timezone'] : ''));
+
+				$end = $start->modify('+' . max(0, (int) ($input['span'] - 1)) . ' days');
+
+				$input['end_date'] = $end->format('Y-m-d');
+
+				if (!$input['allday']) {
+					$input['end_time'] = $end->format('H:i:s');
+				}
+			} else {
+				$input['end_date'] = $input['start_date'];
+			}
+		}
+
 		if ($input['allday'] || !isset($input['end_time'])) {
 			$input['allday'] = true;
 			$input['end_time'] = $input['start_time'];

From 6b0aa4b3684b1a4dcaae7b682e3d6e102a09bac8 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Thu, 7 Dec 2023 12:54:13 -0700
Subject: [PATCH 04/22] Moves SMF\Event to SMF\Calendar\Event

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Actions/Calendar.php     |  2 +-
 Sources/Actions/Display.php      |  2 +-
 Sources/Actions/Post.php         |  4 +--
 Sources/Actions/Post2.php        |  2 +-
 Sources/{ => Calendar}/Event.php | 42 +++++++++++++++++++-------------
 Sources/Calendar/index.php       |  9 +++++++
 6 files changed, 39 insertions(+), 22 deletions(-)
 rename Sources/{ => Calendar}/Event.php (97%)
 create mode 100644 Sources/Calendar/index.php

diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index 38a3a4bfdd..6a03dcf0f3 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -18,10 +18,10 @@
 use SMF\Board;
 use SMF\BrowserDetector;
 use SMF\Cache\CacheApi;
+use SMF\Calendar\Event;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
 use SMF\ErrorHandler;
-use SMF\Event;
 use SMF\IntegrationHook;
 use SMF\Lang;
 use SMF\Theme;
diff --git a/Sources/Actions/Display.php b/Sources/Actions/Display.php
index c234039183..32979cb5aa 100644
--- a/Sources/Actions/Display.php
+++ b/Sources/Actions/Display.php
@@ -19,11 +19,11 @@
 use SMF\Attachment;
 use SMF\Board;
 use SMF\Cache\CacheApi;
+use SMF\Calendar\Event;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
 use SMF\Editor;
 use SMF\ErrorHandler;
-use SMF\Event;
 use SMF\IntegrationHook;
 use SMF\Lang;
 use SMF\Msg;
diff --git a/Sources/Actions/Post.php b/Sources/Actions/Post.php
index 55f690b3c7..c9171e8ce6 100644
--- a/Sources/Actions/Post.php
+++ b/Sources/Actions/Post.php
@@ -19,12 +19,12 @@
 use SMF\BBCodeParser;
 use SMF\Board;
 use SMF\Cache\CacheApi;
+use SMF\Calendar\Event;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
 use SMF\Draft;
 use SMF\Editor;
 use SMF\ErrorHandler;
-use SMF\Event;
 use SMF\IntegrationHook;
 use SMF\Lang;
 use SMF\Msg;
@@ -732,7 +732,7 @@ protected function initiateEvent(): void
 
 		// Start loading up the event info.
 		if (isset($_REQUEST['eventid'])) {
-			list(Utils::$context['event']) = Event::load((int) $_REQUEST['eventid']);
+			Utils::$context['event'] = current(Event::load((int) $_REQUEST['eventid']));
 		}
 
 		if (!isset(Utils::$context['event']) || !(Utils::$context['event'] instanceof Event)) {
diff --git a/Sources/Actions/Post2.php b/Sources/Actions/Post2.php
index ba0714c164..86eb07f19a 100644
--- a/Sources/Actions/Post2.php
+++ b/Sources/Actions/Post2.php
@@ -20,11 +20,11 @@
 use SMF\Board;
 use SMF\BrowserDetector;
 use SMF\Cache\CacheApi;
+use SMF\Calendar\Event;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
 use SMF\Draft;
 use SMF\ErrorHandler;
-use SMF\Event;
 use SMF\IntegrationHook;
 use SMF\Lang;
 use SMF\Logging;
diff --git a/Sources/Event.php b/Sources/Calendar/Event.php
similarity index 97%
rename from Sources/Event.php
rename to Sources/Calendar/Event.php
index e0152ba320..8246f58585 100644
--- a/Sources/Event.php
+++ b/Sources/Calendar/Event.php
@@ -13,10 +13,18 @@
 
 declare(strict_types=1);
 
-namespace SMF;
+namespace SMF\Calendar;
 
 use SMF\Actions\Calendar;
+use SMF\ArrayAccessHelper;
+use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
+use SMF\ErrorHandler;
+use SMF\IntegrationHook;
+use SMF\Time;
+use SMF\TimeZone;
+use SMF\User;
+use SMF\Utils;
 
 /**
  * Represents a calendar event.
@@ -845,7 +853,7 @@ public function __isset(string $prop): bool
 	/**
 	 * Loads events by ID number or by topic.
 	 *
-	 * @param int|array $id ID number of the event or topic.
+	 * @param int $id ID number of the event or topic.
 	 * @param bool $is_topic If true, $id is the topic ID. Default: false.
 	 * @param bool $use_permissions Whether to use permissions. Default: true.
 	 * @return array|bool Instances of this class for the loaded events.
@@ -1292,21 +1300,21 @@ protected static function standardizeEventOptions(array $input): array
 
 		$input['timezone'] = $tz->getName();
 
-		foreach (['start', 'end'] as $var) {
+		foreach (['start', 'end'] as $prefix) {
 			// Input might come as individual parameters...
-			$year = $input[$var . '_year'] ?? null;
-			$month = $input[$var . '_month'] ?? null;
-			$day = $input[$var . '_day'] ?? null;
-			$hour = $input[$var . '_hour'] ?? null;
-			$minute = $input[$var . '_minute'] ?? null;
-			$second = $input[$var . '_second'] ?? null;
+			$year = $input[$prefix . '_year'] ?? null;
+			$month = $input[$prefix . '_month'] ?? null;
+			$day = $input[$prefix . '_day'] ?? null;
+			$hour = $input[$prefix . '_hour'] ?? null;
+			$minute = $input[$prefix . '_minute'] ?? null;
+			$second = $input[$prefix . '_second'] ?? null;
 
 			// ... or as datetime strings ...
-			$datetime_string = $input[$var . '_datetime'] ?? null;
+			$datetime_string = $input[$prefix . '_datetime'] ?? null;
 
 			// ... or as date strings and time strings.
-			$date_string = $input[$var . '_date'] ?? null;
-			$time_string = $input[$var . '_time'] ?? null;
+			$date_string = $input[$prefix . '_date'] ?? null;
+			$time_string = $input[$prefix . '_time'] ?? null;
 
 			// If the date and time were given in individual parameters, combine them.
 			if (empty($time_string) && isset($hour, $minute, $second)) {
@@ -1357,16 +1365,16 @@ function ($key) {
 			$time_is_valid = isset($hour, $minute, $second) && $hour >= 0 && $hour < 25 && $minute >= 0 && $minute < 60 && $second >= 0 && $second < 60;
 
 			// Replace whatever was supplied with our validated strings.
-			foreach (['year', 'month', 'day', 'hour', 'minute', 'second', 'date', 'time', 'datetime'] as $key) {
-				unset($input[$var . '_' . $key]);
+			foreach (['year', 'month', 'day', 'hour', 'minute', 'second', 'date', 'time', 'datetime'] as $var) {
+				unset($input[$prefix . '_' . $var]);
 			}
 
 			if ($date_is_valid) {
-				$input[$var . '_date'] = sprintf('%04d-%02d-%02d', $year, $month, $day);
+				$input[$prefix . '_date'] = sprintf('%04d-%02d-%02d', $year, $month, $day);
 			}
 
 			if ($time_is_valid && !$input['allday']) {
-				$input[$var . '_time'] = sprintf('%02d:%02d:%02d', $hour, $minute, $second);
+				$input[$prefix . '_time'] = sprintf('%02d:%02d:%02d', $hour, $minute, $second);
 			}
 		}
 
@@ -1383,7 +1391,7 @@ function ($key) {
 
 		if (!isset($input['end_date'])) {
 			if (isset($input['span'])) {
-				$start = new \DateTimeImmutable($input['start_date'] . (empty($input['allday']) ? ' ' . $input['start_time'] . ' ' .  $input['timezone'] : ''));
+				$start = new \DateTimeImmutable($input['start_date'] . (empty($input['allday']) ? ' ' . $input['start_time'] . ' ' . $input['timezone'] : ''));
 
 				$end = $start->modify('+' . max(0, (int) ($input['span'] - 1)) . ' days');
 
diff --git a/Sources/Calendar/index.php b/Sources/Calendar/index.php
new file mode 100644
index 0000000000..976d292448
--- /dev/null
+++ b/Sources/Calendar/index.php
@@ -0,0 +1,9 @@
+<?php
+
+// Try to handle it with the upper level index.php. (it should know what to do.)
+if (file_exists(dirname(__DIR__) . '/index.php'))
+	include (dirname(__DIR__) . '/index.php');
+else
+	exit;
+
+?>
\ No newline at end of file

From 28deff237ece56737903c6c27f94c622b98702ba Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Thu, 7 Dec 2023 13:14:35 -0700
Subject: [PATCH 05/22] Support displaying multiple events attached to one
 topic

UI doesn't yet support adding multiple events to a topic, but that can come later.

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Calendar/Event.php          |  3 +--
 Themes/default/Display.template.php |  2 +-
 Themes/default/css/index.css        | 11 +++++++++++
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index 8246f58585..e213f17056 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -869,7 +869,6 @@ public static function load(int $id, bool $is_topic = false, bool $use_permissio
 		self::$keep_all = true;
 
 		$query_customizations['where'][] = 'cal.id_' . ($is_topic ? 'topic' : 'event') . ' = {int:id}';
-		$query_customizations['limit'] = 1;
 		$query_customizations['params']['id'] = $id;
 
 		if ($use_permissions) {
@@ -947,7 +946,7 @@ public static function get(string $low_date, string $high_date, bool $use_permis
 			'cal.start_date <= {date:high_date}',
 			'cal.end_date >= {date:low_date}',
 		];
-		$order = $query_customizations['order'] ?? [];
+		$order = $query_customizations['order'] ?? ['cal.start_date'];
 		$group = $query_customizations['group'] ?? [];
 		$limit = $query_customizations['limit'] ?? 0;
 		$params = $query_customizations['params'] ?? [
diff --git a/Themes/default/Display.template.php b/Themes/default/Display.template.php
index 68fbed9667..56864dc583 100644
--- a/Themes/default/Display.template.php
+++ b/Themes/default/Display.template.php
@@ -180,7 +180,7 @@ function template_main()
 		<div class="title_bar">
 			<h3 class="titlebg">', Lang::$txt['calendar_linked_events'], '</h3>
 		</div>
-		<div class="information">
+		<div class="information events">
 			<ul>';
 
 		foreach (Utils::$context['linked_calendar_events'] as $event)
diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index 3493cbb612..8eb939e6bf 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -3796,6 +3796,17 @@ h3.titlebg, h4.titlebg, .titlebg, h3.subbg, h4.subbg, .subbg {
 p.information img {
 	vertical-align: middle;
 }
+.information.events {
+	padding: 0;
+}
+.information.events ul {
+	display: flex;
+	flex-flow: row wrap;
+}
+.information.events li {
+	margin: 12px;
+	flex: 1 0 auto;
+}
 #messageindex .information {
 	border-radius: 0;
 	margin: 0;

From 57363c58df59fe7c7e08155c7d991bdcd10d16c4 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Thu, 7 Dec 2023 13:06:12 -0700
Subject: [PATCH 06/22] Implements SMF\Calendar\RRule and
 SMF\Calendar\RecurrenceIterator

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Calendar/RRule.php              |  520 +++++++
 Sources/Calendar/RecurrenceIterator.php | 1658 +++++++++++++++++++++++
 2 files changed, 2178 insertions(+)
 create mode 100644 Sources/Calendar/RRule.php
 create mode 100644 Sources/Calendar/RecurrenceIterator.php

diff --git a/Sources/Calendar/RRule.php b/Sources/Calendar/RRule.php
new file mode 100644
index 0000000000..79ccdcc68f
--- /dev/null
+++ b/Sources/Calendar/RRule.php
@@ -0,0 +1,520 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF\Calendar;
+
+/**
+ * Represents a recurrence rule from RFC 5545.
+ */
+class RRule implements \Stringable
+{
+	/*****************
+	 * Class constants
+	 *****************/
+
+	/**
+	 * @var array
+	 *
+	 * Recurrence frequencies defined in RFC 5545.
+	 */
+	public const FREQUENCIES = [
+		'YEARLY',
+		'MONTHLY',
+		'WEEKLY',
+		'DAILY',
+		'HOURLY',
+		'MINUTELY',
+		'SECONDLY',
+	];
+
+	/**
+	 * @var array
+	 *
+	 * Weekday abbreviations defined in RFC 5545.
+	 *
+	 * The order of the elements matters. Do not change it.
+	 */
+	public const WEEKDAYS = [
+		'MO', 'TU', 'WE', 'TH', 'FR', 'SA', 'SU',
+	];
+
+	/**
+	 * @var array
+	 *
+	 * PHP time zone names that are synonymous with UTC.
+	 */
+	public const UTC_SYNONYMS = [
+		'UTC',
+		'GMT',
+		'GMT+0',
+		'GMT-0',
+		'GMT0',
+		'Greenwich',
+		'UCT',
+		'Universal',
+		'Zulu',
+		'Z',
+		'Etc/GMT',
+		'Etc/GMT+0',
+		'Etc/GMT-0',
+		'Etc/GMT0',
+		'Etc/Greenwich',
+		'Etc/UCT',
+		'Etc/Universal',
+		'Etc/UTC',
+		'Etc/Zulu',
+	];
+
+	/*******************
+	 * Public properties
+	 *******************/
+
+	/**
+	 * @var string
+	 *
+	 * The base frequency of this recurrence rule.
+	 *
+	 * Must be one of the values of self::FREQUENCIES.
+	 */
+	public string $freq;
+
+	/**
+	 * @var int
+	 *
+	 * The value of the recurrence rule's INTERVAL part.
+	 *
+	 * Defaults to 1 if the INTERVAL part is not present.
+	 */
+	public int $interval = 1;
+
+	/**
+	 * @var \DateTimeInterface
+	 *
+	 * When the recurrence ends.
+	 */
+	public \DateTimeInterface $until;
+
+	/**
+	 * @var int
+	 *
+	 * Whether UNTIL is a normal, floating, or all day event type.
+	 *
+	 * Normal means it has a date, a time, and a time zone.
+	 * Floating means it has a date and a time, but no time zone.
+	 * All day means it has a date, but neither a time nor a time zone.
+	 *
+	 * Value must be one of the RecurrenceIterator::TYPE_* constants
+	 */
+	public int $until_type;
+
+	/**
+	 * @var int
+	 *
+	 * The value of the recurrence rule's COUNT part, if present.
+	 */
+	public int $count;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYMONTH part, if present.
+	 */
+	public array $bymonth;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYWEEKNO part, if present.
+	 */
+	public array $byweekno;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYYEARDAY part, if present.
+	 */
+	public array $byyearday;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYMONTHDAY part, if present.
+	 */
+	public array $bymonthday;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYDAY part, if present.
+	 */
+	public array $byday;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYHOUR part, if present.
+	 */
+	public array $byhour;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYMINUTE part, if present.
+	 */
+	public array $byminute;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYSECOND part, if present.
+	 */
+	public array $bysecond;
+
+	/**
+	 * @var array
+	 *
+	 * Values extracted from the recurrence rule's BYSETPOS part, if present.
+	 */
+	public array $bysetpos;
+
+	/**
+	 * @var string
+	 *
+	 * The value of the recurrence rule's WKST part, if present.
+	 */
+	public string $wkst = 'MO';
+
+	/****************
+	 * Public methods
+	 ****************/
+
+	/**
+	 * Constructor.
+	 *
+	 * @param string $rrule An RRule string.
+	 */
+	public function __construct(string $rrule)
+	{
+		// Drop the leading 'RRULE:', if present.
+		$rrule = preg_replace('/^RRULE:/i', '', $rrule);
+
+		// The FREQ part is required.
+		if (!str_contains($rrule, 'FREQ=')) {
+			throw new \ValueError();
+		}
+
+		// Parse the RRule into an associative array.
+		parse_str(strtr($rrule, ';', substr(ini_get('arg_separator.input'), 0, 1)), $rrule);
+
+		// Set initial values of properties.
+		foreach ($rrule as $prop => $value) {
+			$prop = strtolower($prop);
+
+			switch ($prop) {
+				case 'freq':
+					$value = strtoupper($value);
+
+					if (!in_array($value, self::FREQUENCIES)) {
+						continue 2;
+					}
+
+					break;
+
+				case 'wkst':
+					$value = strtoupper($value);
+
+					if (!in_array($value, self::WEEKDAYS)) {
+						continue 2;
+					}
+
+					break;
+
+				case 'until':
+					if (strpos($value, 'TZID') !== false) {
+						foreach (explode(':', $value) as $value_part) {
+							if (strpos($value_part, 'TZID') !== false) {
+								$tzid = str_replace('TZID=', '', $value_part);
+
+								if (in_array($tzid, self::UTC_SYNONYMS)) {
+									$tzid = 'UTC';
+								}
+
+								try {
+									$tz = new \DateTimeZone($tzid);
+								} catch (\Throwable $e) {
+									continue 3;
+								}
+							} else {
+								$value = $value_part;
+							}
+						}
+
+						$value = (new \DateTimeImmutable(substr($value, 0, -1), $tz))->setTimezone(new \DateTimeZone('UTC'));
+
+						$this->until_type = RecurrenceIterator::TYPE_ABSOLUTE;
+					} elseif (substr($value, -1) === 'Z') {
+						$value = new \DateTimeImmutable(substr($value, 0, -1), new \DateTimeZone('UTC'));
+
+						$this->until_type = RecurrenceIterator::TYPE_ABSOLUTE;
+					} else {
+						$this->until_type = strpos($value, 'T') !== false ? RecurrenceIterator::TYPE_FLOATING : RecurrenceIterator::TYPE_ALLDAY;
+
+						$value = new \DateTime($value);
+					}
+
+					break;
+
+				case 'count':
+				case 'interval':
+					$value = max(1, (int) $value);
+					break;
+
+				case 'bysecond':
+					$value = array_filter(
+						array_map('intval', explode(',', $value)),
+						// 60 is allowed because of leap seconds.
+						fn ($v) => $v >= 0 && $v <= 60,
+					);
+					sort($value);
+					break;
+
+				case 'byminute':
+					$value = array_filter(
+						array_map('intval', explode(',', $value)),
+						fn ($v) => $v >= 0 && $v < 60,
+					);
+					sort($value);
+					break;
+
+				case 'byhour':
+					$value = array_filter(
+						array_map('intval', explode(',', $value)),
+						fn ($v) => $v >= 0 && $v < 24,
+					);
+					sort($value);
+					break;
+
+				case 'byday':
+					$value = array_filter(
+						explode(',', $value),
+						function ($v) {
+							// Simple case.
+							if (in_array($v, self::WEEKDAYS)) {
+								return true;
+							}
+
+							// E.g: '-1TH' for 'last Thursday of the month'.
+							return (bool) (preg_match('/^[+-]?\d+(SU|MO|TU|WE|TH|FR|SA)/', $v));
+						},
+					);
+					break;
+
+				case 'bymonthday':
+					$value = array_filter(
+						array_map('intval', explode(',', $value)),
+						fn ($v) => $v >= -31 && $v <= 31 && $v !== 0,
+					);
+					usort(
+						$value,
+						function ($a, $b) {
+							$a += $a < 0 ? 62 : 0;
+							$b += $b < 0 ? 62 : 0;
+
+							return $a <=> $b;
+						},
+					);
+					break;
+
+				case 'byyearday':
+					$value = array_filter(
+						array_map('intval', explode(',', $value)),
+						// 366 allowed because of leap years.
+						fn ($v) => $v >= -366 && $v <= 366 && $v !== 0,
+					);
+					break;
+
+				case 'byweekno':
+					$value = array_filter(
+						array_map('intval', explode(',', $value)),
+						fn ($v) => $v >= -53 && $v <= 53 && $v !== 0,
+					);
+					break;
+
+				case 'bymonth':
+					$value = array_filter(
+						array_map('intval', explode(',', $value)),
+						fn ($v) => $v >= 1 && $v <= 12,
+					);
+					break;
+
+				case 'bysetpos':
+					$value = array_map('intval', explode(',', $value));
+					break;
+
+				default:
+					break;
+			}
+
+			if (property_exists($this, $prop)) {
+				$this->{$prop} = $value;
+			}
+		}
+
+		// Some rule parts are subject to interdependent conditions.
+
+		// BYWEEKNO only applies when the frequency is YEARLY.
+		if ($this->freq !== 'YEARLY') {
+			unset($this->byweekno);
+		}
+
+		// BYYEARDAY never applies with these frequencies.
+		if (in_array($this->freq, ['DAILY', 'WEEKLY', 'MONTHLY'])) {
+			unset($this->byyearday);
+		}
+
+		// BYMONTHDAY never applies when the frequency is WEEKLY.
+		if ($this->freq === 'WEEKLY') {
+			unset($this->bymonthday);
+		}
+
+		// BYDAY can only have integer modifiers in certain cases.
+		if (
+			!empty($this->byday)
+			&& (
+				// Can't have integer modifiers with frequencies besides these.
+				!in_array($this->freq, ['MONTHLY', 'YEARLY'])
+				//  Can't have integer modifiers in combination with BYWEEKNO.
+				|| isset($this->byweekno)
+			)
+		) {
+			foreach ($this->byday as $value) {
+				if (!in_array($value, self::WEEKDAYS)) {
+					unset($this->byday);
+					break;
+				}
+			}
+		}
+
+		// BYSETPOS can only be used in conjunction with another BY*** rule part.
+		if (
+			!isset($this->bysecond)
+			&& !isset($this->byminute)
+			&& !isset($this->byhour)
+			&& !isset($this->byday)
+			&& !isset($this->bymonthday)
+			&& !isset($this->byyearday)
+			&& !isset($this->byweekno)
+			&& !isset($this->bymonth)
+		) {
+			unset($this->bysetpos);
+		}
+	}
+
+	/**
+	 * Allows this object to be handled like a string.
+	 */
+	public function __toString(): string
+	{
+		$rrule = [];
+
+		$parts = [
+			'FREQ',
+			'INTERVAL',
+			'UNTIL',
+			'COUNT',
+			'BYMONTH',
+			'BYWEEKNO',
+			'BYYEARDAY',
+			'BYMONTHDAY',
+			'BYDAY',
+			'BYHOUR',
+			'BYMINUTE',
+			'BYSECOND',
+			'BYSETPOS',
+			'WKST',
+		];
+
+		foreach ($parts as $part) {
+			unset($value);
+			$prop = strtolower($part);
+
+			if (!isset($this->{$prop})) {
+				continue;
+			}
+
+			switch ($prop) {
+				case 'freq':
+					$value = strtoupper($this->{$prop});
+					break;
+
+				// Skip if default.
+				case 'interval':
+					$value = $this->{$prop} > 1 ? $this->{$prop} : null;
+					break;
+
+				// Skip if default or irrelevant.
+				case 'wkst':
+					$value = strtoupper($this->wkst);
+
+					if (
+						// Skip if default.
+						$value === 'MO'
+						// Skip if irrelevant.
+						|| !in_array($this->freq, ['WEEKLY', 'YEARLY'])
+						|| ($this->freq === 'WEEKLY' && empty($this->byday))
+						|| ($this->freq === 'YEARLY' && empty($this->byweekno))
+					) {
+						$value = null;
+					}
+					break;
+
+				case 'bysecond':
+				case 'byminute':
+				case 'byhour':
+				case 'byday':
+				case 'bymonthday':
+				case 'byyearday':
+				case 'byweekno':
+				case 'bymonth':
+				case 'bysetpos':
+					$value = implode(',', $this->{$prop});
+					break;
+
+				// Force the time zone to UTC, just in case someone changed it.
+				case 'until':
+					if ($this->until_type === RecurrenceIterator::TYPE_ALLDAY) {
+						$value = $this->until->setTimezone(new \DateTimeZone('UTC'))->format('Ymd');
+					} elseif ($this->until_type === RecurrenceIterator::TYPE_FLOATING) {
+						$value = $this->until->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\THis');
+					} else {
+						$value = $this->until->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\THis\Z');
+					}
+					break;
+
+				default:
+					$value = (string) $this->{$prop};
+					break;
+			}
+
+			if (isset($value) && strlen($value) > 0) {
+				$rrule[] = $part . '=' . $value;
+			}
+		}
+
+		return implode(';', $rrule);
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/Sources/Calendar/RecurrenceIterator.php b/Sources/Calendar/RecurrenceIterator.php
new file mode 100644
index 0000000000..0ed40fcddc
--- /dev/null
+++ b/Sources/Calendar/RecurrenceIterator.php
@@ -0,0 +1,1658 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF\Calendar;
+
+use SMF\TimeInterval;
+
+/**
+ * Iterator to calculate all occurrences of a recurring event.
+ */
+class RecurrenceIterator implements \Iterator
+{
+	/*****************
+	 * Class constants
+	 *****************/
+
+	/**
+	 * @var int
+	 *
+	 * Indicates that the event has a date, time, and time zone.
+	 *
+	 * For example, an absolute event on '2023-10-26 14:00:00 Europe/Paris'
+	 * will occur on Oct 26, 2023, at 2:00 PM for a user in Paris, France, but
+	 * at 8:00 AM for a user in Toronto, Canada, and at 11:00 PM for a user in
+	 * Sydney, Australia.
+	 */
+	public const TYPE_ABSOLUTE = 0;
+
+	/**
+	 * @var int
+	 *
+	 * Indicates that the event has specific date and time, but no time zone.
+	 *
+	 * For example, a floating event on '2023-10-26 14:00:00' will occur on
+	 * Oct 26, 2023, at 2:00 PM in whatever time zone the viewer happens to
+	 * currently be in.
+	 */
+	public const TYPE_FLOATING = 1;
+
+	/**
+	 * @var int
+	 *
+	 * Indicates that the event has a specific date, but no time or time zone.
+	 *
+	 * For example, an all day event on '2023-10-26' will occur on Oct 26, 2023,
+	 * starting at midnight in whatever time zone the viewer happens to be in,
+	 * and ending on the following midnight in that time zone.
+	 */
+	public const TYPE_ALLDAY = 2;
+
+	/**
+	 * @var array
+	 *
+	 * Maps RFC 5545 weekday abbreviations to full weekday names.
+	 *
+	 * The order of the elements matters. Do not change it.
+	 */
+	public const WEEKDAY_NAMES = [
+		'MO' => 'Monday',
+		'TU' => 'Tuesday',
+		'WE' => 'Wednesday',
+		'TH' => 'Thursday',
+		'FR' => 'Friday',
+		'SA' => 'Saturday',
+		'SU' => 'Sunday',
+	];
+
+	/**
+	 * @var array
+	 *
+	 * Used to calculate a default value for $this->view_end.
+	 *
+	 * These are only used when the RRule repeats forever and no value was
+	 * specified for the constructor's $view parameter.
+	 *
+	 * Keys are possible values of $this->rrule->freq.
+	 * Values are the number of times to add $this->frequency_interval to
+	 * $this->view_start in order to calculate $this->view_end.
+	 *
+	 * These defaults are entirely arbitrary choices by the developer. ;)
+	 */
+	public const DEFAULT_COUNTS = [
+		'YEARLY' => 10,
+		'MONTHLY' => 12,
+		'WEEKLY' => 52,
+		'DAILY' => 365,
+		'HOURLY' => 720,
+		'MINUTELY' => 1440,
+		'SECONDLY' => 3600,
+	];
+
+	/*********************
+	 * Internal properties
+	 *********************/
+
+	/**
+	 * @var array
+	 *
+	 * Info about how to process the various BYxxx rule parts (except BYSETPOS).
+	 *
+	 * As RFC 5545 says:
+	 *
+	 * "BYxxx rule parts modify the recurrence in some manner. BYxxx rule parts
+	 * for a period of time that is the same or greater than the frequency
+	 * generally reduce or limit the number of occurrences of the recurrence
+	 * generated. [...] BYxxx rule parts for a period of time less than the
+	 * frequency generally increase or expand the number of occurrences of the
+	 * recurrence."
+	 *
+	 * For more info on these rule parts and how they modify the recurrence, see
+	 * RFC 5545, §3.3.10.
+	 *
+	 * Note: the order of the elements in this array matters. Do not change it.
+	 */
+	private array $by = [
+		'bysecond' => [
+			'fmt' => 's',
+			'type' => 'int',
+			'is_expansion' => false,
+		],
+		'byminute' => [
+			'fmt' => 'i',
+			'type' => 'int',
+			'is_expansion' => false,
+		],
+		'byhour' => [
+			'fmt' => 'H',
+			'type' => 'int',
+			'is_expansion' => false,
+		],
+		'byday' => [
+			'fmt' => 'D',
+			'type' => 'string',
+			'adjust' => '$current_value = strtoupper(substr($current_value, 0, 2));',
+			'is_expansion' => false,
+		],
+		'bymonthday' => [
+			'fmt' => 'j',
+			'type' => 'int',
+			'is_expansion' => false,
+		],
+		'byyearday' => [
+			'fmt' => 'z',
+			'type' => 'int',
+			'adjust' => '$current_value++;',
+			'is_expansion' => false,
+		],
+		'byweekno' => [
+			'fmt' => 'W',
+			'type' => 'int',
+			'is_expansion' => true,
+		],
+		'bymonth' => [
+			'fmt' => 'm',
+			'type' => 'int',
+			'is_expansion' => false,
+		],
+	];
+
+	/**
+	 * @var RRule
+	 *
+	 * The recurrence rule for this event.
+	 */
+	private RRule $rrule;
+
+	/**
+	 * @var \DateTimeInterface
+	 *
+	 * Date of the first occurrence of the event.
+	 */
+	private \DateTimeInterface $dtstart;
+
+	/**
+	 * @var int
+	 *
+	 * The type of event (normal, floating, or all day), as indicated by one of
+	 * this class's TYPE_* constants.
+	 */
+	private int $type;
+
+	/**
+	 * @var array
+	 *
+	 * Timestamps of dates to add to the recurrence set.
+	 * These are dates besides the ones generated from the RRule.
+	 */
+	private array $rdates = [];
+
+	/**
+	 * @var array
+	 *
+	 * Timestamps of dates to exclude from the recurrence set.
+	 */
+	private array $exdates = [];
+
+	/**
+	 * @var \DateInterval
+	 *
+	 * How far to jump ahead for each main iteration of the recurrence rule.
+	 *
+	 * Derived from $this->rrule->freq and $this->rrule->interval.
+	 */
+	private \DateInterval $frequency_interval;
+
+	/**
+	 * @var int|float
+	 *
+	 * Used for sanity checks.
+	 *
+	 * Value may change based on $this->rrule->freq and/or $this->rrule->count.
+	 */
+	private int|float $max_occurrences;
+
+	/**
+	 * @var \DateTimeImmutable
+	 *
+	 * Occurrences before this date will be skipped when returning results.
+	 */
+	private \DateTimeInterface $view_start;
+
+	/**
+	 * @var \DateTimeImmutable
+	 *
+	 * Occurrences after this date will be skipped when returning results.
+	 */
+	private \DateTimeInterface $view_end;
+
+	/**
+	 * @var \DateTimeImmutable
+	 *
+	 * Occurrences before this date will not be calculated.
+	 *
+	 * This value is typically one frequency interval before $this->view_start.
+	 */
+	private \DateTimeInterface $limit_before;
+
+	/**
+	 * @var \DateTimeImmutable
+	 *
+	 * Occurrences after this date will not be calculated.
+	 *
+	 * This value is typically one frequency interval after $this->view_end.
+	 */
+	private \DateTimeInterface $limit_after;
+
+	/**
+	 * @var array
+	 *
+	 * Date string records of all valid occurrences.
+	 */
+	private array $occurrences = [];
+
+	/**
+	 * @var array
+	 *
+	 * Date string records of the initial recurrence set generated from the
+	 * RRule before any RDates or ExDates are applied.
+	 */
+	private array $rrule_occurrences = [];
+
+	/**
+	 * @var string
+	 *
+	 * \DateTime format to use for the records in $this->occurrences.
+	 */
+	private string $record_format = 'Ymd\THis\Z';
+
+	/**
+	 * @var int
+	 *
+	 * Iterator key. Points to the current element of $this->occurrences when
+	 * iterating over an instance of this class.
+	 */
+	private int $key = 0;
+
+	/****************
+	 * Public methods
+	 ****************/
+
+	/**
+	 * Constructor.
+	 *
+	 * @param RRule $rrule The recurrence rule for this event.
+	 *
+	 * @param \DateTimeInterface $dtstart Date of the event's first occurrence.
+	 *
+	 * @param ?\DateInterval $view Length of the period for which dates will be
+	 *    shown. For example, use \DateInterval('P1M') to show one month's worth
+	 *    of occurrences, \DateInterval('P1W') to show one week's worth, etc.
+	 *    If null, will be determined automatically.
+	 *
+	 * @param ?\DateTimeInterface $view_start Lower limit for dates to be shown.
+	 *    Iterating over the object will never return values before this date.
+	 *    If null, will be set to $this->dtstart.
+	 *
+	 * @param ?int $type One of this class's TYPE_* constants, or null to set
+	 *    it automatically based on the UNTIL value of the RRule. If this is
+	 *    null and the RRule's UNTIL value is null, default is TYPE_ABSOLUTE.
+	 *
+	 * @param ?array $rdates Arbitrary dates to add to the recurrence set.
+	 *    Elements must be arrays containing an instance of \DateTimeInterface
+	 *    and an optional \DateInterval.
+	 *    Used to make exceptions to the general recurrence rule.
+	 *
+	 * @param ?array $exdates Dates to exclude from the recurrence set.
+	 *    Elements must be instances of \DateTimeInterface.
+	 *    Used to make exceptions to the general recurrence rule.
+	 */
+	public function __construct(
+		RRule $rrule,
+		\DateTimeInterface $dtstart,
+		?\DateInterval $view = null,
+		?\DateTimeInterface $view_start = null,
+		?int $type = null,
+		array $rdates = [],
+		array $exdates = [],
+	) {
+		$this->rrule = $rrule;
+
+		$this->type = isset($type) && in_array($type, range(0, 2)) ? $type : ($this->rrule->until_type ?? self::TYPE_ABSOLUTE);
+
+		$this->dtstart = $this->type === self::TYPE_ABSOLUTE ? \DateTimeImmutable::createFromInterface($dtstart) : \DateTime::createFromInterface($dtstart);
+		$this->view_start = $this->type === self::TYPE_ABSOLUTE ? \DateTimeImmutable::createFromInterface($view_start ?? $this->dtstart) : \DateTime::createFromInterface($view_start ?? $this->dtstart);
+
+		$this->setFrequencyInterval();
+
+		// We were given a view duration.
+		if (isset($view)) {
+			$this->view_end = (clone $this->view_start)->add($view);
+		}
+		// Rule contained an UNTIL value, so use that as our view end.
+		elseif (isset($this->rrule->until)) {
+			$this->view_end = $this->type === self::TYPE_ABSOLUTE ? \DateTimeImmutable::createFromInterface($this->rrule->until) : \DateTime::createFromInterface($this->rrule->until);
+		}
+		// Figure out the view end based on the count value.
+		else {
+			$this->view_end = clone $this->view_start;
+
+			// Add the frequency interval enough times to cover the specified
+			// number of occurrences, or the default number if unspecified.
+			for ($i = 0; $i < ($this->rrule->count ?? self::DEFAULT_COUNTS[$this->rrule->freq]); $i++) {
+				$this->view_end = $this->view_end->add($this->frequency_interval);
+			}
+		}
+
+		// If given a view duration and an UNTIL value, end at whichever comes first.
+		if (isset($this->rrule->until) && $this->rrule->until < $this->view_end) {
+			$this->view_end = $this->type === self::TYPE_ABSOLUTE ? \DateTimeImmutable::createFromInterface($this->rrule->until) : \DateTime::createFromInterface($this->rrule->until);
+		}
+
+		// Set some limits.
+		$this->limit_before = !empty($this->rrule->bysetpos) ? (clone $this->dtstart)->sub($this->frequency_interval) : $this->dtstart;
+		$this->limit_after = (clone $this->view_end)->add($this->frequency_interval);
+		$this->max_occurrences = $this->rrule->count ?? self::DEFAULT_COUNTS[$this->rrule->freq] * 1000;
+
+		// Figure out the appropriate way to record the occurrences.
+		switch ($this->type) {
+			case self::TYPE_ALLDAY:
+				$this->record_format = 'Ymd';
+				break;
+
+			case self::TYPE_FLOATING:
+				$this->record_format = 'Ymd\THis';
+				break;
+
+			default:
+				$this->record_format = 'Ymd\THis\Z';
+				break;
+		}
+
+		// Finalize values in $this->by.
+		switch ($this->rrule->freq) {
+			case 'YEARLY':
+				$this->by['bymonth']['is_expansion'] = true;
+				$this->by['byyearday']['is_expansion'] = true;
+				$this->by['bymonthday']['is_expansion'] = true;
+
+				if (empty($this->rrule->bymonthday) && empty($this->rrule->byyearday)) {
+					$this->by['byday']['is_expansion'] = true;
+				}
+				$this->by['byhour']['is_expansion'] = true;
+				$this->by['byminute']['is_expansion'] = true;
+				$this->by['bysecond']['is_expansion'] = true;
+				break;
+
+			case 'MONTHLY':
+				$this->by['bymonthday']['is_expansion'] = true;
+
+				if (empty($this->rrule->bymonthday)) {
+					$this->by['byday']['is_expansion'] = true;
+				}
+				$this->by['byhour']['is_expansion'] = true;
+				$this->by['byminute']['is_expansion'] = true;
+				$this->by['bysecond']['is_expansion'] = true;
+				break;
+
+			case 'WEEKLY':
+				$this->by['byday']['is_expansion'] = true;
+				$this->by['byhour']['is_expansion'] = true;
+				$this->by['byminute']['is_expansion'] = true;
+				$this->by['bysecond']['is_expansion'] = true;
+				break;
+
+			case 'DAILY':
+				$this->by['byhour']['is_expansion'] = true;
+				$this->by['byminute']['is_expansion'] = true;
+				$this->by['bysecond']['is_expansion'] = true;
+				break;
+
+			case 'HOURLY':
+				$this->by['byminute']['is_expansion'] = true;
+				$this->by['bysecond']['is_expansion'] = true;
+				break;
+
+			case 'MINUTELY':
+				$this->by['bysecond']['is_expansion'] = true;
+				break;
+
+			case 'SECONDLY':
+				break;
+		}
+
+		// First, calculate occurrence dates based on the recurrence rule.
+		$this->calculate();
+
+		// Remember the initially calculated recurrence set. We may need it later.
+		$this->rrule_occurrences = $this->occurrences;
+
+		// Next, add any manually specified dates.
+		foreach ($rdates as $rdate) {
+			if ($rdate[0] instanceof \DateTimeInterface) {
+				$this->add(...$rdate);
+			}
+		}
+
+		// Finally, remove any excluded dates.
+		foreach ($exdates as $exdate) {
+			if ($exdate instanceof \DateTimeInterface) {
+				$this->remove($exdate);
+			}
+		}
+	}
+
+	/**
+	 * Returns a copy of $this->dtstart.
+	 */
+	public function getDtStart(): \DateTimeInterface
+	{
+		return clone $this->dtstart;
+	}
+
+	/**
+	 * Returns a copy of the recurrence rule.
+	 */
+	public function getRRule(): RRule
+	{
+		return clone $this->rrule;
+	}
+
+	/**
+	 * Returns a copy of $this->rdates.
+	 */
+	public function getRDates(): array
+	{
+		return $this->rdates;
+	}
+
+	/**
+	 * Returns a copy of $this->exdates.
+	 */
+	public function getExDates(): array
+	{
+		return $this->exdates;
+	}
+
+	/**
+	 * Returns occurrences generated by the RRule only.
+	 */
+	public function getRRuleOccurrences(): array
+	{
+		return $this->rrule_occurrences;
+	}
+
+	/**
+	 * Adds an arbitrary date to the recurrence set.
+	 *
+	 * Used for making exceptions to the general recurrence rule.
+	 * Note that calling this method always rewinds the iterator key.
+	 *
+	 * @param \DateTimeInterface $date The date to add.
+	 * @param ?\DateInterval $duration Optional duration for this occurrence.
+	 *    Only necessary if the duration for this occurrence differs from the
+	 *    usual duration of the event.
+	 */
+	public function add(\DateTimeInterface $date, ?\DateInterval $duration = null): void
+	{
+		$this->rewind();
+
+		if ($date < $this->view_start || $date >= $this->view_end) {
+			return;
+		}
+
+		$string = (clone $date)->setTimezone(new \DateTimeZone('UTC'))->format($this->record_format);
+
+		if (in_array($string, $this->occurrences)) {
+			return;
+		}
+
+		// Re-adding a date that was previously removed.
+		if (in_array($string, $this->exdates)) {
+			$this->exdates = array_values(array_diff($this->exdates, [$string]));
+		}
+		// Adding a new date.
+		else {
+			if (isset($duration)) {
+				$string .= '/' . (string) ($duration instanceof TimeInterval ? $duration : TimeInterval::createFromDateInterval($duration));
+			}
+
+			$this->rdates[] = $string;
+
+			// Increment max_occurrences so that we don't drop any occurrences
+			// generated from the RRule.
+			$this->max_occurrences++;
+		}
+
+		$this->record($date);
+	}
+
+	/**
+	 * Removes a date from the recurrence set.
+	 *
+	 * Used for making exceptions to the general recurrence rule.
+	 * Note that calling this method always rewinds the iterator key.
+	 *
+	 * @param \DateTimeInterface $date The date to remove.
+	 */
+	public function remove(\DateTimeInterface $date): void
+	{
+		$this->rewind();
+
+		$string = $date->format($this->record_format);
+
+		$is_rdate = false;
+
+		foreach ($this->rdates as $key => $rdate) {
+			if (str_starts_with($rdate, $string)) {
+				$is_rdate = true;
+				unset($this->rdates[$key]);
+				$this->rdates = array_values($this->rdates);
+			}
+		}
+
+		if (!$is_rdate && !in_array($string, $this->exdates)) {
+			$this->exdates[] = $string;
+		}
+
+		$this->occurrences = array_values(array_diff($this->occurrences, [$string]));
+	}
+
+	/**
+	 * Checks whether the given date/time occurs in the recurrence set.
+	 *
+	 * @param \DateTimeInterface $date A date.
+	 * @return bool Whether the date occurs in the recurrence set.
+	 */
+	public function dateOccurs(\DateTimeInterface $date): bool
+	{
+		return in_array((clone $date)->setTimezone(new \DateTimeZone('UTC'))->format($this->record_format), $this->occurrences);
+	}
+
+	/**
+	 * Moves the iterator key one step forward, and then returns a
+	 * DateTimeInterface object for the newly selected element in the event's
+	 * recurrence set.
+	 *
+	 * @return \DateTimeInterface|false The next occurrence, or false if there
+	 *    are no more occurrences.
+	 */
+	public function getNext(): \DateTimeInterface|bool
+	{
+		$this->next();
+
+		return $this->current();
+	}
+
+	/**
+	 * Moves the iterator key one step backward, and then returns a
+	 * DateTimeInterface object for the newly selected element in the event's
+	 * recurrence set.
+	 *
+	 * @return \DateTimeInterface|false The previous occurrence, or false if
+	 *    there is no previous occurrence.
+	 */
+	public function getPrev(): \DateTimeInterface|bool
+	{
+		$this->prev();
+
+		return $this->current();
+	}
+
+	/**
+	 * Returns a \DateTimeInterface object for the currently selected element
+	 * in the event's recurrence set.
+	 *
+	 * If $this->type is self::TYPE_FLOATING or self::TYPE_ALLDAY, the returned
+	 * object will be a mutable \DateTime instance so that its time zone can be
+	 * changed to the viewing user's current time zone.
+	 *
+	 * Otherwise, the returned object will a \DateTimeImmutable instance.
+	 *
+	 * @return \DateTimeInterface|false The date of the occurrence, or false on
+	 *    error.
+	 */
+	public function current(): \DateTimeInterface|bool
+	{
+		if (!$this->valid()) {
+			return false;
+		}
+
+		// For TYPE_ABSOLUTE, return a \DateTimeImmutable object.
+		if ($this->type === self::TYPE_ABSOLUTE) {
+			$occurrence = new \DateTimeImmutable($this->occurrences[$this->key]);
+			$occurrence = $occurrence->setTimezone($this->dtstart->getTimezone());
+		}
+		// For TYPE_FLOATING and TYPE_ALLDAY, return a \DateTime object.
+		else {
+			$occurrence = new \DateTime(
+				$this->occurrences[$this->key],
+				$this->dtstart->getTimezone(),
+			);
+		}
+
+		return $occurrence;
+	}
+
+	/**
+	 * Checks whether the current value of the iterator key is valid.
+	 *
+	 * @return bool Whether the current value of the iterator key is valid.
+	 */
+	public function valid(): bool
+	{
+		return isset($this->occurrences[$this->key]);
+	}
+
+	/**
+	 * Get the current value of the iterator key.
+	 *
+	 * @return int The current value of the iterator key.
+	 */
+	public function key(): int
+	{
+		return $this->key;
+	}
+
+	/**
+	 * Moves the iterator key one step forward.
+	 */
+	public function next(): void
+	{
+		$this->key++;
+	}
+
+	/**
+	 * Moves the iterator key one step backward.
+	 */
+	public function prev(): void
+	{
+		$this->key--;
+
+		$this->key = max(0, $this->key);
+	}
+
+	/**
+	 * Moves the iterator key back to the beginning.
+	 */
+	public function rewind(): void
+	{
+		$this->key = 0;
+	}
+
+	/**
+	 * Moves the iterator key to the end.
+	 */
+	public function end(): void
+	{
+		$this->key = !empty($this->occurrences) ? max(array_keys($this->occurrences)) : 0;
+	}
+
+	/**
+	 * Moves the iterator key to a specific position.
+	 *
+	 * If the requested key is invalid, will go to the closest valid one.
+	 *
+	 * @return int The new value of the iterator key.
+	 */
+	public function setKey(int $key): int
+	{
+		// Clamp to valid range.
+		$this->key = min(max($key, 0), (!empty($this->occurrences) ? max(array_keys($this->occurrences)) : 0));
+
+		// If still not valid, find one that is.
+		while (!$this->valid() && $this->key > 0) {
+			$this->prev();
+		}
+
+		return $this->key;
+	}
+
+	/**
+	 * Finds the iterator key that corresponds to the requested value.
+	 *
+	 * @param string $needle The value to search for.
+	 * @return int|false The key for the requested value, or false on error.
+	 */
+	public function search(string $needle): int|bool
+	{
+		return array_search($needle, $this->occurrences);
+	}
+
+	/***********************
+	 * Public static methods
+	 ***********************/
+
+	/**
+	 * Calculates the week number of a date according to RFC 5545.
+	 */
+	public static function calculateWeekNum(\DateTimeInterface $current, string $wkst): int
+	{
+		// If $wkst is Monday, we can skip the extra work.
+		if ($wkst === 'MO') {
+			return (int) $current->format('W');
+		}
+
+		$temp = \DateTime::createFromInterface($current);
+
+		$wkst_diff = array_search($wkst, array_keys(self::WEEKDAY_NAMES));
+		$wkst_diff = ($wkst_diff >= 5 ? $wkst_diff - 7 : $wkst_diff) * -1;
+
+		$temp->modify(sprintf('%1$+d days', $wkst_diff));
+
+		$weeknum = $temp->format('W');
+
+		return (int) $weeknum;
+	}
+
+	/******************
+	 * Internal methods
+	 ******************/
+
+	/**
+	 * Sets the value of $this->frequency_interval.
+	 */
+	private function setFrequencyInterval(): void
+	{
+		$interval_string = 'P';
+
+		if (in_array($this->rrule->freq, ['HOURLY', 'MINUTELY', 'SECONDLY'])) {
+			$interval_string .= 'T';
+		}
+
+		$interval_string .= $this->rrule->interval;
+
+		$interval_string .= substr($this->rrule->freq, 0, 1);
+
+		$this->frequency_interval = new \DateInterval($interval_string);
+	}
+
+	/**
+	 * Adds an occurrence to $this->occurrences.
+	 *
+	 * @return bool True if the occurrence is a new addition; false if it is
+	 *    a duplicate or out of bounds.
+	 */
+	private function record(\DateTimeInterface $occurrence): bool
+	{
+		// If it is too late, don't add it.
+		if ($occurrence > $this->limit_after) {
+			return false;
+		}
+
+		$string = (clone $occurrence)->setTimezone(new \DateTimeZone('UTC'))->format($this->record_format);
+
+		// If it is already in the array, don't add it.
+		if (in_array($string, $this->occurrences)) {
+			return false;
+		}
+
+		// Add and sort.
+		$this->occurrences[] = $string;
+		sort($this->occurrences);
+
+		// If the RRule contains a BYSETPOS rule part, we can't truncate yet.
+		if (!empty($this->rrule->bysetpos)) {
+			return true;
+		}
+
+		// If we don't need to truncate the array, return true now.
+		if ($this->max_occurrences >= count($this->occurrences)) {
+			return true;
+		}
+
+		// We have too many occurrences, so truncate the array.
+		array_splice($this->occurrences, $this->max_occurrences);
+
+		// Is this occurrence still in the array?
+		return in_array($string, $this->occurrences);
+	}
+
+	/**
+	 * Calculates occurrences based on the recurrence rule.
+	 */
+	private function calculate(): void
+	{
+		if ($this->view_end < $this->view_start) {
+			return;
+		}
+
+		$current = \DateTime::createFromInterface($this->dtstart);
+
+		$this->jumpToVisible($current);
+
+		$max = $this->max_occurrences;
+
+		// Calculate all the occurrences and store them in $this->occurrences.
+		while (
+			$current <= $this->limit_after
+			&& (
+				!empty($this->rrule->bysetpos)
+				|| count($this->occurrences) < $max
+			)
+		) {
+			if ($current < $this->view_start) {
+				$this->nextInterval($current);
+
+				// If $this->max_occurrences was derived from an RRule's COUNT,
+				// then skipped occurrences still count against the maximum.
+				if (!empty($this->rrule->count)) {
+					$max--;
+				}
+
+				continue;
+			}
+
+			// Get the expansions.
+			$expansions = [];
+
+			foreach ($this->expand($current) as $expanded) {
+				if ($this->limit($expanded)) {
+					$this->record($expanded);
+				}
+
+				// Failsafe if we get stuck in a loop.
+				$formatted = $expanded->format($this->record_format);
+
+				if (($expansions[$formatted] = ($expansions[$formatted] ?? 0) + 1) > 2) {
+					break;
+				}
+			}
+
+			if ($this->limit($current)) {
+				$this->record($current);
+			}
+
+			// Step forward one frequency interval.
+			$this->nextInterval($current);
+		}
+
+		// Apply BYSETPOS limitation.
+		$this->limitBySetPos();
+
+		// Final cleanup.
+		$view_start = $this->view_start->format($this->record_format);
+		$view_end = $this->view_end->format($this->record_format);
+
+		$this->occurrences = array_values(array_filter(
+			$this->occurrences,
+			fn ($occurrence) => $view_start <= $occurrence && $view_end >= $occurrence,
+		));
+
+		if ($this->max_occurrences < count($this->occurrences)) {
+			array_splice($this->occurrences, $this->max_occurrences);
+		}
+	}
+
+	/**
+	 * If possible, move $current ahead in order to skip values before
+	 * $this->view_start.
+	 *
+	 * @param \DateTime &$current
+	 */
+	private function jumpToVisible(\DateTime &$current): void
+	{
+		if (
+			// Don't jump ahead if $current is aleady in the visible range.
+			$current >= $this->view_start
+			// Can't jump ahead if recurrence rule requires counting the occurrences.
+			|| isset($this->rrule->count)
+		) {
+			return;
+		}
+
+		// Special handling for WEEKLY.
+		if ($this->rrule->freq === 'WEEKLY') {
+			$weekdays = !empty($this->rrule->byday) ? array_map(fn ($weekday) => substr($weekday, -2), $this->rrule->byday) : [strtoupper(substr($current->format('D'), 0, 2))];
+
+			$current->setDate(
+				(int) $this->view_start->format('Y'),
+				(int) $this->view_start->format('m'),
+				(int) $this->view_start->format('d'),
+			);
+
+			while (!in_array(strtoupper(substr($current->format('D'), 0, 2)), $weekdays)) {
+				$current->modify('-1 day');
+			}
+
+			return;
+		}
+
+		// Everything else.
+		foreach ($this->by as $prop => $info) {
+			if (!$info['is_expansion']) {
+				continue;
+			}
+
+			if (!empty($this->rrule->{$prop}) && count($this->rrule->{$prop}) > 1) {
+				return;
+			}
+		}
+
+		switch ($this->rrule->freq) {
+			case 'SECONDLY':
+				$s = (int) $this->view_start->format('s');
+				// no break
+
+			case 'MINUTELY':
+				$i = (int) $this->view_start->format('i');
+				// no break
+
+			case 'HOURLY':
+				$h = (int) $this->view_start->format('h');
+				// no break
+
+			case 'DAILY':
+				$d = (int) $this->view_start->format('d');
+				// no break
+
+			case 'MONTHLY':
+				$m = (int) $this->view_start->format('m');
+				// no break
+
+			case 'YEARLY':
+				$y = (int) $this->view_start->format('Y');
+		}
+
+		$current->setDate($y, $m ?? (int) $current->format('m'), $d ?? (int) $current->format('d'));
+
+		if (isset($h)) {
+			$current->setTime($h, $i ?? (int) $current->format('i'), $s ?? (int) $current->format('s'));
+		}
+	}
+
+	/**
+	 * Move $current ahead to the next interval.
+	 *
+	 * Handles months of varying lengths according to RFC 5545's rules.
+	 *
+	 * @param \DateTime &$current
+	 */
+	private function nextInterval(\DateTime &$current): void
+	{
+		// Monthly is complicated.
+		if ($this->rrule->freq == 'MONTHLY') {
+			$months_to_add = 0;
+			$next_monthday = !empty($this->rrule->bymonthday) ? 1 : (int) $current->format('d');
+			$test = \DateTimeImmutable::createFromMutable($current);
+
+			do {
+				$months_to_add += $this->rrule->interval;
+				$next = clone $current;
+				$next->setDate((int) $next->format('Y'), (int) $next->format('m') + $months_to_add, (int) $next_monthday);
+			} while ($test->setDate((int) $test->format('Y'), (int) $test->format('m') + $months_to_add, (int) $next_monthday)->format('m') % 12 != (($test->format('m') + $months_to_add) % 12));
+
+			$current = $next;
+		}
+		// Everything else is straightforward.
+		else {
+			$current->add($this->frequency_interval);
+		}
+	}
+
+	/**
+	 * Checks whether a calculated occurrence should be included based on BYxxx
+	 * rule parts in the RRule.
+	 *
+	 * Limitations cause occurrences that would normally occur according the
+	 * RRule's stated frequency to be skipped. For example, if the frequency is
+	 * set to HOURLY, that normally means that the event recurs on minute 0 of
+	 * every hour (or whatever minute was set in DTSTART) of every day. But if
+	 * the BYDAY rule part is set to 'TU,TH', then occurrences are limited so
+	 * that the event recurs only at every hour during Tuesdays and Thursdays.
+	 * Occurrences that happen on any other day of the week are skipped.
+	 *
+	 * @param \DateTime $current A occurrence whose value we want to check.
+	 * @return bool Whether the occurrence is allowed.
+	 */
+	private function limit(\DateTime $current): bool
+	{
+		if ($current < $this->limit_before || $current > $this->limit_after) {
+			return false;
+		}
+
+		$valid = true;
+
+		foreach ($this->by as $prop => $info) {
+			if (empty($this->rrule->{$prop})) {
+				continue;
+			}
+
+			// Get the current value.
+			$current_value = $current->format($info['fmt']);
+
+			// Coerce the value to the expected type.
+			settype($current_value, $info['type']);
+
+			// Make any necessary adjustment to the value.
+			if (!empty($info['adjust'])) {
+				eval($info['adjust']);
+			}
+
+			// What are the allowed values?
+			$allowed_values = $this->rrule->{$prop};
+
+			// BYDAY values could have numerical modifiers prepended to them.
+			// We only want the plain weekday abbrevations here.
+			if ($prop === 'byday') {
+				foreach ($allowed_values as &$allowed_value) {
+					$allowed_value = substr($allowed_value, -2);
+				}
+			}
+
+			// These types of values can be negative to indicate that they are
+			// counting from the end. Convert to real values.
+			switch ($prop) {
+				case 'byyearday':
+					foreach ($allowed_values as &$allowed_value) {
+						if ($allowed_value < 0) {
+							$allowed_value += $current->format('L') ? 367 : 366;
+						}
+					}
+					break;
+
+				case 'bymonthday':
+					foreach ($allowed_values as &$allowed_value) {
+						if ($allowed_value < 0) {
+							$allowed_value += $current->format('t') + 1;
+						}
+					}
+					break;
+
+				case 'byweekno':
+					// Are there 52 or 53 numbered weeks in this year?
+					// Checking Dec 28 using a Monday for our week start
+					// will always give us the right answer.
+					$num_weeks = (new \DateTime($current->format('Y') . '-12-28'))->format('W');
+
+					foreach ($allowed_values as &$allowed_value) {
+						if ($allowed_value < 0) {
+							$allowed_value += $num_weeks + 1;
+						}
+					}
+					break;
+			 }
+
+			$valid &= in_array($current_value, $allowed_values);
+		}
+
+		return (bool) $valid;
+	}
+
+	/**
+	 * Applies BYSETPOS limitation to the reccurrence set.
+	 */
+	private function limitBySetPos(): void
+	{
+		if (empty($this->rrule->bysetpos)) {
+			return;
+		}
+
+		switch ($this->rrule->freq) {
+			case 'YEARLY':
+				$pattern = '/^(\d{4})/';
+				break;
+
+			case 'MONTHLY':
+				$pattern = '/^\d{4}(\d{2})/';
+				break;
+
+			case 'DAILY':
+				$pattern = '/^\d{6}(\d{2})/';
+				break;
+
+			case 'HOURLY':
+				$pattern = '/T(\d{2})/';
+				break;
+
+			case 'MINUTELY':
+				$pattern = '/T\d{2}(\d{2})/';
+				break;
+
+			case 'SECONDLY':
+				$pattern = '/T\d{4}(\d{2})/';
+				break;
+		}
+
+		$groups = [];
+
+		$prev_val = null;
+		$group_key = -1;
+
+		foreach ($this->occurrences as $string) {
+			// Weekly.
+			if (!isset($pattern)) {
+				$val = self::calculateWeekNum(new \DateTimeImmutable($string), $this->rrule->wkst);
+			}
+			// Everything else.
+			else {
+				preg_match($pattern, $string, $matches);
+				$val = $matches[1];
+			}
+
+			if ($val !== $prev_val) {
+				$group_key++;
+			}
+
+			$groups[$group_key][] = $string;
+
+			$prev_val = $val;
+		}
+
+		// BYSETPOS starts with an index of 1, not 0, for positive values,
+		// so we have to adjust it.
+		$bysetpos = array_map(
+			fn ($setpos) => $setpos < 0 ? (int) $setpos : (int) $setpos - 1,
+			$this->rrule->bysetpos,
+		);
+
+		$occurrences = [];
+
+		foreach ($groups as $group_key => $strings) {
+			foreach ($bysetpos as $setpos) {
+				$occurrences = array_merge($occurrences, array_slice($strings, $setpos, 1));
+			}
+		}
+
+		$this->occurrences = $occurrences;
+	}
+
+	/**
+	 * Finds additional occurrences based on any BYxxx rule parts in the RRule.
+	 *
+	 * Expansions are occurrences that happen inside one iteration of the
+	 * RRule's stated frequency. For example, if the frequency is set to HOURLY,
+	 * that normally means that the event recurs on minute 0 of every hour (or
+	 * whatever minute was set in DTSTART). But if the RRule's BYMINUTE property
+	 * is set to '0,30', then the occurrences are expanded so that the event
+	 * recurs at minute 0 and minute 30 of every hour.
+	 *
+	 * @param \DateTime $current An occurrence of the event to expand.
+	 * @param string $break_after Name of a $this->by element. Used during
+	 *    recursive calls to this method.
+	 * @return Generator<\DateTimeImmutable>
+	 */
+	private function expand(\DateTime $current, ?string $break_after = null): \Generator
+	{
+		foreach ($this->by as $prop => $info) {
+			// Do the expansions.
+			if (!empty($this->rrule->{$prop}) && $info['is_expansion']) {
+				$temp = \DateTime::createFromInterface($current);
+
+				switch ($prop) {
+					case 'bymonth':
+						foreach ($this->rrule->{$prop} as $value) {
+							if ($value != $temp->format('m')) {
+								$temp->setDate((int) $temp->format('Y'), (int) $value, (int) $temp->format('d'));
+
+								yield $temp;
+
+								foreach ($this->expand($temp, 'byweekno') as $temp2) {
+									yield $temp2;
+								}
+							}
+						}
+						break;
+
+					case 'byweekno':
+						foreach ($this->rrule->{$prop} as $value) {
+							// Unfortunately, we can't use PHP's interpretation
+							// of week numbering. PHP always numbers weeks based
+							// on a Monday start. In contrast, RFC 5545 allows
+							// arbitrary week starts and adjusts the week
+							// numbering based on that. So we have to figure it
+							// out manually.
+							$temp->setDate((int) $temp->format('Y'), 1, 1);
+
+							$first_wkst = 1;
+
+							while (strtoupper(substr($temp->format('D'), 0, 2)) !== $this->rrule->wkst) {
+								$temp->modify('+ 1 day');
+								$first_wkst++;
+							}
+
+							if ($first_wkst >= 4) {
+								$temp->modify('- 7 days');
+							}
+
+							$weeknum = 1;
+
+							while (++$weeknum < $value) {
+								$temp->modify('+ 7 days');
+							}
+
+							yield $temp;
+
+							foreach ($this->expand($temp, 'byyearday') as $temp2) {
+								yield $temp2;
+							}
+						}
+						break;
+
+					case 'byyearday':
+						$current_value = $current->format('z');
+						eval($info['adjust']);
+
+						foreach ($this->rrule->{$prop} as $value) {
+							if ($value != $current_value) {
+								$temp = \DateTime::createFromFormat('Y z H:i:s e', $temp->format('Y ') . ($value - 1) . $temp->format(' H:i:s e'));
+
+								yield $temp;
+
+								foreach ($this->expand($temp, 'bymonthday') as $temp2) {
+									yield $temp2;
+								}
+							}
+						}
+						break;
+
+					case 'bymonthday':
+						foreach ($this->rrule->{$prop} as $value) {
+							if ($value < 0) {
+								$value += $temp->format('t') + 1;
+							}
+
+							if ($value != $temp->format('d')) {
+								$temp->setDate((int) $temp->format('Y'), (int) $temp->format('m'), (int) $value);
+
+								yield $temp;
+
+								foreach ($this->expand($temp, 'byday') as $temp2) {
+									yield $temp2;
+								}
+							}
+						}
+						break;
+
+					case 'byday':
+						$current_value = $temp->format('D');
+						eval($info['adjust']);
+
+						// Special handling for yearly.
+						if ($this->rrule->freq === 'YEARLY') {
+							if (!empty($this->rrule->bymonth)) {
+								foreach ($this->expandMonthByDay($temp, $this->rrule->byday, $current_value) as $temp2) {
+									yield $temp2;
+								}
+							} else {
+								foreach ($this->expandYearByDay($temp, $this->rrule->byday, $current_value) as $temp2) {
+									yield $temp2;
+								}
+							}
+						}
+						// Special handling for monthly.
+						elseif ($this->rrule->freq === 'MONTHLY') {
+							foreach ($this->expandMonthByDay($temp, $this->rrule->byday, $current_value) as $temp2) {
+								yield $temp2;
+							}
+						}
+						// Special handling for weekly.
+						elseif ($this->rrule->freq === 'WEEKLY') {
+							$weeknum = self::calculateWeekNum($temp, $this->rrule->wkst);
+
+							// Move temp to start of week.
+							$temp->modify('+ 1 day');
+							$temp->modify('previous ' . self::WEEKDAY_NAMES[$this->rrule->wkst] . ' ' . $temp->format('H:i:s e'));
+
+							$temp_value = strtoupper(substr($temp->format('D'), 0, 2));
+
+							foreach ($this->sortWeekdays($this->rrule->byday) as $value) {
+								if ($value != $temp_value) {
+									$temp->modify('next ' . self::WEEKDAY_NAMES[$value] . ' ' . $temp->format('H:i:s e'));
+								}
+
+								if (self::calculateWeekNum($temp, $this->rrule->wkst) === $weeknum) {
+									yield $temp;
+
+									foreach ($this->expand($temp, 'byhour') as $temp2) {
+										yield $temp2;
+									}
+								}
+							}
+						}
+						// Everything else.
+						else {
+							foreach ($this->rrule->byday as $value) {
+								if ($value != $current_value) {
+									$temp->modify('next ' . self::WEEKDAY_NAMES[$value] . ' ' . $temp->format('H:i:s e'));
+
+									yield $temp;
+
+									foreach ($this->expand($temp, 'byhour') as $temp2) {
+										yield $temp2;
+									}
+								}
+							}
+						}
+						break;
+
+					case 'byhour':
+						foreach ($this->rrule->byhour as $value) {
+							if ($value != $temp->format('H')) {
+								$temp->setTime((int) $value, (int) $temp->format('i'), (int) $temp->format('s'));
+
+								yield $temp;
+
+								foreach ($this->expand($temp, 'byminute') as $temp2) {
+									yield $temp2;
+								}
+							}
+						}
+						break;
+
+					case 'byminute':
+						foreach ($this->rrule->byminute as $value) {
+							if ($value != $temp->format('i')) {
+								$temp->setTime((int) $temp->format('H'), (int) $value, (int) $temp->format('s'));
+
+								yield $temp;
+
+								foreach ($this->expand($temp, 'bysecond') as $temp2) {
+									yield $temp2;
+								}
+							}
+						}
+						break;
+
+					case 'bysecond':
+						foreach ($this->rrule->bysecond as $value) {
+							if ($value != $temp->format('s')) {
+								$temp->setTime((int) $temp->format('H'), (int) $temp->format('i'), (int) $value);
+
+								yield $temp;
+							}
+						}
+						break;
+				}
+			}
+
+			if (!empty($break_after) && $break_after == $prop) {
+				break;
+			}
+		}
+	}
+
+	/**
+	 * Used when expanding an occurrence that is part of a monthly recurrence
+	 * set that has a byday rule, or part of a yearly recurrence set that has
+	 * both a bymonth rule and a byday rule.
+	 *
+	 * @param \DateTime $current An occurrence of the event to expand.
+	 * @param array $expansion_values Values from the byday rule.
+	 * @param string The abbreviated name of the $current occurrence's weekday.
+	 * @return Generator<\DateTimeImmutable>
+	 */
+	private function expandMonthByDay(\DateTime $current, array $expansion_values, string $current_value): \Generator
+	{
+		$upperlimit = clone $current;
+
+		if ($this->frequency_interval->m === 1) {
+			$upperlimit->add($this->frequency_interval);
+		} elseif (!empty($this->rrule->bymonth) && in_array((($upperlimit->format('m') + 1) % 12), $this->rrule->bymonth)) {
+			$upperlimit->modify('last day of ' . $upperlimit->format('F H:i:s e'));
+			$upperlimit->modify('+ 1 day');
+		} else {
+			$upperlimit->setDate((int) $upperlimit->format('Y'), (int) $upperlimit->format('m'), 1);
+			$upperlimit->modify('last day of ' . $upperlimit->format('F H:i:s e'));
+		}
+
+		$expansion_values = $this->sortWeekdays($expansion_values);
+
+		foreach ($expansion_values as $k => $v) {
+			// Separate out the numerical modifer (if any) from the day name.
+			preg_match('/^([+-]?\d*)(MO|TU|WE|TH|FR|SA|SU)?/', $v, $matches);
+
+			$expansion_values[$k] = [
+				'modifier' => (int) ($matches[1] ?? 0),
+				'weekday' => $matches[2],
+			];
+		}
+
+		$temp = clone $current;
+
+		$key = 0;
+		$i = 0;
+
+		while ($temp <= $upperlimit) {
+			// Positive modifer means nth weekday of the month.
+			// E.g.: '2TH' means the second Thursday.
+			if ($expansion_values[$key]['modifier'] > 0) {
+				// To work nicely with PHP's parsing of 'next <dayname>',
+				// go to last day of previous month, then walk forward.
+				$temp->setDate((int) $temp->format('Y'), (int) $temp->format('m'), 1);
+				$temp->modify('- 1 day');
+
+				// Go to first occurrence of the weekday in the month.
+				$temp->modify('next ' . self::WEEKDAY_NAMES[$expansion_values[$key]['weekday']] . ' ' . $temp->format('H:i:s e'));
+
+				// Move forward to the requested occurrence.
+				if ($expansion_values[$key]['modifier'] > 1) {
+					$temp->modify('+ ' . (($expansion_values[$key]['modifier'] - 1) * 7) . ' days');
+				}
+
+				if ($temp <= $upperlimit && $temp >= $this->limit_before) {
+					yield $temp;
+
+					foreach ($this->expand($temp, 'byhour') as $temp2) {
+						if ($temp2 <= $upperlimit && $temp2 >= $this->limit_before) {
+							yield $temp2;
+						}
+					}
+				}
+
+				if ($key === count($expansion_values) - 1) {
+					break;
+				}
+			}
+			// Negative modifer means nth last weekday of the month.
+			// E.g.: '-2TH' means the second last Thursday.
+			elseif ($expansion_values[$key]['modifier'] < 0) {
+				// To work nicely with PHP's parsing of 'previous <dayname>',
+				// go to first day of next month, then walk backward.
+				$temp->setDate((int) $temp->format('Y'), (int) $temp->format('m') + 1, 1);
+
+				// Go to last occurrence of the weekday in the month.
+				$temp->modify('previous ' . self::WEEKDAY_NAMES[$expansion_values[$key]['weekday']] . ' ' . $temp->format('H:i:s e'));
+
+				// Move backward to the requested occurrence.
+				if ($expansion_values[$key]['modifier'] < -1) {
+					$temp->modify('- ' . ((abs($expansion_values[$key]['modifier']) - 1) * 7) . ' days');
+				}
+
+				if ($temp <= $upperlimit && $temp >= $this->limit_before) {
+					yield $temp;
+
+					foreach ($this->expand($temp, 'byhour') as $temp2) {
+						if ($temp2 <= $upperlimit && $temp2 >= $this->limit_before) {
+							yield $temp2;
+						}
+					}
+				}
+
+				if ($key === count($expansion_values) - 1) {
+					break;
+				}
+			}
+			// No modifer means every matching weekday.
+			// E.g.: 'TH' means every Thursday.
+			else {
+				// On the first iteration of this loop only, go to the last day
+				// of the previous month.
+				if ($i === 0) {
+					$temp->setDate((int) $temp->format('Y'), (int) $temp->format('m'), 1);
+					$temp->modify('- 1 day');
+				}
+
+				$temp->modify('+ 1 day');
+
+				if ($temp <= $upperlimit && $temp >= $this->limit_before) {
+					yield $temp;
+
+					foreach ($this->expand($temp, 'byhour') as $temp2) {
+						if ($temp2 <= $upperlimit && $temp2 >= $this->limit_before) {
+							yield $temp2;
+						}
+					}
+				}
+			}
+
+			$key++;
+			$key %= count($expansion_values);
+			$i++;
+		}
+	}
+
+	/**
+	 * Used when expanding an occurrence that is part of a yearly recurrence
+	 * set that has a byday rule but not a bymonth rule.
+	 *
+	 * @param \DateTime $current An occurrence of the event to expand.
+	 * @param array $expansion_values Values from the byday rule.
+	 * @param string The abbreviated name of the $current occurrence's weekday.
+	 * @return Generator<\DateTimeImmutable>
+	 */
+	private function expandYearByDay(\DateTime $current, array $expansion_values, string $current_value): \Generator
+	{
+		$upperlimit = clone $current;
+		$upperlimit->add($this->frequency_interval);
+
+		$expansion_values = $this->sortWeekdays($expansion_values);
+
+		foreach ($expansion_values as $k => $v) {
+			// Separate out the numerical modifer (if any) from the day name.
+			preg_match('/^([+-]?\d*)(MO|TU|WE|TH|FR|SA|SU)?/', $v, $matches);
+
+			$expansion_values[$k] = [
+				'modifier' => (int) ($matches[1] ?? 0),
+				'weekday' => $matches[2],
+			];
+		}
+
+		$temp = clone $current;
+
+		$key = 0;
+
+		while ($temp <= $upperlimit) {
+			// Positive modifer means nth weekday of the year.
+			// E.g.: '2TH' means the second Thursday.
+			if ($expansion_values[$key]['modifier'] > 0) {
+				// To work nicely with PHP's parsing of 'next <dayname>',
+				// go to last day of previous year, then walk forward.
+				$temp->setDate((int) $temp->format('Y'), 1, 1);
+				$temp->modify('- 1 day');
+
+				// Go to first occurrence of the weekday in the year.
+				$temp->modify('next ' . self::WEEKDAY_NAMES[$expansion_values[$key]['weekday']] . ' ' . $temp->format('H:i:s e'));
+
+				// Move forward to the requested occurrence.
+				if ($expansion_values[$key]['modifier'] > 1) {
+					$temp->modify('+ ' . (($expansion_values[$key]['modifier'] - 1) * 7) . ' days');
+				}
+
+				if ($temp <= $upperlimit) {
+					yield $temp;
+
+					foreach ($this->expand($temp, 'byhour') as $temp2) {
+						if ($temp2 <= $upperlimit) {
+							yield $temp2;
+						}
+					}
+				}
+			}
+			// Negative modifer means nth last weekday of the year.
+			// E.g.: '-2TH' means the second last Thursday.
+			elseif ($expansion_values[$key]['modifier'] < 0) {
+				// To work nicely with PHP's parsing of 'previous <dayname>',
+				// go to first day of next year, then walk backward.
+				$temp->setDate((int) $temp->format('Y'), 12, 31);
+				$temp->modify('+ 1 day');
+
+				// Go to last occurrence of the weekday in the year.
+				$temp->modify('previous ' . self::WEEKDAY_NAMES[$expansion_values[$key]['weekday']] . ' ' . $temp->format('H:i:s e'));
+
+				// Move backward to the requested occurrence.
+				if ($expansion_values[$key]['modifier'] < -1) {
+					$temp->modify('- ' . ((abs($expansion_values[$key]['modifier']) - 1) * 7) . ' days');
+				}
+
+				if ($temp <= $upperlimit) {
+					yield $temp;
+
+					foreach ($this->expand($temp, 'byhour') as $temp2) {
+						if ($temp2 <= $upperlimit) {
+							yield $temp2;
+						}
+					}
+				}
+			}
+			// No modifer means every matching weekday.
+			// E.g.: 'TH' means every Thursday.
+			else {
+				$temp->modify('next ' . self::WEEKDAY_NAMES[$expansion_values[$key]['weekday']] . ' ' . $temp->format('H:i:s e'));
+
+				if ($temp <= $upperlimit) {
+					yield $temp;
+
+					foreach ($this->expand($temp, 'byhour') as $temp2) {
+						if ($temp2 <= $upperlimit) {
+							yield $temp2;
+						}
+					}
+				}
+			}
+
+			$key++;
+			$key %= count($expansion_values);
+		}
+	}
+
+	/**
+	 * Sorts an array of weekday abbreviations so that $this->rrule->wkst is
+	 * always the first item.
+	 *
+	 * @param array $weekdays An array of weekday abbreviations.
+	 * @return array Sorted version of $weekdays.
+	 */
+	private function sortWeekdays(array $weekdays): array
+	{
+		$weekday_abbrevs = array_keys(self::WEEKDAY_NAMES);
+
+		while (current($weekday_abbrevs) !== $this->rrule->wkst) {
+			$temp = array_shift($weekday_abbrevs);
+			$weekday_abbrevs[] = $temp;
+		}
+
+		// Handle strings with numerical modifers correctly.
+		$temp = [];
+
+		foreach ($weekdays as $weekday) {
+			$temp[substr($weekday, -2)][] = $weekday;
+		}
+
+		// Remove weekday abbreviations that aren't in $weekdays.
+		$weekday_abbrevs = array_intersect($weekday_abbrevs, array_keys($temp));
+
+		// Rebuild $weekdays.
+		$weekdays = [];
+
+		foreach ($weekday_abbrevs as $abbrev) {
+			$weekdays = array_merge($weekdays, $temp[$abbrev]);
+		}
+
+		return $weekdays;
+	}
+}
+
+?>
\ No newline at end of file

From 6acffac3238b9443a067de203f576107a4304e4c Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Thu, 7 Dec 2023 13:12:35 -0700
Subject: [PATCH 07/22] Database changes to support recurring events

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 other/install.php                | 27 ++++++++++++
 other/install_3-0_MySQL.sql      | 20 ++++++---
 other/install_3-0_PostgreSQL.sql | 18 +++++---
 other/upgrade.php                | 27 ++++++++++++
 other/upgrade_3-0_MySQL.sql      | 76 ++++++++++++++++++++++++++++++++
 other/upgrade_3-0_PostgreSQL.sql | 75 +++++++++++++++++++++++++++++++
 6 files changed, 232 insertions(+), 11 deletions(-)

diff --git a/other/install.php b/other/install.php
index 035ddd52b6..fc7d026027 100644
--- a/other/install.php
+++ b/other/install.php
@@ -23,6 +23,7 @@
 use SMF\Url;
 use SMF\User;
 use SMF\Utils;
+use SMF\Uuid;
 
 define('SMF_VERSION', '3.0 Alpha 1');
 define('SMF_FULL_VERSION', 'SMF ' . SMF_VERSION);
@@ -1485,6 +1486,32 @@ function DatabasePopulation()
 		['id_smiley', 'smiley_set'],
 	);
 
+	// Set the UID column for calendar events.
+	$calendar_updates = [];
+	$request = Db::$db->query(
+		'',
+		'SELECT id_event, uid
+		FROM {db_prefix}calendar',
+		[],
+	);
+
+	while ($row = Db::$db->fetch_assoc($request)) {
+		if ($row['uid'] === '') {
+			$calendar_updates[] = ['id_event' => $row['id_event'], 'uid' => (string) new Uuid()];
+		}
+	}
+	Db::$db->free_result($request);
+
+	foreach ($calendar_updates as $calendar_update) {
+		Db::$db->query(
+			'',
+			'UPDATE {db_prefix}calendar
+			SET uid = {string:uid}
+			WHERE id_event = {int:id_event}',
+			$calendar_update,
+		);
+	}
+
 	// Let's optimize those new tables, but not on InnoDB, ok?
 	if (!$has_innodb) {
 		$tables = Db::$db->list_tables(Db::$db->name, Db::$db->prefix . '%');
diff --git a/other/install_3-0_MySQL.sql b/other/install_3-0_MySQL.sql
index fca8f7057e..875b8ec083 100644
--- a/other/install_3-0_MySQL.sql
+++ b/other/install_3-0_MySQL.sql
@@ -163,16 +163,24 @@ CREATE TABLE {$db_prefix}board_permissions_view
 
 CREATE TABLE {$db_prefix}calendar (
 	id_event SMALLINT UNSIGNED AUTO_INCREMENT,
-	start_date date NOT NULL DEFAULT '1004-01-01',
-	end_date date NOT NULL DEFAULT '1004-01-01',
 	id_board SMALLINT UNSIGNED NOT NULL DEFAULT '0',
 	id_topic MEDIUMINT UNSIGNED NOT NULL DEFAULT '0',
 	title VARCHAR(255) NOT NULL DEFAULT '',
 	id_member MEDIUMINT UNSIGNED NOT NULL DEFAULT '0',
-	start_time time,
-	end_time time,
+	start_date DATE NOT NULL DEFAULT '1004-01-01',
+	end_date DATE NOT NULL DEFAULT '1004-01-01',
+	start_time TIME,
+	end_time TIME,
 	timezone VARCHAR(80),
 	location VARCHAR(255) NOT NULL DEFAULT '',
+	duration VARCHAR(32) NOT NULL DEFAULT '',
+	rrule VARCHAR(1024) NOT NULL DEFAULT 'FREQ=YEARLY;COUNT=1',
+	rdates TEXT NOT NULL,
+	exdates TEXT NOT NULL,
+	adjustments JSON DEFAULT NULL;
+	sequence SMALLINT UNSIGNED NOT NULL DEFAULT '0';
+	uid VARCHAR(255) NOT NULL DEFAULT '',
+	type TINYINT UNSIGNED NOT NULL DEFAULT '0';
 	PRIMARY KEY (id_event),
 	INDEX idx_start_date (start_date),
 	INDEX idx_end_date (end_date),
@@ -1991,8 +1999,8 @@ VALUES ('smfVersion', '{$smf_version}'),
 	('boardindex_max_depth', '5'),
 	('cal_enabled', '0'),
 	('cal_showInTopic', '1'),
-	('cal_maxyear', '2030'),
-	('cal_minyear', '2008'),
+	('cal_maxyear', '2040'),
+	('cal_minyear', '2018'),
 	('cal_daysaslink', '0'),
 	('cal_defaultboard', ''),
 	('cal_showholidays', '1'),
diff --git a/other/install_3-0_PostgreSQL.sql b/other/install_3-0_PostgreSQL.sql
index 86b7340766..3165afe740 100644
--- a/other/install_3-0_PostgreSQL.sql
+++ b/other/install_3-0_PostgreSQL.sql
@@ -324,16 +324,24 @@ CREATE SEQUENCE {$db_prefix}calendar_seq;
 
 CREATE TABLE {$db_prefix}calendar (
 	id_event smallint DEFAULT nextval('{$db_prefix}calendar_seq'),
-	start_date date NOT NULL DEFAULT '1004-01-01',
-	end_date date NOT NULL DEFAULT '1004-01-01',
 	id_board smallint NOT NULL DEFAULT '0',
 	id_topic int NOT NULL DEFAULT '0',
 	title varchar(255) NOT NULL DEFAULT '',
 	id_member int NOT NULL DEFAULT '0',
+	start_date date NOT NULL DEFAULT '1004-01-01',
+	end_date date NOT NULL DEFAULT '1004-01-01',
 	start_time time,
 	end_time time,
 	timezone varchar(80),
-	location VARCHAR(255) NOT NULL DEFAULT '',
+	location varchar(255) NOT NULL DEFAULT '',
+	duration varchar(32) NOT NULL DEFAULT '',
+	rrule varchar(1024) NOT NULL DEFAULT 'FREQ=YEARLY;COUNT=1',
+	rdates text NOT NULL,
+	exdates text NOT NULL,
+	adjustments jsonb DEFAULT NULL;
+	sequence smallint NOT NULL DEFAULT '0';
+	uid VARCHAR(255) NOT NULL DEFAULT '',
+	type smallint NOT NULL DEFAULT '0';
 	PRIMARY KEY (id_event)
 );
 
@@ -2547,8 +2555,8 @@ VALUES ('smfVersion', '{$smf_version}'),
 	('boardindex_max_depth', '5'),
 	('cal_enabled', '0'),
 	('cal_showInTopic', '1'),
-	('cal_maxyear', '2030'),
-	('cal_minyear', '2008'),
+	('cal_maxyear', '2040'),
+	('cal_minyear', '2018'),
 	('cal_daysaslink', '0'),
 	('cal_defaultboard', ''),
 	('cal_showholidays', '1'),
diff --git a/other/upgrade.php b/other/upgrade.php
index a24ff9dfbe..e3b548ff55 100644
--- a/other/upgrade.php
+++ b/other/upgrade.php
@@ -20,6 +20,7 @@
 use SMF\TaskRunner;
 use SMF\User;
 use SMF\Utils;
+use SMF\Uuid;
 use SMF\WebFetch\WebFetchApi;
 
 // Version information...
@@ -1908,6 +1909,32 @@ function DatabaseChanges()
 
 	$_GET['substep'] = 0;
 
+	// Set the UID column for calendar events.
+	$calendar_updates = [];
+	$request = Db::$db->query(
+		'',
+		'SELECT id_event, uid
+		FROM {db_prefix}calendar',
+		[],
+	);
+
+	while ($row = Db::$db->fetch_assoc($request)) {
+		if ($row['uid'] === '') {
+			$calendar_updates[] = ['id_event' => $row['id_event'], 'uid' => (string) new Uuid()];
+		}
+	}
+	Db::$db->free_result($request);
+
+	foreach ($calendar_updates as $calendar_update) {
+		Db::$db->query(
+			'',
+			'UPDATE {db_prefix}calendar
+			SET uid = {string:uid}
+			WHERE id_event = {int:id_event}',
+			$calendar_update,
+		);
+	}
+
 	// So the template knows we're done.
 	if (!$support_js) {
 		$upcontext['changes_complete'] = true;
diff --git a/other/upgrade_3-0_MySQL.sql b/other/upgrade_3-0_MySQL.sql
index 45ed54ef59..79b486df9f 100644
--- a/other/upgrade_3-0_MySQL.sql
+++ b/other/upgrade_3-0_MySQL.sql
@@ -89,3 +89,79 @@ foreach (Config::$modSettings as $variable => $value) {
 }
 ---}
 ---#
+
+
+/******************************************************************************/
+--- Adding support for recurring events...
+/******************************************************************************/
+
+---# Add duration, rrule, rdates, and exdates columns to calendar table
+ALTER TABLE {$db_prefix}calendar
+MODIFY COLUMN start_date DATE AFTER id_member;
+ADD COLUMN duration VARCHAR(32) NOT NULL DEFAULT '';
+ADD COLUMN rrule VARCHAR(1024) NOT NULL DEFAULT 'FREQ=YEARLY;COUNT=1';
+ADD COLUMN rdates TEXT NOT NULL;
+ADD COLUMN exdates TEXT NOT NULL;
+ADD COLUMN adjustments JSON DEFAULT NULL;
+ADD COLUMN sequence SMALLINT UNSIGNED NOT NULL DEFAULT '0';
+ADD COLUMN uid VARCHAR(255) NOT NULL DEFAULT '',
+ADD COLUMN type TINYINT UNSIGNED NOT NULL DEFAULT '0';
+---#
+
+---# Set duration and rrule values and change end_date
+---{
+	$updates = [];
+
+	$request = Db::$db->query(
+		'',
+		'SELECT id_event, start_date, end_date, start_time, end_time, timezone
+		FROM {db_prefix}calendar',
+		[]
+	);
+
+	while ($row = Db::$db->fetch_assoc($request)) {
+		$row = array_diff($row, array_filter($row, 'is_null'));
+
+		$allday = !isset($row['start_time']) || !isset($row['end_time']) || !isset($row['timezone']) || !in_array($row['timezone'], timezone_identifiers_list(\DateTimeZone::ALL_WITH_BC));
+
+		$start = new \DateTime($row['start_date'] . (!$allday ? ' ' . $row['start_time'] . ' ' . $row['timezone'] : ''));
+		$end = new \DateTime($row['end_date'] . (!$allday ? ' ' . $row['end_time'] . ' ' . $row['timezone'] : ''));
+
+		if ($allday) {
+			$end->modify('+1 day');
+		}
+
+		$duration = date_diff($start, $end);
+
+		$format = '';
+		foreach (['y', 'm', 'd', 'h', 'i', 's'] as $part) {
+			if ($part === 'h') {
+				$format .= 'T';
+			}
+
+			if (!empty($duration->{$part})) {
+				$format .= '%' . $part . ($part === 'i' ? 'M' : strtoupper($part));
+			}
+		}
+		$format = rtrim('P' . $format, 'PT');
+
+		$updates[$row['id_event']] = [
+			'id_event' => $row['id_event'],
+			'duration' => $duration->format($format),
+			'end_date' => $end->format('Y-m-d'),
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+		];
+	}
+	Db::$db->free_result($request);
+
+	foreach ($updates as $id_event => $changes) {
+		Db::$db->query(
+			'',
+			'UPDATE {db_prefix}calendar
+			SET duration = {string:duration}, end_date = {date:end_date}, rrule = {string:rrule}
+			WHERE id_event = {int:id_event}',
+			$changes
+		);
+	}
+---}
+---#
\ No newline at end of file
diff --git a/other/upgrade_3-0_PostgreSQL.sql b/other/upgrade_3-0_PostgreSQL.sql
index 45ed54ef59..089ec17dc4 100644
--- a/other/upgrade_3-0_PostgreSQL.sql
+++ b/other/upgrade_3-0_PostgreSQL.sql
@@ -89,3 +89,78 @@ foreach (Config::$modSettings as $variable => $value) {
 }
 ---}
 ---#
+
+/******************************************************************************/
+--- Adding support for recurring events...
+/******************************************************************************/
+
+---# Add duration, rrule, rdates, and exdates columns to calendar table
+ALTER TABLE {$db_prefix}calendar
+ADD COLUMN IF NOT EXISTS duration varchar(32) NOT NULL DEFAULT '';
+ADD COLUMN IF NOT EXISTS rrule varchar(1024) NOT NULL DEFAULT 'FREQ=YEARLY;COUNT=1';
+ADD COLUMN IF NOT EXISTS rdates text NOT NULL;
+ADD COLUMN IF NOT EXISTS exdates text NOT NULL;
+ADD COLUMN IF NOT EXISTS adjustments jsonb DEFAULT NULL;
+ADD COLUMN IF NOT EXISTS sequence smallint NOT NULL DEFAULT '0';
+ADD COLUMN IF NOT EXISTS uid varchar(255) NOT NULL DEFAULT '',
+ADD COLUMN IF NOT EXISTS type smallint NOT NULL DEFAULT '0';
+
+---#
+
+---# Set duration and rrule values and change end_date
+---{
+	$updates = [];
+
+	$request = Db::$db->query(
+		'',
+		'SELECT id_event, start_date, end_date, start_time, end_time, timezone
+		FROM {db_prefix}calendar',
+		[]
+	);
+
+	while ($row = Db::$db->fetch_assoc($request)) {
+		$row = array_diff($row, array_filter($row, 'is_null'));
+
+		$allday = !isset($row['start_time']) || !isset($row['end_time']) || !isset($row['timezone']) || !in_array($row['timezone'], timezone_identifiers_list(\DateTimeZone::ALL_WITH_BC));
+
+		$start = new \DateTime($row['start_date'] . (!$allday ? ' ' . $row['start_time'] . ' ' . $row['timezone'] : ''));
+		$end = new \DateTime($row['end_date'] . (!$allday ? ' ' . $row['end_time'] . ' ' . $row['timezone'] : ''));
+
+		if ($allday) {
+			$end->modify('+1 day');
+		}
+
+		$duration = date_diff($start, $end);
+
+		$format = '';
+		foreach (['y', 'm', 'd', 'h', 'i', 's'] as $part) {
+			if ($part === 'h') {
+				$format .= 'T';
+			}
+
+			if (!empty($duration->{$part})) {
+				$format .= '%' . $part . ($part === 'i' ? 'M' : strtoupper($part));
+			}
+		}
+		$format = rtrim('P' . $format, 'PT');
+
+		$updates[$row['id_event']] = [
+			'id_event' => $row['id_event'],
+			'duration' => $duration->format($format),
+			'end_date' => $end->format('Y-m-d'),
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+		];
+	}
+	Db::$db->free_result($request);
+
+	foreach ($updates as $id_event => $changes) {
+		Db::$db->query(
+			'',
+			'UPDATE {db_prefix}calendar
+			SET duration = {string:duration}, end_date = {date:end_date}, rrule = {string:rrule}
+			WHERE id_event = {int:id_event}',
+			$changes
+		);
+	}
+---}
+---#
\ No newline at end of file

From 141dc8083ca8cfe44157f5e8901f8fd6ec8124ee Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Mon, 11 Dec 2023 01:13:17 -0700
Subject: [PATCH 08/22] Adds support for showing recurring events

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Actions/Calendar.php         |   48 +-
 Sources/Actions/Display.php          |   14 +-
 Sources/Actions/Post.php             |    2 +-
 Sources/Calendar/Event.php           | 1245 +++++++++++++++++---------
 Sources/Calendar/EventOccurrence.php |  476 ++++++++++
 Themes/default/Calendar.template.php |   17 +-
 other/upgrade_3-0_MySQL.sql          |    5 +
 other/upgrade_3-0_PostgreSQL.sql     |    5 +
 8 files changed, 1365 insertions(+), 447 deletions(-)
 create mode 100644 Sources/Calendar/EventOccurrence.php

diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index 6a03dcf0f3..437b311765 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -26,6 +26,7 @@
 use SMF\Lang;
 use SMF\Theme;
 use SMF\Time;
+use SMF\TimeInterval;
 use SMF\TimeZone;
 use SMF\Topic;
 use SMF\User;
@@ -118,7 +119,7 @@ public function show(): void
 		Theme::loadTemplate('Calendar');
 		Theme::loadCSSFile('calendar.css', ['force_current' => false, 'validate' => true, 'rtl' => 'calendar.rtl.css'], 'smf_calendar');
 
-		// Did the specify an individual event ID? If so, let's splice the year/month in to what we would otherwise be doing.
+		// Did they specify an individual event ID? If so, let's splice the year/month in to what we would otherwise be doing.
 		if (isset($_GET['event'])) {
 			$evid = (int) $_GET['event'];
 
@@ -378,7 +379,6 @@ public function post(): void
 					'topic' => 0,
 					'title' => Utils::entitySubstr($_REQUEST['evtitle'], 0, 100),
 					'location' => Utils::entitySubstr($_REQUEST['event_location'], 0, 255),
-					'member' => User::$me->id,
 				];
 				Event::create($eventOptions);
 			}
@@ -455,13 +455,14 @@ public function post(): void
 
 		// An all day event? Set up some nice defaults in case the user wants to change that
 		if (Utils::$context['event']->allday == true) {
+			$now = Time::create('now');
 			Utils::$context['event']->tz = User::getTimezone();
-			Utils::$context['event']->start->modify(Time::create('now')->format('%H:%M:%S'));
-			Utils::$context['event']->end->modify(Time::create('now + 1 hour')->format('%H:%M:%S'));
+			Utils::$context['event']->start->modify(Time::create('now')->format('H:i:s'));
+			Utils::$context['event']->duration = new TimeInterval('PT' . ($now->format('H') < 23 ? '1H' : (59 - $now->format('i')) . 'M'));
 		}
 
 		// Need this so the user can select a timezone for the event.
-		Utils::$context['all_timezones'] = TimeZone::list(Utils::$context['event']->start_date);
+		Utils::$context['all_timezones'] = TimeZone::list(Utils::$context['event']->start_datetime);
 
 		// If the event's timezone is not in SMF's standard list of time zones, try to fix it.
 		Utils::$context['event']->fixTimezone();
@@ -767,27 +768,31 @@ public static function getBirthdayRange(string $low_date, string $high_date): ar
 	 */
 	public static function getEventRange(string $low_date, string $high_date, bool $use_permissions = true): array
 	{
-		$events = [];
+		$occurrences = [];
 
-		$one_day = date_interval_create_from_date_string('1 day');
-		$tz = timezone_open(User::getTimezone());
+		$one_day = new \DateInterval('P1D');
+		$tz = new \DateTimeZone(User::getTimezone());
+		$high_date = (new \DateTimeImmutable($high_date . ' +1 day'))->format('Y-m-d');
 
-		foreach (Event::loadRange($low_date, $high_date, $use_permissions) as $event) {
-			$cal_date = new Time($event->start_date_local, $tz);
+		foreach (Event::getOccurrencesInRange($low_date, $high_date, $use_permissions) as $occurrence) {
+			$cal_date = new Time($occurrence->start_date_local, $tz);
 
-			while ($cal_date->getTimestamp() <= $event->end->getTimestamp() && $cal_date->format('Y-m-d') <= $high_date) {
-				$events[$cal_date->format('Y-m-d')][] = $event;
-				date_add($cal_date, $one_day);
+			while (
+				$cal_date->getTimestamp() < $occurrence->end->getTimestamp()
+				&& $cal_date->format('Y-m-d') < $high_date
+			) {
+				$occurrences[$cal_date->format('Y-m-d')][] = $occurrence;
+				$cal_date->add($one_day);
 			}
 		}
 
-		foreach ($events as $mday => $array) {
-			$events[$mday][count($array) - 1]['is_last'] = true;
+		foreach ($occurrences as $mday => $array) {
+			$occurrences[$mday][count($array) - 1]['is_last'] = true;
 		}
 
-		ksort($events);
+		ksort($occurrences);
 
-		return $events;
+		return $occurrences;
 	}
 
 	/**
@@ -1212,19 +1217,22 @@ public static function getCalendarList(string $start_date, string $end_date, arr
 		$calendarGrid['holidays'] = $calendarOptions['show_holidays'] ? self::getHolidayRange($start_date, $end_date) : [];
 		$calendarGrid['events'] = $calendarOptions['show_events'] ? self::getEventRange($start_date, $end_date) : [];
 
-		// Get rid of duplicate events
+		// Get rid of duplicate events.
+		// This does not get rid of SEPARATE occurrences of a recurring event.
+		// Instead, it gets rid of duplicates of the SAME occurrence, which can
+		// happen when the event duration extends beyond midnight.
 		$temp = [];
 
 		foreach ($calendarGrid['events'] as $date => $date_events) {
 			foreach ($date_events as $event_key => $event_val) {
-				if (in_array($event_val['id'], $temp)) {
+				if (in_array($event_val['id'] . ' ' . $event_val['start']->format('c'), $temp)) {
 					unset($calendarGrid['events'][$date][$event_key]);
 
 					if (empty($calendarGrid['events'][$date])) {
 						unset($calendarGrid['events'][$date]);
 					}
 				} else {
-					$temp[] = $event_val['id'];
+					$temp[] = $event_val['id'] . ' ' . $event_val['start']->format('c');
 				}
 			}
 		}
diff --git a/Sources/Actions/Display.php b/Sources/Actions/Display.php
index 32979cb5aa..a2f840a9d6 100644
--- a/Sources/Actions/Display.php
+++ b/Sources/Actions/Display.php
@@ -1059,8 +1059,18 @@ protected function setupTemplate(): void
 	protected function loadEvents(): void
 	{
 		// If we want to show event information in the topic, prepare the data.
-		if (User::$me->allowedTo('calendar_view') && !empty(Config::$modSettings['cal_showInTopic']) && !empty(Config::$modSettings['cal_enabled'])) {
-			Utils::$context['linked_calendar_events'] = Event::load(Topic::$info->id, true);
+		if (
+			User::$me->allowedTo('calendar_view')
+			&& !empty(Config::$modSettings['cal_showInTopic'])
+			&& !empty(Config::$modSettings['cal_enabled'])
+		) {
+			foreach(Event::load(Topic::$info->id, true) as $event) {
+				if (($occurrence = $event->getUpcomingOccurrence()) === false) {
+					$occurrence = $event->getLastOccurrence();
+				}
+
+				Utils::$context['linked_calendar_events'][] = $occurrence;
+			}
 
 			if (!empty(Utils::$context['linked_calendar_events'])) {
 				Utils::$context['linked_calendar_events'][count(Utils::$context['linked_calendar_events']) - 1]['is_last'] = true;
diff --git a/Sources/Actions/Post.php b/Sources/Actions/Post.php
index c9171e8ce6..1ac0774948 100644
--- a/Sources/Actions/Post.php
+++ b/Sources/Actions/Post.php
@@ -776,7 +776,7 @@ protected function initiateEvent(): void
 		}
 
 		// Need this so the user can select a timezone for the event.
-		Utils::$context['all_timezones'] = TimeZone::list(Utils::$context['event']->start_date);
+		Utils::$context['all_timezones'] = TimeZone::list(Utils::$context['event']->timestamp);
 
 		// If the event's timezone is not in SMF's standard list of time zones, try to fix it.
 		Utils::$context['event']->fixTimezone();
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index e213f17056..a41962fba4 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -21,17 +21,16 @@
 use SMF\Db\DatabaseApi as Db;
 use SMF\ErrorHandler;
 use SMF\IntegrationHook;
+use SMF\Theme;
 use SMF\Time;
+use SMF\TimeInterval;
 use SMF\TimeZone;
 use SMF\User;
 use SMF\Utils;
+use SMF\Uuid;
 
 /**
- * Represents a calendar event.
- *
- * @todo Implement recurring events.
- * @todo Use this class to represent holidays and birthdays. They're all-day
- * events, after all.
+ * Represents a (possibly recurring) calendar event, birthday, or holiday.
  */
 class Event implements \ArrayAccess
 {
@@ -41,10 +40,9 @@ class Event implements \ArrayAccess
 	 * Class constants
 	 *****************/
 
-	public const TYPE_EVENT_SIMPLE = 0;
-	public const TYPE_EVENT_RECURRING = 1; // Not yet implemented.
+	public const TYPE_EVENT = 0;
+	public const TYPE_HOLIDAY = 1; // Not yet implemented.
 	public const TYPE_BIRTHDAY = 2; // Not yet implemented.
-	public const TYPE_HOLIDAY = 4; // Not yet implemented.
 
 	/*******************
 	 * Public properties
@@ -57,27 +55,62 @@ class Event implements \ArrayAccess
 	 */
 	public int $id;
 
+	/**
+	 * @var string
+	 *
+	 * This event's UID string. (Note: UID is not synonymous with UUID!)
+	 *
+	 * For events that were created by SMF, the UID will in fact be a UUID.
+	 * But if the event was imported from iCal data, it could be anything.
+	 */
+	public string $uid;
+
+	/**
+	 * @var string
+	 *
+	 * The recurrence ID of the first individual occurrence of the event.
+	 *
+	 * See RFC 5545, section 3.8.4.4.
+	 */
+	public string $id_first;
+
 	/**
 	 * @var int
 	 *
 	 * This event's type.
 	 * Value must be one of this class's TYPE_* constants.
 	 */
-	public int $type = self::TYPE_EVENT_SIMPLE;
+	public int $type = self::TYPE_EVENT;
 
 	/**
 	 * @var \SMF\Time
 	 *
-	 * An SMF\Time object representing the start of the event.
+	 * A Time object representing the start of the event's first occurrence.
+	 */
+	public Time $start;
+
+	/**
+	 * @var SMF\TimeInterval
+	 *
+	 * A TimeInterval object representing the duration of each occurrence of
+	 * the event.
+	 */
+	public TimeInterval $duration;
+
+	/**
+	 * @var RecurrenceIterator
+	 *
+	 * A RecurrenceIterator object to get individual occurrences of the event.
 	 */
-	public \SMF\Time $start;
+	public RecurrenceIterator $recurrence_iterator;
 
 	/**
 	 * @var \SMF\Time
 	 *
-	 * An SMF\Time object representing the end of the event.
+	 * A Time object representing the date after which no further occurrences
+	 * of the event happen.
 	 */
-	public \SMF\Time $end;
+	public Time $recurrence_end;
 
 	/**
 	 * @var bool
@@ -179,6 +212,7 @@ class Event implements \ArrayAccess
 	protected array $prop_aliases = [
 		'id_event' => 'id',
 		'eventid' => 'id',
+		'end_date' => 'recurrence_end',
 		'id_board' => 'board',
 		'id_topic' => 'topic',
 		'id_first_msg' => 'msg',
@@ -193,17 +227,40 @@ class Event implements \ArrayAccess
 		'end_object' => 'end',
 	];
 
-	/****************************
-	 * Internal static properties
-	 ****************************/
+	/**
+	 * @var \DateTimeImmutable
+	 *
+	 * Occurrences before this date will be skipped when returning results.
+	 */
+	protected \DateTimeInterface $view_start;
 
 	/**
-	 * @var bool
+	 * @var \DateTimeImmutable
+	 *
+	 * Occurrences after this date will be skipped when returning results.
+	 */
+	protected \DateTimeInterface $view_end;
+
+	/**
+	 * @var string
 	 *
-	 * If true, Event::get() will not destroy instances after yielding them.
-	 * This is used internally by Event::load().
+	 * The recurrence rule for the RecurrenceIterator.
 	 */
-	protected static bool $keep_all = false;
+	protected string $rrule = '';
+
+	/**
+	 * @var array
+	 *
+	 * Arbitrary dates to add to the recurrence set.
+	 */
+	protected array $rdates = [];
+
+	/**
+	 * @var array
+	 *
+	 * Arbitrary dates to exclude from the recurrence set.
+	 */
+	protected array $exdates = [];
 
 	/****************
 	 * Public methods
@@ -214,21 +271,49 @@ class Event implements \ArrayAccess
 	 *
 	 * @param int $id The ID number of the event.
 	 * @param array $props Properties to set for this event.
-	 * @return object An instance of this class.
 	 */
 	public function __construct(int $id = 0, array $props = [])
 	{
 		// Preparing default data to show in the calendar posting form.
 		if ($id < 0) {
 			$this->id = $id;
-			$props['start_timestamp'] = time();
-			$props['end_timestamp'] = time() + 3600;
-			$props['timezone'] = User::getTimezone();
-			$props['member'] = User::$me->id;
-			$props['name'] = User::$me->name;
+			$props['start'] = new Time('now ' . User::getTimezone());
+			$props['duration'] = new TimeInterval('PT1H');
+			$props['recurrence_end'] = (clone $props['start'])->add($props['duration']);
+			$props['member'] = $props['member'] ?? User::$me->id;
+			$props['name'] = $props['name'] ?? User::$me->name;
 		}
 		// Creating a new event.
 		elseif ($id == 0) {
+			if (!isset($props['start']) || !($props['start'] instanceof \DateTimeInterface)) {
+				ErrorHandler::fatalLang('invalid_date', false);
+			} elseif (!($props['start'] instanceof Time)) {
+				$props['start'] = Time::createFromInterface($props['start']);
+			}
+
+			if (!isset($props['duration'])) {
+				if (!isset($props['end']) || !($props['end'] instanceof \DateTimeInterface)) {
+					ErrorHandler::fatalLang('invalid_date', false);
+				} else {
+					$props['duration'] = $props['start']->diff($props['end']);
+					unset($props['end']);
+				}
+			}
+
+			if (!isset($props['recurrence_end']) && isset($props['duration'])) {
+				$props['recurrence_end'] = (clone $props['start'])->add($props['duration']);
+			}
+
+			if (!isset($props['rrule'])) {
+				$props['rrule'] = 'FREQ=YEARLY;COUNT=1';
+			} else {
+				// The RRule's week start value can affect recurrence results,
+				// so make sure to save it using the current user's preference.
+				$props['rrule'] = new RRule($props['rrule']);
+				$props['rrule']->wkst = RRule::WEEKDAYS[$start_day = ((Theme::$current->options['calendar_start_day'] ?? 0) + 6) % 7];
+				$props['rrule'] = (string) $props['rrule'];
+			}
+
 			$props['member'] = $props['member'] ?? User::$me->id;
 			$props['name'] = $props['name'] ?? User::$me->name;
 		}
@@ -238,14 +323,81 @@ public function __construct(int $id = 0, array $props = [])
 			self::$loaded[$this->id] = $this;
 		}
 
-		$this->set($props);
+		$props['rdates'] = array_filter($props['rdates'] ?? []);
+		$props['exdates'] = array_filter($props['exdates'] ?? []);
 
-		// This shouldn't happen, but just in case...
-		if (!isset($this->start)) {
-			$this->start = new Time('today');
-			$this->end = new Time('today');
-			$this->allday = true;
+		// Set essential properties.
+		$this->uid = empty($props['uid']) ? (string) new Uuid() : $props['uid'];
+
+		$this->rrule = empty($props['rrule']) ? 'FREQ=YEARLY;COUNT=1' : $props['rrule'];
+
+		$this->start = $props['start'] instanceof Time ? $props['start'] : Time::createFromInterface($props['start']);
+
+		$this->allday = !empty($props['allday']);
+
+		$this->duration = TimeInterval::createFromDateInterval($props['duration']) ?? new TimeInterval(!empty($this->allday) ? 'P1D' : 'PT1H');
+
+		if (isset($props['view_start'])) {
+			$this->view_start = $props['view_start'] instanceof \DateTimeInterface ? $props['view_start'] : new \DateTimeImmutable($props['view_start']);
+		} else {
+			$this->view_start = clone $this->start;
+		}
+
+		if (isset($props['view_end'])) {
+			$this->view_end = $props['view_end'] instanceof \DateTimeInterface ? $props['view_end'] : new \DateTimeImmutable($props['view_end']);
+		} else {
+			$this->view_end = (clone $this->view_start)->add(new TimeInterval('P1Y'));
+		}
+
+		if (!empty($props['rdates'])) {
+			$this->rdates = is_array($props['rdates']) ? $props['rdates'] : explode(',', $props['rdates']);
+
+			$vs = $this->view_start->format('Ymd');
+			$ve = $this->view_end->format('Ymd');
+
+			foreach ($this->rdates as $key => $rdate) {
+				$d = substr($rdate, 0, 8);
+
+				if ($d < $vs || $d > $ve) {
+					unset($this->rdates[$key]);
+
+					continue;
+				}
+
+				$rdate = explode('/', $rdate);
+				$this->rdates[$key] = [
+					new \DateTimeImmutable($rdate[0]),
+					isset($rdate[1]) ? new TimeInterval($rdate[1]) : null,
+				];
+			}
+		}
+
+		if (!empty($props['exdates'])) {
+			$this->exdates = is_array($props['exdates']) ? $props['exdates'] : explode(',', $props['exdates']);
+
+			foreach ($this->exdates as $key => $exdate) {
+				$this->exdates[$key] = new \DateTimeImmutable($exdate);
+			}
 		}
+
+		unset(
+			$props['rrule'],
+			$props['start'],
+			$props['allday'],
+			$props['duration'],
+			$props['view_start'],
+			$props['view_end'],
+			$props['rdates'],
+			$props['exdates'],
+			$props['adjustments'],
+		);
+
+		$this->id_first = $this->allday ? $this->start->format('Ymd') : (clone $this->start)->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\\THis\\Z');
+
+		$this->createRecurrenceIterator();
+
+		// Set any other properties.
+		$this->set($props);
 	}
 
 	/**
@@ -262,33 +414,42 @@ public function save(): void
 				'end_date' => 'date',
 				'id_board' => 'int',
 				'id_topic' => 'int',
-				'title' => 'string-60',
+				'title' => 'string-255',
 				'id_member' => 'int',
 				'location' => 'string-255',
+				'duration' => 'string-32',
+				'rrule' => 'string',
+				'rdates' => 'string',
+				'exdates' => 'string',
+				'uid' => 'string-255',
+				'type' => 'int',
 			];
 
 			$params = [
 				$this->start->format('Y-m-d'),
-				$this->end->format('Y-m-d'),
+				(clone $this->recurrence_end)->sub($this->duration)->format('Y-m-d'),
 				$this->board,
 				$this->topic,
-				$this->title,
+				Utils::truncate($this->title, 255),
 				$this->member,
-				$this->location,
+				Utils::truncate($this->location, 255),
+				(string) $this->duration,
+				(string) ($this->recurrence_iterator->getRRule()),
+				implode(',', $this->recurrence_iterator->getRDates()),
+				implode(',', $this->recurrence_iterator->getExDates()),
+				$this->uid,
+				$this->type,
 			];
 
 			if (!$this->allday) {
 				$columns['start_time'] = 'time';
 				$params[] = $this->start->format('H:i:s');
 
-				$columns['end_time'] = 'time';
-				$params[] = $this->end->format('H:i:s');
-
 				$columns['timezone'] = 'string';
 				$params[] = $this->start->format('e');
 			}
 
-			IntegrationHook::call('integrate_create_event', [(array) $this, &$columns, &$params]);
+			IntegrationHook::call('integrate_create_event', [$this, &$columns, &$params]);
 
 			$this->id = Db::$db->insert(
 				'',
@@ -306,33 +467,41 @@ public function save(): void
 			$set = [
 				'start_date = {date:start_date}',
 				'end_date = {date:end_date}',
-				'title = SUBSTRING({string:title}, 1, 60)',
+				'title = {string:title}',
 				'id_board = {int:id_board}',
 				'id_topic = {int:id_topic}',
-				'location = SUBSTRING({string:location}, 1, 255)',
+				'location = {string:location}',
+				'duration = {string:duration}',
+				'rrule = {string:rrule}',
+				'rdates = {string:rdates}',
+				'exdates = {string:exdates}',
+				'uid = {string:uid}',
+				'type = {int:type}',
 			];
 
 			$params = [
 				'id' => $this->id,
 				'start_date' => $this->start->format('Y-m-d'),
-				'end_date' => $this->end->format('Y-m-d'),
-				'title' => $this->title,
-				'location' => $this->location,
+				'end_date' => (clone $this->recurrence_end)->sub($this->duration)->format('Y-m-d'),
+				'title' => Utils::truncate($this->title, 255),
+				'location' => Utils::truncate($this->location, 255),
 				'id_board' => $this->board,
 				'id_topic' => $this->topic,
+				'duration' => (string) $this->duration,
+				'rrule' => (string) ($this->recurrence_iterator->getRRule()),
+				'rdates' => implode(',', $this->recurrence_iterator->getRDates()),
+				'exdates' => implode(',', $this->recurrence_iterator->getExDates()),
+				'uid' => $this->uid,
+				'type' => $this->type,
 			];
 
 			if ($this->allday) {
 				$set[] = 'start_time = NULL';
-				$set[] = 'end_time = NULL';
 				$set[] = 'timezone = NULL';
 			} else {
 				$set[] = 'start_time = {time:start_time}';
 				$params['start_time'] = $this->start->format('H:i:s');
 
-				$set[] = 'end_time = {time:end_time}';
-				$params['end_time'] = $this->end->format('H:i:s');
-
 				$set[] = 'timezone = {string:timezone}';
 				$params['timezone'] = $this->start->format('e');
 			}
@@ -354,251 +523,342 @@ public function save(): void
 		]);
 	}
 
+	// /**
+	//  * @todo Builds an iCalendar document for the event, including all
+	//  * recurrence info.
+	//  *
+	//  * @return string An iCalendar VEVENT document.
+	//  */
+	// public function getVEvent(): string
+	// {
+	// 	return '';
+	// }
+
 	/**
+	 * Returns a generator that yields all occurrences of the event between
+	 * $this->view_start and $this->view_end.
 	 *
+	 * @return Generator<EventOccurrence> Iterating over result gives
+	 *    EventOccurrence instances.
 	 */
-	public function getVEvent(): string
+	public function getAllVisibleOccurrences(): \Generator
 	{
-		// Check the title isn't too long - iCal requires some formatting if so.
-		$title = str_split($this->title, 30);
+		// Where are we currently?
+		$orig_key = $this->recurrence_iterator->key();
 
-		foreach ($title as $id => $line) {
-			if ($id != 0) {
-				$title[$id] = ' ' . $title[$id];
-			}
+		// Go to the start.
+		$this->recurrence_iterator->rewind();
+
+		while ($this->recurrence_iterator->valid()) {
+			yield $this->createOccurrence($this->recurrence_iterator->current());
+			$this->recurrence_iterator->next();
 		}
 
-		// This is what we will be sending later.
-		$filecontents = [];
-		$filecontents[] = 'BEGIN:VEVENT';
-		$filecontents[] = 'ORGANIZER;CN="' . $this->name . '":MAILTO:' . Config::$webmaster_email;
-		$filecontents[] = 'DTSTAMP:' . date('Ymd\\THis\\Z', time());
-		$filecontents[] = 'DTSTART' . (!$this->allday ? ';TZID=' . $this->tz : ';VALUE=DATE') . ':' . $this->start->format('Ymd' . ($this->allday ? '' : '\\THis'));
+		// Go back to where we were before.
+		$this->recurrence_iterator->setKey($orig_key);
+	}
 
-		// Event has a duration/
-		if (
-			(!$this->allday && $this->start_iso_gmdate != $this->end_iso_gmdate)
-			|| ($this->allday && $this->start_date != $this->end_date)
-		) {
-			$filecontents[] = 'DTEND' . (!$this->allday ? ';TZID=' . $this->tz : ';VALUE=DATE') . ':' . $this->end->format('Ymd' . ($this->allday ? '' : '\\THis'));
+	/**
+	 * Gets the next occurrence of the event after the date given by $when.
+	 *
+	 * @param ?\DateTimeInterface $when The moment from which we should start
+	 *    looking for the next occurrence. If null, uses now.
+	 * @return EventOccurrence|false An EventOccurrence object, or false if no
+	 *    occurrences happen after $when.
+	 */
+	public function getUpcomingOccurrence(?\DateTimeInterface $when = null): EventOccurrence|false
+	{
+		if (!isset($when)) {
+			$when = new \DateTimeImmutable('now');
 		}
 
-		// Event has changed? Advance the sequence for this UID.
-		if ($this->sequence > 0) {
-			$filecontents[] = 'SEQUENCE:' . $this->sequence;
+		if (!$this->recurrence_iterator->valid() || $this->recurrence_iterator->current() > $when) {
+			$this->recurrence_iterator->rewind();
 		}
 
-		if (!empty($this->location)) {
-			$filecontents[] = 'LOCATION:' . str_replace(',', '\\,', $this->location);
+		if (!$this->recurrence_iterator->valid()) {
+			return false;
 		}
 
-		$filecontents[] = 'SUMMARY:' . implode('', $title);
-		$filecontents[] = 'UID:' . $this->id . '@' . str_replace(' ', '-', Config::$mbname);
-		$filecontents[] = 'END:VEVENT';
+		while ($this->recurrence_iterator->valid() && $this->recurrence_iterator->current() < $when) {
+			$this->recurrence_iterator->next();
 
-		return implode("\n", $filecontents);
+			if (!$this->recurrence_iterator->valid()) {
+				return false;
+			}
+		}
+
+		return $this->createOccurrence($this->recurrence_iterator->current());
 	}
 
 	/**
+	 * Gets the first occurrence of the event.
 	 *
+	 * @return EventOccurrence|false EventOccurrence object, or false on error.
 	 */
-	public function fixTimezone(): void
+	public function getFirstOccurrence(): EventOccurrence|false
 	{
-		$all_timezones = Utils::$context['all_timezones'] ?? TimeZone::list($this->start_date);
+		// Where are we currently?
+		$orig_key = $this->recurrence_iterator->key();
 
-		if (!isset($all_timezones[$this->timezone])) {
-			$later = strtotime('@' . $this->start_timestamp . ' + 1 year');
-			$tzinfo = timezone_transitions_get(timezone_open($this->timezone), $this->start_timestamp, $later);
-
-			$found = false;
+		// Go to the start.
+		$this->recurrence_iterator->rewind();
 
-			foreach ($all_timezones as $possible_tzid => $dummy) {
-				// Ignore the "-----" option
-				if (empty($possible_tzid)) {
-					continue;
-				}
-
-				$possible_tzinfo = timezone_transitions_get(timezone_open($possible_tzid), $this->start_timestamp, $later);
+		// Create the occurrence object.
+		if ($this->recurrence_iterator->valid()) {
+			$occurrence = $this->createOccurrence($this->recurrence_iterator->current());
+		}
 
-				if ($tzinfo === $possible_tzinfo) {
-					$this->timezone = $possible_tzid;
-					$found = true;
-					break;
-				}
-			}
+		// Go back to where we were before.
+		$this->recurrence_iterator->setKey($orig_key);
 
-			// Hm. That's weird. Well, just prepend it to the list and let the user deal with it.
-			if (!$found) {
-				$all_timezones = [$this->timezone => '[UTC' . $this->start->format('P') . '] - ' . $this->timezone] + $all_timezones;
-			}
-		}
+		// Return the occurrence object, or false on error.
+		return $occurrence ?? false;
 	}
 
 	/**
-	 * Sets custom properties.
+	 * Gets the last occurrence of the event.
 	 *
-	 * @param string $prop The property name.
-	 * @param mixed $value The value to set.
+	 * @return EventOccurrence|false EventOccurrence object, or false on error.
 	 */
-	public function __set(string $prop, mixed $value): void
+	public function getLastOccurrence(): EventOccurrence|false
 	{
-		if (property_exists($this, $prop)) {
-			$type = isset($this->{$prop}) ? gettype($this->{$prop}) : null;
+		// Where are we currently?
+		$orig_key = $this->recurrence_iterator->key();
 
-			if (!empty($type)) {
-				settype($value, $type);
-			}
+		// Go to the end.
+		$this->recurrence_iterator->end();
 
-			$this->{$prop} = $value;
-		} elseif (array_key_exists($prop, $this->prop_aliases)) {
-			// Can't unset a virtual property.
-			if (is_null($value)) {
-				return;
-			}
+		// Create the occurrence object.
+		if ($this->recurrence_iterator->valid()) {
+			$occurrence = $this->createOccurrence($this->recurrence_iterator->current());
+		}
 
-			$real_prop = $this->prop_aliases[$prop];
+		// Go back to where we were before.
+		$this->recurrence_iterator->setKey($orig_key);
 
-			if (strpos($real_prop, '!') === 0) {
-				$real_prop = ltrim($real_prop, '!');
-				$value = !$value;
-			}
+		// Return the occurrence object, or false on error.
+		return $occurrence ?? false;
+	}
 
-			if (strpos($real_prop, '[') !== false) {
-				$real_prop = explode('[', rtrim($real_prop, ']'));
+	/**
+	 * Gets an occurrence of the event by its recurrence ID.
+	 *
+	 * @param string $id The recurrence ID string.
+	 * @return EventOccurrence|false EventOccurrence object, or false on error.
+	 */
+	public function getOccurrence(string $id): EventOccurrence|false
+	{
+		// Where are we currently?
+		$orig_key = $this->recurrence_iterator->key();
 
-				$this->{$real_prop[0]}[$real_prop[1]] = $value;
-			} else {
-				if ($real_prop == 'id') {
-					$this->{$real_prop} = (int) $value;
-				} else {
-					settype($value, gettype($this->{$real_prop}));
-					$this->{$real_prop} = $value;
-				}
-			}
-		} else {
-			// For simplicity's sake...
-			if (in_array($prop, ['year', 'month', 'day', 'hour', 'minute', 'second'])) {
-				$prop = 'start_' . $prop;
-			}
+		// Search for the requested ID.
+		if (($key = $this->recurrence_iterator->search($id)) !== false) {
+			// Select the requested occurrence.
+			$this->recurrence_iterator->setKey($key);
 
-			if (($start_end = substr($prop, 0, (int) strpos($prop, '_'))) !== 'end') {
-				$start_end = 'start';
-			}
+			// Create the occurrence object.
+			$occurrence = $this->createOccurrence($this->recurrence_iterator->current());
+		}
 
-			if (!isset($this->{$start_end})) {
-				$this->{$start_end} = new Time();
-			}
+		// Go back to where we were before.
+		$this->recurrence_iterator->setKey($orig_key);
 
-			switch ($prop) {
-				case 'start_datetime':
-				case 'end_datetime':
-					$this->{$start_end}->datetime = $value;
-					break;
+		// Return the occurrence object, or false on error.
+		return $occurrence ?? false;
+	}
 
-				case 'start_date':
-				case 'end_date':
-					$this->{$start_end}->date = $value;
-					break;
+	/**
+	 * Sets custom properties.
+	 *
+	 * @param string $prop The property name.
+	 * @param mixed $value The value to set.
+	 */
+	public function __set(string $prop, mixed $value): void
+	{
+		if (!isset($this->start)) {
+			$this->start = new Time();
+		}
 
-				case 'start_time':
-				case 'end_time':
-					$this->{$start_end}->time = $value;
-					break;
+		if (!isset($this->duration)) {
+			$this->duration = new TimeInterval(!empty($this->allday) ? 'P1D' : 'PT1H');
+		}
 
-				case 'start_date_orig':
-				case 'end_date_orig':
-					$this->{$start_end}->date_orig = $value;
-					break;
+		if (str_starts_with($prop, 'end') || str_starts_with($prop, 'last')) {
+			$end = (clone $this->start)->add($this->duration);
+		}
 
-				case 'start_time_orig':
-				case 'end_time_orig':
-					$this->{$start_end}->time_orig = $value;
-					break;
+		if (str_starts_with($prop, 'last')) {
+			$last = (clone $end)->modify('-1 ' . ($this->allday ? 'day' : 'second'));
+		}
 
-				case 'start_date_local':
-				case 'end_date_local':
-					$this->{$start_end}->date_local = $value;
-					break;
+		switch ($prop) {
+			// Special handling for stuff that affects start.
+			case 'start':
+				if ($value instanceof \DateTimeInterface) {
+					$this->start = Time::createFromInterface($value);
+				}
+				break;
 
-				case 'start_time_local':
-				case 'end_time_local':
-					$this->{$start_end}->time_local = $value;
-					break;
+			case 'datetime':
+			case 'date':
+			case 'date_local':
+			case 'date_orig':
+			case 'time':
+			case 'time_local':
+			case 'time_orig':
+			case 'year':
+			case 'month':
+			case 'day':
+			case 'hour':
+			case 'minute':
+			case 'second':
+			case 'timestamp':
+			case 'iso_gmdate':
+			case 'tz':
+			case 'tzid':
+			case 'timezone':
+				$this->start->{$prop} = $value;
+				break;
 
-				case 'start_year':
-				case 'end_year':
-					$this->{$start_end}->year = $value;
-					break;
+			case 'start_datetime':
+			case 'start_date':
+			case 'start_date_local':
+			case 'start_date_orig':
+			case 'start_time':
+			case 'start_time_local':
+			case 'start_time_orig':
+			case 'start_year':
+			case 'start_month':
+			case 'start_day':
+			case 'start_hour':
+			case 'start_minute':
+			case 'start_second':
+			case 'start_timestamp':
+			case 'start_iso_gmdate':
+				$this->start->{substr($prop, 6)} = $value;
+				break;
 
-				case 'start_month':
-				case 'end_month':
-					$this->{$start_end}->month = $value;
-					break;
+			// Special handling for duration.
+			case 'duration':
+				if (!($value instanceof \DateInterval)) {
+					try {
+						$value = new TimeInterval((string) $value);
+					} catch (\Throwable $e) {
+						break;
+					}
+				} elseif (!($value instanceof TimeInterval)) {
+					$value = TimeInterval::createFromDateInterval($value);
+				}
+				$this->duration = $value;
+				break;
 
-				case 'start_day':
-				case 'end_day':
-					$this->{$start_end}->day = $value;
-					break;
+			case 'end':
+				if (!($value instanceof \DateTimeInterface)) {
+					try {
+						$value = new \DateTimeImmutable((is_numeric($value) ? '@' : '') . $value);
+					} catch (\Throwable $e) {
+						break;
+					}
+				}
+				$this->duration = $this->start->diff($value);
+				break;
 
-				case 'start_hour':
-				case 'end_hour':
-					$this->{$start_end}->hour = $value;
-					break;
+			case 'end_datetime':
+			case 'end_date':
+			case 'end_date_local':
+			case 'end_date_orig':
+			case 'end_time':
+			case 'end_time_local':
+			case 'end_time_orig':
+			case 'end_year':
+			case 'end_month':
+			case 'end_day':
+			case 'end_hour':
+			case 'end_minute':
+			case 'end_second':
+			case 'end_timestamp':
+			case 'end_iso_gmdate':
+				$end->{substr($prop, 4)} = $value;
+				$this->duration = $this->start->diff($end);
+				break;
 
-				case 'start_minute':
-				case 'end_minute':
-					$this->{$start_end}->minute = $value;
-					break;
+			case 'last':
+				if (!($value instanceof \DateTimeInterface)) {
+					try {
+						$value = new \DateTimeImmutable((is_numeric($value) ? '@' : '') . $value);
+					} catch (\Throwable $e) {
+						break;
+					}
+				}
+				$this->duration = $this->start->diff($value->modify('+1 ' . ($this->allday ? 'day' : 'second')));
+				break;
 
-				case 'start_second':
-				case 'end_second':
-					$this->{$start_end}->second = $value;
-					// no break
+			case 'last_datetime':
+			case 'last_date':
+			case 'last_date_local':
+			case 'last_date_orig':
+			case 'last_time':
+			case 'last_time_local':
+			case 'last_time_orig':
+			case 'last_year':
+			case 'last_month':
+			case 'last_day':
+			case 'last_hour':
+			case 'last_minute':
+			case 'last_second':
+			case 'last_timestamp':
+			case 'last_iso_gmdate':
+				$last->{substr($prop, 5)} = $value;
+				$end = (clone $last)->modify('+1 ' . ($this->allday ? 'day' : 'second'));
+				$this->duration = $this->start->diff($end);
+				break;
 
-				case 'start_timestamp':
-				case 'end_timestamp':
-					$this->{$start_end}->timestamp = $value;
-					break;
+			// Special handling for stuff that affects recurrence.
+			case 'rrule':
+			case 'view_start':
+			case 'view_end':
+				$this->{$prop} = $value;
+				$this->createRecurrenceIterator();
+				break;
 
-				case 'start_iso_gmdate':
-				case 'end_iso_gmdate':
-					$this->{$start_end}->iso_gmdate = $value;
-					break;
+			case 'rdates':
+				$this->rdates = is_array($value) ? $value : explode(',', (string) $value);
 
-				case 'tz':
-				case 'tzid':
-				case 'timezone':
-					if ($value instanceof \DateTimeZone) {
-						$this->start->setTimezone($value);
-						$this->end->setTimezone($value);
-					} else {
-						$this->start->timezone = $value;
-						$this->end->timezone = $value;
-					}
+				foreach ($this->rdates as $key => $rdate) {
+					$rdate = explode('/', $rdate);
+					$this->rdates[$key] = [
+						new \DateTimeImmutable($rdate[0]),
+						isset($rdate[1]) ? new TimeInterval($rdate[1]) : null,
+					];
+				}
+				$this->createRecurrenceIterator();
+				break;
 
-					break;
+			case 'exdates':
+				$this->exdates = is_array($value) ? $value : explode(',', (string) $value);
 
-				// These computed properties are read-only.
-				case 'tz_abbrev':
-				case 'new':
-				case 'is_selected':
-				case 'href':
-				case 'link':
-				case 'can_edit':
-				case 'modify_href':
-				case 'can_export':
-				case 'export_href':
-					break;
+				foreach ($this->exdates as $key => $exdate) {
+					$this->exdates[$key] = new \DateTimeImmutable($exdate);
+				}
+				$this->createRecurrenceIterator();
+				break;
 
-				default:
-					$this->custom[$prop] = $value;
-					break;
-			}
-		}
+			// These computed properties are read-only.
+			case 'new':
+			case 'is_selected':
+			case 'href':
+			case 'link':
+			case 'can_edit':
+			case 'modify_href':
+			case 'can_export':
+			case 'export_href':
+				break;
 
-		// Ensure that the dates still make sense with each other.
-		if (isset($this->start, $this->end)) {
-			self::fixEndDate();
+			// Everything else.
+			default:
+				$this->customPropertySet($prop, $value);
+				break;
 		}
 	}
 
@@ -606,123 +866,101 @@ public function __set(string $prop, mixed $value): void
 	 * Gets custom property values.
 	 *
 	 * @param string $prop The property name.
+	 * @return mixed The property value.
 	 */
 	public function __get(string $prop): mixed
 	{
-		if (property_exists($this, $prop)) {
-			return $this->{$prop} ?? null;
+		if (str_starts_with($prop, 'end') || str_starts_with($prop, 'last')) {
+			$end = (clone $this->start)->add($this->duration);
 		}
 
-		if (array_key_exists($prop, $this->prop_aliases)) {
-			$real_prop = $this->prop_aliases[$prop];
-
-			if (($not = strpos($real_prop, '!') === 0)) {
-				$real_prop = ltrim($real_prop, '!');
-			}
-
-			if (strpos($real_prop, '[') !== false) {
-				$real_prop = explode('[', rtrim($real_prop, ']'));
-
-				$value = $this->{$real_prop[0]}[$real_prop[1]];
-			} else {
-				$value = $this->{$real_prop};
-			}
-
-			return $not ? !$value : $value;
-		}
-
-		if (in_array($prop, ['year', 'month', 'day', 'hour', 'minute', 'second'])) {
-			$prop = 'start_' . $prop;
-		}
-
-		if (($start_end = substr($prop, 0, (int) strpos($prop, '_'))) !== 'end') {
-			$start_end = 'start';
+		if (str_starts_with($prop, 'last')) {
+			$last = (clone $end)->modify('-1 ' . ($this->allday ? 'day' : 'second'));
 		}
 
 		switch ($prop) {
-			case 'start_datetime':
-			case 'end_datetime':
-				$value = $this->{$start_end}->datetime;
+			case 'datetime':
+			case 'date':
+			case 'date_local':
+			case 'date_orig':
+			case 'time':
+			case 'time_local':
+			case 'time_orig':
+			case 'year':
+			case 'month':
+			case 'day':
+			case 'hour':
+			case 'minute':
+			case 'second':
+			case 'timestamp':
+			case 'iso_gmdate':
+			case 'tz':
+			case 'tzid':
+			case 'timezone':
+			case 'tz_abbrev':
+				$value = $this->start->{$prop};
 				break;
 
+			case 'start_datetime':
 			case 'start_date':
-			case 'end_date':
-				$value = $this->{$start_end}->date;
-				break;
-
 			case 'start_date_local':
-			case 'end_date_local':
-				$value = $this->{$start_end}->date_local;
-				break;
-
 			case 'start_date_orig':
-			case 'end_date_orig':
-				$value = $this->{$start_end}->date_orig;
-				break;
-
 			case 'start_time':
-			case 'end_time':
-				$value = $this->{$start_end}->time;
-				break;
-
 			case 'start_time_local':
-			case 'end_time_local':
-				$value = $this->{$start_end}->time_local;
-				break;
-
 			case 'start_time_orig':
-			case 'end_time_orig':
-				$value = $this->{$start_end}->time_orig;
-				break;
-
 			case 'start_year':
-			case 'end_year':
-				$value = $this->{$start_end}->format('Y');
-				break;
-
 			case 'start_month':
-			case 'end_month':
-				$value = $this->{$start_end}->format('m');
-				break;
-
 			case 'start_day':
-			case 'end_day':
-				$value = $this->{$start_end}->format('d');
-				break;
-
 			case 'start_hour':
-			case 'end_hour':
-				$value = $this->{$start_end}->format('H');
-				break;
-
 			case 'start_minute':
-			case 'end_minute':
-				$value = $this->{$start_end}->format('i');
-				break;
-
 			case 'start_second':
-			case 'end_second':
-				$value = $this->{$start_end}->format('s');
+			case 'start_timestamp':
+			case 'start_iso_gmdate':
+				$value = $this->start->{substr($prop, 6)};
 				break;
 
-			case 'start_timestamp':
-			case 'end_timestamp':
-				$value = $this->{$start_end}->getTimestamp() - ($this->allday ? $this->{$start_end}->getTimestamp() % 86400 : 0);
+			case 'end':
+				$value = $end;
 				break;
 
-			case 'start_iso_gmdate':
+			case 'end_datetime':
+			case 'end_date':
+			case 'end_date_local':
+			case 'end_date_orig':
+			case 'end_time':
+			case 'end_time_local':
+			case 'end_time_orig':
+			case 'end_year':
+			case 'end_month':
+			case 'end_day':
+			case 'end_hour':
+			case 'end_minute':
+			case 'end_second':
+			case 'end_timestamp':
 			case 'end_iso_gmdate':
-				$value = $this->allday ? preg_replace('/T\d\d:\d\d:\d\d/', 'T00:00:00', $this->{$start_end}->iso_gmdate) : $this->{$start_end}->iso_gmdate;
+				$value = $end->{substr($prop, 4)};
 				break;
 
-			case 'tz':
-			case 'tzid':
-			case 'timezone':
-				$value = $this->start->timezone;
+			case 'last':
+				$value = $last;
 				break;
 
-			case 'tz_abbrev':
-				$value = $this->start->tz_abbrev;
+			case 'last_datetime':
+			case 'last_date':
+			case 'last_date_local':
+			case 'last_date_orig':
+			case 'last_time':
+			case 'last_time_local':
+			case 'last_time_orig':
+			case 'last_year':
+			case 'last_month':
+			case 'last_day':
+			case 'last_hour':
+			case 'last_minute':
+			case 'last_second':
+			case 'last_timestamp':
+			case 'last_iso_gmdate':
+				$value = $last->{substr($prop, 5)};
 				break;
 
 			case 'new':
@@ -757,11 +995,25 @@ public function __get(string $prop): mixed
 				$value = Config::$scripturl . '?action=calendar;sa=ical;eventid=' . $this->id . ';' . Utils::$context['session_var'] . '=' . Utils::$context['session_id'];
 				break;
 
+			case 'rrule':
+				$value = isset($this->recurrence_iterator) ? $this->recurrence_iterator->getRRule() : null;
+				break;
+
+			case 'rdates':
+				$value = isset($this->recurrence_iterator) ? $this->recurrence_iterator->getRDates() : null;
+				break;
+
+			case 'exdates':
+				$value = isset($this->recurrence_iterator) ? $this->recurrence_iterator->getExDates() : null;
+				break;
+
 			default:
-				$value = $this->custom[$prop] ?? null;
+				$value = $this->customPropertyGet($prop);
 				break;
 		}
 
+		unset($end, $last);
+
 		return $value;
 	}
 
@@ -769,67 +1021,80 @@ public function __get(string $prop): mixed
 	 * Checks whether a custom property has been set.
 	 *
 	 * @param string $prop The property name.
+	 * @return bool Whether the property has been set.
 	 */
 	public function __isset(string $prop): bool
 	{
-		if (property_exists($this, $prop)) {
-			return isset($this->{$prop});
-		}
-
-		if (array_key_exists($prop, $this->prop_aliases)) {
-			$real_prop = ltrim($this->prop_aliases[$prop], '!');
-
-			if (strpos($real_prop, '[') !== false) {
-				$real_prop = explode('[', rtrim($real_prop, ']'));
-
-				return isset($this->{$real_prop[0]}[$real_prop[1]]);
-			}
-
-			return isset($this->{$real_prop});
-		}
-
-		if (in_array($prop, ['year', 'month', 'day', 'hour', 'minute', 'second'])) {
-			$prop = 'start_' . $prop;
-		}
-
 		switch ($prop) {
 			case 'start_datetime':
 			case 'start_date':
+			case 'start_date_local':
+			case 'start_date_orig':
 			case 'start_time':
+			case 'start_time_local':
+			case 'start_time_orig':
 			case 'start_year':
 			case 'start_month':
 			case 'start_day':
 			case 'start_hour':
 			case 'start_minute':
 			case 'start_second':
-			case 'start_date_local':
-			case 'start_date_orig':
-			case 'start_time_local':
-			case 'start_time_orig':
 			case 'start_timestamp':
 			case 'start_iso_gmdate':
+			case 'datetime':
+			case 'date':
+			case 'date_local':
+			case 'date_orig':
+			case 'time':
+			case 'time_local':
+			case 'time_orig':
+			case 'year':
+			case 'month':
+			case 'day':
+			case 'hour':
+			case 'minute':
+			case 'second':
+			case 'timestamp':
+			case 'iso_gmdate':
 			case 'tz':
 			case 'tzid':
 			case 'timezone':
 			case 'tz_abbrev':
-				return property_exists($this, 'start');
+				return isset($this->start);
 
+			case 'end':
 			case 'end_datetime':
 			case 'end_date':
+			case 'end_date_local':
+			case 'end_date_orig':
 			case 'end_time':
+			case 'end_time_local':
+			case 'end_time_orig':
 			case 'end_year':
 			case 'end_month':
 			case 'end_day':
 			case 'end_hour':
 			case 'end_minute':
 			case 'end_second':
-			case 'end_date_local':
-			case 'end_date_orig':
-			case 'end_time_local':
-			case 'end_time_orig':
 			case 'end_timestamp':
 			case 'end_iso_gmdate':
-				return property_exists($this, 'end');
+			case 'last':
+			case 'last_datetime':
+			case 'last_date':
+			case 'last_date_local':
+			case 'last_date_orig':
+			case 'last_time':
+			case 'last_time_local':
+			case 'last_time_orig':
+			case 'last_year':
+			case 'last_month':
+			case 'last_day':
+			case 'last_hour':
+			case 'last_minute':
+			case 'last_second':
+			case 'last_timestamp':
+			case 'last_iso_gmdate':
+				return isset($this->start, $this->duration);
 
 			case 'new':
 			case 'is_selected':
@@ -842,7 +1107,42 @@ public function __isset(string $prop): bool
 				return true;
 
 			default:
-				return isset($this->custom[$prop]);
+				return $this->customPropertyIsset($prop);
+		}
+	}
+
+	/**
+	 *
+	 */
+	public function fixTimezone(): void
+	{
+		$all_timezones = TimeZone::list($this->start->date);
+
+		if (!isset($all_timezones[$this->start->timezone])) {
+			$later = strtotime('@' . $this->start->timestamp . ' + 1 year');
+			$tzinfo = (new \DateTimeZone($this->start->timezone))->getTransitions($this->start->timestamp, $later);
+
+			$found = false;
+
+			foreach ($all_timezones as $possible_tzid => $dummy) {
+				// Ignore the "-----" option
+				if (empty($possible_tzid)) {
+					continue;
+				}
+
+				$possible_tzinfo = (new \DateTimeZone($possible_tzid))->getTransitions($this->start->timestamp, $later);
+
+				if ($tzinfo === $possible_tzinfo) {
+					$this->start->timezone = $possible_tzid;
+					$found = true;
+					break;
+				}
+			}
+
+			// Hm. That's weird. Well, just prepend it to the list and let the user deal with it.
+			if (!$found) {
+				$all_timezones = [$this->start->timezone => '[UTC' . $this->start->format('P') . '] - ' . $this->start->timezone] + $all_timezones;
+			}
 		}
 	}
 
@@ -851,82 +1151,120 @@ public function __isset(string $prop): bool
 	 ***********************/
 
 	/**
-	 * Loads events by ID number or by topic.
+	 * Loads an event by ID number or by topic ID.
 	 *
 	 * @param int $id ID number of the event or topic.
 	 * @param bool $is_topic If true, $id is the topic ID. Default: false.
 	 * @param bool $use_permissions Whether to use permissions. Default: true.
-	 * @return array|bool Instances of this class for the loaded events.
+	 * @return array Instances of this class for the loaded events.
 	 */
-	public static function load(int $id, bool $is_topic = false, bool $use_permissions = true): array|bool
+	public static function load(int $id, bool $is_topic = false, bool $use_permissions = true): array
 	{
 		if ($id <= 0) {
-			return $is_topic ? false : [new self($id)];
+			return [];
 		}
 
-		$loaded = [];
+		if (!$is_topic && isset(self::$loaded[$id])) {
+			return [self::$loaded[$id]];
+		}
 
-		self::$keep_all = true;
+		$loaded = [];
 
-		$query_customizations['where'][] = 'cal.id_' . ($is_topic ? 'topic' : 'event') . ' = {int:id}';
-		$query_customizations['params']['id'] = $id;
+		$selects = [
+			'cal.*',
+			'b.id_board',
+			'b.member_groups',
+			't.id_first_msg',
+			't.approved',
+			'm.modified_time',
+			'mem.real_name',
+		];
+		$joins = [
+			'LEFT JOIN {db_prefix}boards AS b ON (b.id_board = cal.id_board)',
+			'LEFT JOIN {db_prefix}topics AS t ON (t.id_topic = cal.id_topic)',
+			'LEFT JOIN {db_prefix}messages AS m ON (m.id_msg  = t.id_first_msg)',
+			'LEFT JOIN {db_prefix}members AS mem ON (mem.id_member = cal.id_member)',
+		];
+		$where = ['cal.id_' . ($is_topic ? 'topic' : 'event') . ' = {int:id}'];
+		$order = ['cal.start_date'];
+		$group = [];
+		$limit = 0;
+		$params = [
+			'id' => $id,
+			'no_board_link' => 0,
+		];
 
 		if ($use_permissions) {
-			$query_customizations['where'][] = '(cal.id_board = {int:no_board_link} OR {query_wanna_see_board})';
-
-			$query_customizations['params']['no_board_link'] = 0;
+			$where[] = '(cal.id_board = {int:no_board_link} OR {query_wanna_see_board})';
 		}
 
-		foreach (self::get('', '', $use_permissions, $query_customizations) as $event) {
-			$loaded[] = $event;
-		}
+		IntegrationHook::call('integrate_query_event', [&$selects, &$params, &$joins, &$where, &$order, &$group, &$limit]);
 
-		self::$keep_all = false;
+		foreach(self::queryData($selects, $params, $joins, $where, $order, $group, $limit) as $row) {
+			// If the attached topic is not approved then for the moment pretend it doesn't exist.
+			if (!empty($row['id_first_msg']) && Config::$modSettings['postmod_active'] && !$row['approved']) {
+				continue;
+			}
 
-		return $loaded;
-	}
+			unset($row['approved']);
 
-	/**
-	 * Loads events within the given date range.
-	 *
-	 * @param string $low_date The low end of the range, inclusive, in YYYY-MM-DD format.
-	 * @param string $high_date The high end of the range, inclusive, in YYYY-MM-DD format.
-	 * @param bool $use_permissions Whether to use permissions. Default: true.
-	 * @param array $query_customizations Customizations to the SQL query.
-	 * @return array Instances of this class for the loaded events.
-	 */
-	public static function loadRange(string $low_date, string $high_date, bool $use_permissions = true, array $query_customizations = []): array
-	{
-		$loaded = [];
+			$id = (int) $row['id_event'];
+			$row['use_permissions'] = $use_permissions;
 
-		self::$keep_all = true;
+			$rrule = new RRule($row['rrule']);
 
-		foreach (self::get($low_date, $high_date, $use_permissions, $query_customizations) as $event) {
-			$loaded[$event->id] = $event;
-		}
+			switch ($rrule->freq) {
+				case 'SECONDLY':
+					$unit = 'seconds';
+					break;
+
+				case 'MINUTELY':
+					$unit = 'minutes';
+					break;
+
+				case 'HOURLY':
+					$unit = 'hours';
+					break;
+
+				case 'DAILY':
+					$unit = 'days';
+					break;
+
+				case 'WEEKLY':
+					$unit = 'weeks';
+					break;
+
+				case 'MONTHLY':
+					$unit = 'months';
+					break;
+
+				default:
+					$unit = 'years';
+					break;
+			}
 
-		self::$keep_all = false;
+			$row['view_end'] = new \DateTimeImmutable('now + ' . (RecurrenceIterator::DEFAULT_COUNTS[$rrule->freq]) . ' ' . $unit);
+
+			$loaded[] = (new self($id, $row));
+		}
 
-		// Return the instances we just loaded.
 		return $loaded;
 	}
 
 	/**
 	 * Generator that yields instances of this class.
 	 *
-	 * @todo SMF does not yet take advantage of this generator very well.
-	 * Instead of loading all the events in the range via Event::loadRange(),
-	 * it would be better to call Event::get() directly in order to reduce
-	 * memory load.
-	 *
 	 * @param string $low_date The low end of the range, inclusive, in YYYY-MM-DD format.
 	 * @param string $high_date The high end of the range, inclusive, in YYYY-MM-DD format.
 	 * @param bool $use_permissions Whether to use permissions. Default: true.
 	 * @param array $query_customizations Customizations to the SQL query.
-	 * @return \Generator<object> Iterating over result gives Event instances.
+	 * @return Generator<Event> Iterating over result gives Event instances.
 	 */
 	public static function get(string $low_date, string $high_date, bool $use_permissions = true, array $query_customizations = []): \Generator
 	{
+		$low_date = !empty($low_date) ? $low_date : '1000-01-01';
+		$high_date = !empty($high_date) ? $high_date : '9999-12-31';
+
 		$selects = $query_customizations['selects'] ?? [
 			'cal.*',
 			'b.id_board',
@@ -945,6 +1283,7 @@ public static function get(string $low_date, string $high_date, bool $use_permis
 		$where = $query_customizations['where'] ?? [
 			'cal.start_date <= {date:high_date}',
 			'cal.end_date >= {date:low_date}',
+			'type = {int:type}',
 		];
 		$order = $query_customizations['order'] ?? ['cal.start_date'];
 		$group = $query_customizations['group'] ?? [];
@@ -953,6 +1292,7 @@ public static function get(string $low_date, string $high_date, bool $use_permis
 			'high_date' => $high_date,
 			'low_date' => $low_date,
 			'no_board_link' => 0,
+			'type' => self::TYPE_EVENT,
 		];
 
 		if ($use_permissions) {
@@ -972,10 +1312,29 @@ public static function get(string $low_date, string $high_date, bool $use_permis
 			$id = (int) $row['id_event'];
 			$row['use_permissions'] = $use_permissions;
 
+			$row['view_start'] = new \DateTimeImmutable($low_date);
+			$row['view_end'] = new \DateTimeImmutable($high_date);
+
 			yield (new self($id, $row));
+		}
+	}
 
-			if (!self::$keep_all) {
-				unset(self::$loaded[$id]);
+	/**
+	 * Gets events within the given date range, and returns a generator that
+	 * yields all occurrences of those events within that range.
+	 *
+	 * @param string $low_date The low end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param string $high_date The high end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param bool $use_permissions Whether to use permissions. Default: true.
+	 * @param array $query_customizations Customizations to the SQL query.
+	 * @return Generator<EventOccurrence> Iterating over result gives
+	 *    EventOccurrence instances.
+	 */
+	public static function getOccurrencesInRange(string $low_date, string $high_date, bool $use_permissions = true, array $query_customizations = []): \Generator
+	{
+		foreach (self::get($low_date, $high_date, $use_permissions, $query_customizations) as $event) {
+			foreach ($event->getAllVisibleOccurrences() as $occurrence) {
+				yield $occurrence;
 			}
 		}
 	}
@@ -995,7 +1354,7 @@ public static function create(array $eventOptions): void
 		}
 
 		// Set the start and end dates.
-		self::setStartEnd($eventOptions);
+		self::setStartAndDuration($eventOptions);
 
 		$event = new self(0, $eventOptions);
 		$event->save();
@@ -1041,8 +1400,8 @@ public static function modify(int $id, array &$eventOptions): void
 			$eventOptions[$key] = Utils::htmlspecialchars($eventOptions[$key] ?? '', ENT_QUOTES);
 		}
 
-		// Set the new start and end dates.
-		self::setStartEnd($eventOptions);
+		// Set the new start date and duration.
+		self::setStartAndDuration($eventOptions);
 
 		list($event) = self::load($id);
 		$event->set($eventOptions);
@@ -1081,24 +1440,63 @@ public static function remove(int $id): void
 	 ******************/
 
 	/**
-	 * Ensures that the start and end dates have a sane relationship.
+	 * Sets $this->recurrence_iterator, but only if all necessary properties
+	 * have been set.
+	 *
+	 * @return bool Whether the recurrence iterator was created successfully.
 	 */
-	protected function fixEndDate(): void
+	protected function createRecurrenceIterator(): bool
 	{
-		// Must always use the same time zone for both dates.
-		if ($this->end->format('e') !== $this->start->format('e')) {
-			$this->end->setTimezone($this->start->getTimezone());
+		static $args_hash;
+
+		if (
+			empty($this->rrule)
+			|| !isset($this->start, $this->view_start, $this->view_end, $this->allday)
+		) {
+			return false;
 		}
 
-		// End date can't be before the start date.
-		if ($this->end->getTimestamp() < $this->start->getTimestamp()) {
-			$this->end->setTimestamp($this->start->getTimestamp());
+		$temp_hash = md5($this->rrule . $this->start->format('c') . $this->view_start->format('c') . $this->view_end->format('c') . (int) $this->allday);
+
+		if (isset($this->recurrence_iterator, $args_hash) && $args_hash === $temp_hash) {
+			return true;
 		}
 
-		// If the event is too long, cap it at the max.
-		if (!empty(Config::$modSettings['cal_maxspan']) && $this->start->diff($this->end)->format('%a') > Config::$modSettings['cal_maxspan']) {
-			$this->end = (clone $this->start)->modify('+' . Config::$modSettings['cal_maxspan'] . ' days');
+		$args_hash = $temp_hash;
+
+		$this->recurrence_iterator = new RecurrenceIterator(
+			new RRule($this->rrule),
+			$this->start,
+			$this->view_start->diff($this->view_end),
+			$this->view_start,
+			$this->allday ? RecurrenceIterator::TYPE_ALLDAY : RecurrenceIterator::TYPE_ABSOLUTE,
+			$this->rdates ?? [],
+			$this->exdates ?? [],
+		);
+
+		return true;
+	}
+
+	/**
+	 *
+	 * @param \DateTimeInterface $start The start time.
+	 * @param ?TimeInterval $duration Custom duration for this occurrence. If
+	 *    this is left null, the duration of the parent event will be used.
+	 * @return EventOccurrence
+	 */
+	protected function createOccurrence(\DateTimeInterface $start, ?TimeInterval $duration = null): EventOccurrence
+	{
+		$props = [
+			'start' => Time::createFromInterface($start),
+		];
+
+		if (isset($duration)) {
+			$props['duration'] = $duration;
 		}
+
+		$props['id'] = $this->allday ? $props['start']->format('Ymd') : (clone $props['start'])->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\\THis\\Z');
+
+		return new EventOccurrence($this->id, $props);
 	}
 
 	/*************************
@@ -1145,14 +1543,22 @@ protected static function queryData(array $selects, array $params = [], array $j
 			$row = array_diff($row, array_filter($row, 'is_null'));
 
 			// Is this an all-day event?
-			$row['allday'] = !isset($row['start_time']) || !isset($row['end_time']) || !isset($row['timezone']) || !in_array($row['timezone'], timezone_identifiers_list(\DateTimeZone::ALL_WITH_BC));
+			$row['allday'] = !isset($row['start_time']) || !isset($row['timezone']) || !in_array($row['timezone'], timezone_identifiers_list(\DateTimeZone::ALL_WITH_BC));
 
-			// Replace time and date scalars with Time objects.
-			$row['start'] = new Time($row['start_date'] . (!$row['allday'] ? ' ' . $row['start_time'] . ' ' . $row['timezone'] : ''));
+			// Replace start time and date scalars with a Time object.
+			$row['start'] = new Time($row['start_date'] . (!$row['allday'] ? ' ' . $row['start_time'] . ' ' . $row['timezone'] : ' ' . User::getTimezone()));
+			unset($row['start_date'], $row['start_time'], $row['timezone']);
 
-			$row['end'] = new Time($row['end_date'] . (!$row['allday'] ? ' ' . $row['end_time'] . ' ' . $row['timezone'] : ''));
+			// Replace duration string with a DateInterval object.
+			$row['duration'] = new TimeInterval($row['duration']);
 
-			unset($row['start_date'], $row['start_time'], $row['end_date'], $row['end_time'], $row['timezone']);
+			// end_date actually means the recurrence end date.
+			$row['recurrence_end'] = (clone $row['start'])->modify($row['end_date'])->add($row['duration']);
+			unset($row['end_date']);
+
+			// Are there any adjustments to the calculated recurrence dates?
+			$row['rdates'] = explode(',', $row['rdates'] ?? '');
+			$row['exdates'] = explode(',', $row['exdates'] ?? '');
 
 			// The groups should be an array.
 			$row['member_groups'] = isset($row['member_groups']) ? explode(',', $row['member_groups']) : [];
@@ -1174,7 +1580,7 @@ protected static function queryData(array $selects, array $params = [], array $j
 	 * @param array $eventOptions An array of optional time and date parameters
 	 *    (span, start_year, end_month, etc., etc.)
 	 */
-	protected static function setStartEnd(array &$eventOptions): void
+	protected static function setStartAndDuration(array &$eventOptions): void
 	{
 		// Convert unprefixed time unit parameters to start_* parameters.
 		foreach (['year', 'month', 'day', 'hour', 'minute', 'second'] as $key) {
@@ -1213,6 +1619,13 @@ protected static function setStartEnd(array &$eventOptions): void
 		// Ensure 'allday' is a boolean.
 		$eventOptions['allday'] = !empty($eventOptions['allday']);
 
+		// Now replace 'end' with 'duration'.
+		if ($eventOptions['allday']) {
+			$eventOptions['end']->modify('+1 day');
+		}
+		$eventOptions['duration'] = $eventOptions['start']->diff($eventOptions['end']);
+		unset($eventOptions['end']);
+
 		// Unset all null values and all scalar date/time parameters.
 		$scalars = [
 			'year',
diff --git a/Sources/Calendar/EventOccurrence.php b/Sources/Calendar/EventOccurrence.php
new file mode 100644
index 0000000000..2914e26731
--- /dev/null
+++ b/Sources/Calendar/EventOccurrence.php
@@ -0,0 +1,476 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF\Calendar;
+
+use SMF\Actions\Calendar;
+use SMF\ArrayAccessHelper;
+use SMF\Config;
+use SMF\Time;
+
+/**
+ * Represents a single occurrence of a calendar event.
+ */
+class EventOccurrence implements \ArrayAccess
+{
+	use ArrayAccessHelper;
+
+	/*******************
+	 * Public properties
+	 *******************/
+
+	/**
+	 * @var string
+	 *
+	 * The recurrence ID of this individual occurrence of the event.
+	 *
+	 * See RFC 5545, section 3.8.4.4.
+	 */
+	public string $id;
+
+	/**
+	 * @var int
+	 *
+	 * The ID number of the parent event.
+	 *
+	 * All occurrences of an event have the same $id_event value.
+	 */
+	public int $id_event;
+
+	/**
+	 * @var SMF\Time
+	 *
+	 * A Time object representing the start of this occurrence of the event.
+	 */
+	public Time $start;
+
+	/*********************
+	 * Internal properties
+	 *********************/
+
+	/**
+	 * @var array
+	 *
+	 * Alternate names for some object properties.
+	 */
+	protected array $prop_aliases = [
+		'eventid' => 'id_event',
+		'id_board' => 'board',
+		'id_topic' => 'topic',
+		'id_first_msg' => 'msg',
+		'sequence' => 'modified_time',
+		'id_member' => 'member',
+		'poster' => 'member',
+		'real_name' => 'name',
+		'realname' => 'name',
+		'member_groups' => 'groups',
+		'allowed_groups' => 'groups',
+		'start_object' => 'start',
+		'end_object' => 'end',
+	];
+
+	/****************
+	 * Public methods
+	 ****************/
+
+	/**
+	 * Constructor.
+	 *
+	 * @param int $id_event The ID number of the parent event.
+	 * @param array $props Properties to set for this occurrence.
+	 * @return EventOccurrence An instance of this class.
+	 */
+	public function __construct(int $id_event = 0, array $props = [])
+	{
+		$this->id_event = $id_event;
+
+		if (!isset($props['start'])) {
+			throw new \ValueError();
+		}
+
+		$this->set($props);
+
+		if (!isset($this->id)) {
+			$this->id = $this->allday ? $this->start->format('Ymd') : (clone $this->start)->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\\THis\\Z');
+		}
+	}
+
+	/**
+	 * Builds an iCalendar document for this occurrence of the event.
+	 *
+	 * @return string An iCalendar VEVENT document.
+	 */
+	public function getVEvent(): string
+	{
+		// Check the title isn't too long - iCal requires some formatting if so.
+		$title = str_split($this->title, 30);
+
+		foreach ($title as $id => $line) {
+			if ($id != 0) {
+				$title[$id] = ' ' . $title[$id];
+			}
+		}
+
+		// This is what we will be sending later.
+		$filecontents = [];
+		$filecontents[] = 'BEGIN:VEVENT';
+		$filecontents[] = 'ORGANIZER;CN="' . $this->name . '":MAILTO:' . Config::$webmaster_email;
+		$filecontents[] = 'DTSTAMP:' . date('Ymd\\THis\\Z', time());
+		$filecontents[] = 'DTSTART' . ($this->allday ? ';VALUE=DATE' : (!in_array($this->tz, RRule::UTC_SYNONYMS) ? ';TZID=' . $this->tz : '')) . ':' . $this->start->format('Ymd' . ($this->allday ? '' : '\\THis' . (in_array($this->tz, RRule::UTC_SYNONYMS) ? '\\Z' : '')));
+
+		// Event has a duration/
+		if (
+			(!$this->allday && $this->start_iso_gmdate != $this->end_iso_gmdate)
+			|| ($this->allday && $this->start_date != $this->end_date)
+		) {
+			$filecontents[] = 'DTEND' . ($this->allday ? ';VALUE=DATE' : (!in_array($this->tz, RRule::UTC_SYNONYMS) ? ';TZID=' . $this->tz : '')) . ':' . $this->end->format('Ymd' . ($this->allday ? '' : '\\THis' . (in_array($this->tz, RRule::UTC_SYNONYMS) ? '\\Z' : '')));
+		}
+
+		// Event has changed? Advance the sequence for this UID.
+		if ($this->sequence > 0) {
+			$filecontents[] = 'SEQUENCE:' . $this->sequence;
+		}
+
+		if (!empty($this->location)) {
+			$filecontents[] = 'LOCATION:' . str_replace(',', '\\,', $this->location);
+		}
+
+		$filecontents[] = 'SUMMARY:' . implode('', $title);
+		$filecontents[] = 'UID:' . $this->uid;
+		$filecontents[] = 'RECURRENCE-ID' . ($this->allday ? ';VALUE=DATE' : '') . ':' . $this->id;
+		$filecontents[] = 'END:VEVENT';
+
+		return implode("\n", $filecontents);
+	}
+
+	/**
+	 * Sets custom properties.
+	 *
+	 * @param string $prop The property name.
+	 * @param mixed $value The value to set.
+	 */
+	public function __set(string $prop, $value): void
+	{
+		if (!isset($this->start)) {
+			$this->start = new Time();
+		}
+
+		if (str_starts_with($prop, 'end')) {
+			$end = (clone $this->start)->add($this->duration);
+		}
+
+		switch ($prop) {
+			// Special handling for stuff that affects start.
+			case 'start':
+				if ($value instanceof \DateTimeInterface) {
+					$this->start = Time::createFromInterface($value);
+				}
+				break;
+
+			case 'datetime':
+			case 'date':
+			case 'date_local':
+			case 'date_orig':
+			case 'time':
+			case 'time_local':
+			case 'time_orig':
+			case 'year':
+			case 'month':
+			case 'day':
+			case 'hour':
+			case 'minute':
+			case 'second':
+			case 'timestamp':
+			case 'iso_gmdate':
+			case 'tz':
+			case 'tzid':
+			case 'timezone':
+				$this->start->{$prop} = $value;
+				break;
+
+			case 'start_datetime':
+			case 'start_date':
+			case 'start_date_local':
+			case 'start_date_orig':
+			case 'start_time':
+			case 'start_time_local':
+			case 'start_time_orig':
+			case 'start_year':
+			case 'start_month':
+			case 'start_day':
+			case 'start_hour':
+			case 'start_minute':
+			case 'start_second':
+			case 'start_timestamp':
+			case 'start_iso_gmdate':
+				$this->start->{substr($prop, 6)} = $value;
+				break;
+
+			// Special handling for duration.
+			case 'duration':
+				if (!($value instanceof \DateInterval)) {
+					try {
+						$value = new \DateInterval((string) $value);
+					} catch (\Throwable $e) {
+						break;
+					}
+				}
+				$this->custom['duration'] = $value;
+				break;
+
+			case 'end':
+				if (!($value instanceof \DateTimeInterface)) {
+					try {
+						$value = new \DateTimeImmutable((is_numeric($value) ? '@' : '') . $value);
+					} catch (\Throwable $e) {
+						break;
+					}
+				}
+				$this->custom['duration'] = $this->start->diff($value);
+				break;
+
+			case 'end_datetime':
+			case 'end_date':
+			case 'end_date_local':
+			case 'end_date_orig':
+			case 'end_time':
+			case 'end_time_local':
+			case 'end_time_orig':
+			case 'end_year':
+			case 'end_month':
+			case 'end_day':
+			case 'end_hour':
+			case 'end_minute':
+			case 'end_second':
+			case 'end_timestamp':
+			case 'end_iso_gmdate':
+				$end->{substr($prop, 4)} = $value;
+				$this->custom['duration'] = $this->start->diff($end);
+				break;
+
+			// These properties are read-only.
+			case 'age':
+			case 'uid':
+			case 'tz_abbrev':
+			case 'new':
+			case 'is_selected':
+			case 'href':
+			case 'link':
+			case 'can_edit':
+			case 'modify_href':
+			case 'can_export':
+			case 'export_href':
+				break;
+
+			default:
+				$this->customPropertySet($prop, $value);
+				break;
+		}
+	}
+
+	/**
+	 * Gets custom property values.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __get(string $prop): mixed
+	{
+		if (str_starts_with($prop, 'end')) {
+			$end = (clone $this->start)->add($this->custom['duration'] ?? $this->getParentEvent()->duration);
+		}
+
+		switch ($prop) {
+			case 'datetime':
+			case 'date':
+			case 'date_local':
+			case 'date_orig':
+			case 'time':
+			case 'time_local':
+			case 'time_orig':
+			case 'year':
+			case 'month':
+			case 'day':
+			case 'hour':
+			case 'minute':
+			case 'second':
+			case 'timestamp':
+			case 'iso_gmdate':
+			case 'tz':
+			case 'tzid':
+			case 'timezone':
+			case 'tz_abbrev':
+				return $this->start->{$prop};
+
+			case 'start_datetime':
+			case 'start_date':
+			case 'start_date_local':
+			case 'start_date_orig':
+			case 'start_time':
+			case 'start_time_local':
+			case 'start_time_orig':
+			case 'start_year':
+			case 'start_month':
+			case 'start_day':
+			case 'start_hour':
+			case 'start_minute':
+			case 'start_second':
+			case 'start_timestamp':
+			case 'start_iso_gmdate':
+				return $this->start->{substr($prop, 6)};
+
+			case 'end':
+				return $end;
+
+			case 'end_datetime':
+			case 'end_date':
+			case 'end_date_local':
+			case 'end_date_orig':
+			case 'end_time':
+			case 'end_time_local':
+			case 'end_time_orig':
+			case 'end_year':
+			case 'end_month':
+			case 'end_day':
+			case 'end_hour':
+			case 'end_minute':
+			case 'end_second':
+			case 'end_timestamp':
+			case 'end_iso_gmdate':
+				return $end->{substr($prop, 4)};
+
+			// These inherit from the parent event unless overridden for this occurrence.
+			case 'allday':
+			case 'duration':
+			case 'title':
+			case 'location':
+				return $this->custom[$prop] ?? $this->getParentEvent()->{$prop};
+
+			// These always inherit from the parent event.
+			case 'uid':
+			case 'type':
+			case 'board':
+			case 'topic':
+			case 'msg':
+			case 'modified_time':
+			case 'member':
+			case 'name':
+			case 'groups':
+			case 'new':
+			case 'is_selected':
+			case 'href':
+			case 'link':
+			case 'can_edit':
+			case 'modify_href':
+			case 'can_export':
+			case 'export_href':
+				return $this->getParentEvent()->{$prop};
+
+			default:
+				return $this->customPropertyGet($prop);
+		}
+	}
+
+	/**
+	 * Checks whether a custom property has been set.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __isset(string $prop): bool
+	{
+		if (in_array($prop, ['year', 'month', 'day', 'hour', 'minute', 'second'])) {
+			$prop = 'start_' . $prop;
+		}
+
+		switch ($prop) {
+			case 'start_datetime':
+			case 'start_date':
+			case 'start_time':
+			case 'start_year':
+			case 'start_month':
+			case 'start_day':
+			case 'start_hour':
+			case 'start_minute':
+			case 'start_second':
+			case 'start_date_local':
+			case 'start_date_orig':
+			case 'start_time_local':
+			case 'start_time_orig':
+			case 'start_timestamp':
+			case 'start_iso_gmdate':
+			case 'tz':
+			case 'tzid':
+			case 'timezone':
+			case 'tz_abbrev':
+			case 'end_datetime':
+			case 'end_date':
+			case 'end_time':
+			case 'end_year':
+			case 'end_month':
+			case 'end_day':
+			case 'end_hour':
+			case 'end_minute':
+			case 'end_second':
+			case 'end_date_local':
+			case 'end_date_orig':
+			case 'end_time_local':
+			case 'end_time_orig':
+			case 'end_timestamp':
+			case 'end_iso_gmdate':
+				return property_exists($this, 'start');
+
+			case 'uid':
+			case 'type':
+			case 'allday':
+			case 'duration':
+			case 'title':
+			case 'location':
+			case 'board':
+			case 'topic':
+			case 'msg':
+			case 'modified_time':
+			case 'member':
+			case 'name':
+			case 'groups':
+			case 'new':
+			case 'is_selected':
+			case 'href':
+			case 'link':
+			case 'can_edit':
+			case 'modify_href':
+			case 'can_export':
+			case 'export_href':
+				return true;
+
+			default:
+				return $this->customPropertyIsset($prop);
+		}
+	}
+
+	/**
+	 * Retrieves the Event that this EventOccurrence is an occurrence of.
+	 *
+	 * @return Event The parent Event.
+	 */
+	public function getParentEvent(): Event
+	{
+		if (!isset(Event::$loaded[$this->id_event])) {
+			Event::load($this->id_event);
+		}
+
+		return Event::$loaded[$this->id_event];
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index f67631e5dd..4bb7f53a6c 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -115,7 +115,7 @@ function template_show_upcoming_list($grid_name)
 
 				if (!empty($event['allday']))
 				{
-					echo '<time datetime="' . $event['start_iso_gmdate'] . '">', trim($event['start_date_local']), '</time>', ($event['start_date'] != $event['end_date']) ? ' &ndash; <time datetime="' . $event['end_iso_gmdate'] . '">' . trim($event['end_date_local']) . '</time>' : '';
+					echo '<time datetime="' . $event['start_iso_gmdate'] . '">', trim($event['start_date_local']), '</time>', ($event['start_date_local'] < $event['last_date_local']) ? ' &ndash; <time datetime="' . $event['last_iso_gmdate'] . '">' . trim($event['last_date_local']) . '</time>' : '';
 				}
 				else
 				{
@@ -431,12 +431,13 @@ function($a, $b)
 								', $event['link'], '<br>
 								<span class="event_time', empty($event_icons_needed) ? ' floatright' : '', '">';
 
-							if (!empty($event['start_time_local']) && $event['start_date'] == $day['date'])
+							if (!empty($event['allday'])) {
+								echo Lang::$txt['calendar_allday'];
+							} elseif (!empty($event['start_time_local']) && $event['start_date'] == $day['date']) {
 								echo trim(str_replace(':00 ', ' ', $event['start_time_local']));
-							elseif (!empty($event['end_time_local']) && $event['end_date'] == $day['date'])
+							} elseif (!empty($event['end_time_local']) && $event['end_date'] == $day['date']) {
 								echo strtolower(Lang::$txt['ends']), ' ', trim(str_replace(':00 ', ' ', $event['end_time_local']));
-							elseif (!empty($event['allday']))
-								echo Lang::$txt['calendar_allday'];
+							}
 
 							echo '
 								</span>';
@@ -483,9 +484,9 @@ function($a, $b)
 			elseif ($is_mini === false)
 			{
 				if (empty($current_month_started) && !empty(Utils::$context['calendar_grid_prev']))
-					echo '<a href="', Config::$scripturl, '?action=calendar;year=', Utils::$context['calendar_grid_prev']['current_year'], ';month=', Utils::$context['calendar_grid_prev']['current_month'], '">', Utils::$context['calendar_grid_prev']['last_of_month'] - $calendar_data['shift']-- +1, '</a>';
+					echo '<a href="', Config::$scripturl, '?action=calendar;viewmonth;year=', Utils::$context['calendar_grid_prev']['current_year'], ';month=', Utils::$context['calendar_grid_prev']['current_month'], '">', Utils::$context['calendar_grid_prev']['last_of_month'] - $calendar_data['shift']-- +1, '</a>';
 				elseif (!empty($current_month_started) && !empty(Utils::$context['calendar_grid_next']))
-					echo '<a href="', Config::$scripturl, '?action=calendar;year=', Utils::$context['calendar_grid_next']['current_year'], ';month=', Utils::$context['calendar_grid_next']['current_month'], '">', $current_month_started + 1 == $count ? (!empty($calendar_data['short_month_titles']) ? Lang::$txt['months_short'][Utils::$context['calendar_grid_next']['current_month']] . ' ' : Lang::$txt['months_titles'][Utils::$context['calendar_grid_next']['current_month']] . ' ') : '', $final_count++, '</a>';
+					echo '<a href="', Config::$scripturl, '?action=calendar;viewmonth;year=', Utils::$context['calendar_grid_next']['current_year'], ';month=', Utils::$context['calendar_grid_next']['current_month'], '">', $current_month_started + 1 == $count ? (!empty($calendar_data['short_month_titles']) ? Lang::$txt['months_short'][Utils::$context['calendar_grid_next']['current_month']] . ' ' : Lang::$txt['months_titles'][Utils::$context['calendar_grid_next']['current_month']] . ' ') : '', $final_count++, '</a>';
 			}
 
 			// Close this day and increase var count.
@@ -559,7 +560,7 @@ function template_show_week_grid($grid_name)
 		// Our actual month...
 		echo '
 				<div class="week_month_title">
-					<a href="', Config::$scripturl, '?action=calendar;month=', $month_data['current_month'], '">
+					<a href="', Config::$scripturl, '?action=calendar;viewmonth;month=', $month_data['current_month'], '">
 						', Lang::$txt['months_titles'][$month_data['current_month']], '
 					</a>
 				</div>';
diff --git a/other/upgrade_3-0_MySQL.sql b/other/upgrade_3-0_MySQL.sql
index 79b486df9f..5763d05165 100644
--- a/other/upgrade_3-0_MySQL.sql
+++ b/other/upgrade_3-0_MySQL.sql
@@ -164,4 +164,9 @@ ADD COLUMN type TINYINT UNSIGNED NOT NULL DEFAULT '0';
 		);
 	}
 ---}
+---#
+
+---# Drop end_time column from calendar table
+ALTER TABLE {$db_prefix}calendar
+DROP COLUMN end_time;
 ---#
\ No newline at end of file
diff --git a/other/upgrade_3-0_PostgreSQL.sql b/other/upgrade_3-0_PostgreSQL.sql
index 089ec17dc4..38f6527175 100644
--- a/other/upgrade_3-0_PostgreSQL.sql
+++ b/other/upgrade_3-0_PostgreSQL.sql
@@ -163,4 +163,9 @@ ADD COLUMN IF NOT EXISTS type smallint NOT NULL DEFAULT '0';
 		);
 	}
 ---}
+---#
+
+---# Drop end_time column from calendar table
+ALTER TABLE {$db_prefix}calendar
+DROP COLUMN end_time;
 ---#
\ No newline at end of file

From 1f8f8725ca9ade5efe48bcfc7624f526070620e8 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Mon, 11 Dec 2023 01:14:07 -0700
Subject: [PATCH 09/22] Adds support for creating recurring events

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/General.php             |  18 +-
 Sources/Actions/Calendar.php            |  12 +-
 Sources/Actions/Post.php                |  12 +-
 Sources/Calendar/Event.php              | 472 ++++++++++++++--
 Sources/Calendar/RecurrenceIterator.php |   8 +
 Themes/default/Calendar.template.php    |  77 +--
 Themes/default/EventEditor.template.php | 425 +++++++++++++++
 Themes/default/Post.template.php        |  50 +-
 Themes/default/css/index.css            |  43 +-
 Themes/default/css/responsive.css       |  66 +--
 Themes/default/scripts/event.js         | 682 ++++++++++++++++++++++++
 11 files changed, 1618 insertions(+), 247 deletions(-)
 create mode 100644 Themes/default/EventEditor.template.php
 create mode 100644 Themes/default/scripts/event.js

diff --git a/Languages/en_US/General.php b/Languages/en_US/General.php
index 905a812c32..06e5998b79 100644
--- a/Languages/en_US/General.php
+++ b/Languages/en_US/General.php
@@ -709,7 +709,7 @@
 $txt['calendar_month'] = 'Month';
 $txt['calendar_year'] = 'Year';
 $txt['calendar_day'] = 'Day';
-$txt['calendar_event_title'] = 'Event Title';
+$txt['calendar_event_title'] = 'Title';
 $txt['calendar_event_options'] = 'Event Options';
 $txt['calendar_post_in'] = 'Post in';
 $txt['calendar_edit'] = 'Edit Event';
@@ -735,6 +735,22 @@
 $txt['calendar_list'] = 'List';
 $txt['calendar_empty'] = 'There are no events to display.';
 
+$txt['calendar_repeat_recurrence_label'] = 'Repeats';
+$txt['calendar_repeat_interval_label'] = 'Every';
+$txt['calendar_repeat_bymonthday_label'] = 'On';
+$txt['calendar_repeat_byday_label'] = 'On';
+$txt['calendar_repeat_bymonth_label'] = 'In';
+$txt['calendar_repeat_rrule_presets'] = ['never' => 'Never', 'FREQ=DAILY' => 'Every day', 'FREQ=WEEKLY' => 'Every week', 'FREQ=MONTHLY' => 'Every month', 'FREQ=YEARLY' => 'Every year', 'custom' => 'Custom...'];
+$txt['calendar_repeat_frequency_units'] = ['YEARLY' => 'year(s)', 'MONTHLY' => 'month(s)', 'WEEKLY' => 'week(s)', 'DAILY' => 'day(s)', 'HOURLY' => 'hour(s)', 'MINUTELY' => 'minute(s)', 'SECONDLY' => 'second(s)'];
+$txt['calendar_repeat_until_options'] = ['forever' => 'Forever', 'until' => 'Until', 'count' => 'Number of times'];
+$txt['calendar_repeat_byday_num_options'] = [1 => 'the first', 2 => 'the second', 3 => 'the third', 4 => 'the fourth', 5 => 'the fifth', -1 => 'the last', -2 => 'the second last'];
+$txt['calendar_repeat_weekday'] = 'weekday';
+$txt['calendar_repeat_weekend_day'] = 'weekend day';
+$txt['calendar_repeat_add_condition'] = 'Add Another';
+$txt['calendar_repeat_advanced_options_label'] = 'More options...';
+$txt['calendar_repeat_rdates_label'] = 'Additional dates';
+$txt['calendar_repeat_exdates_label'] = 'Skipped dates';
+
 $txt['movetopic_change_subject'] = 'Change the topic’s subject';
 $txt['movetopic_new_subject'] = 'New subject';
 $txt['movetopic_change_all_subjects'] = 'Change every message’s subject';
diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index 437b311765..7cd4c5c250 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -493,15 +493,9 @@ public function post(): void
 			'name' => Utils::$context['page_title'],
 		];
 
-		self::loadDatePicker('#event_time_input .date_input');
-		self::loadTimePicker('#event_time_input .time_input', Time::getShortTimeFormat());
-		self::loadDatePair('#event_time_input', 'date_input', 'time_input');
-		Theme::addInlineJavaScript('
-		$("#allday").click(function(){
-			$("#start_time").attr("disabled", this.checked);
-			$("#end_time").attr("disabled", this.checked);
-			$("#tz").attr("disabled", this.checked);
-		});', true);
+		Theme::loadTemplate('EventEditor');
+		Theme::addJavaScriptVar('monthly_byday_items', (string) (count(Utils::$context['event']->byday_items) - 1));
+		Theme::loadJavaScriptFile('event.js', ['defer' => true], 'smf_event');
 	}
 
 	/**
diff --git a/Sources/Actions/Post.php b/Sources/Actions/Post.php
index 1ac0774948..e11942ce33 100644
--- a/Sources/Actions/Post.php
+++ b/Sources/Actions/Post.php
@@ -781,15 +781,9 @@ protected function initiateEvent(): void
 		// If the event's timezone is not in SMF's standard list of time zones, try to fix it.
 		Utils::$context['event']->fixTimezone();
 
-		Calendar::loadDatePicker('#event_time_input .date_input');
-		Calendar::loadTimePicker('#event_time_input .time_input', $time_string);
-		Calendar::loadDatePair('#event_time_input', 'date_input', 'time_input');
-		Theme::addInlineJavaScript('
-		$("#allday").click(function(){
-			$("#start_time").attr("disabled", this.checked);
-			$("#end_time").attr("disabled", this.checked);
-			$("#tz").attr("disabled", this.checked);
-		});	', true);
+		Theme::loadTemplate('EventEditor');
+		Theme::addJavaScriptVar('monthly_byday_items', (string) (count(Utils::$context['event']->byday_items) - 1));
+		Theme::loadJavaScriptFile('event.js', ['defer' => true], 'smf_event');
 
 		Utils::$context['event']->board = !empty(Board::$info->id) ? Board::$info->id : (int) Config::$modSettings['cal_defaultboard'];
 		Utils::$context['event']->topic = !empty(Topic::$info->id) ? Topic::$info->id : 0;
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index a41962fba4..7ef390ae88 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -21,6 +21,7 @@
 use SMF\Db\DatabaseApi as Db;
 use SMF\ErrorHandler;
 use SMF\IntegrationHook;
+use SMF\Lang;
 use SMF\Theme;
 use SMF\Time;
 use SMF\TimeInterval;
@@ -31,6 +32,8 @@
 
 /**
  * Represents a (possibly recurring) calendar event, birthday, or holiday.
+ *
+ * @todo Add support for editing specific instances as exceptions to the RRule.
  */
 class Event implements \ArrayAccess
 {
@@ -104,14 +107,6 @@ class Event implements \ArrayAccess
 	 */
 	public RecurrenceIterator $recurrence_iterator;
 
-	/**
-	 * @var \SMF\Time
-	 *
-	 * A Time object representing the date after which no further occurrences
-	 * of the event happen.
-	 */
-	public Time $recurrence_end;
-
 	/**
 	 * @var bool
 	 *
@@ -182,6 +177,60 @@ class Event implements \ArrayAccess
 	 */
 	public array $groups = [];
 
+	/**
+	 * @var array
+	 *
+	 * Weekdays sorted according to the WKST value, or the current user's
+	 * preferences if WKST is not already set.
+	 */
+	public array $sorted_weekdays = [];
+
+	/**
+	 * @var array
+	 *
+	 * Possible values for the RRule select menu in the UI.
+	 *
+	 * The descriptions will be overwritten using the language strings in
+	 * Lang::$txt['calendar_repeat_rrule_presets']
+	 */
+	public array $rrule_presets = [
+		'never' => 'Never',
+		'FREQ=DAILY' => 'Every day',
+		'FREQ=WEEKLY' => 'Every week',
+		'FREQ=MONTHLY' => 'Every month',
+		'FREQ=YEARLY' => 'Every year',
+		'custom' => 'Custom...',
+	];
+
+	/**
+	 * @var array
+	 *
+	 * Maps frequency values to unit strings.
+	 *
+	 * The descriptions will be overwritten using the language strings in
+	 * Lang::$txt['calendar_repeat_frequency_units']
+	 */
+	public array $frequency_units = [
+		'DAILY' => 'day(s)',
+		'WEEKLY' => 'week(s)',
+		'MONTHLY' => 'month(s)',
+		'YEARLY' => 'year(s)',
+	];
+
+	/**
+	 * @var array
+	 *
+	 * Possible values for the BYDAY_num select menu in the UI.
+	 */
+	public array $byday_num_options = [];
+
+	/**
+	 * @var array
+	 *
+	 * Existing values for the BYDAY_* select menus in the UI.
+	 */
+	public array $byday_items = [];
+
 	/**************************
 	 * Public static properties
 	 **************************/
@@ -212,7 +261,6 @@ class Event implements \ArrayAccess
 	protected array $prop_aliases = [
 		'id_event' => 'id',
 		'eventid' => 'id',
-		'end_date' => 'recurrence_end',
 		'id_board' => 'board',
 		'id_topic' => 'topic',
 		'id_first_msg' => 'msg',
@@ -274,53 +322,56 @@ class Event implements \ArrayAccess
 	 */
 	public function __construct(int $id = 0, array $props = [])
 	{
-		// Preparing default data to show in the calendar posting form.
-		if ($id < 0) {
-			$this->id = $id;
-			$props['start'] = new Time('now ' . User::getTimezone());
-			$props['duration'] = new TimeInterval('PT1H');
-			$props['recurrence_end'] = (clone $props['start'])->add($props['duration']);
-			$props['member'] = $props['member'] ?? User::$me->id;
-			$props['name'] = $props['name'] ?? User::$me->name;
-		}
-		// Creating a new event.
-		elseif ($id == 0) {
-			if (!isset($props['start']) || !($props['start'] instanceof \DateTimeInterface)) {
-				ErrorHandler::fatalLang('invalid_date', false);
-			} elseif (!($props['start'] instanceof Time)) {
-				$props['start'] = Time::createFromInterface($props['start']);
-			}
+		// Just in case someone passes -2 or something.
+		$id = max(-1, $id);
+
+		switch ($id) {
+			// Preparing default data to show in the calendar posting form.
+			case -1:
+				$this->id = $id;
+				$props['start'] = $props['start'] ?? new Time('now ' . User::getTimezone());
+				$props['duration'] = $props['duration'] ?? new TimeInterval('PT1H');
+				$props['member'] = $props['member'] ?? User::$me->id;
+				$props['name'] = $props['name'] ?? User::$me->name;
+				break;
 
-			if (!isset($props['duration'])) {
-				if (!isset($props['end']) || !($props['end'] instanceof \DateTimeInterface)) {
+			// Creating a new event.
+			case 0:
+				if (!isset($props['start']) || !($props['start'] instanceof \DateTimeInterface)) {
 					ErrorHandler::fatalLang('invalid_date', false);
+				} elseif (!($props['start'] instanceof Time)) {
+					$props['start'] = Time::createFromInterface($props['start']);
+				}
+
+				if (!isset($props['duration'])) {
+					if (!isset($props['end']) || !($props['end'] instanceof \DateTimeInterface)) {
+						ErrorHandler::fatalLang('invalid_date', false);
+					} else {
+						$props['duration'] = $props['start']->diff($props['end']);
+						unset($props['end']);
+					}
+				}
+
+				if (!isset($props['rrule'])) {
+					$props['rrule'] = 'FREQ=YEARLY;COUNT=1';
 				} else {
-					$props['duration'] = $props['start']->diff($props['end']);
-					unset($props['end']);
+					// The RRule's week start value can affect recurrence results,
+					// so make sure to save it using the current user's preference.
+					$props['rrule'] = new RRule($props['rrule']);
+					$props['rrule']->wkst = RRule::WEEKDAYS[$start_day = ((Theme::$current->options['calendar_start_day'] ?? 0) + 6) % 7];
+					$props['rrule'] = (string) $props['rrule'];
 				}
-			}
 
-			if (!isset($props['recurrence_end']) && isset($props['duration'])) {
-				$props['recurrence_end'] = (clone $props['start'])->add($props['duration']);
-			}
+				$props['member'] = $props['member'] ?? User::$me->id;
+				$props['name'] = $props['name'] ?? User::$me->name;
 
-			if (!isset($props['rrule'])) {
-				$props['rrule'] = 'FREQ=YEARLY;COUNT=1';
-			} else {
-				// The RRule's week start value can affect recurrence results,
-				// so make sure to save it using the current user's preference.
-				$props['rrule'] = new RRule($props['rrule']);
-				$props['rrule']->wkst = RRule::WEEKDAYS[$start_day = ((Theme::$current->options['calendar_start_day'] ?? 0) + 6) % 7];
-				$props['rrule'] = (string) $props['rrule'];
-			}
+				break;
 
-			$props['member'] = $props['member'] ?? User::$me->id;
-			$props['name'] = $props['name'] ?? User::$me->name;
-		}
-		// Loading an existing event.
-		else {
-			$this->id = $id;
-			self::$loaded[$this->id] = $this;
+			// Loading an existing event.
+			default:
+				$this->id = $id;
+				self::$loaded[$this->id] = $this;
+				break;
 		}
 
 		$props['rdates'] = array_filter($props['rdates'] ?? []);
@@ -398,6 +449,65 @@ public function __construct(int $id = 0, array $props = [])
 
 		// Set any other properties.
 		$this->set($props);
+
+		// Now set all the options for the UI.
+		foreach ($this->frequency_units as $freq => $unit) {
+			$this->frequency_units[$freq] = Lang::$txt['calendar_repeat_frequency_units'][$freq] ?? $unit;
+		}
+
+		// Our Lang::$txt arrays use Sunday = 0, but ISO day numbering uses Monday = 0.
+		$this->sorted_weekdays = array_flip(RRule::WEEKDAYS);
+
+		while (key($this->sorted_weekdays) != RRule::WEEKDAYS[((Theme::$current->options['calendar_start_day'] ?? 0) + 6) % 7]) {
+			$temp_key = key($this->sorted_weekdays);
+			$temp_val = array_shift($this->sorted_weekdays);
+			$this->sorted_weekdays[$temp_key] = $temp_val;
+		}
+
+		foreach ($this->sorted_weekdays as $abbrev => $iso_num) {
+			$txt_key = ($iso_num + 1) % 7;
+			$this->sorted_weekdays[$abbrev] = [
+				'iso_num' => $iso_num,
+				'txt_key' => $txt_key,
+				'abbrev' => $abbrev,
+				'short' => Lang::$txt['days_short'][$txt_key],
+				'long' => Lang::$txt['days'][$txt_key],
+			];
+		}
+
+		foreach (Lang::$txt['calendar_repeat_rrule_presets'] as $rrule => $description) {
+			if (isset($this->rrule_presets[$rrule])) {
+				$this->rrule_presets[$rrule] = $description;
+			}
+		}
+
+		$this->byday_num_options = Lang::$txt['calendar_repeat_byday_num_options'];
+
+		uksort(
+			$this->byday_num_options,
+			function ($a, $b) {
+				if ($a < 0 && $b > 0) {
+					return 1;
+				}
+
+				if ($a > 0 && $b < 0) {
+					return -1;
+				}
+
+				return abs($a) <=> abs($b);
+			},
+		);
+
+		// Populate $this->byday_items.
+		if (!empty($this->recurrence_iterator->getRRule()->byday)) {
+			foreach ($this->recurrence_iterator->getRRule()->byday as $item) {
+				list($num, $name) = preg_split('/(?=MO|TU|WE|TH|FR|SA|SU)/', $item);
+				$num = empty($num) ? 1 : (int) $num;
+				$this->byday_items[] = ['num' => $num, 'name' => $name];
+			}
+		} else {
+			$this->byday_items[] = ['num' => 0, 'name' => ''];
+		}
 	}
 
 	/**
@@ -405,10 +515,40 @@ public function __construct(int $id = 0, array $props = [])
 	 */
 	public function save(): void
 	{
-		$is_edit = !empty($this->id);
+		$is_edit = ($this->id ?? 0) > 0;
+
+		if (!empty($this->recurrence_iterator->getRRule()->until)) {
+			// When we have an until value, life is easy.
+			$recurrence_end = Time::createFromInterface($this->recurrence_iterator->getRRule()->until)->modify('-1 second');
+		} elseif (!empty($this->recurrence_iterator->getRRule()->count)) {
+			// Save current values.
+			$view_start = clone $this->view_start;
+			$view_end = clone $this->view_end;
+			$recurrence_iterator = clone $this->recurrence_iterator;
+
+			// Make new recurrence iterator that gets all occurrences.
+			$this->rrule = (string) $recurrence_iterator->getRRule();
+			$this->view_start = clone $this->start;
+			$this->view_end = new Time('9999-12-31');
+
+			unset($this->recurrence_iterator);
+			$this->createRecurrenceIterator();
+
+			// Get last occurrence.
+			$this->recurrence_iterator->end();
+			$recurrence_end = Time::createFromInterface($this->recurrence_iterator->current());
+
+			// Put everything back.
+			$this->view_start = $view_start;
+			$this->view_end = $view_end;
+			$this->recurrence_iterator = $recurrence_iterator;
+		} else {
+			// Forever.
+			$recurrence_end = new Time('9999-12-31');
+		}
 
 		// Saving a new event.
-		if (empty($this->id)) {
+		if (!$is_edit) {
 			$columns = [
 				'start_date' => 'date',
 				'end_date' => 'date',
@@ -427,7 +567,7 @@ public function save(): void
 
 			$params = [
 				$this->start->format('Y-m-d'),
-				(clone $this->recurrence_end)->sub($this->duration)->format('Y-m-d'),
+				$recurrence_end->format('Y-m-d'),
 				$this->board,
 				$this->topic,
 				Utils::truncate($this->title, 255),
@@ -451,6 +591,10 @@ public function save(): void
 
 			IntegrationHook::call('integrate_create_event', [$this, &$columns, &$params]);
 
+			if (isset($this->id)) {
+				unset(self::$loaded[$this->id]);
+			}
+
 			$this->id = Db::$db->insert(
 				'',
 				'{db_prefix}calendar',
@@ -482,7 +626,7 @@ public function save(): void
 			$params = [
 				'id' => $this->id,
 				'start_date' => $this->start->format('Y-m-d'),
-				'end_date' => (clone $this->recurrence_end)->sub($this->duration)->format('Y-m-d'),
+				'end_date' => $recurrence_end->format('Y-m-d'),
 				'title' => Utils::truncate($this->title, 255),
 				'location' => Utils::truncate($this->location, 255),
 				'id_board' => $this->board,
@@ -534,6 +678,33 @@ public function save(): void
 	// 	return '';
 	// }
 
+	/**
+	 * Adds an arbitrary date to the recurrence set.
+	 *
+	 * Used for making exceptions to the general recurrence rule.
+	 *
+	 * @param \DateTimeInterface $date The date to add.
+	 * @param ?\DateInterval $duration Optional duration for this occurrence.
+	 *    Only necessary if the duration for this occurrence differs from the
+	 *    usual duration of the event.
+	 */
+	public function addOccurrence(\DateTimeInterface $date, ?\DateInterval $duration = null): void
+	{
+		$this->recurrence_iterator->add($date, $duration);
+	}
+
+	/**
+	 * Removes a date from the recurrence set.
+	 *
+	 * Used for making exceptions to the general recurrence rule.
+	 *
+	 * @param \DateTimeInterface $date The date to remove.
+	 */
+	public function removeOccurrence(\DateTimeInterface $date): void
+	{
+		$this->recurrence_iterator->remove($date);
+	}
+
 	/**
 	 * Returns a generator that yields all occurrences of the event between
 	 * $this->view_start and $this->view_end.
@@ -999,6 +1170,22 @@ public function __get(string $prop): mixed
 				$value = isset($this->recurrence_iterator) ? $this->recurrence_iterator->getRRule() : null;
 				break;
 
+			case 'rrule_preset':
+				if (isset($this->recurrence_iterator)) {
+					$value = $this->recurrence_iterator->getRRule();
+				} else {
+					$value = null;
+					break;
+				}
+
+				if (($value->count ?? 0) === 1) {
+					$value = 'never';
+				} else {
+					unset($value->count, $value->until, $value->until_type, $value->wkst);
+					$value = (string) $value;
+				}
+				break;
+
 			case 'rdates':
 				$value = isset($this->recurrence_iterator) ? $this->recurrence_iterator->getRDates() : null;
 				break;
@@ -1354,9 +1541,17 @@ public static function create(array $eventOptions): void
 		}
 
 		// Set the start and end dates.
-		self::setStartAndDuration($eventOptions);
+		self::setRequestedStartAndDuration($eventOptions);
+
+		$eventOptions['view_start'] = \DateTimeImmutable::createFromInterface($eventOptions['start']);
+		$eventOptions['view_end'] = new \DateTimeImmutable('9999-12-31T23:59:59 UTC');
+
+		self::setRequestedRRule($eventOptions);
 
 		$event = new self(0, $eventOptions);
+
+		self::setRequestedRDatesAndExDates($event);
+
 		$event->save();
 
 		// If this isn't tied to a topic, we need to notify people about it.
@@ -1401,10 +1596,18 @@ public static function modify(int $id, array &$eventOptions): void
 		}
 
 		// Set the new start date and duration.
-		self::setStartAndDuration($eventOptions);
+		self::setRequestedStartAndDuration($eventOptions);
+
+		$eventOptions['view_start'] = \DateTimeImmutable::createFromInterface($eventOptions['start']);
+		$eventOptions['view_end'] = new \DateTimeImmutable('9999-12-31T23:59:59 UTC');
+
+		self::setRequestedRRule($eventOptions);
 
 		list($event) = self::load($id);
 		$event->set($eventOptions);
+
+		self::setRequestedRDatesAndExDates($event);
+
 		$event->save();
 	}
 
@@ -1552,8 +1755,7 @@ protected static function queryData(array $selects, array $params = [], array $j
 			// Replace duration string with a DateInterval object.
 			$row['duration'] = new TimeInterval($row['duration']);
 
-			// end_date actually means the recurrence end date.
-			$row['recurrence_end'] = (clone $row['start'])->modify($row['end_date'])->add($row['duration']);
+			// end_date is only used for narrowing the query.
 			unset($row['end_date']);
 
 			// Are there any adjustments to the calculated recurrence dates?
@@ -1580,7 +1782,7 @@ protected static function queryData(array $selects, array $params = [], array $j
 	 * @param array $eventOptions An array of optional time and date parameters
 	 *    (span, start_year, end_month, etc., etc.)
 	 */
-	protected static function setStartAndDuration(array &$eventOptions): void
+	protected static function setRequestedStartAndDuration(array &$eventOptions): void
 	{
 		// Convert unprefixed time unit parameters to start_* parameters.
 		foreach (['year', 'month', 'day', 'hour', 'minute', 'second'] as $key) {
@@ -1677,6 +1879,160 @@ protected static function setStartAndDuration(array &$eventOptions): void
 		}
 	}
 
+	/**
+	 * Set the RRule for a posted event for insertion into the database.
+	 *
+	 * @param array $eventOptions An array of optional time and date parameters
+	 *    (span, start_year, end_month, etc., etc.)
+	 */
+	protected static function setRequestedRRule(array &$eventOptions): void
+	{
+		if (isset($_REQUEST['COUNT']) && (int) $_REQUEST['COUNT'] <= 1) {
+			$_REQUEST['RRULE'] = 'never';
+		}
+
+		if (!empty($_REQUEST['RRULE']) && $_REQUEST['RRULE'] !== 'custom') {
+			if ($_REQUEST['RRULE'] === 'never') {
+				unset($_REQUEST['RRULE']);
+				$eventOptions['rrule'] = 'FREQ=YEARLY;COUNT=1';
+
+				return;
+			}
+
+			if (!empty($_REQUEST['UNTIL'])) {
+				$_REQUEST['RRULE'] .= ';UNTIL=' . $_REQUEST['UNTIL'];
+			} elseif (!empty($_REQUEST['COUNT'])) {
+				$_REQUEST['RRULE'] .= ';COUNT=' . $_REQUEST['COUNT'];
+			}
+
+			try {
+				$eventOptions['rrule'] = new RRule(Utils::htmlspecialchars($_REQUEST['RRULE']));
+
+				if (
+					$eventOptions['rrule']->freq === 'WEEKLY'
+					|| !empty($eventOptions['rrule']->byday)
+				) {
+					$eventOptions['rrule']->wkst = RRule::WEEKDAYS[((Theme::$current->options['calendar_start_day'] ?? 0) + 6) % 7];
+				}
+
+				$eventOptions['rrule'] = (string) $eventOptions['rrule'];
+			} catch (\Throwable $e) {
+				unset($_REQUEST['RRULE']);
+				$eventOptions['rrule'] = 'FREQ=YEARLY;COUNT=1';
+			}
+		} elseif (in_array($_REQUEST['FREQ'] ?? null, RRule::FREQUENCIES)) {
+			$rrule = [];
+
+			if (isset($_REQUEST['BYDAY_num'], $_REQUEST['BYDAY_name'])) {
+				foreach ($_REQUEST['BYDAY_num'] as $key => $value) {
+					// E.g. "second Tuesday" = "BYDAY=2TU"
+					if (!str_contains($_REQUEST['BYDAY_name'][$key], ',')) {
+						$_REQUEST['BYDAY'][$key] = ((int) $_REQUEST['BYDAY_num'][$key]) . $_REQUEST['BYDAY_name'][$key];
+					}
+					// E.g. "last weekday" = "BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-1"
+					else {
+						$_REQUEST['BYDAY'] = [];
+						$_REQUEST['BYDAY'][0] = $_REQUEST['BYDAY_name'][$key];
+						$_REQUEST['BYSETPOS'] = $_REQUEST['BYDAY_num'][$key];
+						break;
+					}
+				}
+
+				$_REQUEST['BYDAY'] = implode(',', array_unique($_REQUEST['BYDAY']));
+				unset($_REQUEST['BYDAY_num'], $_REQUEST['BYDAY_name']);
+			}
+
+			foreach (
+				[
+					'FREQ',
+					'INTERVAL',
+					'UNTIL',
+					'COUNT',
+					'BYMONTH',
+					'BYWEEKNO',
+					'BYYEARDAY',
+					'BYMONTHDAY',
+					'BYDAY',
+					'BYHOUR',
+					'BYMINUTE',
+					'BYSECOND',
+					'BYSETPOS',
+				] as $part
+			) {
+				if (isset($_REQUEST[$part])) {
+					if (is_array($_REQUEST[$part])) {
+						$rrule[] = $part . '=' . Utils::htmlspecialchars(implode(',', $_REQUEST[$part]));
+					} else {
+						$rrule[] = $part . '=' . Utils::htmlspecialchars($_REQUEST[$part]);
+					}
+				}
+			}
+
+			$rrule = implode(';', $rrule);
+
+			try {
+				$eventOptions['rrule'] = new RRule(Utils::htmlspecialchars($rrule));
+
+				if (
+					$eventOptions['rrule']->freq === 'WEEKLY'
+					|| !empty($eventOptions['rrule']->byday)
+				) {
+					$eventOptions['rrule']->wkst = RRule::WEEKDAYS[((Theme::$current->options['calendar_start_day'] ?? 0) + 6) % 7];
+				}
+
+				$eventOptions['rrule'] = (string) $eventOptions['rrule'];
+			} catch (\Throwable $e) {
+				$eventOptions['rrule'] = 'FREQ=YEARLY;COUNT=1';
+			}
+
+			unset($rrule);
+		}
+	}
+
+	/**
+	 * Set the RDates for a posted event for insertion into the database.
+	 *
+	 * @param Event $event An event that is being created or modified.
+	 */
+	protected static function setRequestedRDatesAndExDates(Event $event): void
+	{
+		// Clear out all existing RDates and ExDates.
+		foreach ($event->recurrence_iterator->getRDates() as $rdate) {
+			$event->removeOccurrence(new \DateTimeImmutable($rdate));
+		}
+
+		foreach ($event->recurrence_iterator->getExDates() as $exdate) {
+			$event->addOccurrence(new \DateTimeImmutable($exdate));
+		}
+
+		// Add all the RDates and ExDates.
+		foreach (['RDATE', 'EXDATE'] as $date_type) {
+			if (!isset($_REQUEST[$date_type . '_date'])) {
+				continue;
+			}
+
+			foreach ($_REQUEST[$date_type . '_date'] as $key => $date) {
+				if (empty($date)) {
+					continue;
+				}
+
+				if (empty($event->allday) && isset($_REQUEST[$date_type . '_time'][$key])) {
+					$date = new Time($date . 'T' . $_REQUEST[$date_type . '_time'][$key] . ' ' . $event->start->format('e'));
+				} else {
+					$date = new Time($date . ' ' . $event->start->format('e'));
+				}
+
+				$date->setTimezone(new \DateTimeZone('UTC'));
+
+				if ($date_type === 'RDATE') {
+					$event->addOccurrence($date);
+				} else {
+					$event->removeOccurrence($date);
+				}
+			}
+		}
+	}
+
 	/**
 	 * Standardizes various forms of input about start and end times.
 	 *
diff --git a/Sources/Calendar/RecurrenceIterator.php b/Sources/Calendar/RecurrenceIterator.php
index 0ed40fcddc..8bc53b2282 100644
--- a/Sources/Calendar/RecurrenceIterator.php
+++ b/Sources/Calendar/RecurrenceIterator.php
@@ -462,6 +462,14 @@ public function getDtStart(): \DateTimeInterface
 		return clone $this->dtstart;
 	}
 
+	/**
+	 * Returns a copy of $this->frequency_interval.
+	 */
+	public function getFrequencyInterval(): \DateInterval
+	{
+		return clone $this->frequency_interval;
+	}
+
 	/**
 	 * Returns a copy of the recurrence rule.
 	 */
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index 4bb7f53a6c..90fa9eafd0 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -805,82 +805,9 @@ function template_event_post()
 				</div>';
 
 	echo '
-				<div class="roundframe noup">
-					<fieldset id="event_main">
-						<legend><span', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>', Lang::$txt['calendar_event_title'], '</span></legend>
-						<input type="hidden" name="calendar" value="1">
-						<div class="event_options_left" id="event_title">
-							<div>
-								<input type="text" id="evtitle" name="evtitle" maxlength="255" size="55" value="', Utils::$context['event']['title'], '" tabindex="', Utils::$context['tabindex']++, '">
-							</div>
-						</div>';
+				<div class="roundframe noup">';
 
-	// If this is a new event let the user specify which board they want the linked post to be put into.
-	if (Utils::$context['event']['new'] && !empty(Utils::$context['event']['categories']))
-	{
-		echo '
-						<div class="event_options_right" id="event_board">
-							<div>
-								<span class="label">', Lang::$txt['calendar_post_in'], '</span>
-								<input type="checkbox" name="link_to_board"', (!empty(Utils::$context['event']['board']) ? ' checked' : ''), ' onclick="toggleLinked(this.form);">
-								<select name="board"', empty(Utils::$context['event']['board']) ? ' disabled' : '', '>';
-
-		foreach (Utils::$context['event']['categories'] as $category)
-		{
-			echo '
-									<optgroup label="', $category['name'], '">';
-
-			foreach ($category['boards'] as $board)
-				echo '
-										<option value="', $board['id'], '"', $board['selected'] ? ' selected' : '', '>', $board['child_level'] > 0 ? str_repeat('==', $board['child_level'] - 1) . '=&gt;' : '', ' ', $board['name'], '</option>';
-			echo '
-									</optgroup>';
-		}
-		echo '
-								</select>
-							</div>
-						</div><!-- #event_board -->';
-	}
-
-	// Note to theme writers: The JavaScript expects the input fields for the start and end dates & times to be contained in a wrapper element with the id "event_time_input"
-	echo '
-					</fieldset>
-					<fieldset id="event_options">
-						<legend>', Lang::$txt['calendar_event_options'], '</legend>
-						<div class="event_options_left" id="event_time_input">
-							<div>
-								<span class="label">', Lang::$txt['start'], '</span>
-								<input type="text" name="start_date" id="start_date" value="', trim(Utils::$context['event']['start_date_orig']), '" tabindex="', Utils::$context['tabindex']++, '" class="date_input start" data-type="date">
-								<input type="text" name="start_time" id="start_time" maxlength="11" value="', Utils::$context['event']['start_time_orig'], '" tabindex="', Utils::$context['tabindex']++, '" class="time_input start" data-type="time"', !empty(Utils::$context['event']['allday']) ? ' disabled' : '', '>
-							</div>
-							<div>
-								<span class="label">', Lang::$txt['end'], '</span>
-								<input type="text" name="end_date" id="end_date" value="', trim(Utils::$context['event']['end_date_orig']), '" tabindex="', Utils::$context['tabindex']++, '" class="date_input end" data-type="date"', Config::$modSettings['cal_maxspan'] == 1 ? ' disabled' : '', '>
-								<input type="text" name="end_time" id="end_time" maxlength="11" value="', Utils::$context['event']['end_time_orig'], '" tabindex="', Utils::$context['tabindex']++, '" class="time_input end" data-type="time"', !empty(Utils::$context['event']['allday']) ? ' disabled' : '', '>
-							</div>
-						</div><!-- #event_time_input -->
-						<div class="event_options_right" id="event_time_options">
-							<div id="event_allday">
-								<label for="allday"><span class="label">', Lang::$txt['calendar_allday'], '</span></label>
-								<input type="checkbox" name="allday" id="allday"', !empty(Utils::$context['event']['allday']) ? ' checked' : '', ' tabindex="', Utils::$context['tabindex']++, '">
-							</div>
-							<div id="event_timezone">
-								<span class="label">', Lang::$txt['calendar_timezone'], '</span>
-								<select name="tz" id="tz"', !empty(Utils::$context['event']['allday']) ? ' disabled' : '', '>';
-
-	foreach (Utils::$context['all_timezones'] as $tz => $tzname)
-		echo '
-									<option', is_numeric($tz) ? ' value="" disabled' : ' value="' . $tz . '"', $tz === Utils::$context['event']['tz'] ? ' selected' : '', '>', $tzname, '</option>';
-
-	echo '
-								</select>
-							</div>
-						</div><!-- #event_time_options -->
-						<div>
-							<span class="label">', Lang::$txt['location'], '</span>
-							<input type="text" name="event_location" id="event_location" maxlength="255" value="', !empty(Utils::$context['event']['location']) ? Utils::$context['event']['location'] : '', '" tabindex="', Utils::$context['tabindex']++, '">
-						</div>
-					</fieldset>';
+	template_event_options();
 
 	echo '
 					<input type="submit" value="', empty(Utils::$context['event']['new']) ? Lang::$txt['save'] : Lang::$txt['post'], '" class="button">';
diff --git a/Themes/default/EventEditor.template.php b/Themes/default/EventEditor.template.php
new file mode 100644
index 0000000000..655f501eaa
--- /dev/null
+++ b/Themes/default/EventEditor.template.php
@@ -0,0 +1,425 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+use SMF\Config;
+use SMF\Lang;
+use SMF\Utils;
+
+/**
+ * Template for the event options fieldset that is used when creating an event.
+ *
+ * Used by Calendar.template.php and Post.template.php
+ */
+function template_event_options()
+{
+	echo '
+					<fieldset id="event_options">
+						<legend>', Lang::$txt['calendar_event_options'], '</legend>
+						<input type="hidden" name="calendar" value="1">';
+
+	// If this is a new event let the user specify which board they want the linked post to be put into.
+	if (!empty(Utils::$context['event']->new) && !empty(Utils::$context['event']->categories)) {
+		echo '
+						<dl id="event_board">
+							<dt class="clear">
+								<label>', Lang::$txt['calendar_post_in'], '</label>
+							</dt>
+							<dd>
+								<input type="checkbox" name="link_to_board"', (!empty(Utils::$context['event']->board) ? ' checked' : ''), ' onclick="toggleLinked(this.form);">
+								<select name="board"', empty(Utils::$context['event']->board) ? ' disabled' : '', '>';
+
+		foreach (Utils::$context['event']->categories as $category) {
+			echo '
+									<optgroup label="', $category['name'], '">';
+
+			foreach ($category['boards'] as $board) {
+				echo '
+										<option value="', $board['id'], '"', $board['selected'] ? ' selected' : '', '>', $board['child_level'] > 0 ? str_repeat('==', $board['child_level'] - 1) . '=&gt;' : '', ' ', $board['name'], '</option>';
+			}
+
+			echo '
+									</optgroup>';
+		}
+
+		echo '
+								</select>
+							</dd>
+						</dl>';
+	}
+
+	// Basic event info
+	echo '
+						<dl id="event_basic_info">
+							<dt class="clear">
+								<label', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>', Lang::$txt['calendar_event_title'], '</label>
+							</dt>
+							<dd>
+								<input type="text" id="evtitle" name="evtitle" maxlength="255" value="', Utils::$context['event']->title, '"', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>
+							</dd>
+
+							<dt class="clear">
+								<label>', Lang::$txt['location'], '</label>
+							</dt>
+							<dd>
+								<input type="text" name="event_location" id="event_location" maxlength="255" value="', Utils::$context['event']->location, '">
+							</dd>
+						</dl>';
+
+	// Date and time info.
+	echo '
+						<hr class="clear">
+						<dl id="event_date_and_time">
+							<dt class="clear">
+								<label for="allday">', Lang::$txt['calendar_allday'], '</label>
+							</dt>
+							<dd>
+								<input type="checkbox" name="allday" id="allday"', !empty(Utils::$context['event']->allday) ? ' checked' : '', '>
+
+							</dd>
+
+							<dt class="clear">
+								<label>', Lang::$txt['start'], '</label>
+							</dt>
+							<dd>
+								<input type="date" name="start_date" id="start_date" value="', Utils::$context['event']->start->format('Y-m-d'), '" class="date_input start">
+								<input type="time" name="start_time" id="start_time" value="', Utils::$context['event']->start->format('H:i'), '" class="time_input start"', !empty(Utils::$context['event']->allday) ? ' disabled' : '', '>
+							</dd>
+
+							<dt class="clear">
+								<label>', Lang::$txt['end'], '</label>
+							</dt>
+							<dd>
+								<input type="date" name="end_date" id="end_date" value="', Utils::$context['event']->end->format('Y-m-d'), '" class="date_input end"', Config::$modSettings['cal_maxspan'] == 1 ? ' disabled' : '', '>
+								<input type="time" name="end_time" id="end_time" value="', Utils::$context['event']->end->format('H:i'), '" class="time_input end"', !empty(Utils::$context['event']->allday) ? ' disabled' : '', '>
+
+							</dd>
+
+							<dt id="tz_dt" class="clear">
+								<label>', Lang::$txt['calendar_timezone'], '</label>
+							</dt>
+							<dd id="tz_dd">';
+
+	// Setting max-width on selects inside floating elements can be flaky,
+	// so we need to calculate the width value manually.
+	echo '
+								<select name="tz" id="tz"', !empty(Utils::$context['event']->allday) ? ' disabled' : '', ' style="width:min(', max(array_map(fn ($tzname) => Utils::entityStrlen($tzname), Utils::$context['all_timezones'])) * 0.9, 'ch, 100%)">';
+
+	foreach (Utils::$context['all_timezones'] as $tz => $tzname) {
+		echo '
+									<option', is_numeric($tz) ? ' value="" disabled' : ' value="' . $tz . '"', $tz === Utils::$context['event']->tz ? ' selected' : '', '>', $tzname, '</option>';
+	}
+
+	echo '
+								</select>
+							</dd>
+						</dl>';
+
+	// Recurring event options.
+	echo '
+						<dl id="rrule_options">';
+
+	// RRULE presets.
+	echo '
+							<dt class="clear">
+								<label>', Lang::$txt['calendar_repeat_recurrence_label'], '</label>
+							</dt>
+							<dd>
+								<select name="RRULE" id="rrule" class="rrule_input">';
+
+	foreach (Utils::$context['event']->rrule_presets as $rrule => $description) {
+		echo '
+									<option value="', $rrule, '"', $rrule === Utils::$context['event']->rrule_preset || $rrule === 'custom' && !isset(Utils::$context['event']->rrule_presets[Utils::$context['event']->rrule_preset]) ? ' selected' : '', '>', $description, '</option>';
+	}
+
+	echo '
+								</select>';
+
+	// When to end the recurrence.
+	echo '
+								<span id="rrule_end" class="rrule_input_wrapper">
+									<select id="end_option" class="rrule_input">
+										<option value="forever">', Lang::$txt['calendar_repeat_until_options']['forever'], '</option>
+										<option value="until"', !empty(Utils::$context['event']->recurrence_iterator->getRRule()->until) ? ' selected' : '', '>', Lang::$txt['calendar_repeat_until_options']['until'], '</option>
+										<option value="count"', (Utils::$context['event']->recurrence_iterator->getRRule()->count ?? 0) > 1 ? ' selected' : '', '>', Lang::$txt['calendar_repeat_until_options']['count'], '</option>
+									</select>
+									<input type="date" name="UNTIL" id="until" class="rrule_input"', !empty(Utils::$context['event']->recurrence_iterator->getRRule()->until) ? ' value="' . Utils::$context['event']->recurrence_iterator->getRRule()->until->format('Y-m-d') . '"' : ' disabled', '>
+									<input type="number" name="COUNT" id="count" class="rrule_input" min="1"', (Utils::$context['event']->recurrence_iterator->getRRule()->count ?? 0) > 1 ? ' value="' . Utils::$context['event']->recurrence_iterator->getRRule()->count . '"' : ' value="1" disabled', '>
+								</span>
+							</dd>
+						</dl>';
+
+	// Custom frequency and interval (e.g. "every 2 weeks")
+	echo '
+						<dl id="freq_interval_options" class="rrule_input_wrapper">
+							<dt class="clear">
+								<label>', Lang::$txt['calendar_repeat_interval_label'], '</label>
+							</dt>
+							<dd>
+								<input type="number" name="INTERVAL" value="', Utils::$context['event']->recurrence_iterator->getRRule()->interval, '" min="1" class="rrule_input" disabled>
+								<select name="FREQ" id="freq" class="rrule_input">';
+
+	foreach (Utils::$context['event']->frequency_units as $freq => $unit) {
+		echo '
+									<option value="', $freq, '"', Utils::$context['event']->recurrence_iterator->getRRule()->freq === $freq ? ' selected' : '', '>', $unit, '</option>';
+	}
+
+	echo '
+								</select>
+							</dd>
+						</dl>';
+
+	// Custom yearly options.
+	echo '
+						<dl id="yearly_options" class="rrule_input_wrapper">
+							<dt class="clear">
+								<label>', Lang::$txt['calendar_repeat_bymonth_label'], '</label>
+							</dt>
+							<dd>
+								<div class="rrule_input_row">';
+
+	for ($i = 1; $i <= 12; $i++) {
+		echo '
+									<label class="bymonth_label">
+										<input type="checkbox" name="BYMONTH[]" value="' . $i . '" id="bymonth_', $i,'" class="rrule_input" disabled>
+										<span>' . Lang::$txt['months_short'][$i] . '</span>
+									</label>';
+
+		if ($i % 6 === 0) {
+			echo '
+								</div>
+								<div class="rrule_input_row">';
+		}
+	}
+
+	echo '
+								</div>
+							</dd>
+						</dl>';
+
+	// Custom monthly options.
+	echo '
+						<dl id="monthly_options" class="rrule_input_wrapper">';
+
+	// Custom monthly: by day of month.
+	echo '
+							<dt class="clear" id="dt_monthly_option_type_bymonthday">
+								<label>
+									', Lang::$txt['calendar_repeat_bymonthday_label'], '
+									<input type="radio" name="monthly_option_type" id="monthly_option_type_bymonthday"', !empty(Utils::$context['event']->recurrence_iterator->getRRule()->bymonthday) ? ' checked' : '', '>
+								</label>
+							</dt>
+							<dd id="dd_monthly_option_type_bymonthday">
+								<div id="month_bymonthday_options" class="rrule_input">
+									<div class="rrule_input inline_block">
+										<div class="rrule_input_row">';
+
+	for ($i = 1; $i <= 31; $i++) {
+		echo '
+											<label class="bymonthday_label">
+												<input type="checkbox" name="BYMONTHDAY[]" id="bymonthday_' . $i . '" value="' . $i . '"  class="rrule_input" disabled> <span>' . $i . '</span>
+											</label>';
+
+		if ($i % 7 === 0) {
+			echo '
+										</div>
+										<div class="rrule_input_row">';
+		}
+	}
+
+	echo '
+										</div>
+									</div>
+								</div>
+							</dd>';
+
+	// Custom monthly: by weekday and offset (e.g. "the second Tuesday")
+	echo '
+							<dt class="clear">
+								<label>
+									', Lang::$txt['calendar_repeat_byday_label'], '
+									<input type="radio" name="monthly_option_type" id="monthly_option_type_byday"', !empty(Utils::$context['event']->recurrence_iterator->getRRule()->byday) ? ' checked' : '', '>
+								</label>
+							</dt>
+							<dd id="month_byday_options">
+								<div class="rrule_input clear">';
+
+	foreach (Utils::$context['event']->byday_items as $byday_item_key => $byday_item) {
+		echo '
+									<div>
+										<select id="byday_num_select_', $byday_item_key, '" name="BYDAY_num[', $byday_item_key, ']" class="rrule_input byday_num_select" disabled>';
+
+		foreach (Utils::$context['event']->byday_num_options as $num => $ordinal) {
+			if (isset($prev_num) && ($num < 0) !== ($prev_num < 0)) {
+				echo '
+											<option disabled>------</option>';
+		}
+
+		echo '
+											<option value="', $num, '" class="byday_num_', ($num < 0 ? 'neg' : '') . abs($num), '"', $num == $byday_item['num'] ? ' selected' : '', '>', $ordinal, '</option>';
+
+			$prev_num = $num;
+		}
+		unset($prev_num);
+
+		echo '
+										</select>
+										<select id="byday_name_select_', $byday_item_key, '" name="BYDAY_name[', $byday_item_key, ']" class="rrule_input byday_name_select" disabled>';
+
+		foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
+			echo '
+											<option value="', $weekday['abbrev'], '" class="byday_name_', $weekday['abbrev'], '"', $weekday['abbrev'] == $byday_item['name'] ? ' selected' : '', '>', $weekday['long'], '</option>';
+		}
+
+		echo '
+											<option disabled>------</option>
+											<option value="MO,TU,WE,TH,FR">', Lang::$txt['calendar_repeat_weekday'], '</option>
+											<option value="SA,SU">', Lang::$txt['calendar_repeat_weekend_day'], '</option>
+										</select>
+									</div>';
+	}
+
+	echo '
+								</div>
+								<div>
+									<a id="event_add_byday" class="rrule_input button floatnone">', Lang::$txt['calendar_repeat_add_condition'], '</a>
+								</div>
+								<template id="byday_template">
+									<div>
+										<select name="BYDAY_num[-1]" class="rrule_input byday_num_select">';
+
+	foreach (Utils::$context['event']->byday_num_options as $num => $ordinal) {
+		if (isset($prev_num) && ($num < 0) !== ($prev_num < 0)) {
+			echo '
+											<option disabled>------</option>';
+	}
+
+	echo '
+											<option value="', $num, '" class="byday_num_', ($num < 0 ? 'neg' : '') . abs($num), '">', $ordinal, '</option>';
+
+		$prev_num = $num;
+	}
+	unset($prev_num);
+
+	echo '
+										</select>
+										<select name="BYDAY_name[-1]" class="rrule_input byday_name_select">';
+
+	foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
+		echo '
+											<option value="', $weekday['abbrev'], '" class="byday_name_', $weekday['abbrev'], '">', $weekday['long'], '</option>';
+	}
+
+	echo '
+											<option disabled>------</option>
+											<option value="MO,TU,WE,TH,FR">', Lang::$txt['calendar_repeat_weekday'], '</option>
+											<option value="SA,SU">', Lang::$txt['calendar_repeat_weekend_day'], '</option>
+										</select>
+									</div>
+								</template>
+							</dd>
+						</dl>';
+
+	// Custom weekly options.
+	echo '
+						<dl id="weekly_options" class="rrule_input_wrapper">
+							<dt class="clear">
+								<label>', Lang::$txt['calendar_repeat_byday_label'], '</label>
+							</dt>
+							<dd class="rrule_input_row">';
+
+	foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
+		echo '
+									<label class="byday_label">
+										<input type="checkbox" name="BYDAY[]" id="byday_', $weekday['abbrev'], '" value="', $weekday['abbrev'], '"  class="rrule_input"', in_array($weekday['abbrev'], Utils::$context['event']->recurrence_iterator->getRRule()->byday ?? []) ? ' checked' : '', ' disabled>
+										<span>', $weekday['short'], '</span>
+									</label>';
+	}
+
+	echo '
+							</dd>
+						</dl>';
+
+	// Advanced options.
+	echo '
+						<details id="advanced_options" class="rrule_input_wrapper"' . (!empty(Utils::$context['event']->recurrence_iterator->getRDates()) || !empty(Utils::$context['event']->recurrence_iterator->getEXDates()) ? ' open' : '') . '>
+							<summary>', Lang::$txt['calendar_repeat_advanced_options_label'], '</summary>';
+
+	// Arbitrary dates to add to the recurrence set.
+	echo '
+							<dl id="rdates">
+								<dt class="clear">
+									<label>', Lang::$txt['calendar_repeat_rdates_label'], '</label>
+								</dt>
+								<dd>
+									<div id="rdate_list">';
+
+	foreach (Utils::$context['event']->recurrence_iterator->getRDates() as $key => $rdate) {
+		$rdate = new SMF\Time($rdate);
+		$rdate->setTimezone(Utils::$context['event']->start->getTimezone());
+
+		echo '
+										<div>
+											<input type="date" name="RDATE_date[', $key, ']" value="', $rdate->format('Y-m-d'), '" class="date_input">
+											<input type="time" name="RDATE_time[', $key, ']" value="', $rdate->format('H:i'), '" class="time_input">
+											<a class="main_icons delete"></a>
+										</div>';
+	}
+
+	echo '
+									</div>
+									<div>
+										<a id="event_add_rdate" data-container="rdate_list" data-inputname="RDATE" class="button floatnone">', Lang::$txt['calendar_repeat_add_condition'], '</a>
+									</div>
+								</dd>
+							</dl>';
+
+	// Dates to exclude from the recurrence set.
+	echo '
+							<dl id="exdates">
+								<dt class="clear">
+									<label>', Lang::$txt['calendar_repeat_exdates_label'], '</label>
+								</dt>
+								<dd>
+									<div id="exdate_list">';
+
+	foreach (Utils::$context['event']->recurrence_iterator->getExDates() as $key => $exdate) {
+		$exdate = new SMF\Time($exdate);
+
+		echo '
+										<div>
+											<input type="date" name="EXDATE_date[', $key, ']" value="', $exdate->format('Y-m-d'), '" class="date_input">
+											<input type="time" name="EXDATE_time[', $key, ']" value="', $exdate->format('H:i'), '" class="time_input">
+										</div>';
+	}
+
+	echo '
+									</div>
+									<div>
+										<a id="event_add_exdate" data-container="exdate_list" data-inputname="EXDATE" class="button floatnone">', Lang::$txt['calendar_repeat_add_condition'], '</a>
+									</div>
+									<template id="additional_dates_template">
+										<div>
+											<input type="date" name="" value="" class="date_input">
+											<input type="time" name="" value="" class="time_input">
+											<a class="main_icons delete"></a>
+										</div>
+									</template>
+								</dd>
+							</dl>';
+
+	echo '
+						</details>
+					</fieldset>';
+}
+
+?>
\ No newline at end of file
diff --git a/Themes/default/Post.template.php b/Themes/default/Post.template.php
index c9f2bd0550..5cccc71d1e 100644
--- a/Themes/default/Post.template.php
+++ b/Themes/default/Post.template.php
@@ -142,57 +142,13 @@ function addPollOption()
 	// Are you posting a calendar event?
 	if (Utils::$context['make_event'])
 	{
-		// Note to theme writers: The JavaScripts expect the input fields for the start and end dates & times to be contained in a wrapper element with the id "event_time_input"
 		echo '
 					<hr class="clear">
-					<div id="post_event">
-						<fieldset id="event_options">
-							<legend', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>', Lang::$txt['calendar_event_options'], '</legend>
-							<input type="hidden" name="calendar" value="1">
-							<div class="event_options" id="event_title">
-								<div>
-									<span class="label">', Lang::$txt['calendar_event_title'], '</span>
-									<input type="text" id="evtitle" name="evtitle" maxlength="255" value="', Utils::$context['event']['title'], '" tabindex="', Utils::$context['tabindex']++, '">
-								</div>
-							</div>
-							<div class="event_options">
-								<div class="event_options_left" id="event_time_input">
-									<div>
-										<span class="label">', Lang::$txt['start'], '</span>
-										<input type="text" name="start_date" id="start_date" value="', trim(Utils::$context['event']['start_date_orig']), '" tabindex="', Utils::$context['tabindex']++, '" class="date_input start" data-type="date">
-										<input type="text" name="start_time" id="start_time" maxlength="11" value="', Utils::$context['event']['start_time_orig'], '" tabindex="', Utils::$context['tabindex']++, '" class="time_input start" data-type="time"', !empty(Utils::$context['event']['allday']) ? ' disabled' : '', '>
-									</div>
-									<div>
-										<span class="label">', Lang::$txt['end'], '</span>
-										<input type="text" name="end_date" id="end_date" value="', trim(Utils::$context['event']['end_date_orig']), '" tabindex="', Utils::$context['tabindex']++, '" class="date_input end" data-type="date"', Config::$modSettings['cal_maxspan'] == 1 ? ' disabled' : '', '>
-										<input type="text" name="end_time" id="end_time" maxlength="11" value="', Utils::$context['event']['end_time_orig'], '" tabindex="', Utils::$context['tabindex']++, '" class="time_input end" data-type="time"', !empty(Utils::$context['event']['allday']) ? ' disabled' : '', '>
-									</div>
-								</div>
-								<div class="event_options_right" id="event_time_options">
-									<div id="event_allday">
-										<label for="allday"><span class="label">', Lang::$txt['calendar_allday'], '</span></label>
-										<input type="checkbox" name="allday" id="allday"', !empty(Utils::$context['event']['allday']) ? ' checked' : '', ' tabindex="', Utils::$context['tabindex']++, '">
-									</div>
-									<div id="event_timezone">
-										<span class="label">', Lang::$txt['calendar_timezone'], '</span>
-										<select name="tz" id="tz"', !empty(Utils::$context['event']['allday']) ? ' disabled' : '', '>';
+					<div id="post_event">';
 
-			foreach (Utils::$context['all_timezones'] as $tz => $tzname)
-				echo '
-											<option', is_numeric($tz) ? ' value="" disabled' : ' value="' . $tz . '"', $tz === Utils::$context['event']['tz'] ? ' selected' : '', '>', $tzname, '</option>';
+		template_event_options();
 
-			echo '
-										</select>
-									</div>
-								</div>
-							</div>
-							<div class="event_options">
-								<div>
-									<span class="label">', Lang::$txt['location'], '</span>
-									<input type="text" name="event_location" id="event_location" maxlength="255" value="', Utils::$context['event']['location'], '" tabindex="', Utils::$context['tabindex']++, '">
-								</div>
-							</div>
-						</fieldset>
+		echo '
 					</div><!-- #post_event -->';
 	}
 
diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index 8eb939e6bf..77e4ef4000 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -1515,18 +1515,39 @@ ul li.greeting {
 }
 #post_event input[type="checkbox"] {
 	height: auto;
+	vertical-align: initial;
 }
 #post_event input[type="text"][disabled] {
 	color: transparent;
 }
-#post_event select, #event_options input[type="text"], #tz {
-	max-width: calc(100% - 75px);
+#tz {
+	max-width: 100%;
+}
+#rrule_end {
+	white-space: nowrap;
+}
+.rrule_input.inline_block {
+	vertical-align: top;
+}
+.byday_label,
+.bymonth_label,
+.bymonthday_label {
+	white-space: nowrap;
 }
-#post_event select, #evtitle, #event_location {
-	width: calc(100% - 75px);
+.byday_label span,
+.bymonth_label span,
+.bymonthday_label span {
+	display: inline-block;
+}
+.bymonth_label span {
+	width: 4ch;
 }
-#post_event input[type="checkbox"] + select {
-	max-width: calc(100% - 95px);
+.bymonthday_label span {
+	width: 2ch;
+	text-align: center;
+}
+.bymonthday_label input:disabled + span {
+	opacity: 0.5;
 }
 
 /* Styles for the recent messages section.
@@ -3502,19 +3523,25 @@ form#postmodify .roundframe {
 	padding: 6px;
 	overflow: hidden;
 }
-#post_header dt {
+#post_header dt,
+#event_options dt {
 	float: left;
 	padding: 0;
 	width: 15%;
 	margin: 6px 0 0 0;
 	font-weight: bold;
 }
-#post_header dd {
+#post_header dd,
+#event_options dd {
 	float: left;
 	padding: 0;
 	width: 83%;
 	margin: 4px 0;
 }
+#post_header input[type="text"],
+#event_basic_info input[type="text"] {
+	width: 100%;
+}
 #post_header img {
 	vertical-align: middle;
 }
diff --git a/Themes/default/css/responsive.css b/Themes/default/css/responsive.css
index 5757c83d49..abe23147e3 100644
--- a/Themes/default/css/responsive.css
+++ b/Themes/default/css/responsive.css
@@ -48,28 +48,6 @@
 	#top_info .welcome {
 		display: none;
 	}
-	/* Calendar */
-	#event_time_options {
-		width: 44%;
-	}
-	#event_title {
-		padding: 0;
-	}
-	#evtitle {
-		width: 98%;
-	}
-	.event_options_left, .event_options_right {
-		display: block;
-		max-width: unset;
-		width: unset;
-	}
-	#event_title input[type="text"] {
-		width: 100%;
-	}
-	#post_event #event_board select {
-		width: calc(100% - 90px);
-		max-width: unset;
-	}
 }
 
 /* We have shared things... */
@@ -369,8 +347,13 @@
 	form#postmodify .roundframe, #post_event .roundframe {
 		padding: 5px;
 	}
-	#post_header input {
-		width: 100%;
+	#post_header input,
+	#event_options input[type="text"],
+	#event_options input[type="date"],
+	#event_options input[type="time"],
+	#event_options select {
+/* 		width: 100% !important; */
+/* 		max-width: initial; */
 	}
 	#post_confirm_buttons .smalltext {
 		display: none;
@@ -580,13 +563,13 @@
 @media (min-width: 481px) and (max-width: 560px) {
 	/* Calendar */
 	#event_time_options {
-		width: 40%;
+/* 		width: 40%; */
 	}
 	#event_title, #event_board {
-		width: 100%;
+/* 		width: 100%; */
 	}
 	#evtitle {
-		width: 98%;
+/* 		width: 98%; */
 	}
 }
 
@@ -666,12 +649,26 @@
 	}
 
 	/* Post Section */
-	#post_header dd {
+	#post_header dd,
+	#event_options dd {
 		width: 55%;
 	}
-	#post_header dt {
+	#post_header dt,
+	#event_options dt {
 		width: 35%;
 	}
+	#rrule_options dd,
+	#rrule_end {
+		display: inline-flex;
+		flex-flow: column;
+	}
+	.byday_label span {
+		width: 3ch;
+	}
+	.bymonth_label,
+	.bymonthday_label {
+		float: left;
+	}
 	img#icons {
 		margin: 0 0 0 5px;
 	}
@@ -803,17 +800,6 @@
 		float: none;
 	}
 
-	/* Calendar */
-	.event_options_left, .event_options_right {
-		width: 100%;
-	}
-	#event_title, #event_board {
-		width: 100%;
-	}
-	#evtitle {
-		width: 98%;
-	}
-
 	/* Menu tests */
 	#header_news_lists_preview, tr[id^="list_news_lists_"] td:nth-child(even),
 	#header_smiley_set_list_default, #header_smiley_set_list_url, #header_smiley_set_list_check,
diff --git a/Themes/default/scripts/event.js b/Themes/default/scripts/event.js
new file mode 100644
index 0000000000..16b65adacc
--- /dev/null
+++ b/Themes/default/scripts/event.js
@@ -0,0 +1,682 @@
+window.addEventListener("DOMContentLoaded", updateEventUI);
+
+for (const elem of document.querySelectorAll("#start_date, #start_time, #end_date, #end_time, #allday, #tz, #rrule, #freq, #end_option, #monthly_option_type_bymonthday, #monthly_option_type_byday, #byday_num_select_0, #byday_name_select_0, #weekly_options .rrule_input[name=\'BYDAY\[\]\'], #monthly_options .rrule_input[name=\'BYDAY_num\[\]\'], #monthly_options .rrule_input[name=\'BYDAY_name\[\]\'], #monthly_options .rrule_input[name=\'BYMONTHDAY\[\]\']")) {
+	elem.addEventListener("change", updateEventUI);
+}
+
+document.getElementById("event_add_byday").addEventListener("click", addByDayItem);
+
+for (const elem of document.querySelectorAll("#event_add_rdate, #event_add_exdate")) {
+	elem.addEventListener("click", addRDateOrExDate);
+}
+
+for (const elem of document.querySelectorAll("#rdate_list a, #exdate_list a")) {
+	elem.addEventListener("click", removeRDateOrExDate);
+}
+
+let rdates_count = document.querySelectorAll("#rdate_list input[type='date']").length;
+let exdates_count = document.querySelectorAll("#exdate_list input[type='date']").length;
+
+let current_start_date = new Date(document.getElementById("start_date").value + 'T' + document.getElementById("start_time").value);
+let current_end_date = new Date(document.getElementById("end_date").value + 'T' + document.getElementById("end_time").value);
+
+const weekday_abbrevs = ["SU", "MO", "TU", "WE", "TH", "FR", "SA"];
+
+// Update all the parts of the event editing UI.
+function updateEventUI()
+{
+	let start_date = new Date(document.getElementById("start_date").value + 'T' + document.getElementById("start_time").value);
+	let end_date = new Date(document.getElementById("end_date").value + 'T' + document.getElementById("end_time").value);
+
+	let weekday = getWeekday(start_date);
+
+	// Disable or enable the time-related fields as necessary.
+	document.getElementById("start_time").disabled = document.getElementById("allday").checked;
+	document.getElementById("end_time").disabled = document.getElementById("allday").checked;
+	document.getElementById("tz").disabled = document.getElementById("allday").checked;
+
+	// Reset the recurring event options to be hidden and disabled.
+	// We'll turn the appropriate ones back on below.
+	for (const elem of document.querySelectorAll(".rrule_input_wrapper")) {
+		elem.style.display = "none";
+	}
+
+	for (const elem of document.querySelectorAll(".rrule_input")) {
+		elem.disabled = true;
+	}
+
+	// If using a custom RRule, show the relevant options.
+	if (document.getElementById("rrule").value === "custom") {
+		// Show select menu for FREQ options.
+		document.getElementById("freq_interval_options").style.display = "";
+
+		for (const elem of document.querySelectorAll("#freq_interval_options .rrule_input")) {
+			elem.disabled = false;
+		}
+
+		// Show additional options based on the selected frequency.
+		switch (document.getElementById("freq").value) {
+			case "YEARLY":
+				for (const elem of document.querySelectorAll("#yearly_options .rrule_input")) {
+					elem.disabled = false;
+				}
+
+				// If necessary, align date fields to BYMONTH inputs.
+				if (this.name == "BYMONTH[]") {
+					let checked_months = [];
+
+					for (const elem of document.querySelectorAll("#yearly_options .rrule_input[name=\'BYMONTH\[\]\']")) {
+						if (elem.checked) {
+							checked_months.push(elem.id.substring(8));
+						}
+					}
+
+					let found = false;
+
+					let m;
+					for (m of checked_months) {
+						if (m >= (start_date.getMonth() + 1)) {
+							found = true;
+							break;
+						}
+					}
+
+					if (!found) {
+						checked_months.reverse();
+						for (m of checked_months) {
+							if (m < (start_date.getMonth() + 1)) {
+								found = true;
+								break;
+							}
+						}
+					}
+
+					if (found) {
+						let temp_date = new Date(
+							start_date.getFullYear(),
+							m - 1,
+							start_date.getDate(),
+							start_date.getHours(),
+							start_date.getMinutes(),
+							start_date.getSeconds(),
+							start_date.getMilliseconds()
+						);
+
+						start_date = updateStartDate(temp_date);
+						end_date = updateEndDate(temp_date, end_date);
+					}
+				}
+
+				// Ensure the yearly BYMONTH inputs align with start_date.
+				if (!document.getElementById("bymonth_" + (start_date.getMonth() + 1)).checked) {
+					for (const elem of document.querySelectorAll(".rrule_input[name=\'BYMONTH\[\]\']")) {
+						elem.checked = false;
+					}
+				}
+				document.getElementById("bymonth_" + (start_date.getMonth() + 1)).checked = true;
+
+				document.getElementById("yearly_options").style.display = "";
+				// no break
+
+			case "MONTHLY":
+				// Enable both radio buttons to allow choosing the type of montly recurrence.
+				for (const elem of document.querySelectorAll("#monthly_options input[name=\'monthly_option_type\']")) {
+					elem.disabled = false;
+				}
+
+				// Make sure one of the radio buttons is checked.
+				if (
+					!document.getElementById("monthly_option_type_bymonthday").checked
+					&& !document.getElementById("monthly_option_type_byday").checked
+				) {
+					document.getElementById("monthly_option_type_bymonthday").checked = true;
+				}
+
+				// Enable either the BYMONTHDAY inputs or BYDAY_* select menus.
+				for (const elem of document.querySelectorAll("#month_bymonthday_options .rrule_input")) {
+					elem.disabled = document.getElementById("monthly_option_type_byday").checked;
+				}
+
+				for (const elem of document.querySelectorAll("#month_byday_options .rrule_input")) {
+					elem.disabled = !document.getElementById("monthly_option_type_byday").checked;
+
+					if (elem.classList.contains('button')) {
+						elem.style.display = document.getElementById("monthly_option_type_byday").checked ? "" : "none";
+					}
+				}
+
+				// Need to know the current values in the BYDAY_* select menus.
+				let byday_num = document.getElementById("byday_num_select_0").value;
+				let byday_name = document.getElementById("byday_name_select_0").value;
+
+				// Need to know the last day of the month for stuff below.
+				const end_of_month = new Date(
+					start_date.getFullYear(),
+					start_date.getMonth() + 1,
+					0,
+					start_date.getHours(),
+					start_date.getMinutes(),
+					start_date.getSeconds(),
+					start_date.getMilliseconds()
+				);
+
+				let selected_days = [];
+
+				for (const weekday_abbrev of weekday_abbrevs) {
+					if (byday_name.includes(weekday_abbrev)) {
+						selected_days.push(weekday_abbrevs.indexOf(weekday_abbrev));
+					}
+				}
+
+				// If necessary, align date fields to BYDAY_* selection.
+				if (this.id === "byday_num_select_0" || this.id === "byday_name_select_0") {
+					let temp_date = getNewStartDateByDay(start_date, end_of_month, byday_num, selected_days);
+
+					if (temp_date.getMonth() !== start_date.getMonth() && byday_num == 5) {
+						enableOrDisableFifth();
+						byday_num = document.getElementById("byday_num_select_0").value;
+						byday_name = document.getElementById("byday_name_select_0").value;
+						selected_days = [weekday_abbrevs.indexOf(byday_name)];
+
+						temp_date = getNewStartDateByDay(start_date, end_of_month, byday_num, selected_days);
+					}
+
+					if (temp_date.getMonth() === start_date.getMonth()) {
+						start_date = updateStartDate(temp_date);
+						end_date = updateEndDate(start_date, end_date);
+					}
+				}
+
+				// If necessary, align date fields to BYMONTHDAY inputs.
+				if (this.name == "BYMONTHDAY[]" && !document.getElementById("bymonthday_" + start_date.getDate()).checked) {
+					let checked_dates = [];
+
+					for (const elem of document.querySelectorAll("#monthly_options .rrule_input[name=\'BYMONTHDAY\[\]\']")) {
+						if (elem.checked) {
+							checked_dates.push(elem.id.substring(11));
+						}
+					}
+
+					let found = false;
+
+					let d;
+					for (d of checked_dates) {
+						if (d >= start_date.getDate()) {
+							found = true;
+							break;
+						}
+					}
+
+					if (!found) {
+						checked_dates.reverse();
+						for (d of checked_dates) {
+							if (d < start_date.getDate()) {
+								found = true;
+								break;
+							}
+						}
+					}
+
+					if (found) {
+						let temp_date = new Date(
+							start_date.getFullYear(),
+							start_date.getMonth(),
+							d,
+							start_date.getHours(),
+							start_date.getMinutes(),
+							start_date.getSeconds(),
+							start_date.getMilliseconds()
+						);
+
+						start_date = updateStartDate(temp_date);
+						end_date = updateEndDate(temp_date, end_date);
+					}
+				}
+
+				// Update weekday in case it changed.
+				weekday = getWeekday(start_date);
+
+				// If necessary, reset the BYMONTHDAY inputs.
+				if (!document.getElementById("bymonthday_" + start_date.getDate()).checked) {
+					for (const elem of document.querySelectorAll("#monthly_options .rrule_input[name=\'BYMONTHDAY\[\]\']")) {
+						elem.checked = false;
+					}
+				}
+
+				// Ensure the BYMONTHDAY input for start_date is checked.
+				document.getElementById("bymonthday_" + start_date.getDate()).checked = true;
+
+				// If necessary, update the BYDAY_* select menus.
+				if (!byday_name.includes(weekday)) {
+					for (const elem of document.querySelectorAll("#byday_name_select_0 .byday_name_" + weekday)) {
+						elem.selected = true;
+					}
+
+					byday_name = weekday;
+					selected_days = [weekday_abbrevs.indexOf(weekday)];
+				}
+
+				if (byday_num < 0) {
+					let temp_byday_num = 0;
+
+					for (let d = end_of_month.getDate(); d > start_date.getDate(); d--) {
+						let temp_date = new Date(
+							start_date.getFullYear(),
+							start_date.getMonth(),
+							d,
+							start_date.getHours(),
+							start_date.getMinutes(),
+							start_date.getSeconds(),
+							start_date.getMilliseconds()
+						);
+
+						if (selected_days.includes(temp_date.getDay())) {
+							++temp_byday_num;
+						}
+					}
+
+					++temp_byday_num;
+
+					if (temp_byday_num <= 2) {
+						for (const elem of document.querySelectorAll("#byday_num_select_0 .byday_num_neg" + temp_byday_num)) {
+							elem.selected = true;
+						}
+					} else {
+						byday_num = 0;
+						byday_name = weekday;
+						selected_days = [weekday_abbrevs.indexOf(weekday)];
+						for (const elem of document.querySelectorAll("#byday_name_select_0 .byday_name_" + weekday)) {
+							elem.selected = true;
+						}
+					}
+				}
+
+				if (byday_num >= 0) {
+					let temp_byday_num = 0;
+
+					for (let d = 1; d < start_date.getDate(); d++) {
+						let temp_date = new Date(
+							start_date.getFullYear(),
+							start_date.getMonth(),
+							d,
+							start_date.getHours(),
+							start_date.getMinutes(),
+							start_date.getSeconds(),
+							start_date.getMilliseconds()
+						);
+
+						if (selected_days.includes(temp_date.getDay())) {
+							++temp_byday_num;
+						}
+					}
+
+					++temp_byday_num;
+
+					for (const elem of document.querySelectorAll("#byday_num_select_0 .byday_num_" + temp_byday_num)) {
+						elem.selected = true;
+					}
+				}
+
+				document.getElementById("monthly_options").style.display = "";
+
+				if (document.getElementById("freq").value === "YEARLY") {
+					document.getElementById("dt_monthly_option_type_bymonthday").style.display = "none";
+					document.getElementById("dd_monthly_option_type_bymonthday").style.display = "none";
+					document.getElementById("monthly_option_type_bymonthday").disabled = true;
+					document.getElementById("monthly_option_type_byday").type = "checkbox";
+				} else {
+					document.getElementById("dt_monthly_option_type_bymonthday").style.display = "";
+					document.getElementById("dd_monthly_option_type_bymonthday").style.display = "";
+					document.getElementById("monthly_option_type_byday").type = "radio";
+				}
+				break;
+
+			case "WEEKLY":
+				for (const elem of document.querySelectorAll("#weekly_options .rrule_input")) {
+					elem.disabled = false;
+				}
+
+				if (this.name == "BYDAY[]" && !document.getElementById("byday_" + weekday).checked) {
+					let checked_days = [];
+
+					for (const elem of document.querySelectorAll("#weekly_options .rrule_input[name=\'BYDAY\[\]\']")) {
+						if (elem.checked) {
+							checked_days.push(elem.id.substring(6));
+						}
+					}
+
+					let cd;
+					for (cd of checked_days) {
+						if (weekday_abbrevs.indexOf(cd) > weekday_abbrevs.indexOf(weekday)) {
+							found = true;
+							break;
+						}
+					}
+
+					if (!found) {
+						checked_days.reverse();
+						for (cd of checked_days) {
+							if (weekday_abbrevs.indexOf(cd) < weekday_abbrevs.indexOf(weekday)) {
+								found = true;
+								break;
+							}
+						}
+					}
+
+					if (found) {
+						let temp_date = start_date;
+
+						// Rewind to previous Sunday or first day of month.
+						while (temp_date.getDay() > 0) {
+							temp_date.setDate(temp_date.getDate() - 1);
+
+							if (temp_date.getMonth() < start_date.getMonth()) {
+								temp_date.setDate(temp_date.getDate() + 1);
+								break;
+							}
+						}
+
+						// Now step forward until we get to the day we need.
+						while (temp_date.getDay() != weekday_abbrevs.indexOf(cd)) {
+							temp_date.setDate(temp_date.getDate() + 1);
+						}
+
+						start_date = updateStartDate(temp_date);
+						end_date = updateEndDate(start_date, end_date);
+					}
+				}
+
+				// Update weekday in case it changed.
+				weekday = getWeekday(start_date);
+
+				// If necessary, reset the BYDAY values.
+				if (!document.getElementById("byday_" + weekday).checked) {
+					for (const elem of document.querySelectorAll("#weekly_options .rrule_input[name=\'BYDAY\[\]\']")) {
+						elem.checked = false;
+					}
+				}
+
+				document.getElementById("byday_" + weekday).checked = true;
+				document.getElementById("weekly_options").style.display = "";
+				break;
+
+		}
+	} else {
+		document.getElementById("freq_interval_options").style.display = "none";
+		document.getElementById("freq").value = "DAILY";
+
+		for (const elem of document.querySelectorAll(".rrule_input_wrapper")) {
+			elem.style.display = "none";
+		}
+
+		for (const elem of document.querySelectorAll(".rrule_input")) {
+			elem.disabled = true;
+		}
+
+		for (const elem of document.querySelectorAll("#rrule_options .rrule_input")) {
+			elem.disabled = false;
+		}
+
+		for (const elem of document.querySelectorAll(".rrule_input[name=\'BYMONTHDAY\[\]\']")) {
+			elem.checked = false;
+		}
+	}
+
+	end_date = updateEndDate(start_date, end_date);
+
+	// Show the basic RRule select menu.
+	for (const elem of document.querySelectorAll(".rrule_options")) {
+		elem.style.display = "";
+	}
+
+	for (const elem of document.querySelectorAll("#rrule")) {
+		elem.disabled = false;
+	}
+
+	// If necessary, show the options for RRule end.
+	if (document.getElementById("rrule").value !== "never") {
+		const end_option = document.getElementById("end_option");
+		const until = document.getElementById("until");
+		const count = document.getElementById("count");
+
+		document.getElementById("rrule_end").style.display = "";
+
+		end_option.disabled = false;
+		end_option.style.display = "";
+
+		until.disabled = (end_option.value !== "until");
+		until.required = (end_option.value === "until");
+		until.style.display = (end_option.value !== "until") ? "none" : "";
+
+		count.disabled = (end_option.value !== "count");
+		count.required = (end_option.value === "count");
+		count.style.display = (end_option.value !== "count") ? "none" : "";
+	}
+
+	enableOrDisableFifth();
+
+	// Show or hide the options for additional and excluded dates.
+	if (
+		document.getElementById("rrule")
+		&& document.getElementById("rrule").value === "never"
+		&& document.querySelector("#advanced_options input")
+		&& document.querySelector("#advanced_options input").value === ""
+	) {
+		document.getElementById("advanced_options").style.display = "none";
+
+		for (const elem of document.querySelectorAll("#advanced_options input")) {
+			elem.disabled = true;
+		}
+	} else {
+		document.getElementById("advanced_options").style.display = "";
+
+		for (const elem of document.querySelectorAll("#advanced_options input")) {
+			elem.disabled = false;
+		}
+	}
+}
+
+// Updates start_date and start_time elements to new values.
+function updateStartDate(start_date)
+{
+	document.getElementById("start_date").value = start_date.getFullYear() + '-' + (start_date.getMonth() < 9 ? '0' : '') + (start_date.getMonth() + 1) + '-' + (start_date.getDate() < 10 ? '0' : '') + start_date.getDate();
+
+	return start_date;
+}
+
+// If start_date or start_time elements changed, automatically updates
+// end_date and end_time elements to preserve the event duration.
+function updateEndDate(start_date, end_date)
+{
+	if (current_start_date.getTime() !== start_date.getTime()) {
+		const start_diff = start_date.getTime() - current_start_date.getTime();
+
+		end_date.setTime(end_date.getTime() + start_diff);
+
+		document.getElementById("end_date").value = end_date.getFullYear() + '-' + (end_date.getMonth() < 9 ? '0' : '') + (end_date.getMonth() + 1) + '-' + (end_date.getDate() < 10 ? '0' : '') + end_date.getDate();
+		document.getElementById("end_time").value = end_date.toTimeString().substring(0, 5);
+
+		document.getElementById("end_date").min = document.getElementById("start_date").value;
+
+		if (document.getElementById("start_date").value === document.getElementById("end_date").value) {
+			document.getElementById("end_time").min = document.getElementById("start_time").value;
+		} else {
+			document.getElementById("end_time").removeAttribute("min");
+		}
+	}
+
+	// Ensure start and end have a sane relationship.
+	if (start_date.getTime() > end_date.getTime()) {
+		const current_duration = current_end_date.getTime() - current_start_date.getTime();
+
+		end_date = start_date;
+		end_date.setTime(end_date.getTime() + current_duration);
+
+		document.getElementById("end_date").value = end_date.getFullYear() + '-' + (end_date.getMonth() < 9 ? '0' : '') + (end_date.getMonth() + 1) + '-' + (end_date.getDate() < 10 ? '0' : '') + end_date.getDate();
+		document.getElementById("end_time").value = end_date.toTimeString().substring(0, 5);
+	}
+
+	// If necessary, also update the UNTIL field.
+	let until = new Date(document.getElementById("until").value + "T23:59:59.999");
+
+	document.getElementById("until").min = document.getElementById("start_date").value;
+
+	if (start_date.getTime() > until.getTime()) {
+		document.getElementById("until").value = document.getElementById("end_date").value;
+	}
+
+	// Remember any changes to start and end dates.
+	current_start_date = start_date;
+	current_end_date = end_date;
+
+	return end_date;
+}
+
+// Gets the weekday abbreviation of a date.
+function getWeekday(date)
+{
+	return weekday_abbrevs[date.getDay()];
+}
+
+//
+function getNewStartDateByDay(start_date, end_of_month, byday_num, selected_days)
+{
+	let temp_date = new Date(
+		start_date.getFullYear(),
+		start_date.getMonth(),
+		byday_num > 0 ? 1 : end_of_month.getDate(),
+		start_date.getHours(),
+		start_date.getMinutes(),
+		start_date.getSeconds(),
+		start_date.getMilliseconds()
+	);
+
+	let offset = 0;
+
+	while (
+		(
+			!selected_days.includes(temp_date.getDay())
+			|| offset != byday_num
+		)
+		&& temp_date.getMonth() === start_date.getMonth()
+	) {
+		if (selected_days.includes(temp_date.getDay())) {
+			offset = offset + (byday_num > 0 ? 1 : -1);
+
+			if (offset == byday_num) {
+				break;
+			}
+		}
+
+		temp_date.setDate(temp_date.getDate() + (byday_num > 0 ? 1 : -1));
+	}
+
+	return temp_date;
+}
+
+// Determine whether the BYDAY_num select menu's "fifth" option should be enabled or not.
+function enableOrDisableFifth()
+{
+	const start_date = new Date(document.getElementById("start_date").value + 'T' + document.getElementById("start_time").value);
+
+	const end_of_month = new Date(
+		start_date.getFullYear(),
+		start_date.getMonth() + 1,
+		0,
+		start_date.getHours(),
+		start_date.getMinutes(),
+		start_date.getSeconds(),
+		start_date.getMilliseconds()
+	);
+
+	const byday_name = document.getElementById("byday_name_select_0").value;
+
+	let selected_days = [];
+
+	for (const weekday_abbrev of weekday_abbrevs) {
+		if (byday_name.includes(weekday_abbrev)) {
+			selected_days.push(weekday_abbrevs.indexOf(weekday_abbrev));
+		}
+	}
+
+	let enable_fifth = false;
+	let temp_date = end_of_month;
+	while (temp_date.getDate() > 28) {
+		if (selected_days.includes(temp_date.getDay())) {
+			enable_fifth = true;
+		}
+
+		temp_date.setDate(temp_date.getDate() - 1);
+	}
+
+	for (const elem_fifth of document.querySelectorAll("#byday_num_select_0 .byday_num_5")) {
+		elem_fifth.disabled = !enable_fifth;
+		// If "fifth" is selected but disabled, change selection to "last" instead.
+		if (elem_fifth.disabled && elem_fifth.selected) {
+			elem_fifth.selected = false;
+
+			for (const elem_neg1 of document.querySelectorAll("#byday_num_select_0 .byday_num_neg1")) {
+				elem_neg1.selected = true;
+			}
+		}
+	}
+}
+
+function addByDayItem()
+{
+	if ("content" in document.createElement("template")) {
+		const container = document.querySelector("#month_byday_options .rrule_input");
+		const template = document.getElementById("byday_template");
+
+		const clone = template.content.cloneNode(true);
+
+		const byday_num_select = clone.querySelector(".byday_num_select");
+		byday_num_select.id = "byday_num_select_" + (++monthly_byday_items);
+
+		const byday_name_select = clone.querySelector(".byday_name_select");
+		byday_name_select.id = "byday_name_select_" + monthly_byday_items;
+
+		container.appendChild(clone);
+	}
+}
+
+function addRDateOrExDate()
+{
+	if ("content" in document.createElement("template")) {
+		const container = document.getElementById(this.dataset.container);
+		const template = document.getElementById("additional_dates_template");
+
+		let item_count;
+		if (this.dataset.inputname === 'RDATE') {
+			item_count = ++rdates_count;
+		} else if (this.dataset.inputname === 'EXDATE') {
+			item_count = ++exdates_count;
+		} else {
+			return;
+		}
+
+		const clone = template.content.cloneNode(true);
+
+		const date_input = clone.querySelector('input[type="date"]');
+		date_input.name = this.dataset.inputname + "_date[" + (item_count) + "]";
+
+		const time_input = clone.querySelector('input[type="time"]');
+		time_input.name = this.dataset.inputname + "_time[" + item_count + "]";
+
+		const removeButton = clone.querySelector('a.delete');
+		removeButton.addEventListener("click", removeRDateOrExDate);
+
+		container.appendChild(clone);
+	}
+}
+
+function removeRDateOrExDate()
+{
+	if (this.closest("dl").id === 'rdates') {
+		--rdates_count;
+	} else if (this.closest("dl").id === 'exdates') {
+		--exdates_count;
+	}
+
+	this.parentElement.remove();
+}
\ No newline at end of file

From 10408830c2c8f1189875dd803fe53fa65099e82c Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Fri, 15 Dec 2023 23:16:52 -0700
Subject: [PATCH 10/22] Use HTML5 date and time inputs throughout calendar UI

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Actions/Calendar.php                  | 183 +-----------------
 Themes/default/Calendar.template.php          |   6 +-
 Themes/default/scripts/calendar.js            |  42 ++++
 .../scripts/jquery-ui.datepicker.min.js       |   7 -
 Themes/default/scripts/jquery.datepair.min.js |   7 -
 .../default/scripts/jquery.timepicker.min.js  |   7 -
 6 files changed, 51 insertions(+), 201 deletions(-)
 create mode 100644 Themes/default/scripts/calendar.js
 delete mode 100644 Themes/default/scripts/jquery-ui.datepicker.min.js
 delete mode 100755 Themes/default/scripts/jquery.datepair.min.js
 delete mode 100755 Themes/default/scripts/jquery.timepicker.min.js

diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index 7cd4c5c250..d30e7d0943 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -118,6 +118,7 @@ public function show(): void
 		// This is gonna be needed...
 		Theme::loadTemplate('Calendar');
 		Theme::loadCSSFile('calendar.css', ['force_current' => false, 'validate' => true, 'rtl' => 'calendar.rtl.css'], 'smf_calendar');
+		Theme::loadJavaScriptFile('calendar.js', ['defer' => true], 'smf_calendar');
 
 		// Did they specify an individual event ID? If so, let's splice the year/month in to what we would otherwise be doing.
 		if (isset($_GET['event'])) {
@@ -913,10 +914,9 @@ public static function getTodayInfo(): array
 	 * @param string $selected_date A date in YYYY-MM-DD format
 	 * @param array $calendarOptions An array of calendar options
 	 * @param bool $is_previous Whether this is the previous month
-	 * @param bool $has_picker Whether to add javascript to handle a date picker
 	 * @return array A large array containing all the information needed to show a calendar grid for the given month
 	 */
-	public static function getCalendarGrid(string $selected_date, array $calendarOptions, bool $is_previous = false, bool $has_picker = true): array
+	public static function getCalendarGrid(string $selected_date, array $calendarOptions, bool $is_previous = false): array
 	{
 		$selected_object = new Time($selected_date . ' ' . User::getTimezone());
 
@@ -952,6 +952,7 @@ public static function getCalendarGrid(string $selected_date, array $calendarOpt
 				'disabled' => Config::$modSettings['cal_maxyear'] < $next_object->format('Y'),
 			],
 			'start_date' => $selected_object->format(Time::getDateFormat()),
+			'iso_start_date' => $selected_object->format('Y-m-d'),
 		];
 
 		// Get today's date.
@@ -1058,11 +1059,6 @@ public static function getCalendarGrid(string $selected_date, array $calendarOpt
 
 		$calendarGrid['next_calendar']['href'] = Config::$scripturl . '?action=calendar;viewmonth;year=' . $calendarGrid['next_calendar']['year'] . ';month=' . $calendarGrid['next_calendar']['month'] . ';day=' . $calendarGrid['previous_calendar']['day'];
 
-		if ($has_picker) {
-			self::loadDatePicker('#calendar_navigation .date_input');
-			self::loadDatePair('#calendar_navigation', 'date_input');
-		}
-
 		return $calendarGrid;
 	}
 
@@ -1128,6 +1124,7 @@ public static function getCalendarWeek(string $selected_date, array $calendarOpt
 				'disabled' => Config::$modSettings['cal_maxyear'] < $next_object->format('Y'),
 			],
 			'start_date' => $selected_object->format(Time::getDateFormat()),
+			'iso_start_date' => $selected_object->format('Y-m-d'),
 			'show_events' => $calendarOptions['show_events'],
 			'show_holidays' => $calendarOptions['show_holidays'],
 			'show_birthdays' => $calendarOptions['show_birthdays'],
@@ -1176,9 +1173,6 @@ public static function getCalendarWeek(string $selected_date, array $calendarOpt
 
 		$calendarGrid['next_week']['href'] = Config::$scripturl . '?action=calendar;viewweek;year=' . $calendarGrid['next_week']['year'] . ';month=' . $calendarGrid['next_week']['month'] . ';day=' . $calendarGrid['next_week']['day'];
 
-		self::loadDatePicker('#calendar_navigation .date_input');
-		self::loadDatePair('#calendar_navigation', 'date_input', '');
-
 		return $calendarGrid;
 	}
 
@@ -1201,10 +1195,12 @@ public static function getCalendarList(string $start_date, string $end_date, arr
 			'start_year' => $start_object->format('Y'),
 			'start_month' => $start_object->format('m'),
 			'start_day' => $start_object->format('d'),
+			'iso_start_date' => $start_object->format('Y-m-d'),
 			'end_date' => $end_object->format(Time::getDateFormat()),
 			'end_year' => $end_object->format('Y'),
 			'end_month' => $end_object->format('m'),
 			'end_day' => $end_object->format('d'),
+			'iso_end_date' => $end_object->format('Y-m-d'),
 		];
 
 		$calendarGrid['birthdays'] = $calendarOptions['show_birthdays'] ? self::getBirthdayRange($start_date, $end_date) : [];
@@ -1243,176 +1239,9 @@ public static function getCalendarList(string $start_date, string $end_date, arr
 			}
 		}
 
-		self::loadDatePicker('#calendar_range .date_input');
-		self::loadDatePair('#calendar_range', 'date_input', '');
-
 		return $calendarGrid;
 	}
 
-	/**
-	 * Loads the necessary JavaScript and CSS to create a datepicker.
-	 *
-	 * @param string $selector A CSS selector for the input field(s) that the datepicker should be attached to.
-	 * @param string $date_format The date format to use, in strftime() format.
-	 */
-	public static function loadDatePicker(string $selector = 'input.date_input', string $date_format = ''): void
-	{
-		if (empty($date_format)) {
-			$date_format = Time::getDateFormat();
-		}
-
-		// Convert to format used by datepicker
-		$date_format = strtr($date_format, [
-			// Day
-			'%a' => 'D', '%A' => 'DD', '%e' => 'd', '%d' => 'dd', '%j' => 'oo', '%u' => '', '%w' => '',
-			// Week
-			'%U' => '', '%V' => '', '%W' => '',
-			// Month
-			'%b' => 'M', '%B' => 'MM', '%h' => 'M', '%m' => 'mm',
-			// Year
-			'%C' => '', '%g' => 'y', '%G' => 'yy', '%y' => 'y', '%Y' => 'yy',
-			// Time (we remove all of these)
-			'%H' => '', '%k' => '', '%I' => '', '%l' => '', '%M' => '', '%p' => '', '%P' => '',
-			'%r' => '', '%R' => '', '%S' => '', '%T' => '', '%X' => '', '%z' => '', '%Z' => '',
-			// Time and Date Stamps
-			'%c' => 'D, d M yy', '%D' => 'mm/dd/y', '%F' => 'yy-mm-dd', '%s' => '@', '%x' => 'D, d M yy',
-			// Miscellaneous
-			'%n' => ' ', '%t' => ' ', '%%' => '%',
-		]);
-
-		Theme::loadCSSFile('jquery-ui.datepicker.css', [], 'smf_datepicker');
-		Theme::loadJavaScriptFile('jquery-ui.datepicker.min.js', ['defer' => true], 'smf_datepicker');
-		Theme::addInlineJavaScript('
-		$("' . $selector . '").datepicker({
-			dateFormat: "' . $date_format . '",
-			autoSize: true,
-			isRTL: ' . (Utils::$context['right_to_left'] ? 'true' : 'false') . ',
-			constrainInput: true,
-			showAnim: "",
-			showButtonPanel: false,
-			yearRange: "' . Config::$modSettings['cal_minyear'] . ':' . Config::$modSettings['cal_maxyear'] . '",
-			hideIfNoPrevNext: true,
-			monthNames: ["' . implode('", "', Lang::$txt['months_titles']) . '"],
-			monthNamesShort: ["' . implode('", "', Lang::$txt['months_short']) . '"],
-			dayNames: ["' . implode('", "', Lang::$txt['days']) . '"],
-			dayNamesShort: ["' . implode('", "', Lang::$txt['days_short']) . '"],
-			dayNamesMin: ["' . implode('", "', Lang::$txt['days_short']) . '"],
-			prevText: "' . Lang::$txt['prev_month'] . '",
-			nextText: "' . Lang::$txt['next_month'] . '",
-			firstDay: ' . (!empty(Theme::$current->options['calendar_start_day']) ? Theme::$current->options['calendar_start_day'] : 0) . ',
-		});', true);
-	}
-
-	/**
-	 * Loads the necessary JavaScript and CSS to create a timepicker.
-	 *
-	 * @param string $selector A CSS selector for the input field(s) that the timepicker should be attached to.
-	 * @param string $time_format A time format in strftime format
-	 */
-	public static function loadTimePicker(string $selector = 'input.time_input', string $time_format = ''): void
-	{
-		if (empty($time_format)) {
-			$time_format = Time::getTimeFormat();
-		}
-
-		// Format used for timepicker
-		$time_format = strtr($time_format, [
-			'%H' => 'H',
-			'%k' => 'G',
-			'%I' => 'h',
-			'%l' => 'g',
-			'%M' => 'i',
-			'%p' => 'A',
-			'%P' => 'a',
-			'%r' => 'h:i:s A',
-			'%R' => 'H:i',
-			'%S' => 's',
-			'%T' => 'H:i:s',
-			'%X' => 'H:i:s',
-		]);
-
-		Theme::loadCSSFile('jquery.timepicker.css', [], 'smf_timepicker');
-		Theme::loadJavaScriptFile('jquery.timepicker.min.js', ['defer' => true], 'smf_timepicker');
-		Theme::addInlineJavaScript('
-		$("' . $selector . '").timepicker({
-			timeFormat: "' . $time_format . '",
-			showDuration: true,
-			maxTime: "23:59:59",
-			lang: {
-				am: "' . strtolower(Lang::$txt['time_am']) . '",
-				pm: "' . strtolower(Lang::$txt['time_pm']) . '",
-				AM: "' . strtoupper(Lang::$txt['time_am']) . '",
-				PM: "' . strtoupper(Lang::$txt['time_pm']) . '",
-				decimal: "' . Lang::$txt['decimal_separator'] . '",
-				mins: "' . Lang::$txt['minutes_short'] . '",
-				hr: "' . Lang::$txt['hour_short'] . '",
-				hrs: "' . Lang::$txt['hours_short'] . '",
-			}
-		});', true);
-	}
-
-	/**
-	 * Loads the necessary JavaScript for Datepair.js.
-	 *
-	 * Datepair.js helps to keep date ranges sane in the UI.
-	 *
-	 * @param string $container CSS selector for the containing element of the date/time inputs to be paired.
-	 * @param string $date_class The CSS class of the date inputs to be paired.
-	 * @param string $time_class The CSS class of the time inputs to be paired.
-	 */
-	public static function loadDatePair(string $container, string $date_class = '', string $time_class = ''): void
-	{
-		$container = (string) $container;
-		$date_class = (string) $date_class;
-		$time_class = (string) $time_class;
-
-		if ($container == '') {
-			return;
-		}
-
-		Theme::loadJavaScriptFile('jquery.datepair.min.js', ['defer' => true], 'smf_datepair');
-
-		$datepair_options = '';
-
-		// If we're not using a date input, we might as well disable these.
-		if ($date_class == '') {
-			$datepair_options .= '
-			parseDate: function (el) {},
-			updateDate: function (el, v) {},';
-		} else {
-			$datepair_options .= '
-			dateClass: "' . $date_class . '",';
-
-			// Customize Datepair to work with jQuery UI's datepicker.
-			$datepair_options .= '
-			parseDate: function (el) {
-				var val = $(el).datepicker("getDate");
-				if (!val) {
-					return null;
-				}
-				var utc = new Date(val);
-				return utc && new Date(utc.getTime() + (utc.getTimezoneOffset() * 60000));
-			},
-			updateDate: function (el, v) {
-				$(el).datepicker("setDate", new Date(v.getTime() - (v.getTimezoneOffset() * 60000)));
-			},';
-		}
-
-		// If not using a time input, disable time functions.
-		if ($time_class == '') {
-			$datepair_options .= '
-			parseTime: function(input){},
-			updateTime: function(input, dateObj){},
-			setMinTime: function(input, dateObj){},';
-		} else {
-			$datepair_options .= '
-			timeClass: "' . $time_class . '",';
-		}
-
-		Theme::addInlineJavaScript('
-		$("' . $container . '").datepair({' . $datepair_options . "\n\t});", true);
-	}
-
 	/**
 	 * Retrieve all events for the given days, independently of the users offset.
 	 * cache callback function used to retrieve the birthdays, holidays, and events between now and now + days_to_index.
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index 90fa9eafd0..6170c7992c 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -757,12 +757,12 @@ function template_calendar_top($calendar_data)
 
 	echo '
 			<form action="', Config::$scripturl, '?action=calendar;', Utils::$context['calendar_view'], '" id="', !empty($calendar_data['end_date']) ? 'calendar_range' : 'calendar_navigation', '" method="post" accept-charset="', Utils::$context['character_set'], '">
-				<input type="text" name="start_date" id="start_date" value="', trim($calendar_data['start_date']), '" tabindex="', Utils::$context['tabindex']++, '" class="date_input start" data-type="date">';
+				<input type="date" name="start_date" id="start_date" value="', $calendar_data['iso_start_date'], '" tabindex="', Utils::$context['tabindex']++, '" class="date_input start" data-type="date">';
 
 	if (!empty($calendar_data['end_date']))
 		echo '
-				<span>', strtolower(Lang::$txt['to']), '</span>
-				<input type="text" name="end_date" id="end_date" value="', trim($calendar_data['end_date']), '" tabindex="', Utils::$context['tabindex']++, '" class="date_input end" data-type="date">';
+				<span>', Utils::strtolower(Lang::$txt['to']), '</span>
+				<input type="date" name="end_date" id="end_date" value="', $calendar_data['iso_end_date'], '" tabindex="', Utils::$context['tabindex']++, '" class="date_input end" data-type="date">';
 
 	echo '
 				<input type="submit" class="button" style="float:none" id="view_button" value="', Lang::$txt['view'], '">
diff --git a/Themes/default/scripts/calendar.js b/Themes/default/scripts/calendar.js
new file mode 100644
index 0000000000..510a94950a
--- /dev/null
+++ b/Themes/default/scripts/calendar.js
@@ -0,0 +1,42 @@
+window.addEventListener("DOMContentLoaded", function() {
+	updateCalendarUI();
+});
+
+document.getElementById("start_date").addEventListener("change", updateCalendarUI);
+document.getElementById("end_date").addEventListener("change", updateCalendarUI);
+
+let current_start_date = new Date(document.getElementById("start_date").value + "T12:00:00");
+let current_end_date = new Date(document.getElementById("end_date").value + "T12:00:00");
+
+// Update the date pickers in the calendar UI.
+function updateCalendarUI()
+{
+	let start_date = new Date(document.getElementById("start_date").value + "T12:00:00");
+	let end_date = new Date(document.getElementById("end_date").value + "T12:00:00");
+
+	if (this.id !== 'end_date') {
+		if (current_start_date.getTime() !== start_date.getTime()) {
+			const start_diff = start_date.getTime() - current_start_date.getTime();
+
+			end_date.setTime(end_date.getTime() + start_diff);
+
+			document.getElementById("end_date").value = end_date.getFullYear() + '-' + (end_date.getMonth() < 9 ? '0' : '') + (end_date.getMonth() + 1) + '-' + (end_date.getDate() < 10 ? '0' : '') + end_date.getDate();
+		}
+	}
+
+	// Ensure start and end have a sane relationship.
+	if (start_date.getTime() > end_date.getTime()) {
+		const current_duration = current_end_date.getTime() - current_start_date.getTime();
+
+		end_date = start_date;
+		end_date.setTime(end_date.getTime() + current_duration);
+
+		document.getElementById("end_date").value = end_date.getFullYear() + '-' + (end_date.getMonth() < 9 ? '0' : '') + (end_date.getMonth() + 1) + '-' + (end_date.getDate() < 10 ? '0' : '') + end_date.getDate();
+	}
+
+	document.getElementById("end_date").min = document.getElementById("start_date").value;
+
+	// Remember any changes to start and end dates.
+	current_start_date = start_date;
+	current_end_date = end_date;
+}
\ No newline at end of file
diff --git a/Themes/default/scripts/jquery-ui.datepicker.min.js b/Themes/default/scripts/jquery-ui.datepicker.min.js
deleted file mode 100644
index af059439b3..0000000000
--- a/Themes/default/scripts/jquery-ui.datepicker.min.js
+++ /dev/null
@@ -1,7 +0,0 @@
-/*! jQuery UI - v1.12.0 - 2016-08-30
-* https://jqueryui.com
-* Includes: keycode.js, widgets/datepicker.js
-* Copyright jQuery Foundation and other contributors; Licensed MIT */
-
-(function(t){"function"==typeof define&&define.amd?define(["jquery"],t):t(jQuery)})(function(t){function e(t){for(var e,i;t.length&&t[0]!==document;){if(e=t.css("position"),("absolute"===e||"relative"===e||"fixed"===e)&&(i=parseInt(t.css("zIndex"),10),!isNaN(i)&&0!==i))return i;t=t.parent()}return 0}function i(){this._curInst=null,this._keyEvent=!1,this._disabledInputs=[],this._datepickerShowing=!1,this._inDialog=!1,this._mainDivId="ui-datepicker-div",this._inlineClass="ui-datepicker-inline",this._appendClass="ui-datepicker-append",this._triggerClass="ui-datepicker-trigger",this._dialogClass="ui-datepicker-dialog",this._disableClass="ui-datepicker-disabled",this._unselectableClass="ui-datepicker-unselectable",this._currentClass="ui-datepicker-current-day",this._dayOverClass="ui-datepicker-days-cell-over",this.regional=[],this.regional[""]={closeText:"Done",prevText:"Prev",nextText:"Next",currentText:"Today",monthNames:["January","February","March","April","May","June","July","August","September","October","November","December"],monthNamesShort:["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"],dayNames:["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"],dayNamesShort:["Sun","Mon","Tue","Wed","Thu","Fri","Sat"],dayNamesMin:["Su","Mo","Tu","We","Th","Fr","Sa"],weekHeader:"Wk",dateFormat:"mm/dd/yy",firstDay:0,isRTL:!1,showMonthAfterYear:!1,yearSuffix:""},this._defaults={showOn:"focus",showAnim:"fadeIn",showOptions:{},defaultDate:null,appendText:"",buttonText:"...",buttonImage:"",buttonImageOnly:!1,hideIfNoPrevNext:!1,navigationAsDateFormat:!1,gotoCurrent:!1,changeMonth:!1,changeYear:!1,yearRange:"c-10:c+10",showOtherMonths:!1,selectOtherMonths:!1,showWeek:!1,calculateWeek:this.iso8601Week,shortYearCutoff:"+10",minDate:null,maxDate:null,duration:"fast",beforeShowDay:null,beforeShow:null,onSelect:null,onChangeMonthYear:null,onClose:null,numberOfMonths:1,showCurrentAtPos:0,stepMonths:1,stepBigMonths:12,altField:"",altFormat:"",constrainInput:!0,showButtonPanel:!1,autoSize:!1,disabled:!1},t.extend(this._defaults,this.regional[""]),this.regional.en=t.extend(!0,{},this.regional[""]),this.regional["en-US"]=t.extend(!0,{},this.regional.en),this.dpDiv=s(t("<div id='"+this._mainDivId+"' class='ui-datepicker ui-widget ui-widget-content ui-helper-clearfix ui-corner-all'></div>"))}function s(e){var i="button, .ui-datepicker-prev, .ui-datepicker-next, .ui-datepicker-calendar td a";return e.on("mouseout",i,function(){t(this).removeClass("ui-state-hover"),-1!==this.className.indexOf("ui-datepicker-prev")&&t(this).removeClass("ui-datepicker-prev-hover"),-1!==this.className.indexOf("ui-datepicker-next")&&t(this).removeClass("ui-datepicker-next-hover")}).on("mouseover",i,n)}function n(){t.datepicker._isDisabledDatepicker(a.inline?a.dpDiv.parent()[0]:a.input[0])||(t(this).parents(".ui-datepicker-calendar").find("a").removeClass("ui-state-hover"),t(this).addClass("ui-state-hover"),-1!==this.className.indexOf("ui-datepicker-prev")&&t(this).addClass("ui-datepicker-prev-hover"),-1!==this.className.indexOf("ui-datepicker-next")&&t(this).addClass("ui-datepicker-next-hover"))}function o(e,i){t.extend(e,i);for(var s in i)null==i[s]&&(e[s]=i[s]);return e}t.ui=t.ui||{},t.ui.version="1.12.0",t.ui.keyCode={BACKSPACE:8,COMMA:188,DELETE:46,DOWN:40,END:35,ENTER:13,ESCAPE:27,HOME:36,LEFT:37,PAGE_DOWN:34,PAGE_UP:33,PERIOD:190,RIGHT:39,SPACE:32,TAB:9,UP:38},t.extend(t.ui,{datepicker:{version:"1.12.0"}});var a;t.extend(i.prototype,{markerClassName:"hasDatepicker",maxRows:4,_widgetDatepicker:function(){return this.dpDiv},setDefaults:function(t){return o(this._defaults,t||{}),this},_attachDatepicker:function(e,i){var s,n,o;s=e.nodeName.toLowerCase(),n="div"===s||"span"===s,e.id||(this.uuid+=1,e.id="dp"+this.uuid),o=this._newInst(t(e),n),o.settings=t.extend({},i||{}),"input"===s?this._connectDatepicker(e,o):n&&this._inlineDatepicker(e,o)},_newInst:function(e,i){var n=e[0].id.replace(/([^A-Za-z0-9_\-])/g,"\\\\$1");return{id:n,input:e,selectedDay:0,selectedMonth:0,selectedYear:0,drawMonth:0,drawYear:0,inline:i,dpDiv:i?s(t("<div class='"+this._inlineClass+" ui-datepicker ui-widget ui-widget-content ui-helper-clearfix ui-corner-all'></div>")):this.dpDiv}},_connectDatepicker:function(e,i){var s=t(e);i.append=t([]),i.trigger=t([]),s.hasClass(this.markerClassName)||(this._attachments(s,i),s.addClass(this.markerClassName).on("keydown",this._doKeyDown).on("keypress",this._doKeyPress).on("keyup",this._doKeyUp),this._autoSize(i),t.data(e,"datepicker",i),i.settings.disabled&&this._disableDatepicker(e))},_attachments:function(e,i){var s,n,o,a=this._get(i,"appendText"),r=this._get(i,"isRTL");i.append&&i.append.remove(),a&&(i.append=t("<span class='"+this._appendClass+"'>"+a+"</span>"),e[r?"before":"after"](i.append)),e.off("focus",this._showDatepicker),i.trigger&&i.trigger.remove(),s=this._get(i,"showOn"),("focus"===s||"both"===s)&&e.on("focus",this._showDatepicker),("button"===s||"both"===s)&&(n=this._get(i,"buttonText"),o=this._get(i,"buttonImage"),i.trigger=t(this._get(i,"buttonImageOnly")?t("<img/>").addClass(this._triggerClass).attr({src:o,alt:n,title:n}):t("<button type='button'></button>").addClass(this._triggerClass).html(o?t("<img/>").attr({src:o,alt:n,title:n}):n)),e[r?"before":"after"](i.trigger),i.trigger.on("click",function(){return t.datepicker._datepickerShowing&&t.datepicker._lastInput===e[0]?t.datepicker._hideDatepicker():t.datepicker._datepickerShowing&&t.datepicker._lastInput!==e[0]?(t.datepicker._hideDatepicker(),t.datepicker._showDatepicker(e[0])):t.datepicker._showDatepicker(e[0]),!1}))},_autoSize:function(t){if(this._get(t,"autoSize")&&!t.inline){var e,i,s,n,o=new Date(2009,11,20),a=this._get(t,"dateFormat");a.match(/[DM]/)&&(e=function(t){for(i=0,s=0,n=0;t.length>n;n++)t[n].length>i&&(i=t[n].length,s=n);return s},o.setMonth(e(this._get(t,a.match(/MM/)?"monthNames":"monthNamesShort"))),o.setDate(e(this._get(t,a.match(/DD/)?"dayNames":"dayNamesShort"))+20-o.getDay())),t.input.attr("size",this._formatDate(t,o).length)}},_inlineDatepicker:function(e,i){var s=t(e);s.hasClass(this.markerClassName)||(s.addClass(this.markerClassName).append(i.dpDiv),t.data(e,"datepicker",i),this._setDate(i,this._getDefaultDate(i),!0),this._updateDatepicker(i),this._updateAlternate(i),i.settings.disabled&&this._disableDatepicker(e),i.dpDiv.css("display","block"))},_dialogDatepicker:function(e,i,s,n,a){var r,l,h,c,u,d=this._dialogInst;return d||(this.uuid+=1,r="dp"+this.uuid,this._dialogInput=t("<input type='text' id='"+r+"' style='position: absolute; top: -100px; width: 0px;'/>"),this._dialogInput.on("keydown",this._doKeyDown),t("body").append(this._dialogInput),d=this._dialogInst=this._newInst(this._dialogInput,!1),d.settings={},t.data(this._dialogInput[0],"datepicker",d)),o(d.settings,n||{}),i=i&&i.constructor===Date?this._formatDate(d,i):i,this._dialogInput.val(i),this._pos=a?a.length?a:[a.pageX,a.pageY]:null,this._pos||(l=document.documentElement.clientWidth,h=document.documentElement.clientHeight,c=document.documentElement.scrollLeft||document.body.scrollLeft,u=document.documentElement.scrollTop||document.body.scrollTop,this._pos=[l/2-100+c,h/2-150+u]),this._dialogInput.css("left",this._pos[0]+20+"px").css("top",this._pos[1]+"px"),d.settings.onSelect=s,this._inDialog=!0,this.dpDiv.addClass(this._dialogClass),this._showDatepicker(this._dialogInput[0]),t.blockUI&&t.blockUI(this.dpDiv),t.data(this._dialogInput[0],"datepicker",d),this},_destroyDatepicker:function(e){var i,s=t(e),n=t.data(e,"datepicker");s.hasClass(this.markerClassName)&&(i=e.nodeName.toLowerCase(),t.removeData(e,"datepicker"),"input"===i?(n.append.remove(),n.trigger.remove(),s.removeClass(this.markerClassName).off("focus",this._showDatepicker).off("keydown",this._doKeyDown).off("keypress",this._doKeyPress).off("keyup",this._doKeyUp)):("div"===i||"span"===i)&&s.removeClass(this.markerClassName).empty(),a===n&&(a=null))},_enableDatepicker:function(e){var i,s,n=t(e),o=t.data(e,"datepicker");n.hasClass(this.markerClassName)&&(i=e.nodeName.toLowerCase(),"input"===i?(e.disabled=!1,o.trigger.filter("button").each(function(){this.disabled=!1}).end().filter("img").css({opacity:"1.0",cursor:""})):("div"===i||"span"===i)&&(s=n.children("."+this._inlineClass),s.children().removeClass("ui-state-disabled"),s.find("select.ui-datepicker-month, select.ui-datepicker-year").prop("disabled",!1)),this._disabledInputs=t.map(this._disabledInputs,function(t){return t===e?null:t}))},_disableDatepicker:function(e){var i,s,n=t(e),o=t.data(e,"datepicker");n.hasClass(this.markerClassName)&&(i=e.nodeName.toLowerCase(),"input"===i?(e.disabled=!0,o.trigger.filter("button").each(function(){this.disabled=!0}).end().filter("img").css({opacity:"0.5",cursor:"default"})):("div"===i||"span"===i)&&(s=n.children("."+this._inlineClass),s.children().addClass("ui-state-disabled"),s.find("select.ui-datepicker-month, select.ui-datepicker-year").prop("disabled",!0)),this._disabledInputs=t.map(this._disabledInputs,function(t){return t===e?null:t}),this._disabledInputs[this._disabledInputs.length]=e)},_isDisabledDatepicker:function(t){if(!t)return!1;for(var e=0;this._disabledInputs.length>e;e++)if(this._disabledInputs[e]===t)return!0;return!1},_getInst:function(e){try{return t.data(e,"datepicker")}catch(i){throw"Missing instance data for this datepicker"}},_optionDatepicker:function(e,i,s){var n,a,r,l,h=this._getInst(e);return 2===arguments.length&&"string"==typeof i?"defaults"===i?t.extend({},t.datepicker._defaults):h?"all"===i?t.extend({},h.settings):this._get(h,i):null:(n=i||{},"string"==typeof i&&(n={},n[i]=s),h&&(this._curInst===h&&this._hideDatepicker(),a=this._getDateDatepicker(e,!0),r=this._getMinMaxDate(h,"min"),l=this._getMinMaxDate(h,"max"),o(h.settings,n),null!==r&&void 0!==n.dateFormat&&void 0===n.minDate&&(h.settings.minDate=this._formatDate(h,r)),null!==l&&void 0!==n.dateFormat&&void 0===n.maxDate&&(h.settings.maxDate=this._formatDate(h,l)),"disabled"in n&&(n.disabled?this._disableDatepicker(e):this._enableDatepicker(e)),this._attachments(t(e),h),this._autoSize(h),this._setDate(h,a),this._updateAlternate(h),this._updateDatepicker(h)),void 0)},_changeDatepicker:function(t,e,i){this._optionDatepicker(t,e,i)},_refreshDatepicker:function(t){var e=this._getInst(t);e&&this._updateDatepicker(e)},_setDateDatepicker:function(t,e){var i=this._getInst(t);i&&(this._setDate(i,e),this._updateDatepicker(i),this._updateAlternate(i))},_getDateDatepicker:function(t,e){var i=this._getInst(t);return i&&!i.inline&&this._setDateFromField(i,e),i?this._getDate(i):null},_doKeyDown:function(e){var i,s,n,o=t.datepicker._getInst(e.target),a=!0,r=o.dpDiv.is(".ui-datepicker-rtl");if(o._keyEvent=!0,t.datepicker._datepickerShowing)switch(e.keyCode){case 9:t.datepicker._hideDatepicker(),a=!1;break;case 13:return n=t("td."+t.datepicker._dayOverClass+":not(."+t.datepicker._currentClass+")",o.dpDiv),n[0]&&t.datepicker._selectDay(e.target,o.selectedMonth,o.selectedYear,n[0]),i=t.datepicker._get(o,"onSelect"),i?(s=t.datepicker._formatDate(o),i.apply(o.input?o.input[0]:null,[s,o])):t.datepicker._hideDatepicker(),!1;case 27:t.datepicker._hideDatepicker();break;case 33:t.datepicker._adjustDate(e.target,e.ctrlKey?-t.datepicker._get(o,"stepBigMonths"):-t.datepicker._get(o,"stepMonths"),"M");break;case 34:t.datepicker._adjustDate(e.target,e.ctrlKey?+t.datepicker._get(o,"stepBigMonths"):+t.datepicker._get(o,"stepMonths"),"M");break;case 35:(e.ctrlKey||e.metaKey)&&t.datepicker._clearDate(e.target),a=e.ctrlKey||e.metaKey;break;case 36:(e.ctrlKey||e.metaKey)&&t.datepicker._gotoToday(e.target),a=e.ctrlKey||e.metaKey;break;case 37:(e.ctrlKey||e.metaKey)&&t.datepicker._adjustDate(e.target,r?1:-1,"D"),a=e.ctrlKey||e.metaKey,e.originalEvent.altKey&&t.datepicker._adjustDate(e.target,e.ctrlKey?-t.datepicker._get(o,"stepBigMonths"):-t.datepicker._get(o,"stepMonths"),"M");break;case 38:(e.ctrlKey||e.metaKey)&&t.datepicker._adjustDate(e.target,-7,"D"),a=e.ctrlKey||e.metaKey;break;case 39:(e.ctrlKey||e.metaKey)&&t.datepicker._adjustDate(e.target,r?-1:1,"D"),a=e.ctrlKey||e.metaKey,e.originalEvent.altKey&&t.datepicker._adjustDate(e.target,e.ctrlKey?+t.datepicker._get(o,"stepBigMonths"):+t.datepicker._get(o,"stepMonths"),"M");break;case 40:(e.ctrlKey||e.metaKey)&&t.datepicker._adjustDate(e.target,7,"D"),a=e.ctrlKey||e.metaKey;break;default:a=!1}else 36===e.keyCode&&e.ctrlKey?t.datepicker._showDatepicker(this):a=!1;a&&(e.preventDefault(),e.stopPropagation())},_doKeyPress:function(e){var i,s,n=t.datepicker._getInst(e.target);return t.datepicker._get(n,"constrainInput")?(i=t.datepicker._possibleChars(t.datepicker._get(n,"dateFormat")),s=String.fromCharCode(null==e.charCode?e.keyCode:e.charCode),e.ctrlKey||e.metaKey||" ">s||!i||i.indexOf(s)>-1):void 0},_doKeyUp:function(e){var i,s=t.datepicker._getInst(e.target);if(s.input.val()!==s.lastVal)try{i=t.datepicker.parseDate(t.datepicker._get(s,"dateFormat"),s.input?s.input.val():null,t.datepicker._getFormatConfig(s)),i&&(t.datepicker._setDateFromField(s),t.datepicker._updateAlternate(s),t.datepicker._updateDatepicker(s))}catch(n){}return!0},_showDatepicker:function(i){if(i=i.target||i,"input"!==i.nodeName.toLowerCase()&&(i=t("input",i.parentNode)[0]),!t.datepicker._isDisabledDatepicker(i)&&t.datepicker._lastInput!==i){var s,n,a,r,l,h,c;s=t.datepicker._getInst(i),t.datepicker._curInst&&t.datepicker._curInst!==s&&(t.datepicker._curInst.dpDiv.stop(!0,!0),s&&t.datepicker._datepickerShowing&&t.datepicker._hideDatepicker(t.datepicker._curInst.input[0])),n=t.datepicker._get(s,"beforeShow"),a=n?n.apply(i,[i,s]):{},a!==!1&&(o(s.settings,a),s.lastVal=null,t.datepicker._lastInput=i,t.datepicker._setDateFromField(s),t.datepicker._inDialog&&(i.value=""),t.datepicker._pos||(t.datepicker._pos=t.datepicker._findPos(i),t.datepicker._pos[1]+=i.offsetHeight),r=!1,t(i).parents().each(function(){return r|="fixed"===t(this).css("position"),!r}),l={left:t.datepicker._pos[0],top:t.datepicker._pos[1]},t.datepicker._pos=null,s.dpDiv.empty(),s.dpDiv.css({position:"absolute",display:"block",top:"-1000px"}),t.datepicker._updateDatepicker(s),l=t.datepicker._checkOffset(s,l,r),s.dpDiv.css({position:t.datepicker._inDialog&&t.blockUI?"static":r?"fixed":"absolute",display:"none",left:l.left+"px",top:l.top+"px"}),s.inline||(h=t.datepicker._get(s,"showAnim"),c=t.datepicker._get(s,"duration"),s.dpDiv.css("z-index",e(t(i))+1),t.datepicker._datepickerShowing=!0,t.effects&&t.effects.effect[h]?s.dpDiv.show(h,t.datepicker._get(s,"showOptions"),c):s.dpDiv[h||"show"](h?c:null),t.datepicker._shouldFocusInput(s)&&s.input.trigger("focus"),t.datepicker._curInst=s))}},_updateDatepicker:function(e){this.maxRows=4,a=e,e.dpDiv.empty().append(this._generateHTML(e)),this._attachHandlers(e);var i,s=this._getNumberOfMonths(e),o=s[1],r=17,l=e.dpDiv.find("."+this._dayOverClass+" a");l.length>0&&n.apply(l.get(0)),e.dpDiv.removeClass("ui-datepicker-multi-2 ui-datepicker-multi-3 ui-datepicker-multi-4").width(""),o>1&&e.dpDiv.addClass("ui-datepicker-multi-"+o).css("width",r*o+"em"),e.dpDiv[(1!==s[0]||1!==s[1]?"add":"remove")+"Class"]("ui-datepicker-multi"),e.dpDiv[(this._get(e,"isRTL")?"add":"remove")+"Class"]("ui-datepicker-rtl"),e===t.datepicker._curInst&&t.datepicker._datepickerShowing&&t.datepicker._shouldFocusInput(e)&&e.input.trigger("focus"),e.yearshtml&&(i=e.yearshtml,setTimeout(function(){i===e.yearshtml&&e.yearshtml&&e.dpDiv.find("select.ui-datepicker-year:first").replaceWith(e.yearshtml),i=e.yearshtml=null},0))},_shouldFocusInput:function(t){return t.input&&t.input.is(":visible")&&!t.input.is(":disabled")&&!t.input.is(":focus")},_checkOffset:function(e,i,s){var n=e.dpDiv.outerWidth(),o=e.dpDiv.outerHeight(),a=e.input?e.input.outerWidth():0,r=e.input?e.input.outerHeight():0,l=document.documentElement.clientWidth+(s?0:t(document).scrollLeft()),h=document.documentElement.clientHeight+(s?0:t(document).scrollTop());return i.left-=this._get(e,"isRTL")?n-a:0,i.left-=s&&i.left===e.input.offset().left?t(document).scrollLeft():0,i.top-=s&&i.top===e.input.offset().top+r?t(document).scrollTop():0,i.left-=Math.min(i.left,i.left+n>l&&l>n?Math.abs(i.left+n-l):0),i.top-=Math.min(i.top,i.top+o>h&&h>o?Math.abs(o+r):0),i},_findPos:function(e){for(var i,s=this._getInst(e),n=this._get(s,"isRTL");e&&("hidden"===e.type||1!==e.nodeType||t.expr.filters.hidden(e));)e=e[n?"previousSibling":"nextSibling"];return i=t(e).offset(),[i.left,i.top]},_hideDatepicker:function(e){var i,s,n,o,a=this._curInst;!a||e&&a!==t.data(e,"datepicker")||this._datepickerShowing&&(i=this._get(a,"showAnim"),s=this._get(a,"duration"),n=function(){t.datepicker._tidyDialog(a)},t.effects&&(t.effects.effect[i]||t.effects[i])?a.dpDiv.hide(i,t.datepicker._get(a,"showOptions"),s,n):a.dpDiv["slideDown"===i?"slideUp":"fadeIn"===i?"fadeOut":"hide"](i?s:null,n),i||n(),this._datepickerShowing=!1,o=this._get(a,"onClose"),o&&o.apply(a.input?a.input[0]:null,[a.input?a.input.val():"",a]),this._lastInput=null,this._inDialog&&(this._dialogInput.css({position:"absolute",left:"0",top:"-100px"}),t.blockUI&&(t.unblockUI(),t("body").append(this.dpDiv))),this._inDialog=!1)},_tidyDialog:function(t){t.dpDiv.removeClass(this._dialogClass).off(".ui-datepicker-calendar")},_checkExternalClick:function(e){if(t.datepicker._curInst){var i=t(e.target),s=t.datepicker._getInst(i[0]);(i[0].id!==t.datepicker._mainDivId&&0===i.parents("#"+t.datepicker._mainDivId).length&&!i.hasClass(t.datepicker.markerClassName)&&!i.closest("."+t.datepicker._triggerClass).length&&t.datepicker._datepickerShowing&&(!t.datepicker._inDialog||!t.blockUI)||i.hasClass(t.datepicker.markerClassName)&&t.datepicker._curInst!==s)&&t.datepicker._hideDatepicker()}},_adjustDate:function(e,i,s){var n=t(e),o=this._getInst(n[0]);this._isDisabledDatepicker(n[0])||(this._adjustInstDate(o,i+("M"===s?this._get(o,"showCurrentAtPos"):0),s),this._updateDatepicker(o))},_gotoToday:function(e){var i,s=t(e),n=this._getInst(s[0]);this._get(n,"gotoCurrent")&&n.currentDay?(n.selectedDay=n.currentDay,n.drawMonth=n.selectedMonth=n.currentMonth,n.drawYear=n.selectedYear=n.currentYear):(i=new Date,n.selectedDay=i.getDate(),n.drawMonth=n.selectedMonth=i.getMonth(),n.drawYear=n.selectedYear=i.getFullYear()),this._notifyChange(n),this._adjustDate(s)},_selectMonthYear:function(e,i,s){var n=t(e),o=this._getInst(n[0]);o["selected"+("M"===s?"Month":"Year")]=o["draw"+("M"===s?"Month":"Year")]=parseInt(i.options[i.selectedIndex].value,10),this._notifyChange(o),this._adjustDate(n)},_selectDay:function(e,i,s,n){var o,a=t(e);t(n).hasClass(this._unselectableClass)||this._isDisabledDatepicker(a[0])||(o=this._getInst(a[0]),o.selectedDay=o.currentDay=t("a",n).html(),o.selectedMonth=o.currentMonth=i,o.selectedYear=o.currentYear=s,this._selectDate(e,this._formatDate(o,o.currentDay,o.currentMonth,o.currentYear)))},_clearDate:function(e){var i=t(e);this._selectDate(i,"")},_selectDate:function(e,i){var s,n=t(e),o=this._getInst(n[0]);i=null!=i?i:this._formatDate(o),o.input&&o.input.val(i),this._updateAlternate(o),s=this._get(o,"onSelect"),s?s.apply(o.input?o.input[0]:null,[i,o]):o.input&&o.input.trigger("change"),o.inline?this._updateDatepicker(o):(this._hideDatepicker(),this._lastInput=o.input[0],"object"!=typeof o.input[0]&&o.input.trigger("focus"),this._lastInput=null)},_updateAlternate:function(e){var i,s,n,o=this._get(e,"altField");o&&(i=this._get(e,"altFormat")||this._get(e,"dateFormat"),s=this._getDate(e),n=this.formatDate(i,s,this._getFormatConfig(e)),t(o).val(n))},noWeekends:function(t){var e=t.getDay();return[e>0&&6>e,""]},iso8601Week:function(t){var e,i=new Date(t.getTime());return i.setDate(i.getDate()+4-(i.getDay()||7)),e=i.getTime(),i.setMonth(0),i.setDate(1),Math.floor(Math.round((e-i)/864e5)/7)+1},parseDate:function(e,i,s){if(null==e||null==i)throw"Invalid arguments";if(i="object"==typeof i?""+i:i+"",""===i)return null;var n,o,a,r,l=0,h=(s?s.shortYearCutoff:null)||this._defaults.shortYearCutoff,c="string"!=typeof h?h:(new Date).getFullYear()%100+parseInt(h,10),u=(s?s.dayNamesShort:null)||this._defaults.dayNamesShort,d=(s?s.dayNames:null)||this._defaults.dayNames,p=(s?s.monthNamesShort:null)||this._defaults.monthNamesShort,f=(s?s.monthNames:null)||this._defaults.monthNames,g=-1,m=-1,_=-1,v=-1,b=!1,y=function(t){var i=e.length>n+1&&e.charAt(n+1)===t;return i&&n++,i},w=function(t){var e=y(t),s="@"===t?14:"!"===t?20:"y"===t&&e?4:"o"===t?3:2,n="y"===t?s:1,o=RegExp("^\\d{"+n+","+s+"}"),a=i.substring(l).match(o);if(!a)throw"Missing number at position "+l;return l+=a[0].length,parseInt(a[0],10)},k=function(e,s,n){var o=-1,a=t.map(y(e)?n:s,function(t,e){return[[e,t]]}).sort(function(t,e){return-(t[1].length-e[1].length)});if(t.each(a,function(t,e){var s=e[1];return i.substr(l,s.length).toLowerCase()===s.toLowerCase()?(o=e[0],l+=s.length,!1):void 0}),-1!==o)return o+1;throw"Unknown name at position "+l},x=function(){if(i.charAt(l)!==e.charAt(n))throw"Unexpected literal at position "+l;l++};for(n=0;e.length>n;n++)if(b)"'"!==e.charAt(n)||y("'")?x():b=!1;else switch(e.charAt(n)){case"d":_=w("d");break;case"D":k("D",u,d);break;case"o":v=w("o");break;case"m":m=w("m");break;case"M":m=k("M",p,f);break;case"y":g=w("y");break;case"@":r=new Date(w("@")),g=r.getFullYear(),m=r.getMonth()+1,_=r.getDate();break;case"!":r=new Date((w("!")-this._ticksTo1970)/1e4),g=r.getFullYear(),m=r.getMonth()+1,_=r.getDate();break;case"'":y("'")?x():b=!0;break;default:x()}if(i.length>l&&(a=i.substr(l),!/^\s+/.test(a)))throw"Extra/unparsed characters found in date: "+a;if(-1===g?g=(new Date).getFullYear():100>g&&(g+=(new Date).getFullYear()-(new Date).getFullYear()%100+(c>=g?0:-100)),v>-1)for(m=1,_=v;;){if(o=this._getDaysInMonth(g,m-1),o>=_)break;m++,_-=o}if(r=this._daylightSavingAdjust(new Date(g,m-1,_)),r.getFullYear()!==g||r.getMonth()+1!==m||r.getDate()!==_)throw"Invalid date";return r},ATOM:"yy-mm-dd",COOKIE:"D, dd M yy",ISO_8601:"yy-mm-dd",RFC_822:"D, d M y",RFC_850:"DD, dd-M-y",RFC_1036:"D, d M y",RFC_1123:"D, d M yy",RFC_2822:"D, d M yy",RSS:"D, d M y",TICKS:"!",TIMESTAMP:"@",W3C:"yy-mm-dd",_ticksTo1970:1e7*60*60*24*(718685+Math.floor(492.5)-Math.floor(19.7)+Math.floor(4.925)),formatDate:function(t,e,i){if(!e)return"";var s,n=(i?i.dayNamesShort:null)||this._defaults.dayNamesShort,o=(i?i.dayNames:null)||this._defaults.dayNames,a=(i?i.monthNamesShort:null)||this._defaults.monthNamesShort,r=(i?i.monthNames:null)||this._defaults.monthNames,l=function(e){var i=t.length>s+1&&t.charAt(s+1)===e;return i&&s++,i},h=function(t,e,i){var s=""+e;if(l(t))for(;i>s.length;)s="0"+s;return s},c=function(t,e,i,s){return l(t)?s[e]:i[e]},u="",d=!1;if(e)for(s=0;t.length>s;s++)if(d)"'"!==t.charAt(s)||l("'")?u+=t.charAt(s):d=!1;else switch(t.charAt(s)){case"d":u+=h("d",e.getDate(),2);break;case"D":u+=c("D",e.getDay(),n,o);break;case"o":u+=h("o",Math.round((new Date(e.getFullYear(),e.getMonth(),e.getDate()).getTime()-new Date(e.getFullYear(),0,0).getTime())/864e5),3);break;case"m":u+=h("m",e.getMonth()+1,2);break;case"M":u+=c("M",e.getMonth(),a,r);break;case"y":u+=l("y")?e.getFullYear():(10>e.getFullYear()%100?"0":"")+e.getFullYear()%100;break;case"@":u+=e.getTime();break;case"!":u+=1e4*e.getTime()+this._ticksTo1970;break;case"'":l("'")?u+="'":d=!0;break;default:u+=t.charAt(s)}return u},_possibleChars:function(t){var e,i="",s=!1,n=function(i){var s=t.length>e+1&&t.charAt(e+1)===i;return s&&e++,s};for(e=0;t.length>e;e++)if(s)"'"!==t.charAt(e)||n("'")?i+=t.charAt(e):s=!1;else switch(t.charAt(e)){case"d":case"m":case"y":case"@":i+="0123456789";break;case"D":case"M":return null;case"'":n("'")?i+="'":s=!0;break;default:i+=t.charAt(e)}return i},_get:function(t,e){return void 0!==t.settings[e]?t.settings[e]:this._defaults[e]},_setDateFromField:function(t,e){if(t.input.val()!==t.lastVal){var i=this._get(t,"dateFormat"),s=t.lastVal=t.input?t.input.val():null,n=this._getDefaultDate(t),o=n,a=this._getFormatConfig(t);try{o=this.parseDate(i,s,a)||n}catch(r){s=e?"":s}t.selectedDay=o.getDate(),t.drawMonth=t.selectedMonth=o.getMonth(),t.drawYear=t.selectedYear=o.getFullYear(),t.currentDay=s?o.getDate():0,t.currentMonth=s?o.getMonth():0,t.currentYear=s?o.getFullYear():0,this._adjustInstDate(t)}},_getDefaultDate:function(t){return this._restrictMinMax(t,this._determineDate(t,this._get(t,"defaultDate"),new Date))},_determineDate:function(e,i,s){var n=function(t){var e=new Date;return e.setDate(e.getDate()+t),e},o=function(i){try{return t.datepicker.parseDate(t.datepicker._get(e,"dateFormat"),i,t.datepicker._getFormatConfig(e))}catch(s){}for(var n=(i.toLowerCase().match(/^c/)?t.datepicker._getDate(e):null)||new Date,o=n.getFullYear(),a=n.getMonth(),r=n.getDate(),l=/([+\-]?[0-9]+)\s*(d|D|w|W|m|M|y|Y)?/g,h=l.exec(i);h;){switch(h[2]||"d"){case"d":case"D":r+=parseInt(h[1],10);break;case"w":case"W":r+=7*parseInt(h[1],10);break;case"m":case"M":a+=parseInt(h[1],10),r=Math.min(r,t.datepicker._getDaysInMonth(o,a));break;case"y":case"Y":o+=parseInt(h[1],10),r=Math.min(r,t.datepicker._getDaysInMonth(o,a))}h=l.exec(i)}return new Date(o,a,r)},a=null==i||""===i?s:"string"==typeof i?o(i):"number"==typeof i?isNaN(i)?s:n(i):new Date(i.getTime());return a=a&&"Invalid Date"==""+a?s:a,a&&(a.setHours(0),a.setMinutes(0),a.setSeconds(0),a.setMilliseconds(0)),this._daylightSavingAdjust(a)},_daylightSavingAdjust:function(t){return t?(t.setHours(t.getHours()>12?t.getHours()+2:0),t):null},_setDate:function(t,e,i){var s=!e,n=t.selectedMonth,o=t.selectedYear,a=this._restrictMinMax(t,this._determineDate(t,e,new Date));t.selectedDay=t.currentDay=a.getDate(),t.drawMonth=t.selectedMonth=t.currentMonth=a.getMonth(),t.drawYear=t.selectedYear=t.currentYear=a.getFullYear(),n===t.selectedMonth&&o===t.selectedYear||i||this._notifyChange(t),this._adjustInstDate(t),t.input&&t.input.val(s?"":this._formatDate(t))},_getDate:function(t){var e=!t.currentYear||t.input&&""===t.input.val()?null:this._daylightSavingAdjust(new Date(t.currentYear,t.currentMonth,t.currentDay));return e},_attachHandlers:function(e){var i=this._get(e,"stepMonths"),s="#"+e.id.replace(/\\\\/g,"\\");e.dpDiv.find("[data-handler]").map(function(){var e={prev:function(){t.datepicker._adjustDate(s,-i,"M")},next:function(){t.datepicker._adjustDate(s,+i,"M")},hide:function(){t.datepicker._hideDatepicker()},today:function(){t.datepicker._gotoToday(s)},selectDay:function(){return t.datepicker._selectDay(s,+this.getAttribute("data-month"),+this.getAttribute("data-year"),this),!1},selectMonth:function(){return t.datepicker._selectMonthYear(s,this,"M"),!1},selectYear:function(){return t.datepicker._selectMonthYear(s,this,"Y"),!1}};t(this).on(this.getAttribute("data-event"),e[this.getAttribute("data-handler")])})},_generateHTML:function(t){var e,i,s,n,o,a,r,l,h,c,u,d,p,f,g,m,_,v,b,y,w,k,x,C,D,T,I,M,P,S,N,H,A,z,O,E,W,F,L,R=new Date,Y=this._daylightSavingAdjust(new Date(R.getFullYear(),R.getMonth(),R.getDate())),B=this._get(t,"isRTL"),j=this._get(t,"showButtonPanel"),q=this._get(t,"hideIfNoPrevNext"),K=this._get(t,"navigationAsDateFormat"),U=this._getNumberOfMonths(t),V=this._get(t,"showCurrentAtPos"),X=this._get(t,"stepMonths"),$=1!==U[0]||1!==U[1],G=this._daylightSavingAdjust(t.currentDay?new Date(t.currentYear,t.currentMonth,t.currentDay):new Date(9999,9,9)),J=this._getMinMaxDate(t,"min"),Q=this._getMinMaxDate(t,"max"),Z=t.drawMonth-V,te=t.drawYear;if(0>Z&&(Z+=12,te--),Q)for(e=this._daylightSavingAdjust(new Date(Q.getFullYear(),Q.getMonth()-U[0]*U[1]+1,Q.getDate())),e=J&&J>e?J:e;this._daylightSavingAdjust(new Date(te,Z,1))>e;)Z--,0>Z&&(Z=11,te--);for(t.drawMonth=Z,t.drawYear=te,i=this._get(t,"prevText"),i=K?this.formatDate(i,this._daylightSavingAdjust(new Date(te,Z-X,1)),this._getFormatConfig(t)):i,s=this._canAdjustMonth(t,-1,te,Z)?"<a class='ui-datepicker-prev ui-corner-all' data-handler='prev' data-event='click' title='"+i+"'><span class='ui-icon ui-icon-circle-triangle-"+(B?"e":"w")+"'>"+i+"</span></a>":q?"":"<a class='ui-datepicker-prev ui-corner-all ui-state-disabled' title='"+i+"'><span class='ui-icon ui-icon-circle-triangle-"+(B?"e":"w")+"'>"+i+"</span></a>",n=this._get(t,"nextText"),n=K?this.formatDate(n,this._daylightSavingAdjust(new Date(te,Z+X,1)),this._getFormatConfig(t)):n,o=this._canAdjustMonth(t,1,te,Z)?"<a class='ui-datepicker-next ui-corner-all' data-handler='next' data-event='click' title='"+n+"'><span class='ui-icon ui-icon-circle-triangle-"+(B?"w":"e")+"'>"+n+"</span></a>":q?"":"<a class='ui-datepicker-next ui-corner-all ui-state-disabled' title='"+n+"'><span class='ui-icon ui-icon-circle-triangle-"+(B?"w":"e")+"'>"+n+"</span></a>",a=this._get(t,"currentText"),r=this._get(t,"gotoCurrent")&&t.currentDay?G:Y,a=K?this.formatDate(a,r,this._getFormatConfig(t)):a,l=t.inline?"":"<button type='button' class='ui-datepicker-close ui-state-default ui-priority-primary ui-corner-all' data-handler='hide' data-event='click'>"+this._get(t,"closeText")+"</button>",h=j?"<div class='ui-datepicker-buttonpane ui-widget-content'>"+(B?l:"")+(this._isInRange(t,r)?"<button type='button' class='ui-datepicker-current ui-state-default ui-priority-secondary ui-corner-all' data-handler='today' data-event='click'>"+a+"</button>":"")+(B?"":l)+"</div>":"",c=parseInt(this._get(t,"firstDay"),10),c=isNaN(c)?0:c,u=this._get(t,"showWeek"),d=this._get(t,"dayNames"),p=this._get(t,"dayNamesMin"),f=this._get(t,"monthNames"),g=this._get(t,"monthNamesShort"),m=this._get(t,"beforeShowDay"),_=this._get(t,"showOtherMonths"),v=this._get(t,"selectOtherMonths"),b=this._getDefaultDate(t),y="",k=0;U[0]>k;k++){for(x="",this.maxRows=4,C=0;U[1]>C;C++){if(D=this._daylightSavingAdjust(new Date(te,Z,t.selectedDay)),T=" ui-corner-all",I="",$){if(I+="<div class='ui-datepicker-group",U[1]>1)switch(C){case 0:I+=" ui-datepicker-group-first",T=" ui-corner-"+(B?"right":"left");break;case U[1]-1:I+=" ui-datepicker-group-last",T=" ui-corner-"+(B?"left":"right");break;default:I+=" ui-datepicker-group-middle",T=""}I+="'>"}for(I+="<div class='ui-datepicker-header ui-widget-header ui-helper-clearfix"+T+"'>"+(/all|left/.test(T)&&0===k?B?o:s:"")+(/all|right/.test(T)&&0===k?B?s:o:"")+this._generateMonthYearHeader(t,Z,te,J,Q,k>0||C>0,f,g)+"</div><table class='ui-datepicker-calendar'><thead>"+"<tr>",M=u?"<th class='ui-datepicker-week-col'>"+this._get(t,"weekHeader")+"</th>":"",w=0;7>w;w++)P=(w+c)%7,M+="<th scope='col'"+((w+c+6)%7>=5?" class='ui-datepicker-week-end'":"")+">"+"<span title='"+d[P]+"'>"+p[P]+"</span></th>";for(I+=M+"</tr></thead><tbody>",S=this._getDaysInMonth(te,Z),te===t.selectedYear&&Z===t.selectedMonth&&(t.selectedDay=Math.min(t.selectedDay,S)),N=(this._getFirstDayOfMonth(te,Z)-c+7)%7,H=Math.ceil((N+S)/7),A=$?this.maxRows>H?this.maxRows:H:H,this.maxRows=A,z=this._daylightSavingAdjust(new Date(te,Z,1-N)),O=0;A>O;O++){for(I+="<tr>",E=u?"<td class='ui-datepicker-week-col'>"+this._get(t,"calculateWeek")(z)+"</td>":"",w=0;7>w;w++)W=m?m.apply(t.input?t.input[0]:null,[z]):[!0,""],F=z.getMonth()!==Z,L=F&&!v||!W[0]||J&&J>z||Q&&z>Q,E+="<td class='"+((w+c+6)%7>=5?" ui-datepicker-week-end":"")+(F?" ui-datepicker-other-month":"")+(z.getTime()===D.getTime()&&Z===t.selectedMonth&&t._keyEvent||b.getTime()===z.getTime()&&b.getTime()===D.getTime()?" "+this._dayOverClass:"")+(L?" "+this._unselectableClass+" ui-state-disabled":"")+(F&&!_?"":" "+W[1]+(z.getTime()===G.getTime()?" "+this._currentClass:"")+(z.getTime()===Y.getTime()?" ui-datepicker-today":""))+"'"+(F&&!_||!W[2]?"":" title='"+W[2].replace(/'/g,"&#39;")+"'")+(L?"":" data-handler='selectDay' data-event='click' data-month='"+z.getMonth()+"' data-year='"+z.getFullYear()+"'")+">"+(F&&!_?"&#xa0;":L?"<span class='ui-state-default'>"+z.getDate()+"</span>":"<a class='ui-state-default"+(z.getTime()===Y.getTime()?" ui-state-highlight":"")+(z.getTime()===G.getTime()?" ui-state-active":"")+(F?" ui-priority-secondary":"")+"' href='#'>"+z.getDate()+"</a>")+"</td>",z.setDate(z.getDate()+1),z=this._daylightSavingAdjust(z);I+=E+"</tr>"}Z++,Z>11&&(Z=0,te++),I+="</tbody></table>"+($?"</div>"+(U[0]>0&&C===U[1]-1?"<div class='ui-datepicker-row-break'></div>":""):""),x+=I}y+=x}return y+=h,t._keyEvent=!1,y},_generateMonthYearHeader:function(t,e,i,s,n,o,a,r){var l,h,c,u,d,p,f,g,m=this._get(t,"changeMonth"),_=this._get(t,"changeYear"),v=this._get(t,"showMonthAfterYear"),b="<div class='ui-datepicker-title'>",y="";
-if(o||!m)y+="<span class='ui-datepicker-month'>"+a[e]+"</span>";else{for(l=s&&s.getFullYear()===i,h=n&&n.getFullYear()===i,y+="<select class='ui-datepicker-month' data-handler='selectMonth' data-event='change'>",c=0;12>c;c++)(!l||c>=s.getMonth())&&(!h||n.getMonth()>=c)&&(y+="<option value='"+c+"'"+(c===e?" selected='selected'":"")+">"+r[c]+"</option>");y+="</select>"}if(v||(b+=y+(!o&&m&&_?"":"&#xa0;")),!t.yearshtml)if(t.yearshtml="",o||!_)b+="<span class='ui-datepicker-year'>"+i+"</span>";else{for(u=this._get(t,"yearRange").split(":"),d=(new Date).getFullYear(),p=function(t){var e=t.match(/c[+\-].*/)?i+parseInt(t.substring(1),10):t.match(/[+\-].*/)?d+parseInt(t,10):parseInt(t,10);return isNaN(e)?d:e},f=p(u[0]),g=Math.max(f,p(u[1]||"")),f=s?Math.max(f,s.getFullYear()):f,g=n?Math.min(g,n.getFullYear()):g,t.yearshtml+="<select class='ui-datepicker-year' data-handler='selectYear' data-event='change'>";g>=f;f++)t.yearshtml+="<option value='"+f+"'"+(f===i?" selected='selected'":"")+">"+f+"</option>";t.yearshtml+="</select>",b+=t.yearshtml,t.yearshtml=null}return b+=this._get(t,"yearSuffix"),v&&(b+=(!o&&m&&_?"":"&#xa0;")+y),b+="</div>"},_adjustInstDate:function(t,e,i){var s=t.selectedYear+("Y"===i?e:0),n=t.selectedMonth+("M"===i?e:0),o=Math.min(t.selectedDay,this._getDaysInMonth(s,n))+("D"===i?e:0),a=this._restrictMinMax(t,this._daylightSavingAdjust(new Date(s,n,o)));t.selectedDay=a.getDate(),t.drawMonth=t.selectedMonth=a.getMonth(),t.drawYear=t.selectedYear=a.getFullYear(),("M"===i||"Y"===i)&&this._notifyChange(t)},_restrictMinMax:function(t,e){var i=this._getMinMaxDate(t,"min"),s=this._getMinMaxDate(t,"max"),n=i&&i>e?i:e;return s&&n>s?s:n},_notifyChange:function(t){var e=this._get(t,"onChangeMonthYear");e&&e.apply(t.input?t.input[0]:null,[t.selectedYear,t.selectedMonth+1,t])},_getNumberOfMonths:function(t){var e=this._get(t,"numberOfMonths");return null==e?[1,1]:"number"==typeof e?[1,e]:e},_getMinMaxDate:function(t,e){return this._determineDate(t,this._get(t,e+"Date"),null)},_getDaysInMonth:function(t,e){return 32-this._daylightSavingAdjust(new Date(t,e,32)).getDate()},_getFirstDayOfMonth:function(t,e){return new Date(t,e,1).getDay()},_canAdjustMonth:function(t,e,i,s){var n=this._getNumberOfMonths(t),o=this._daylightSavingAdjust(new Date(i,s+(0>e?e:n[0]*n[1]),1));return 0>e&&o.setDate(this._getDaysInMonth(o.getFullYear(),o.getMonth())),this._isInRange(t,o)},_isInRange:function(t,e){var i,s,n=this._getMinMaxDate(t,"min"),o=this._getMinMaxDate(t,"max"),a=null,r=null,l=this._get(t,"yearRange");return l&&(i=l.split(":"),s=(new Date).getFullYear(),a=parseInt(i[0],10),r=parseInt(i[1],10),i[0].match(/[+\-].*/)&&(a+=s),i[1].match(/[+\-].*/)&&(r+=s)),(!n||e.getTime()>=n.getTime())&&(!o||e.getTime()<=o.getTime())&&(!a||e.getFullYear()>=a)&&(!r||r>=e.getFullYear())},_getFormatConfig:function(t){var e=this._get(t,"shortYearCutoff");return e="string"!=typeof e?e:(new Date).getFullYear()%100+parseInt(e,10),{shortYearCutoff:e,dayNamesShort:this._get(t,"dayNamesShort"),dayNames:this._get(t,"dayNames"),monthNamesShort:this._get(t,"monthNamesShort"),monthNames:this._get(t,"monthNames")}},_formatDate:function(t,e,i,s){e||(t.currentDay=t.selectedDay,t.currentMonth=t.selectedMonth,t.currentYear=t.selectedYear);var n=e?"object"==typeof e?e:this._daylightSavingAdjust(new Date(s,i,e)):this._daylightSavingAdjust(new Date(t.currentYear,t.currentMonth,t.currentDay));return this.formatDate(this._get(t,"dateFormat"),n,this._getFormatConfig(t))}}),t.fn.datepicker=function(e){if(!this.length)return this;t.datepicker.initialized||(t(document).on("mousedown",t.datepicker._checkExternalClick),t.datepicker.initialized=!0),0===t("#"+t.datepicker._mainDivId).length&&t("body").append(t.datepicker.dpDiv);var i=Array.prototype.slice.call(arguments,1);return"string"!=typeof e||"isDisabled"!==e&&"getDate"!==e&&"widget"!==e?"option"===e&&2===arguments.length&&"string"==typeof arguments[1]?t.datepicker["_"+e+"Datepicker"].apply(t.datepicker,[this[0]].concat(i)):this.each(function(){"string"==typeof e?t.datepicker["_"+e+"Datepicker"].apply(t.datepicker,[this].concat(i)):t.datepicker._attachDatepicker(this,e)}):t.datepicker["_"+e+"Datepicker"].apply(t.datepicker,[this[0]].concat(i))},t.datepicker=new i,t.datepicker.initialized=!1,t.datepicker.uuid=(new Date).getTime(),t.datepicker.version="1.12.0",t.datepicker});
\ No newline at end of file
diff --git a/Themes/default/scripts/jquery.datepair.min.js b/Themes/default/scripts/jquery.datepair.min.js
deleted file mode 100755
index 1d42745623..0000000000
--- a/Themes/default/scripts/jquery.datepair.min.js
+++ /dev/null
@@ -1,7 +0,0 @@
-/*!
- * datepair.js v0.4.16 - A javascript plugin for intelligently selecting date and time ranges inspired by Google Calendar.
- * Copyright (c) 2018 Jon Thornton - http://jonthornton.github.com/Datepair.js
- * License: MIT
- */
-
-!function(a,b){"use strict";function c(a,b){var c=b||{};for(var d in a)d in c||(c[d]=a[d]);return c}function d(a,c){if(h)h(a).trigger(c);else{var d=b.createEvent("CustomEvent");d.initCustomEvent(c,!0,!0,{}),a.dispatchEvent(d)}}function e(a,b){return h?h(a).hasClass(b):a.classList.contains(b)}function f(a,b){this.dateDelta=null,this.timeDelta=null,this._defaults={startClass:"start",endClass:"end",timeClass:"time",dateClass:"date",defaultDateDelta:0,defaultTimeDelta:36e5,anchor:"start",parseTime:function(a){return h(a).timepicker("getTime")},updateTime:function(a,b){h(a).timepicker("setTime",b)},setMinTime:function(a,b){h(a).timepicker("option","minTime",b)},parseDate:function(a){return a.value&&h(a).datepicker("getDate")},updateDate:function(a,b){h(a).datepicker("update",b)}},this.container=a,this.settings=c(this._defaults,b),this.startDateInput=this.container.querySelector("."+this.settings.startClass+"."+this.settings.dateClass),this.endDateInput=this.container.querySelector("."+this.settings.endClass+"."+this.settings.dateClass),this.startTimeInput=this.container.querySelector("."+this.settings.startClass+"."+this.settings.timeClass),this.endTimeInput=this.container.querySelector("."+this.settings.endClass+"."+this.settings.timeClass),this.refresh(),this._bindChangeHandler()}var g=864e5,h=a.Zepto||a.jQuery;f.prototype={constructor:f,option:function(a,b){if("object"==typeof a)this.settings=c(this.settings,a);else if("string"==typeof a&&"undefined"!=typeof b)this.settings[a]=b;else if("string"==typeof a)return this.settings[a];this._updateEndMintime()},getTimeDiff:function(){var a=this.dateDelta+this.timeDelta;return!(a<0)||this.startDateInput&&this.endDateInput||(a+=g),a},refresh:function(){if(this.startDateInput&&this.startDateInput.value&&this.endDateInput&&this.endDateInput.value){var a=this.settings.parseDate(this.startDateInput),b=this.settings.parseDate(this.endDateInput);a&&b&&(this.dateDelta=b.getTime()-a.getTime())}if(this.startTimeInput&&this.startTimeInput.value&&this.endTimeInput&&this.endTimeInput.value){var c=this.settings.parseTime(this.startTimeInput),d=this.settings.parseTime(this.endTimeInput);c&&d&&(this.timeDelta=d.getTime()-c.getTime(),this._updateEndMintime())}},remove:function(){this._unbindChangeHandler()},_bindChangeHandler:function(){h?h(this.container).on("change.datepair",h.proxy(this.handleEvent,this)):this.container.addEventListener("change",this,!1)},_unbindChangeHandler:function(){h?h(this.container).off("change.datepair"):this.container.removeEventListener("change",this,!1)},handleEvent:function(a){this._unbindChangeHandler(),e(a.target,this.settings.dateClass)?""!=a.target.value?(this._dateChanged(a.target),this._timeChanged(a.target)):this.dateDelta=null:e(a.target,this.settings.timeClass)&&(""!=a.target.value?this._timeChanged(a.target):this.timeDelta=null),this._validateRanges(),this._updateEndMintime(),this._bindChangeHandler()},_dateChanged:function(a){if(this.startDateInput&&this.endDateInput){var b=this.settings.parseDate(this.startDateInput),c=this.settings.parseDate(this.endDateInput);if(b&&c)if("start"==this.settings.anchor&&e(a,this.settings.startClass)){var d=new Date(b.getTime()+this.dateDelta);this.settings.updateDate(this.endDateInput,d)}else if("end"==this.settings.anchor&&e(a,this.settings.endClass)){var d=new Date(c.getTime()-this.dateDelta);this.settings.updateDate(this.startDateInput,d)}else if(c<b){var f=e(a,this.settings.startClass)?this.endDateInput:this.startDateInput,h=this.settings.parseDate(a);this.dateDelta=0,this.settings.updateDate(f,h)}else this.dateDelta=c.getTime()-b.getTime();else if(null!==this.settings.defaultDateDelta){if(b){var i=new Date(b.getTime()+this.settings.defaultDateDelta*g);this.settings.updateDate(this.endDateInput,i)}else if(c){var j=new Date(c.getTime()-this.settings.defaultDateDelta*g);this.settings.updateDate(this.startDateInput,j)}this.dateDelta=this.settings.defaultDateDelta*g}else this.dateDelta=null}},_timeChanged:function(a){if(this.startTimeInput&&this.endTimeInput){var b=this.settings.parseTime(this.startTimeInput),c=this.settings.parseTime(this.endTimeInput);if(!b||!c)return void(null!==this.settings.defaultTimeDelta?(this.timeDelta=this.settings.defaultTimeDelta,b?(c=this._setTimeAndReturn(this.endTimeInput,new Date(b.getTime()+this.settings.defaultTimeDelta)),this._doMidnightRollover(b,c)):c&&(b=this._setTimeAndReturn(this.startTimeInput,new Date(c.getTime()-this.settings.defaultTimeDelta)),this._doMidnightRollover(b,c))):this.timeDelta=null);if("start"==this.settings.anchor&&e(a,this.settings.startClass))c=this._setTimeAndReturn(this.endTimeInput,new Date(b.getTime()+this.timeDelta)),this._doMidnightRollover(b,c);else if("end"==this.settings.anchor&&e(a,this.settings.endClass))b=this._setTimeAndReturn(this.startTimeInput,new Date(c.getTime()-this.timeDelta)),this._doMidnightRollover(b,c);else{this._doMidnightRollover(b,c);var d,f;if(this.startDateInput&&this.endDateInput&&(d=this.settings.parseDate(this.startDateInput),f=this.settings.parseDate(this.endDateInput)),+d==+f&&c<b){var g=e(a,this.settings.endClass)?this.endTimeInput:this.startTimeInput,h=e(a,this.settings.startClass)?this.endTimeInput:this.startTimeInput,i=this.settings.parseTime(g);this.timeDelta=0,this.settings.updateTime(h,i)}else this.timeDelta=c.getTime()-b.getTime()}}},_setTimeAndReturn:function(a,b){return this.settings.updateTime(a,b),this.settings.parseTime(a)},_doMidnightRollover:function(a,b){if(this.startDateInput&&this.endDateInput){var c=this.settings.parseDate(this.endDateInput),d=this.settings.parseDate(this.startDateInput),e=b.getTime()-a.getTime(),f=b<a?g:-1*g;null!==this.dateDelta&&this.dateDelta+this.timeDelta<=g&&this.dateDelta+e!=0&&(f>0||0!=this.dateDelta)&&(e>=0&&this.timeDelta<0||e<0&&this.timeDelta>=0)&&("start"==this.settings.anchor?(this.settings.updateDate(this.endDateInput,new Date(c.getTime()+f)),this._dateChanged(this.endDateInput)):"end"==this.settings.anchor&&(this.settings.updateDate(this.startDateInput,new Date(d.getTime()-f)),this._dateChanged(this.startDateInput))),this.timeDelta=e}},_updateEndMintime:function(){if("function"==typeof this.settings.setMinTime){var a=null;"start"==this.settings.anchor&&(!this.dateDelta||this.dateDelta<g||this.timeDelta&&this.dateDelta+this.timeDelta<g)&&(a=this.settings.parseTime(this.startTimeInput)),this.settings.setMinTime(this.endTimeInput,a)}},_validateRanges:function(){return this.startTimeInput&&this.endTimeInput&&null===this.timeDelta?void d(this.container,"rangeIncomplete"):this.startDateInput&&this.endDateInput&&null===this.dateDelta?void d(this.container,"rangeIncomplete"):void(!this.startDateInput||!this.endDateInput||this.dateDelta+this.timeDelta>=0?d(this.container,"rangeSelected"):d(this.container,"rangeError"))}},a.Datepair=f}(window,document),function(a){a&&(a.fn.datepair=function(b){var c;return this.each(function(){var d=a(this),e=d.data("datepair"),f="object"==typeof b&&b;e||(e=new Datepair(this,f),d.data("datepair",e)),"remove"===b&&(c=e.remove(),d.removeData("datepair",e)),"string"==typeof b&&(c=e[b]())}),c||this},a("[data-datepair]").each(function(){var b=a(this);b.datepair(b.data())}))}(window.Zepto||window.jQuery);
diff --git a/Themes/default/scripts/jquery.timepicker.min.js b/Themes/default/scripts/jquery.timepicker.min.js
deleted file mode 100755
index d3a92eac00..0000000000
--- a/Themes/default/scripts/jquery.timepicker.min.js
+++ /dev/null
@@ -1,7 +0,0 @@
-/*!
- * jquery-timepicker v1.11.1 - A jQuery timepicker plugin inspired by Google Calendar. It supports both mouse and keyboard navigation.
- * Copyright (c) 2016 Jon Thornton - http://jonthornton.github.com/jquery-timepicker/
- * License: MIT
- */
-
-!function(a){"object"==typeof exports&&exports&&"object"==typeof module&&module&&module.exports===exports?a(require("jquery")):"function"==typeof define&&define.amd?define(["jquery"],a):a(jQuery)}(function(a){function b(a){var b=a[0];return b.offsetWidth>0&&b.offsetHeight>0}function c(b){if(b.minTime&&(b.minTime=t(b.minTime)),b.maxTime&&(b.maxTime=t(b.maxTime)),b.durationTime&&"function"!=typeof b.durationTime&&(b.durationTime=t(b.durationTime)),"now"==b.scrollDefault)b.scrollDefault=function(){return b.roundingFunction(t(new Date),b)};else if(b.scrollDefault&&"function"!=typeof b.scrollDefault){var c=b.scrollDefault;b.scrollDefault=function(){return b.roundingFunction(t(c),b)}}else b.minTime&&(b.scrollDefault=function(){return b.roundingFunction(b.minTime,b)});if("string"===a.type(b.timeFormat)&&b.timeFormat.match(/[gh]/)&&(b._twelveHourTime=!0),b.showOnFocus===!1&&-1!=b.showOn.indexOf("focus")&&b.showOn.splice(b.showOn.indexOf("focus"),1),b.disableTimeRanges.length>0){for(var d in b.disableTimeRanges)b.disableTimeRanges[d]=[t(b.disableTimeRanges[d][0]),t(b.disableTimeRanges[d][1])];b.disableTimeRanges=b.disableTimeRanges.sort(function(a,b){return a[0]-b[0]});for(var d=b.disableTimeRanges.length-1;d>0;d--)b.disableTimeRanges[d][0]<=b.disableTimeRanges[d-1][1]&&(b.disableTimeRanges[d-1]=[Math.min(b.disableTimeRanges[d][0],b.disableTimeRanges[d-1][0]),Math.max(b.disableTimeRanges[d][1],b.disableTimeRanges[d-1][1])],b.disableTimeRanges.splice(d,1))}return b}function d(b){var c=b.data("timepicker-settings"),d=b.data("timepicker-list");if(d&&d.length&&(d.remove(),b.data("timepicker-list",!1)),c.useSelect){d=a("<select />",{"class":"ui-timepicker-select"});var g=d}else{d=a("<ul />",{"class":"ui-timepicker-list"});var g=a("<div />",{"class":"ui-timepicker-wrapper",tabindex:-1});g.css({display:"none",position:"absolute"}).append(d)}if(c.noneOption)if(c.noneOption===!0&&(c.noneOption=c.useSelect?"Time...":"None"),a.isArray(c.noneOption)){for(var i in c.noneOption)if(parseInt(i,10)==i){var k=e(c.noneOption[i],c.useSelect);d.append(k)}}else{var k=e(c.noneOption,c.useSelect);d.append(k)}if(c.className&&g.addClass(c.className),(null!==c.minTime||null!==c.durationTime)&&c.showDuration){"function"==typeof c.step?"function":c.step;g.addClass("ui-timepicker-with-duration"),g.addClass("ui-timepicker-step-"+c.step)}var l=c.minTime;"function"==typeof c.durationTime?l=t(c.durationTime()):null!==c.durationTime&&(l=c.durationTime);var n=null!==c.minTime?c.minTime:0,o=null!==c.maxTime?c.maxTime:n+u-1;n>o&&(o+=u),o===u-1&&"string"===a.type(c.timeFormat)&&c.show2400&&(o=u);var p=c.disableTimeRanges,v=0,x=p.length,y=c.step;"function"!=typeof y&&(y=function(){return c.step});for(var i=n,z=0;o>=i;z++,i+=60*y(z)){var A=i,B=s(A,c);if(c.useSelect){var C=a("<option />",{value:B});C.text(B)}else{var C=a("<li />");C.addClass(43200>A%86400?"ui-timepicker-am":"ui-timepicker-pm"),C.data("time",86400>=A?A:A%86400),C.text(B)}if((null!==c.minTime||null!==c.durationTime)&&c.showDuration){var D=r(i-l,c.step);if(c.useSelect)C.text(C.text()+" ("+D+")");else{var E=a("<span />",{"class":"ui-timepicker-duration"});E.text(" ("+D+")"),C.append(E)}}x>v&&(A>=p[v][1]&&(v+=1),p[v]&&A>=p[v][0]&&A<p[v][1]&&(c.useSelect?C.prop("disabled",!0):C.addClass("ui-timepicker-disabled"))),d.append(C)}if(g.data("timepicker-input",b),b.data("timepicker-list",g),c.useSelect)b.val()&&d.val(f(t(b.val()),c)),d.on("focus",function(){a(this).data("timepicker-input").trigger("showTimepicker")}),d.on("blur",function(){a(this).data("timepicker-input").trigger("hideTimepicker")}),d.on("change",function(){m(b,a(this).val(),"select")}),m(b,d.val(),"initial"),b.hide().after(d);else{var F=c.appendTo;"string"==typeof F?F=a(F):"function"==typeof F&&(F=F(b)),F.append(g),j(b,d),d.on("mousedown click","li",function(c){b.off("focus.timepicker"),b.on("focus.timepicker-ie-hack",function(){b.off("focus.timepicker-ie-hack"),b.on("focus.timepicker",w.show)}),h(b)||b[0].focus(),d.find("li").removeClass("ui-timepicker-selected"),a(this).addClass("ui-timepicker-selected"),q(b)&&(b.trigger("hideTimepicker"),d.on("mouseup.timepicker click.timepicker","li",function(a){d.off("mouseup.timepicker click.timepicker"),g.hide()}))})}}function e(b,c){var d,e,f;return"object"==typeof b?(d=b.label,e=b.className,f=b.value):"string"==typeof b?d=b:a.error("Invalid noneOption value"),c?a("<option />",{value:f,"class":e,text:d}):a("<li />",{"class":e,text:d}).data("time",String(f))}function f(a,b){return a=b.roundingFunction(a,b),null!==a?s(a,b):void 0}function g(b){if(b.target!=window){var c=a(b.target);c.closest(".ui-timepicker-input").length||c.closest(".ui-timepicker-wrapper").length||(w.hide(),a(document).unbind(".ui-timepicker"),a(window).unbind(".ui-timepicker"))}}function h(a){var b=a.data("timepicker-settings");return(window.navigator.msMaxTouchPoints||"ontouchstart"in document)&&b.disableTouchKeyboard}function i(b,c,d){if(!d&&0!==d)return!1;var e=b.data("timepicker-settings"),f=!1,d=e.roundingFunction(d,e);return c.find("li").each(function(b,c){var e=a(c);if("number"==typeof e.data("time"))return e.data("time")==d?(f=e,!1):void 0}),f}function j(a,b){b.find("li").removeClass("ui-timepicker-selected");var c=t(l(a),a.data("timepicker-settings"));if(null!==c){var d=i(a,b,c);if(d){var e=d.offset().top-b.offset().top;(e+d.outerHeight()>b.outerHeight()||0>e)&&b.scrollTop(b.scrollTop()+d.position().top-d.outerHeight()),d.addClass("ui-timepicker-selected")}}}function k(b,c){if(""!==this.value&&"timepicker"!=c){var d=a(this);if(!d.is(":focus")||b&&"change"==b.type){var e=d.data("timepicker-settings"),f=t(this.value,e);if(null===f)return void d.trigger("timeFormatError");var g=!1;null!==e.minTime&&f<e.minTime&&null!==e.maxTime&&f>e.maxTime&&(g=!0),a.each(e.disableTimeRanges,function(){return f>=this[0]&&f<this[1]?(g=!0,!1):void 0}),e.forceRoundTime&&(f=e.roundingFunction(f,e));var h=s(f,e);g?m(d,h,"error")&&d.trigger("timeRangeError"):m(d,h)}}}function l(a){return a.is("input")?a.val():a.data("ui-timepicker-value")}function m(a,b,c){if(a.is("input")){a.val(b);var d=a.data("timepicker-settings");d.useSelect&&"select"!=c&&"initial"!=c&&a.data("timepicker-list").val(f(t(b),d))}return a.data("ui-timepicker-value")!=b?(a.data("ui-timepicker-value",b),"select"==c?a.trigger("selectTime").trigger("changeTime").trigger("change","timepicker"):"error"!=c&&a.trigger("changeTime"),!0):(a.trigger("selectTime"),!1)}function n(a){switch(a.keyCode){case 13:case 9:return;default:a.preventDefault()}}function o(c){var d=a(this),e=d.data("timepicker-list");if(!e||!b(e)){if(40!=c.keyCode)return!0;w.show.call(d.get(0)),e=d.data("timepicker-list"),h(d)||d.focus()}switch(c.keyCode){case 13:return q(d)&&w.hide.apply(this),c.preventDefault(),!1;case 38:var f=e.find(".ui-timepicker-selected");return f.length?f.is(":first-child")||(f.removeClass("ui-timepicker-selected"),f.prev().addClass("ui-timepicker-selected"),f.prev().position().top<f.outerHeight()&&e.scrollTop(e.scrollTop()-f.outerHeight())):(e.find("li").each(function(b,c){return a(c).position().top>0?(f=a(c),!1):void 0}),f.addClass("ui-timepicker-selected")),!1;case 40:return f=e.find(".ui-timepicker-selected"),0===f.length?(e.find("li").each(function(b,c){return a(c).position().top>0?(f=a(c),!1):void 0}),f.addClass("ui-timepicker-selected")):f.is(":last-child")||(f.removeClass("ui-timepicker-selected"),f.next().addClass("ui-timepicker-selected"),f.next().position().top+2*f.outerHeight()>e.outerHeight()&&e.scrollTop(e.scrollTop()+f.outerHeight())),!1;case 27:e.find("li").removeClass("ui-timepicker-selected"),w.hide();break;case 9:w.hide();break;default:return!0}}function p(c){var d=a(this),e=d.data("timepicker-list"),f=d.data("timepicker-settings");if(!e||!b(e)||f.disableTextInput)return!0;switch(c.keyCode){case 96:case 97:case 98:case 99:case 100:case 101:case 102:case 103:case 104:case 105:case 48:case 49:case 50:case 51:case 52:case 53:case 54:case 55:case 56:case 57:case 65:case 77:case 80:case 186:case 8:case 46:f.typeaheadHighlight?j(d,e):e.hide()}}function q(a){var b=a.data("timepicker-settings"),c=a.data("timepicker-list"),d=null,e=c.find(".ui-timepicker-selected");return e.hasClass("ui-timepicker-disabled")?!1:(e.length&&(d=e.data("time")),null!==d&&("string"!=typeof d&&(d=s(d,b)),m(a,d,"select")),!0)}function r(a,b){a=Math.abs(a);var c,d,e=Math.round(a/60),f=[];return 60>e?f=[e,v.mins]:(c=Math.floor(e/60),d=e%60,30==b&&30==d&&(c+=v.decimal+5),f.push(c),f.push(1==c?v.hr:v.hrs),30!=b&&d&&(f.push(d),f.push(v.mins))),f.join(" ")}function s(b,c){if("number"!=typeof b)return null;var d=parseInt(b%60),e=parseInt(b/60%60),f=parseInt(b/3600%24),g=new Date(1970,0,2,f,e,d,0);if(isNaN(g.getTime()))return null;if("function"===a.type(c.timeFormat))return c.timeFormat(g);for(var h,i,j="",k=0;k<c.timeFormat.length;k++)switch(i=c.timeFormat.charAt(k)){case"a":j+=g.getHours()>11?v.pm:v.am;break;case"A":j+=g.getHours()>11?v.PM:v.AM;break;case"g":h=g.getHours()%12,j+=0===h?"12":h;break;case"G":h=g.getHours(),b===u&&(h=c.show2400?24:0),j+=h;break;case"h":h=g.getHours()%12,0!==h&&10>h&&(h="0"+h),j+=0===h?"12":h;break;case"H":h=g.getHours(),b===u&&(h=c.show2400?24:0),j+=h>9?h:"0"+h;break;case"i":var e=g.getMinutes();j+=e>9?e:"0"+e;break;case"s":d=g.getSeconds(),j+=d>9?d:"0"+d;break;case"\\":k++,j+=c.timeFormat.charAt(k);break;default:j+=i}return j}function t(a,b){if(""===a||null===a)return null;if("object"==typeof a)return 3600*a.getHours()+60*a.getMinutes()+a.getSeconds();if("string"!=typeof a)return a;a=a.toLowerCase().replace(/[\s\.]/g,""),("a"==a.slice(-1)||"p"==a.slice(-1))&&(a+="m");var c="("+v.am.replace(".","")+"|"+v.pm.replace(".","")+"|"+v.AM.replace(".","")+"|"+v.PM.replace(".","")+")?",d=new RegExp("^"+c+"([0-9]?[0-9])\\W?([0-5][0-9])?\\W?([0-5][0-9])?"+c+"$"),e=a.match(d);if(!e)return null;var f=parseInt(1*e[2],10);if(f>24){if(b&&b.wrapHours===!1)return null;f%=24}var g=e[1]||e[5],h=f;if(12>=f&&g){var i=g==v.pm||g==v.PM;h=12==f?i?12:0:f+(i?12:0)}var j=1*e[3]||0,k=1*e[4]||0,l=3600*h+60*j+k;if(12>f&&!g&&b&&b._twelveHourTime&&b.scrollDefault){var m=l-b.scrollDefault();0>m&&m>=u/-2&&(l=(l+u/2)%u)}return l}var u=86400,v={am:"am",pm:"pm",AM:"AM",PM:"PM",decimal:".",mins:"mins",hr:"hr",hrs:"hrs"},w={init:function(b){return this.each(function(){var e=a(this),f=[];for(var g in a.fn.timepicker.defaults)e.data(g)&&(f[g]=e.data(g));var h=a.extend({},a.fn.timepicker.defaults,f,b);if(h.lang&&(v=a.extend(v,h.lang)),h=c(h),e.data("timepicker-settings",h),e.addClass("ui-timepicker-input"),h.useSelect)d(e);else{if(e.prop("autocomplete","off"),h.showOn)for(var i in h.showOn)e.on(h.showOn[i]+".timepicker",w.show);e.on("change.timepicker",k),e.on("keydown.timepicker",o),e.on("keyup.timepicker",p),h.disableTextInput&&e.on("keydown.timepicker",n),k.call(e.get(0))}})},show:function(c){var e=a(this),f=e.data("timepicker-settings");if(c&&c.preventDefault(),f.useSelect)return void e.data("timepicker-list").focus();h(e)&&e.blur();var k=e.data("timepicker-list");if(!e.prop("readonly")&&(k&&0!==k.length&&"function"!=typeof f.durationTime||(d(e),k=e.data("timepicker-list")),!b(k))){e.data("ui-timepicker-value",e.val()),j(e,k),w.hide(),k.show();var m={};f.orientation.match(/r/)?m.left=e.offset().left+e.outerWidth()-k.outerWidth()+parseInt(k.css("marginLeft").replace("px",""),10):m.left=e.offset().left+parseInt(k.css("marginLeft").replace("px",""),10);var n;n=f.orientation.match(/t/)?"t":f.orientation.match(/b/)?"b":e.offset().top+e.outerHeight(!0)+k.outerHeight()>a(window).height()+a(window).scrollTop()?"t":"b","t"==n?(k.addClass("ui-timepicker-positioned-top"),m.top=e.offset().top-k.outerHeight()+parseInt(k.css("marginTop").replace("px",""),10)):(k.removeClass("ui-timepicker-positioned-top"),m.top=e.offset().top+e.outerHeight()+parseInt(k.css("marginTop").replace("px",""),10)),k.offset(m);var o=k.find(".ui-timepicker-selected");if(!o.length){var p=t(l(e));null!==p?o=i(e,k,p):f.scrollDefault&&(o=i(e,k,f.scrollDefault()))}if(o&&o.length){var q=k.scrollTop()+o.position().top-o.outerHeight();k.scrollTop(q)}else k.scrollTop(0);return f.stopScrollPropagation&&a(document).on("wheel.ui-timepicker",".ui-timepicker-wrapper",function(b){b.preventDefault();var c=a(this).scrollTop();a(this).scrollTop(c+b.originalEvent.deltaY)}),a(document).on("touchstart.ui-timepicker mousedown.ui-timepicker",g),a(window).on("resize.ui-timepicker",g),f.closeOnWindowScroll&&a(document).on("scroll.ui-timepicker",g),e.trigger("showTimepicker"),this}},hide:function(c){var d=a(this),e=d.data("timepicker-settings");return e&&e.useSelect&&d.blur(),a(".ui-timepicker-wrapper").each(function(){var c=a(this);if(b(c)){var d=c.data("timepicker-input"),e=d.data("timepicker-settings");e&&e.selectOnBlur&&q(d),c.hide(),d.trigger("hideTimepicker")}}),this},option:function(b,e){return"string"==typeof b&&"undefined"==typeof e?a(this).data("timepicker-settings")[b]:this.each(function(){var f=a(this),g=f.data("timepicker-settings"),h=f.data("timepicker-list");"object"==typeof b?g=a.extend(g,b):"string"==typeof b&&(g[b]=e),g=c(g),f.data("timepicker-settings",g),h&&(h.remove(),f.data("timepicker-list",!1)),g.useSelect&&d(f)})},getSecondsFromMidnight:function(){return t(l(this))},getTime:function(a){var b=this,c=l(b);if(!c)return null;var d=t(c);if(null===d)return null;a||(a=new Date);var e=new Date(a);return e.setHours(d/3600),e.setMinutes(d%3600/60),e.setSeconds(d%60),e.setMilliseconds(0),e},isVisible:function(){var a=this,c=a.data("timepicker-list");return!(!c||!b(c))},setTime:function(a){var b=this,c=b.data("timepicker-settings");if(c.forceRoundTime)var d=f(t(a),c);else var d=s(t(a),c);return a&&null===d&&c.noneOption&&(d=a),m(b,d),b.data("timepicker-list")&&j(b,b.data("timepicker-list")),this},remove:function(){var a=this;if(a.hasClass("ui-timepicker-input")){var b=a.data("timepicker-settings");return a.removeAttr("autocomplete","off"),a.removeClass("ui-timepicker-input"),a.removeData("timepicker-settings"),a.off(".timepicker"),a.data("timepicker-list")&&a.data("timepicker-list").remove(),b.useSelect&&a.show(),a.removeData("timepicker-list"),this}}};a.fn.timepicker=function(b){return this.length?w[b]?this.hasClass("ui-timepicker-input")?w[b].apply(this,Array.prototype.slice.call(arguments,1)):this:"object"!=typeof b&&b?void a.error("Method "+b+" does not exist on jQuery.timepicker"):w.init.apply(this,arguments):this},a.fn.timepicker.defaults={appendTo:"body",className:null,closeOnWindowScroll:!1,disableTextInput:!1,disableTimeRanges:[],disableTouchKeyboard:!1,durationTime:null,forceRoundTime:!1,maxTime:null,minTime:null,noneOption:!1,orientation:"l",roundingFunction:function(a,b){if(null===a)return null;if("number"!=typeof b.step)return a;var c=a%(60*b.step);return c>=30*b.step?a+=60*b.step-c:a-=c,a==u&&b.show2400?a:a%u},scrollDefault:null,selectOnBlur:!1,show2400:!1,showDuration:!1,showOn:["click","focus"],showOnFocus:!0,step:30,stopScrollPropagation:!1,timeFormat:"g:ia",typeaheadHighlight:!0,useSelect:!1,wrapHours:!0}});
\ No newline at end of file

From c3196c3ea729c54ef232415fed4ee14356b85e48 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Mon, 18 Dec 2023 00:41:30 -0700
Subject: [PATCH 11/22] Implements SMF\Calendar\Holiday

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/General.php                |   9 +
 Languages/en_US/Help.php                   |   1 +
 Languages/en_US/ManageCalendar.php         |   1 +
 Sources/Actions/Admin/Calendar.php         | 164 +++---
 Sources/Actions/Calendar.php               | 110 +---
 Sources/Calendar/Event.php                 | 159 +++++-
 Sources/Calendar/Holiday.php               | 569 +++++++++++++++++++
 Sources/ServerSideIncludes.php             |   4 +
 Themes/default/BoardIndex.template.php     |  11 +-
 Themes/default/Calendar.template.php       |  77 ++-
 Themes/default/EventEditor.template.php    | 178 +++---
 Themes/default/ManageCalendar.template.php |  53 +-
 Themes/default/css/calendar.css            |   7 +
 Themes/default/css/index.css               |  11 +-
 Themes/default/scripts/event.js            |  24 +-
 other/install_3-0_MySQL.sql                | 257 ++-------
 other/install_3-0_PostgreSQL.sql           | 268 ++-------
 other/upgrade_3-0_MySQL.sql                | 626 ++++++++++++++++++++
 other/upgrade_3-0_PostgreSQL.sql           | 627 ++++++++++++++++++++-
 19 files changed, 2364 insertions(+), 792 deletions(-)
 create mode 100644 Sources/Calendar/Holiday.php

diff --git a/Languages/en_US/General.php b/Languages/en_US/General.php
index 06e5998b79..0236ddc308 100644
--- a/Languages/en_US/General.php
+++ b/Languages/en_US/General.php
@@ -750,6 +750,15 @@
 $txt['calendar_repeat_advanced_options_label'] = 'More options...';
 $txt['calendar_repeat_rdates_label'] = 'Additional dates';
 $txt['calendar_repeat_exdates_label'] = 'Skipped dates';
+$txt['calendar_repeat_easter_w'] = 'Easter (Western)';
+$txt['calendar_repeat_easter_e'] = 'Easter (Eastern)';
+$txt['calendar_repeat_vernal_equinox'] = 'Vernal Equinox';
+$txt['calendar_repeat_summer_solstice'] = 'Summer Solstice';
+$txt['calendar_repeat_autumnal_equinox'] = 'Autumnal Equinox';
+$txt['calendar_repeat_winter_solstice'] = 'Winter Solstice';
+$txt['calendar_repeat_special'] = 'Special';
+$txt['calendar_repeat_special_rrule_modifier'] = 'Offset';
+$txt['calendar_repeat_offset_examples'] = 'e.g.: +P1D, -PT2H';
 
 $txt['movetopic_change_subject'] = 'Change the topic’s subject';
 $txt['movetopic_new_subject'] = 'New subject';
diff --git a/Languages/en_US/Help.php b/Languages/en_US/Help.php
index 9b2712722d..e1b14cc3e6 100644
--- a/Languages/en_US/Help.php
+++ b/Languages/en_US/Help.php
@@ -194,6 +194,7 @@
 $helptxt['cal_short_months'] = 'If this setting is checked, month names within the calendar will be shortened.<br><br><strong>Enabled:</strong> {short} 1<br><strong>Disabled:</strong> {long} 1';
 // argument(s): $txt['days_short'][1], $txt['days'][1]
 $helptxt['cal_short_days'] = 'If this setting is checked, day names within the calendar will be shortened.<br><br><strong>Enabled:</strong> {short}<br><strong>Disabled:</strong> {long}';
+$helptxt['special_rrule_modifier'] = 'Use this to specify an offset from the value calculated by a special recurrence rule.<br><br>The value must be a postive or negative sign followed by an <a href="https://en.wikipedia.org/wiki/ISO_8601#Durations" class="bbc_link" target="_blank">ISO 8601 duration</a> specification. For example, "+P1D" means one day after the date calculated by the special recurrence rule, while "-P2D" means two days before.';
 
 $helptxt['serversettings'] = '<strong>Server Settings</strong><br>
 	Here you can perform some core configuration for your forum. This page includes the database and URL settings, as well as other
diff --git a/Languages/en_US/ManageCalendar.php b/Languages/en_US/ManageCalendar.php
index 715179cdbc..800cc2dee9 100644
--- a/Languages/en_US/ManageCalendar.php
+++ b/Languages/en_US/ManageCalendar.php
@@ -52,6 +52,7 @@
 $txt['holidays_button_edit'] = 'Edit';
 $txt['holidays_button_remove'] = 'Remove';
 $txt['holidays_no_entries'] = 'There are currently no holidays configured.';
+$txt['holidays_date_varies'] = 'Date varies';
 $txt['every_year'] = 'Every Year';
 
 ?>
\ No newline at end of file
diff --git a/Sources/Actions/Admin/Calendar.php b/Sources/Actions/Admin/Calendar.php
index f0ea3ba846..846c0bc477 100644
--- a/Sources/Actions/Admin/Calendar.php
+++ b/Sources/Actions/Admin/Calendar.php
@@ -19,8 +19,8 @@
 
 use SMF\Actions\ActionInterface;
 use SMF\Actions\BackwardCompatibility;
-use SMF\Actions\Calendar as Cal;
 use SMF\Board;
+use SMF\Calendar\Holiday;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
 use SMF\IntegrationHook;
@@ -30,6 +30,8 @@
 use SMF\SecurityToken;
 use SMF\Theme;
 use SMF\Time;
+use SMF\TimeInterval;
+use SMF\TimeZone;
 use SMF\User;
 use SMF\Utils;
 
@@ -108,10 +110,8 @@ public function holidays(): void
 			SecurityToken::validate('admin-mc');
 
 			foreach ($_REQUEST['holiday'] as $id => $value) {
-				$_REQUEST['holiday'][$id] = (int) $id;
+				Holiday::remove((int) $id);
 			}
-
-			Cal::removeHolidays($_REQUEST['holiday']);
 		}
 
 		SecurityToken::create('admin-mc');
@@ -122,12 +122,10 @@ public function holidays(): void
 			'base_href' => Config::$scripturl . '?action=admin;area=managecalendar;sa=holidays',
 			'default_sort_col' => 'name',
 			'get_items' => [
-				'file' => Config::$sourcedir . '/Actions/Calendar.php',
-				'function' => 'SMF\\Actions\\Calendar::list_getHolidays',
+				'function' => 'SMF\\Calendar\\Holiday::list',
 			],
 			'get_count' => [
-				'file' => Config::$sourcedir . '/Actions/Calendar.php',
-				'function' => 'SMF\\Actions\\Calendar::list_getNumHolidays',
+				'function' => 'SMF\\Calendar\\Holiday::count',
 			],
 			'no_items_label' => Lang::$txt['holidays_no_entries'],
 			'columns' => [
@@ -139,14 +137,14 @@ public function holidays(): void
 						'sprintf' => [
 							'format' => '<a href="' . Config::$scripturl . '?action=admin;area=managecalendar;sa=editholiday;holiday=%1$d">%2$s</a>',
 							'params' => [
-								'id_holiday' => false,
+								'id' => false,
 								'title' => false,
 							],
 						],
 					],
 					'sort' => [
-						'default' => 'title ASC, event_date ASC',
-						'reverse' => 'title DESC, event_date ASC',
+						'default' => 'cal.title ASC, cal.start_date ASC',
+						'reverse' => 'cal.title DESC, cal.start_date ASC',
 					],
 				],
 				'date' => [
@@ -154,17 +152,35 @@ public function holidays(): void
 						'value' => Lang::$txt['date'],
 					],
 					'data' => [
-						'function' => function ($rowData) {
-							// Recurring every year or just a single year?
-							$year = $rowData['year'] == '1004' ? sprintf('(%1$s)', Lang::$txt['every_year']) : $rowData['year'];
-
-							// Construct the date.
-							return sprintf('%1$d %2$s %3$s', $rowData['day'], Lang::$txt['months'][(int) $rowData['month']], $year);
+						'function' => function ($event) {
+							$rrule = $event->recurrence_iterator->getRRule();
+
+							if (
+								!empty($event->special_rrule)
+								|| !empty($rrule->bymonth)
+								|| !empty($rrule->byweekno)
+								|| !empty($rrule->byyearday)
+								|| !empty($rrule->bymonthday)
+								|| !empty($rrule->byday)
+								|| !empty($rrule->byhour)
+								|| !empty($rrule->byminute)
+								|| !empty($rrule->bysecond)
+								|| !empty($rrule->bysetpos)
+								|| $event->recurrence_iterator->getRDates() !== []
+							) {
+								return Lang::$txt['holidays_date_varies'];
+							}
+
+							if (isset($rrule->count) && $rrule->count === 1) {
+								return $event->start->format(Time::getDateFormat());
+							}
+
+							return $event->start->format(Time::getShortDateFormat());
 						},
 					],
 					'sort' => [
-						'default' => 'event_date',
-						'reverse' => 'event_date DESC',
+						'default' => 'cal.start_date',
+						'reverse' => 'cal.start_date DESC',
 					],
 				],
 				'check' => [
@@ -176,7 +192,7 @@ public function holidays(): void
 						'sprintf' => [
 							'format' => '<input type="checkbox" name="holiday[%1$d]">',
 							'params' => [
-								'id_holiday' => false,
+								'id' => false,
 							],
 						],
 						'class' => 'centercol',
@@ -228,51 +244,26 @@ public function edit(): void
 		}
 
 		// Submitting?
-		if (isset($_POST[Utils::$context['session_var']]) && (isset($_REQUEST['delete']) || $_REQUEST['title'] != '')) {
+		if (isset($_POST[Utils::$context['session_var']]) && (isset($_REQUEST['delete']) || ($_REQUEST['evtitle'] ?? '') != '')) {
 			User::$me->checkSession();
 			SecurityToken::validate('admin-eh');
 
-			// Not too long good sir?
-			$_REQUEST['title'] = Utils::entitySubstr(Utils::normalize($_REQUEST['title']), 0, 60);
-			$_REQUEST['holiday'] = isset($_REQUEST['holiday']) ? (int) $_REQUEST['holiday'] : 0;
-
-			if (isset($_REQUEST['delete'])) {
-				Db::$db->query(
-					'',
-					'DELETE FROM {db_prefix}calendar_holidays
-					WHERE id_holiday = {int:selected_holiday}',
-					[
-						'selected_holiday' => $_REQUEST['holiday'],
-					],
-				);
+			$_REQUEST['holiday'] = isset($_REQUEST['holiday']) ? (int) $_REQUEST['holiday'] : -1;
+
+			if ($_REQUEST['holiday'] === -1) {
+				$eventOptions = [
+					'title' => Utils::entitySubstr($_REQUEST['evtitle'], 0, 100),
+					'location' => Utils::entitySubstr($_REQUEST['event_location'], 0, 255),
+				];
+				Holiday::create($eventOptions);
+			} elseif (isset($_REQUEST['delete'])) {
+				Holiday::remove($_REQUEST['holiday']);
 			} else {
-				$date = Time::strftime($_REQUEST['year'] <= 1004 ? '1004-%m-%d' : '%Y-%m-%d', mktime(0, 0, 0, (int) $_REQUEST['month'], (int) $_REQUEST['day'], (int) $_REQUEST['year']));
-
-				if (isset($_REQUEST['edit'])) {
-					Db::$db->query(
-						'',
-						'UPDATE {db_prefix}calendar_holidays
-						SET event_date = {date:holiday_date}, title = {string:holiday_title}
-						WHERE id_holiday = {int:selected_holiday}',
-						[
-							'holiday_date' => $date,
-							'selected_holiday' => $_REQUEST['holiday'],
-							'holiday_title' => $_REQUEST['title'],
-						],
-					);
-				} else {
-					Db::$db->insert(
-						'',
-						'{db_prefix}calendar_holidays',
-						[
-							'event_date' => 'date', 'title' => 'string-60',
-						],
-						[
-							$date, $_REQUEST['title'],
-						],
-						['id_holiday'],
-					);
-				}
+				$eventOptions = [
+					'title' => Utils::entitySubstr($_REQUEST['evtitle'], 0, 100),
+					'location' => Utils::entitySubstr($_REQUEST['event_location'], 0, 255),
+				];
+				Holiday::modify($_REQUEST['holiday'], $eventOptions);
 			}
 
 			Config::updateModSettings([
@@ -285,43 +276,30 @@ public function edit(): void
 
 		SecurityToken::create('admin-eh');
 
-		// Default states...
 		if (Utils::$context['is_new']) {
-			Utils::$context['holiday'] = [
-				'id' => 0,
-				'day' => date('d'),
-				'month' => date('m'),
-				'year' => '0000',
-				'title' => '',
-			];
+			Utils::$context['event'] = new Holiday(-1, ['rrule' => 'FREQ=YEARLY']);
+		} else {
+			Utils::$context['event'] = current(Holiday::load($_REQUEST['holiday']));
 		}
-		// If it's not new load the data.
-		else {
-			$request = Db::$db->query(
-				'',
-				'SELECT id_holiday, YEAR(event_date) AS year, MONTH(event_date) AS month, DAYOFMONTH(event_date) AS day, title
-				FROM {db_prefix}calendar_holidays
-				WHERE id_holiday = {int:selected_holiday}
-				LIMIT 1',
-				[
-					'selected_holiday' => $_REQUEST['holiday'],
-				],
-			);
 
-			while ($row = Db::$db->fetch_assoc($request)) {
-				Utils::$context['holiday'] = [
-					'id' => $row['id_holiday'],
-					'day' => $row['day'],
-					'month' => $row['month'],
-					'year' => $row['year'] <= 4 ? 0 : $row['year'],
-					'title' => $row['title'],
-				];
-			}
-			Db::$db->free_result($request);
+		Utils::$context['event']->selected_occurrence = Utils::$context['event']->getFirstOccurrence();
+
+		// An all day event? Set up some nice defaults in case the user wants to change that
+		if (Utils::$context['event']->allday == true) {
+			Utils::$context['event']->selected_occurrence->tz = User::getTimezone();
+			Utils::$context['event']->selected_occurrence->start->modify(Time::create('now')->format('%H:%M:%S'));
+			Utils::$context['event']->selected_occurrence->duration = new TimeInterval('PT1H');
 		}
 
-		// Last day for the drop down?
-		Utils::$context['holiday']['last_day'] = (int) Time::strftime('%d', mktime(0, 0, 0, Utils::$context['holiday']['month'] == 12 ? 1 : (int) Utils::$context['holiday']['month'] + 1, 0, Utils::$context['holiday']['month'] == 12 ? (int) Utils::$context['holiday']['year'] + 1 : (int) Utils::$context['holiday']['year']));
+		// Need this so the user can select a timezone for the event.
+		Utils::$context['all_timezones'] = TimeZone::list(Utils::$context['event']->start_datetime);
+
+		// If the event's timezone is not in SMF's standard list of time zones, try to fix it.
+		Utils::$context['event']->selected_occurrence->fixTimezone();
+
+		Theme::loadTemplate('EventEditor');
+		Theme::addJavaScriptVar('monthly_byday_items', count(Utils::$context['event']->byday_items) - 1);
+		Theme::loadJavaScriptFile('event.js', ['defer' => true], 'smf_event');
 	}
 
 	/**
diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index d30e7d0943..ac9cb9a29f 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -19,6 +19,7 @@
 use SMF\BrowserDetector;
 use SMF\Cache\CacheApi;
 use SMF\Calendar\Event;
+use SMF\Calendar\Holiday;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
 use SMF\ErrorHandler;
@@ -799,42 +800,12 @@ public static function getEventRange(string $low_date, string $high_date, bool $
 	 */
 	public static function getHolidayRange(string $low_date, string $high_date): array
 	{
-		// Get the lowest and highest dates for "all years".
-		if (substr($low_date, 0, 4) != substr($high_date, 0, 4)) {
-			$allyear_part = 'event_date BETWEEN {date:all_year_low} AND {date:all_year_dec}
-				OR event_date BETWEEN {date:all_year_jan} AND {date:all_year_high}';
-		} else {
-			$allyear_part = 'event_date BETWEEN {date:all_year_low} AND {date:all_year_high}';
-		}
-
-		// Find some holidays... ;).
-		$result = Db::$db->query(
-			'',
-			'SELECT event_date, YEAR(event_date) AS year, title
-			FROM {db_prefix}calendar_holidays
-			WHERE event_date BETWEEN {date:low_date} AND {date:high_date}
-				OR ' . $allyear_part,
-			[
-				'low_date' => $low_date,
-				'high_date' => $high_date,
-				'all_year_low' => '1004' . substr($low_date, 4),
-				'all_year_high' => '1004' . substr($high_date, 4),
-				'all_year_jan' => '1004-01-01',
-				'all_year_dec' => '1004-12-31',
-			],
-		);
 		$holidays = [];
+		$high_date = (new \DateTimeImmutable($high_date . ' +1 day'))->format('Y-m-d');
 
-		while ($row = Db::$db->fetch_assoc($result)) {
-			if (substr($low_date, 0, 4) != substr($high_date, 0, 4)) {
-				$event_year = substr($row['event_date'], 5) < substr($high_date, 5) ? substr($high_date, 0, 4) : substr($low_date, 0, 4);
-			} else {
-				$event_year = substr($low_date, 0, 4);
-			}
-
-			$holidays[$event_year . substr($row['event_date'], 4)][] = $row['title'];
+		foreach(Holiday::getOccurrencesInRange($low_date, $high_date) as $occurrence) {
+			$holidays[$occurrence->start->format('Y-m-d')][] = $occurrence;
 		}
-		Db::$db->free_result($result);
 
 		ksort($holidays);
 
@@ -1233,7 +1204,7 @@ public static function getCalendarList(string $start_date, string $end_date, arr
 		foreach (['birthdays', 'holidays'] as $type) {
 			foreach ($calendarGrid[$type] as $date => $date_content) {
 				// Make sure to apply no offsets
-				$date_local = preg_replace('~(?<=\s)0+(\d)~', '$1', trim(Time::create($date)->format($date_format), " \t\n\r\0\x0B,./;:<>()[]{}\\|-_=+"));
+				$date_local = Time::create($date)->format($date_format);
 
 				$calendarGrid[$type][$date]['date_local'] = $date_local;
 			}
@@ -1534,76 +1505,15 @@ public static function getEventPoster(int $event_id): int|bool
 	}
 
 	/**
-	 * Gets all of the holidays for the listing
-	 *
-	 * @param int $start The item to start with (for pagination purposes)
-	 * @param int $items_per_page How many items to show on each page
-	 * @param string $sort A string indicating how to sort the results
-	 * @return array An array of holidays, each of which is an array containing the id, year, month, day and title of the holiday
-	 */
-	public static function list_getHolidays(int $start, int $items_per_page, string $sort): array
-	{
-		$request = Db::$db->query(
-			'',
-			'SELECT id_holiday, YEAR(event_date) AS year, MONTH(event_date) AS month, DAYOFMONTH(event_date) AS day, title
-			FROM {db_prefix}calendar_holidays
-			ORDER BY {raw:sort}
-			LIMIT {int:start}, {int:max}',
-			[
-				'sort' => $sort,
-				'start' => $start,
-				'max' => $items_per_page,
-			],
-		);
-		$holidays = [];
-
-		while ($row = Db::$db->fetch_assoc($request)) {
-			$holidays[] = $row;
-		}
-		Db::$db->free_result($request);
-
-		return $holidays;
-	}
-
-	/**
-	 * Helper function to get the total number of holidays
+	 * Backward compatibility wrapper for Holiday::remove().
 	 *
-	 * @return int The total number of holidays
-	 */
-	public static function list_getNumHolidays(): int
-	{
-		$request = Db::$db->query(
-			'',
-			'SELECT COUNT(*)
-			FROM {db_prefix}calendar_holidays',
-			[
-			],
-		);
-		list($num_items) = Db::$db->fetch_row($request);
-		Db::$db->free_result($request);
-
-		return (int) $num_items;
-	}
-
-	/**
-	 * Remove a holiday from the calendar
-	 *
-	 * @param array $holiday_ids An array of IDs of holidays to delete
+	 * @param array $holiday_ids An array of IDs of holidays to delete.
 	 */
 	public static function removeHolidays(array $holiday_ids): void
 	{
-		Db::$db->query(
-			'',
-			'DELETE FROM {db_prefix}calendar_holidays
-			WHERE id_holiday IN ({array_int:id_holiday})',
-			[
-				'id_holiday' => $holiday_ids,
-			],
-		);
-
-		Config::updateModSettings([
-			'calendar_updated' => time(),
-		]);
+		foreach ($holiday_ids as $holiday_id) {
+			Holiday::remove($holiday_id);
+		}
 	}
 
 	/**
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index 7ef390ae88..6d9b488c6b 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -31,7 +31,7 @@
 use SMF\Uuid;
 
 /**
- * Represents a (possibly recurring) calendar event, birthday, or holiday.
+ * Represents a (possibly recurring) calendar event.
  *
  * @todo Add support for editing specific instances as exceptions to the RRule.
  */
@@ -44,7 +44,7 @@ class Event implements \ArrayAccess
 	 *****************/
 
 	public const TYPE_EVENT = 0;
-	public const TYPE_HOLIDAY = 1; // Not yet implemented.
+	public const TYPE_HOLIDAY = 1;
 	public const TYPE_BIRTHDAY = 2; // Not yet implemented.
 
 	/*******************
@@ -231,10 +231,55 @@ class Event implements \ArrayAccess
 	 */
 	public array $byday_items = [];
 
+	/**
+	 * @var array
+	 *
+	 * Used to override the usual handling of RRule values.
+	 *
+	 * Value is an array containing a 'base' and a 'modifier'.
+	 * The 'base' is one of the keys from self:special_rrules.
+	 * The 'modifier' is a + or - sign followed by a duration string, or null.
+	 */
+	public array $special_rrule;
+
 	/**************************
 	 * Public static properties
 	 **************************/
 
+	/**
+	 * @var array
+	 *
+	 * Known special values for the 'rrule' field. These are used when dealing
+	 * with recurring events whose recurrence patterns cannot be expressed using
+	 * RFC 5545's notation.
+	 *
+	 * Keys are special strings that may be found in the 'rrule' field in the
+	 * database.
+	 *
+	 * Values are arrays containing the following options:
+	 *
+	 * 'txt_key' indicates a Lang::$txt string for this special RRule.
+	 * If not set, defaults to 'calendar_repeat_special'.
+	 *
+	 * 'group' indicates special RRules that should be listed as alternatives
+	 * to each other. For example, 'group' => ['EASTER_W', 'EASTER_E'] means
+	 * that the Western and Eastern ways of calculating the date of Easter
+	 * should be listed as the two options for Easter. If not set, defaults to
+	 * a list containing only the special string itself.
+	 */
+	public static array $special_rrules = [
+		// Easter (Western)
+		'EASTER_W' => [
+			'txt_key' => 'calendar_repeat_easter_w',
+			'group' => ['EASTER_W', 'EASTER_E'],
+		],
+		// Easter (Eastern)
+		'EASTER_E' => [
+			'txt_key' => 'calendar_repeat_easter_e',
+			'group' => ['EASTER_W', 'EASTER_E'],
+		],
+	];
+
 	/**
 	 * @var array
 	 *
@@ -246,6 +291,14 @@ class Event implements \ArrayAccess
 	 * Internal properties
 	 *********************/
 
+	/**
+	 * @var bool
+	 *
+	 * Whether this event is enabled.
+	 * Always true for events and birthdays. May be false for holidays.
+	 */
+	protected bool $enabled = true;
+
 	/**
 	 * @var bool
 	 *
@@ -325,6 +378,11 @@ public function __construct(int $id = 0, array $props = [])
 		// Just in case someone passes -2 or something.
 		$id = max(-1, $id);
 
+		// Give mods access early in the process.
+		IntegrationHook::call('integrate_construct_event', [$id, &$props]);
+
+		$this->handleSpecialRRule($id, $props);
+
 		switch ($id) {
 			// Preparing default data to show in the calendar posting form.
 			case -1:
@@ -508,6 +566,9 @@ function ($a, $b) {
 		} else {
 			$this->byday_items[] = ['num' => 0, 'name' => ''];
 		}
+
+		// Give mods access again at the end of the process.
+		IntegrationHook::call('integrate_constructed_event', [$this]);
 	}
 
 	/**
@@ -547,6 +608,8 @@ public function save(): void
 			$recurrence_end = new Time('9999-12-31');
 		}
 
+		$rrule = !empty($this->special_rrule) ? implode('', $this->special_rrule) : (string) $this->recurrence_iterator->getRRule();
+
 		// Saving a new event.
 		if (!$is_edit) {
 			$columns = [
@@ -563,6 +626,7 @@ public function save(): void
 				'exdates' => 'string',
 				'uid' => 'string-255',
 				'type' => 'int',
+				'enabled' => 'int',
 			];
 
 			$params = [
@@ -574,11 +638,12 @@ public function save(): void
 				$this->member,
 				Utils::truncate($this->location, 255),
 				(string) $this->duration,
-				(string) ($this->recurrence_iterator->getRRule()),
+				$rrule,
 				implode(',', $this->recurrence_iterator->getRDates()),
 				implode(',', $this->recurrence_iterator->getExDates()),
 				$this->uid,
 				$this->type,
+				(int) $this->enabled,
 			];
 
 			if (!$this->allday) {
@@ -621,6 +686,7 @@ public function save(): void
 				'exdates = {string:exdates}',
 				'uid = {string:uid}',
 				'type = {int:type}',
+				'enabled = {int:enabled}',
 			];
 
 			$params = [
@@ -632,11 +698,12 @@ public function save(): void
 				'id_board' => $this->board,
 				'id_topic' => $this->topic,
 				'duration' => (string) $this->duration,
-				'rrule' => (string) ($this->recurrence_iterator->getRRule()),
+				'rrule' => $rrule,
 				'rdates' => implode(',', $this->recurrence_iterator->getRDates()),
 				'exdates' => implode(',', $this->recurrence_iterator->getExDates()),
 				'uid' => $this->uid,
 				'type' => $this->type,
+				'enabled' => (int) $this->enabled,
 			];
 
 			if ($this->allday) {
@@ -1171,6 +1238,11 @@ public function __get(string $prop): mixed
 				break;
 
 			case 'rrule_preset':
+				if (!empty($this->special_rrule)) {
+					$value = $this->special_rrule['base'];
+					break;
+				}
+
 				if (isset($this->recurrence_iterator)) {
 					$value = $this->recurrence_iterator->getRRule();
 				} else {
@@ -1642,6 +1714,79 @@ public static function remove(int $id): void
 	 * Internal methods
 	 ******************/
 
+	/**
+	 * Some holidays have special values in the 'rrule' field in the database.
+	 * This method detects them and does whatever special handling is necessary.
+	 */
+	protected function handleSpecialRRule($id, &$props): void
+	{
+		if (!isset($props['rrule'])) {
+			return;
+		}
+
+		list($base, $modifier) = array_pad(preg_split('/(?=[+-]P\w+$)/', $props['rrule']), 2, '');
+
+		// Do nothing with unrecognized ones.
+		if (!isset(self::$special_rrules[$base])) {
+			return;
+		}
+
+		// Record what the special RRule value is.
+		$this->special_rrule = compact('base', 'modifier');
+
+		// Special RRules get special handling in the rrule_presets menu in the UI.
+		if (empty(self::$special_rrules[$base]['group'])) {
+			self::$special_rrules[$base]['group'] = [$base];
+		}
+
+		foreach (self::$special_rrules[$base]['group'] as $special_rrule) {
+			$props['rrule_presets'][Lang::$txt['calendar_repeat_special']][$special_rrule] = Lang::$txt['calendar_repeat_rrule_presets'][self::$special_rrules[$special_rrule]['txt_key']] ?? Lang::$txt[self::$special_rrules[$special_rrule]['txt_key']] ?? Lang::$txt['calendar_repeat_rrule_presets'][$special_rrule] ?? Lang::$txt[$special_rrule] ?? $special_rrule;
+		}
+
+		switch ($base) {
+			case 'EASTER_W':
+			case 'EASTER_E':
+				// For Easter, we manually calculate the date for each visible year,
+				// then save that date as an RDate, and then update the RRule to
+				// pretend that it is otherwise a one day occurrence.
+				$low = isset($props['view_start']) ? Time::createFromInterface($props['view_start']) : new Time('first day of this month, midnight');
+				$high = $props['view_end'] ?? new Time('first day of next month, midnight');
+
+				while ($low->format('Y') <= $high->format('Y')) {
+					$rdate = new Time(implode('-', Holiday::easter((int) $low->format('Y'), $base === 'EASTER_E' ? 'Eastern' : 'Western')));
+
+					if ($low->getTimestamp() >= $rdate->getTimestamp()) {
+						$rdate = new Time(implode('-', Holiday::easter((int) $low->format('Y') + 1, $base === 'EASTER_E' ? 'Eastern' : 'Western')));
+					}
+
+					if (!empty($modifier)) {
+						if (str_starts_with($modifier, '-')) {
+							$rdate->sub(new \DateInterval(substr($modifier, 1)));
+						} else {
+							$rdate->add(new \DateInterval(substr($modifier, 1)));
+						}
+					}
+
+					$props['rdates'][] = $rdate->format('Ymd');
+
+					$low->modify('+1 year');
+				}
+
+				$props['rrule'] = 'FREQ=YEARLY;COUNT=1';
+				break;
+
+			default:
+				// Allow mods to handle other holidays with complex rules.
+				IntegrationHook::call('integrate_handle_special_rrule', [$id, &$props]);
+
+				// Ensure the RRule is valid.
+				if (!str_starts_with($props['rrule'], 'FREQ=')) {
+					$props['rrule'] = 'FREQ=YEARLY;COUNT=1';
+				}
+				break;
+		}
+	}
+
 	/**
 	 * Sets $this->recurrence_iterator, but only if all necessary properties
 	 * have been set.
@@ -1681,6 +1826,7 @@ protected function createRecurrenceIterator(): bool
 	}
 
 	/**
+	 * Creates an EventOccurrence object for the given start time.
 	 *
 	 * @param \DateTimeInterface $start The start time.
 	 * @param ?TimeInterval $duration Custom duration for this occurrence. If
@@ -2005,6 +2151,11 @@ protected static function setRequestedRDatesAndExDates(Event $event): void
 			$event->addOccurrence(new \DateTimeImmutable($exdate));
 		}
 
+		// Events with special RRules can't have RDates or ExDates.
+		if (!empty($event->special_rrule)) {
+			return;
+		}
+
 		// Add all the RDates and ExDates.
 		foreach (['RDATE', 'EXDATE'] as $date_type) {
 			if (!isset($_REQUEST[$date_type . '_date'])) {
diff --git a/Sources/Calendar/Holiday.php b/Sources/Calendar/Holiday.php
new file mode 100644
index 0000000000..05fdb2f88a
--- /dev/null
+++ b/Sources/Calendar/Holiday.php
@@ -0,0 +1,569 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF\Calendar;
+
+use SMF\Db\DatabaseApi as Db;
+use SMF\Lang;
+use SMF\Theme;
+use SMF\Time;
+use SMF\Utils;
+
+/**
+ * Represents a holiday.
+ */
+class Holiday extends Event
+{
+	/*******************
+	 * Public properties
+	 *******************/
+
+	/**
+	 * @var int
+	 *
+	 * This event's type.
+	 * Value must be one of the parent class's TYPE_* constants.
+	 */
+	public int $type = self::TYPE_HOLIDAY;
+
+	/**
+	 * @var bool
+	 *
+	 * Whether this holiday is enabled.
+	 */
+	public bool $enabled = true;
+
+	/****************
+	 * Public methods
+	 ****************/
+
+	/**
+	 * Constructor.
+	 *
+	 * @param int $id The ID number of the event.
+	 * @param array $props Properties to set for this event.
+	 * @return object An instance of this class.
+	 */
+	public function __construct(int $id = 0, array $props = [])
+	{
+		$props['type'] = self::TYPE_HOLIDAY;
+
+		parent::__construct($id, $props);
+
+		// For new events, provide all known special RRule options.
+		if ($this->id <= 0) {
+			foreach (self::$special_rrules as $special_rrule => $info) {
+				$this->rrule_presets[Lang::$txt['calendar_repeat_special']][$special_rrule] = Lang::$txt['calendar_repeat_rrule_presets'][$info['txt_key']] ?? Lang::$txt[$info['txt_key']] ?? Lang::$txt['calendar_repeat_rrule_presets'][$special_rrule] ?? Lang::$txt[$special_rrule] ?? $special_rrule;
+			}
+
+			Theme::addJavaScriptVar('special_rrules', array_keys(self::$special_rrules), true);
+		}
+	}
+
+	/**
+	 * Sets custom properties.
+	 *
+	 * @param string $prop The property name.
+	 * @param mixed $value The value to set.
+	 */
+	public function __set(string $prop, $value): void
+	{
+		parent::__set($prop, $value);
+	}
+
+	/**
+	 * Gets custom property values.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __get(string $prop): mixed
+	{
+		return parent::__get($prop);
+	}
+
+	/**
+	 * Checks whether a custom property has been set.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __isset(string $prop): bool
+	{
+		return parent::__isset($prop);
+	}
+
+	/**
+	 * Unsets custom properties.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __unset(string $prop): void
+	{
+		parent::__unset($prop);
+	}
+
+	/***********************
+	 * Public static methods
+	 ***********************/
+
+	/**
+	 * Loads holidays by ID number.
+	 *
+	 * @param int|array $id ID number of the holiday event.
+	 * @param bool $is_topic Ignored.
+	 * @param bool $use_permissions Ignored.
+	 * @return array Instances of this class for the loaded events.
+	 */
+	public static function load(int $id, bool $is_topic = false, bool $use_permissions = true): array
+	{
+		if ($id <= 0) {
+			return [];
+		}
+
+		if (isset(self::$loaded[$id])) {
+			return [self::$loaded[$id]];
+		}
+
+		$loaded = [];
+
+		$selects = [
+			'cal.*',
+		];
+		$where = ['cal.id_event = {int:id}'];
+		$params = [
+			'id' => $id,
+		];
+
+		foreach(self::queryData($selects, $params, [], $where) as $row) {
+			$id = (int) $row['id_event'];
+			$row['use_permissions'] = false;
+
+			if (!empty($row['rdates'])) {
+				$max_rdate = max($row['rdates']);
+				$row['view_end'] = (new \DateTimeImmutable(substr($max_rdate, 0, strcspn($max_rdate, '/'))))->modify('+1 day');
+			}
+
+			$loaded[] = new self($id, $row);
+		}
+
+		return $loaded;
+	}
+
+	/**
+	 * Generator that yields instances of this class.
+	 *
+	 * @param string $low_date The low end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param string $high_date The high end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param bool $only_enabled If true, only show enabled holidays.
+	 * @param array $query_customizations Customizations to the SQL query.
+	 * @return Generator<Holiday> Iterating over result gives Holiday instances.
+	 */
+	public static function get(string $low_date, string $high_date, bool $only_enabled = true, array $query_customizations = []): \Generator
+	{
+		$low_date = new \DateTimeImmutable(!empty($low_date) ? $low_date : 'first day of this month, midnight');
+		$high_date = new \DateTimeImmutable(!empty($high_date) ? $high_date : 'first day of next month, midnight');
+
+		$selects = $query_customizations['selects'] ?? [
+			'cal.*',
+		];
+		$joins = $query_customizations['joins'] ?? [];
+		$where = $query_customizations['where'] ?? [
+			'type = {int:type}',
+		];
+		$order = $query_customizations['order'] ?? ['cal.id_event'];
+		$group = $query_customizations['group'] ?? [];
+		$limit = $query_customizations['limit'] ?? 0;
+		$params = $query_customizations['params'] ?? [
+			'type' => self::TYPE_HOLIDAY,
+		];
+
+		if ($only_enabled) {
+			$where[] = 'enabled = {int:enabled}';
+			$params['enabled'] = 1;
+		}
+
+		// Filter by month (if we are showing 11 or fewer months).
+		if ($high_date->diff($low_date)->days < 335) {
+			$months = [];
+
+			$temp = \DateTime::createFromImmutable($low_date);
+
+			while ($temp->format('Ym') <= $high_date->format('Ym')) {
+				$months[] = (int) $temp->format('m');
+				$temp->modify('+1 month');
+			}
+
+			$months = array_unique($months);
+
+			switch (Db::$db->title) {
+				case POSTGRE_TITLE:
+					$where[] = 'EXTRACT(MONTH FROM cal.start_date) IN ({array_int:months}) OR cal.rrule ~ {string:bymonth_regex}' . (array_intersect([3, 4], $months) !== [] ? ' OR cal.rrule IN ({array_string:easter})' : '');
+					break;
+
+				default:
+					$where[] = 'MONTH(cal.start_date) IN ({array_int:months}) OR REGEXP_LIKE(cal.rrule, {string:bymonth_regex})' . (array_intersect([3, 4], $months) !== [] ? ' OR cal.rrule IN ({array_string:easter})' : '');
+					break;
+			}
+
+			$params['months'] = $months;
+			$params['bymonth_regex'] = 'BYMONTH=(?:(?:' . implode('|', array_diff(range(1, 12), $months)) . '),)*(' . implode('|', $months) . ')';
+			$params['easter'] = ['EASTER_W', 'EASTER_E'];
+		}
+
+		foreach(self::queryData($selects, $params, $joins, $where, $order, $group, $limit) as $row) {
+			$id = (int) $row['id_event'];
+			$row['use_permissions'] = false;
+
+			$row['view_start'] = $low_date;
+			$row['view_end'] = $high_date;
+
+			yield (new self($id, $row));
+		}
+	}
+
+	/**
+	 * Returns Holiday instances for the holidays recorded in the database.
+	 *
+	 * @param int $start The item to start with (for pagination purposes)
+	 * @param int $items_per_page How many items to show on each page
+	 * @param string $sort A string indicating how to sort the results
+	 * @return array An array of Holiday instances.
+	 */
+	public static function list(int $start, int $items_per_page, string $sort = 'cal.title ASC, cal.start_date ASC'): array
+	{
+		$loaded = [];
+
+		$selects = ['cal.*'];
+		$joins = [];
+		$where = ['type = {int:type}'];
+		$order = [$sort];
+		$group = [];
+		$limit = implode(', ', [$start, $items_per_page]);
+		$params = ['type' => self::TYPE_HOLIDAY];
+
+		foreach(self::queryData($selects, $params, $joins, $where, $order, $group, $limit) as $row) {
+			$id = (int) $row['id_event'];
+			$row['use_permissions'] = false;
+
+			if (!empty($row['rdates'])) {
+				$max_rdate = max($row['rdates']);
+				$row['view_end'] = (new \DateTimeImmutable(substr($max_rdate, 0, strcspn($max_rdate, '/'))))->modify('+1 day');
+			}
+
+			$loaded[] = new self($id, $row);
+		}
+
+		return $loaded;
+	}
+
+	/**
+	 * Gets the total number of holidays recorded in the database.
+	 *
+	 * @return int The total number of known holidays.
+	 */
+	public static function count(): int
+	{
+		$request = Db::$db->query(
+			'',
+			'SELECT COUNT(*)
+			FROM {db_prefix}calendar
+			WHERE type = {int:type}',
+			[
+				'type' => self::TYPE_HOLIDAY,
+			],
+		);
+		list($num_items) = Db::$db->fetch_row($request);
+		Db::$db->free_result($request);
+
+		return (int) $num_items;
+	}
+
+	/**
+	 * Gets events within the given date range, and returns a generator that
+	 * yields all occurrences of those events within that range.
+	 *
+	 * @param string $low_date The low end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param string $high_date The high end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param bool $only_enabled If true, only show enabled holidays.
+	 * @param array $query_customizations Customizations to the SQL query.
+	 * @return Generator<EventOccurrence> Iterating over result gives
+	 *    EventOccurrence instances.
+	 */
+	public static function getOccurrencesInRange(string $low_date, string $high_date, bool $only_enabled = true, array $query_customizations = []): \Generator
+	{
+		foreach (self::get($low_date, $high_date, $only_enabled, $query_customizations) as $event) {
+			foreach ($event->getAllVisibleOccurrences() as $occurrence) {
+				yield $occurrence;
+			}
+		}
+	}
+
+	/**
+	 * Creates a holiday and saves it to the database.
+	 *
+	 * Does not check permissions.
+	 *
+	 * @param array $eventOptions Event data ('title', 'start_date', etc.)
+	 */
+	public static function create(array $eventOptions): void
+	{
+		// Sanitize the title and location.
+		foreach (['title', 'location'] as $key) {
+			$eventOptions[$key] = Utils::htmlspecialchars($eventOptions[$key] ?? '', ENT_QUOTES);
+		}
+
+		$eventOptions['type'] = self::TYPE_HOLIDAY;
+
+		// Set the start and end dates.
+		self::setRequestedStartAndDuration($eventOptions);
+
+		$eventOptions['view_start'] = isset($eventOptions['start']) ? \DateTimeImmutable::createFromInterface($eventOptions['start']) : new \DateTimeImmutable('now');
+		$eventOptions['view_end'] = $eventOptions['view_start']->add(new \DateInterval('P1D'));
+
+		self::setRequestedRRule($eventOptions);
+
+		$event = new self(0, $eventOptions);
+
+		self::setRequestedRDatesAndExDates($event);
+
+		$event->save();
+	}
+
+	/**
+	 * Modifies a holiday.
+	 *
+	 * Does not check permissions.
+	 *
+	 * @param int $id The ID of the event.
+	 * @param array $eventOptions An array of event information.
+	 */
+	public static function modify(int $id, array &$eventOptions): void
+	{
+		list($event) = self::load($id);
+
+		// Double check that the loaded event is in fact a holiday.
+		if (!$event->type === self::TYPE_HOLIDAY) {
+			return;
+		}
+
+		// Sanitize the title and location.
+		foreach (['title', 'location'] as $prop) {
+			$eventOptions[$prop] = Utils::htmlspecialchars($eventOptions[$prop] ?? '', ENT_QUOTES);
+		}
+
+		foreach (['allday', 'start_date', 'end_date', 'start_time', 'end_time', 'timezone'] as $prop) {
+			$eventOptions[$prop] = $eventOptions[$prop] ?? $_POST[$prop] ?? $event->{$prop} ?? null;
+		}
+
+		// Set the new start date and duration.
+		self::setRequestedStartAndDuration($eventOptions);
+
+		$eventOptions['view_start'] = isset($eventOptions['start']) ? \DateTimeImmutable::createFromInterface($eventOptions['start']) : new \DateTimeImmutable('now');
+		$eventOptions['view_end'] = $eventOptions['view_start']->add(new \DateInterval('P1D'));
+
+		if (!empty($event->special_rrule)) {
+			unset(
+				$eventOptions['start_date'],
+				$eventOptions['end_date'],
+				$eventOptions['start_time'],
+				$eventOptions['timezone'],
+				$eventOptions['duration'],
+				$eventOptions['rrule'],
+				$eventOptions['rdates'],
+				$eventOptions['exdates'],
+			);
+
+			if (isset(self::$special_rrules[$_POST['RRULE']])) {
+				$event->special_rrule = $_POST['RRULE'];
+
+				if (in_array($event->special_rrule, ['EASTER_W', 'EASTER_E'])) {
+					$eventOptions['start_date'] = implode('-', self::easter((int) $event->start->format('Y'), $event->special_rrule === 'EASTER_E' ? 'Eastern' : 'Western'));
+				}
+			}
+		} else {
+			self::setRequestedRRule($eventOptions);
+		}
+
+		$event->set($eventOptions);
+
+		self::setRequestedRDatesAndExDates($event);
+
+		$event->save();
+	}
+
+	/**
+	 * Removes a holiday.
+	 *
+	 * Does not check permissions.
+	 *
+	 * @param int $id The event's ID.
+	 */
+	public static function remove(int $id): void
+	{
+		$event = current(self::load($id));
+
+		if ($event === false) {
+			return;
+		}
+
+		if (!$event->type === self::TYPE_HOLIDAY) {
+			return;
+		}
+
+		parent::remove($id);
+	}
+
+	/**
+	 * Computes the Western and Eastern dates of Easter for the given year.
+	 *
+	 * In the returned array:
+	 *
+	 *  - 'Western' gives the Gregorian calendar date of Easter as observed by
+	 *    Roman Catholic and Protestant Christians. This is computed using the
+	 *    Gregorian algorithm and presented as a Gregorian date.
+	 *
+	 *  - 'Eastern' gives the Gregorian calendar date of Easter as observed by
+	 *    Eastern Orthodox Christians. This is computed using the Julian
+	 *    algorithm and then converted to a Gregorian date.
+	 *
+	 *  - 'Julian' gives the same date as 'Eastern', except that it is left as a
+	 *    Julian calendar date rather than being converted to a Gregorian date.
+	 *
+	 * For years before 1583, 'Eastern' and 'Western' are the same.
+	 *
+	 * Beware that using 'Julian' to construct a \DateTime object will probably
+	 * have unexpected results. \DateTime only understands Gregorian calendar
+	 * dates.
+	 *
+	 * Instead, use 'Julian' to show dates as they were reckoned in a given
+	 * country prior to that country's adoption of the Gregorian calendar. For
+	 * example, Greece didn't adopt the Gregorian calendar until 1923, so you
+	 * can use the Julian date to show the date of Easter in 1920 the way that
+	 * Greek people would have reckoned it at the time (March 29 rather than
+	 * March 11).
+	 *
+	 * Caveats:
+	 *
+	 *  - The computation of the date of Easter was not standardized until A.D.
+	 *    325, and some regional variations persisted until approx. A.D. 664.
+	 *
+	 *  - Western Christians did not all adopt the Gregorian method of computing
+	 *    the date of Easter at the same time, which means that the observed
+	 *    date of Easter varied across regions in Western Europe for several
+	 *    centuries. Moreover, the adoption of the Gregorian calendar by a
+	 *    country as its civil calendar does not necessarily coincide with the
+	 *    adoption of the Gregorian date of Easter in that country. Choosing the
+	 *    correct computation for a particular location in a particular year
+	 *    therefore requires historical knowledge.
+	 *
+	 * @param ?int $year The year. Must be greater than 30.
+	 * @param ?string $type One of 'Western', 'Eastern', or 'Julian'. If set to
+	 *     'Western', 'Eastern', or 'Julian', only that date will be returned.
+	 *     Otherwise all three dates will be returned in an array.
+	 * @return ?array Info about the Western and/or Eastern dates for Easter,
+	 *     or null on error.
+	 */
+	public static function easter(?int $year = null, ?string $type = null): ?array
+	{
+		if (!isset($year)) {
+			$now = getdate();
+			$year = $now['year'];
+		}
+
+		if ($year <= 30) {
+			return null;
+		}
+
+		$type = ucfirst(strtolower($type));
+
+		$return = [
+			'Western' => ['year' => null, 'month' => null, 'day' => null],
+			'Eastern' => ['year' => null, 'month' => null, 'day' => null],
+			'Julian' => ['year' => null, 'month' => null, 'day' => null],
+		];
+
+		// Compute according to Julian calendar.
+		// https://en.wikipedia.org/w/index.php?title=Date_of_Easter&oldid=1124654731#Meeus's_Julian_algorithm
+		$a = $year % 4;
+		$b = $year % 7;
+		$c = $year % 19;
+		$d = (19 * $c + 15) % 30;
+		$e = (2 * $a + 4 * $b - $d + 34) % 7;
+		$f = ($d + $e + 114);
+
+		$return['Julian']['year'] = $year;
+		$return['Julian']['month'] = intdiv($f, 31);
+		$return['Julian']['day'] = $f % 31 + 1;
+
+		// Convert Julian date to Gregorian date:
+
+		// 1. Covert Julian calendar date to Julian Day number.
+		// https://en.wikipedia.org/w/index.php?title=Julian_day&oldid=996614725#Converting_Julian_calendar_date_to_Julian_Day_Number
+		$jd = 367 * $year - intdiv((7 * ($year + 5001 + intdiv(($return['Julian']['month'] - 9), 7))), 4) + intdiv((275 * $return['Julian']['month']), 9) + $return['Julian']['day'] + 1729777;
+
+		// 2. Convert Julian Day number to Gregorian date.
+		// https://en.wikipedia.org/w/index.php?title=Julian_day&oldid=996614725#Julian_or_Gregorian_calendar_from_Julian_day_number
+		$y = 4716;
+		$j = 1401;
+		$m = 2;
+		$n = 12;
+		$r = 4;
+		$p = 1461;
+		$v = 3;
+		$u = 5;
+		$s = 153;
+		$w = 2;
+		$B = 274277;
+
+		$f = $jd + $j + intdiv(intdiv(4 * $jd + $B, 146097) * 3, 4) - 38;
+
+		$e = $r * $f + $v;
+		$g = intdiv($e % $p, $r);
+		$h = $u * $g + $w;
+
+		$return['Eastern']['day'] = intdiv($h % $s, $u) + 1;
+		$return['Eastern']['month'] = ((intdiv($h, $s) + $m) % $n) + 1;
+		$return['Eastern']['year'] = intdiv($e, $p) - $y + intdiv($n + $m - $return['Eastern']['month'], $n);
+
+		// Compute according to Gregorian calendar.
+		// https://en.wikipedia.org/w/index.php?title=Date_of_Easter&oldid=1180071644#Anonymous_Gregorian_algorithm
+		if ($year > 1582) {
+			$a = $year % 19;
+			$b = intdiv($year, 100);
+			$c = $year % 100;
+			$d = intdiv($b, 4);
+			$e = $b % 4;
+			$g = intdiv((8 * $b + 13), 25);
+			$h = (19 * $a + $b - $d - $g + 15) % 30;
+			$i = intdiv($c, 4);
+			$k = $c % 4;
+			$l = (32 + 2 * $e + 2 * $i - $h - $k) % 7;
+			$m = intdiv(($a + 11 * $h + 19 * $l), 433);
+
+			$return['Western']['year'] = $year;
+			$return['Western']['month'] = intdiv(($h + $l - 7 * $m + 90), 25);
+			$return['Western']['day'] = ($h + $l - 7 * $m + 33 * $return['Western']['month'] + 19) % 32;
+		} else {
+			$return['Western'] = $return['Eastern'];
+		}
+
+		if (isset($return[$type])) {
+			return $return[$type];
+		}
+
+		return $return;
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/Sources/ServerSideIncludes.php b/Sources/ServerSideIncludes.php
index 25f71b6321..212a75a206 100644
--- a/Sources/ServerSideIncludes.php
+++ b/Sources/ServerSideIncludes.php
@@ -1937,6 +1937,8 @@ public static function todaysHolidays(string $output_method = 'echo'): ?array
 		];
 		$return = CacheApi::quickGet('calendar_index_offset_' . User::$me->time_offset, 'Actions/Calendar.php', 'SMF\\Actions\\Calendar::cache_getRecentEvents', [$eventOptions]);
 
+		$return['calendar_holidays'] = array_map(fn ($h) => $h->title, $return['calendar_holidays']);
+
 		// The self::todaysCalendar variants all use the same hook and just pass on $eventOptions so the hooked code can distinguish different cases if necessary
 		IntegrationHook::call('integrate_ssi_calendar', [&$return, $eventOptions]);
 
@@ -2023,6 +2025,8 @@ public static function todaysCalendar(string $output_method = 'echo'): array|str
 		];
 		$return = CacheApi::quickGet('calendar_index_offset_' . User::$me->time_offset, 'Actions/Calendar.php', 'SMF\\Actions\\Calendar::cache_getRecentEvents', [$eventOptions]);
 
+		$return['calendar_holidays'] = array_map(fn ($h) => $h->title, $return['calendar_holidays']);
+
 		// The self::todaysCalendar variants all use the same hook and just pass on $eventOptions so the hooked code can distinguish different cases if necessary
 		IntegrationHook::call('integrate_ssi_calendar', [&$return, $eventOptions]);
 
diff --git a/Themes/default/BoardIndex.template.php b/Themes/default/BoardIndex.template.php
index 87e11d4232..d93ae0a837 100644
--- a/Themes/default/BoardIndex.template.php
+++ b/Themes/default/BoardIndex.template.php
@@ -413,11 +413,18 @@ function template_ic_block_calendar()
 			</div>';
 
 	// Holidays like "Christmas", "Chanukah", and "We Love [Unknown] Day" :P
-	if (!empty(Utils::$context['calendar_holidays']))
+	if (!empty(Utils::$context['calendar_holidays'])) {
+		$holidays = array();
+
+		foreach (Utils::$context['calendar_holidays'] as $holiday) {
+			$holidays[] = $holiday->title . (!empty($holiday->location) ? ' (' . $holiday->location . ')' : '');
+		}
+
 		echo '
 			<p class="inline holiday">
-				<span>', Lang::$txt['calendar_prompt'], '</span> ', implode(', ', Utils::$context['calendar_holidays']), '
+				<span class="label">', Lang::$txt['calendar_prompt'], '</span> ', implode(', ', $holidays), '
 			</p>';
+	}
 
 	// People's birthdays. Like mine. And yours, I guess. Kidding.
 	if (!empty(Utils::$context['calendar_birthdays']))
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index 6170c7992c..f044a38cf9 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -205,18 +205,24 @@ function template_show_upcoming_list($grid_name)
 				<div class="windowbg">
 					<p class="inline holidays">';
 
-		$holidays = array();
+		foreach ($calendar_data['holidays'] as $date) {
+			echo '
+						<span>
+							<strong>', $date['date_local'], '</strong>: ';
 
-		foreach ($calendar_data['holidays'] as $date)
-		{
-			$date_local = $date['date_local'];
 			unset($date['date_local']);
 
-			foreach ($date as $holiday)
-				$holidays[] = $holiday . ' (' . $date_local . ')';
-		}
+			$holidays = array();
+
+			foreach ($date as $holiday) {
+				$holidays[] = $holiday->title . (!empty($holiday->location) ? ' (' . $holiday->location . ')' : '');
+			}
 
-		echo implode(', ', $holidays);
+			echo implode(', ', $holidays);
+
+			echo '.
+						</span>';
+		}
 
 		echo '
 					</p>
@@ -368,7 +374,29 @@ function template_show_month_grid($grid_name, $is_mini = false)
 					if (!empty($day['holidays']))
 						echo '
 						<div class="smalltext holiday">
-							<span>', Lang::$txt['calendar_prompt'], '</span> ', implode(', ', $day['holidays']), '
+							<span class="label">', Lang::$txt['calendar_prompt'], '</span> ';
+
+						$holidays = [];
+
+						foreach ($day['holidays'] as $holiday) {
+							echo '<span class="holiday_wrapper">';
+
+							$holiday_string = $holiday->title;
+
+							if (empty($holiday->allday) && !empty($holiday->start_time_local) && $holiday->start_date == $day['date']) {
+								$holiday_string .= ' <span class="event_time">' . trim(str_replace(':00 ', ' ', $holiday->start_time_local)) . '</span>';
+							}
+
+							if (!empty($holiday->location)) {
+								$holiday_string .= ' <span class="event_location">' . $holiday->location . '</span>';
+							}
+
+							$holidays[] = $holiday_string;
+						}
+
+						echo implode('<span>, <span class="holiday_wrapper">', $holidays);
+
+						echo '</span>
 						</div>';
 
 					// Happy Birthday Dear Member!
@@ -699,11 +727,36 @@ function($a, $b)
 						<td class="', implode(' ', $classes), !empty($day['holidays']) ? ' holidays' : ' disabled', ' holiday_col" data-css-prefix="' . Lang::$txt['calendar_prompt'] . ' ">';
 
 				// Show any holidays!
-				if (!empty($day['holidays']))
-					echo implode('<br>', $day['holidays']);
+				if (!empty($day['holidays'])) {
+					echo '
+							<div class="holiday_wrapper">';
+
+					$holidays = [];
+
+					foreach ($day['holidays'] as $holiday) {
+						$holiday_string = $holiday->title;
+
+						if (empty($holiday->allday) && !empty($holiday->start_time_local) && $holiday->start_date == $day['date']) {
+							$holiday_string .= ' <span class="event_time">' . trim(str_replace(':00 ', ' ', $holiday->start_time_local)) . '</span>';
+						}
+
+						if (!empty($holiday->location)) {
+							$holiday_string .= ' <span class="event_location">' . $holiday->location . '</span>';
+						}
+
+						$holidays[] = $holiday_string;
+					}
+
+					echo implode('
+							</div>
+							<div class="holiday_wrapper">', $holidays);
+
+					echo '
+							</div>';
+				}
 
 				echo '
-							</td>';
+						</td>';
 			}
 
 			if (!empty($calendar_data['show_birthdays']))
diff --git a/Themes/default/EventEditor.template.php b/Themes/default/EventEditor.template.php
index 655f501eaa..2f2cf7b797 100644
--- a/Themes/default/EventEditor.template.php
+++ b/Themes/default/EventEditor.template.php
@@ -11,6 +11,7 @@
  * @version 3.0 Alpha 1
  */
 
+use SMF\Calendar\Event;
 use SMF\Config;
 use SMF\Lang;
 use SMF\Utils;
@@ -83,7 +84,7 @@ function template_event_options()
 								<label for="allday">', Lang::$txt['calendar_allday'], '</label>
 							</dt>
 							<dd>
-								<input type="checkbox" name="allday" id="allday"', !empty(Utils::$context['event']->allday) ? ' checked' : '', '>
+								<input type="checkbox" name="allday" id="allday"', !empty(Utils::$context['event']->allday) ? ' checked' : '', !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', '>
 
 							</dd>
 
@@ -91,17 +92,16 @@ function template_event_options()
 								<label>', Lang::$txt['start'], '</label>
 							</dt>
 							<dd>
-								<input type="date" name="start_date" id="start_date" value="', Utils::$context['event']->start->format('Y-m-d'), '" class="date_input start">
-								<input type="time" name="start_time" id="start_time" value="', Utils::$context['event']->start->format('H:i'), '" class="time_input start"', !empty(Utils::$context['event']->allday) ? ' disabled' : '', '>
+								<input type="date" name="start_date" id="start_date" value="', Utils::$context['event']->start->format('Y-m-d'), '" class="date_input start"', !empty(Utils::$context['event']->special_rrule) ? ' disabled data-force-disabled' : '', '>
+								<input type="time" name="start_time" id="start_time" value="', Utils::$context['event']->start->format('H:i'), '" class="time_input start"', !empty(Utils::$context['event']->allday) || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
 							</dd>
 
 							<dt class="clear">
 								<label>', Lang::$txt['end'], '</label>
 							</dt>
 							<dd>
-								<input type="date" name="end_date" id="end_date" value="', Utils::$context['event']->end->format('Y-m-d'), '" class="date_input end"', Config::$modSettings['cal_maxspan'] == 1 ? ' disabled' : '', '>
-								<input type="time" name="end_time" id="end_time" value="', Utils::$context['event']->end->format('H:i'), '" class="time_input end"', !empty(Utils::$context['event']->allday) ? ' disabled' : '', '>
-
+								<input type="date" name="end_date" id="end_date" value="', Utils::$context['event']->end->format('Y-m-d'), '" class="date_input end"', Config::$modSettings['cal_maxspan'] == 1 || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
+								<input type="time" name="end_time" id="end_time" value="', Utils::$context['event']->end->format('H:i'), '" class="time_input end"', !empty(Utils::$context['event']->allday) || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
 							</dd>
 
 							<dt id="tz_dt" class="clear">
@@ -112,7 +112,7 @@ function template_event_options()
 	// Setting max-width on selects inside floating elements can be flaky,
 	// so we need to calculate the width value manually.
 	echo '
-								<select name="tz" id="tz"', !empty(Utils::$context['event']->allday) ? ' disabled' : '', ' style="width:min(', max(array_map(fn ($tzname) => Utils::entityStrlen($tzname), Utils::$context['all_timezones'])) * 0.9, 'ch, 100%)">';
+								<select name="tz" id="tz"', !empty(Utils::$context['event']->allday) || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', ' style="width:min(', max(array_map(fn ($tzname) => Utils::entityStrlen($tzname), Utils::$context['all_timezones'])) * 0.9, 'ch, 100%)">';
 
 	foreach (Utils::$context['all_timezones'] as $tz => $tzname) {
 		echo '
@@ -137,15 +137,29 @@ function template_event_options()
 								<select name="RRULE" id="rrule" class="rrule_input">';
 
 	foreach (Utils::$context['event']->rrule_presets as $rrule => $description) {
-		echo '
+		if (is_array($description)) {
+			echo '
+									<optgroup label="', $rrule, '">';
+
+			foreach ($description as $special_rrule => $special_rrule_description) {
+				echo '
+											<option value="', $special_rrule, '"', $special_rrule === Utils::$context['event']->rrule_preset || $special_rrule === 'custom' && !isset(Utils::$context['event']->rrule_presets[Utils::$context['event']->rrule_preset]) ? ' selected' : '', '>', $special_rrule_description, '</option>';
+			}
+
+			echo '
+									</optgroup>';
+		} else {
+			echo '
 									<option value="', $rrule, '"', $rrule === Utils::$context['event']->rrule_preset || $rrule === 'custom' && !isset(Utils::$context['event']->rrule_presets[Utils::$context['event']->rrule_preset]) ? ' selected' : '', '>', $description, '</option>';
+		}
 	}
 
 	echo '
 								</select>';
 
 	// When to end the recurrence.
-	echo '
+	if (empty(Utils::$context['event']->special_rrule)) {
+		echo '
 								<span id="rrule_end" class="rrule_input_wrapper">
 									<select id="end_option" class="rrule_input">
 										<option value="forever">', Lang::$txt['calendar_repeat_until_options']['forever'], '</option>
@@ -154,12 +168,31 @@ function template_event_options()
 									</select>
 									<input type="date" name="UNTIL" id="until" class="rrule_input"', !empty(Utils::$context['event']->recurrence_iterator->getRRule()->until) ? ' value="' . Utils::$context['event']->recurrence_iterator->getRRule()->until->format('Y-m-d') . '"' : ' disabled', '>
 									<input type="number" name="COUNT" id="count" class="rrule_input" min="1"', (Utils::$context['event']->recurrence_iterator->getRRule()->count ?? 0) > 1 ? ' value="' . Utils::$context['event']->recurrence_iterator->getRRule()->count . '"' : ' value="1" disabled', '>
-								</span>
+								</span>';
+	}
+
+	echo '
 							</dd>
 						</dl>';
 
-	// Custom frequency and interval (e.g. "every 2 weeks")
-	echo '
+
+	if (!empty(Utils::$context['event']->special_rrule) || (Utils::$context['event']->new && Utils::$context['event']->type === Event::TYPE_HOLIDAY)) {
+		echo '
+						<dl id="special_rrule_options">
+							<dt class="clear">
+								<a id="special_rrule_modifier_help" href="https://stovell.noip.me/~jon/dev/index.php?action=helpadmin;help=special_rrule_modifier" onclick="return reqOverlayDiv(this.href);"><span class="main_icons help" title="Help"></span></a>
+								<label>', Lang::$txt['calendar_repeat_special_rrule_modifier'], '</label>
+							</dt>
+							<dd>
+								<input type="text" name="special_rrule_modifier" id="special_rrule_modifier" placeholder="', Lang::$txt['calendar_repeat_offset_examples'], '" value="' . (Utils::$context['event']->special_rrule['modifier'] ?? '') . '">
+							</dd>
+						</dl>';
+	}
+
+
+	if (empty(Utils::$context['event']->special_rrule)) {
+		// Custom frequency and interval (e.g. "every 2 weeks")
+		echo '
 						<dl id="freq_interval_options" class="rrule_input_wrapper">
 							<dt class="clear">
 								<label>', Lang::$txt['calendar_repeat_interval_label'], '</label>
@@ -168,18 +201,18 @@ function template_event_options()
 								<input type="number" name="INTERVAL" value="', Utils::$context['event']->recurrence_iterator->getRRule()->interval, '" min="1" class="rrule_input" disabled>
 								<select name="FREQ" id="freq" class="rrule_input">';
 
-	foreach (Utils::$context['event']->frequency_units as $freq => $unit) {
-		echo '
+		foreach (Utils::$context['event']->frequency_units as $freq => $unit) {
+			echo '
 									<option value="', $freq, '"', Utils::$context['event']->recurrence_iterator->getRRule()->freq === $freq ? ' selected' : '', '>', $unit, '</option>';
-	}
+		}
 
-	echo '
+		echo '
 								</select>
 							</dd>
 						</dl>';
 
-	// Custom yearly options.
-	echo '
+		// Custom yearly options.
+		echo '
 						<dl id="yearly_options" class="rrule_input_wrapper">
 							<dt class="clear">
 								<label>', Lang::$txt['calendar_repeat_bymonth_label'], '</label>
@@ -187,31 +220,31 @@ function template_event_options()
 							<dd>
 								<div class="rrule_input_row">';
 
-	for ($i = 1; $i <= 12; $i++) {
-		echo '
+		for ($i = 1; $i <= 12; $i++) {
+			echo '
 									<label class="bymonth_label">
 										<input type="checkbox" name="BYMONTH[]" value="' . $i . '" id="bymonth_', $i,'" class="rrule_input" disabled>
 										<span>' . Lang::$txt['months_short'][$i] . '</span>
 									</label>';
 
-		if ($i % 6 === 0) {
-			echo '
+			if ($i % 6 === 0) {
+				echo '
 								</div>
 								<div class="rrule_input_row">';
+			}
 		}
-	}
 
-	echo '
+		echo '
 								</div>
 							</dd>
 						</dl>';
 
-	// Custom monthly options.
-	echo '
+		// Custom monthly options.
+		echo '
 						<dl id="monthly_options" class="rrule_input_wrapper">';
 
-	// Custom monthly: by day of month.
-	echo '
+		// Custom monthly: by day of month.
+		echo '
 							<dt class="clear" id="dt_monthly_option_type_bymonthday">
 								<label>
 									', Lang::$txt['calendar_repeat_bymonthday_label'], '
@@ -223,27 +256,27 @@ function template_event_options()
 									<div class="rrule_input inline_block">
 										<div class="rrule_input_row">';
 
-	for ($i = 1; $i <= 31; $i++) {
-		echo '
+		for ($i = 1; $i <= 31; $i++) {
+			echo '
 											<label class="bymonthday_label">
 												<input type="checkbox" name="BYMONTHDAY[]" id="bymonthday_' . $i . '" value="' . $i . '"  class="rrule_input" disabled> <span>' . $i . '</span>
 											</label>';
 
-		if ($i % 7 === 0) {
-			echo '
+			if ($i % 7 === 0) {
+				echo '
 										</div>
 										<div class="rrule_input_row">';
+			}
 		}
-	}
 
-	echo '
+		echo '
 										</div>
 									</div>
 								</div>
 							</dd>';
 
-	// Custom monthly: by weekday and offset (e.g. "the second Tuesday")
-	echo '
+		// Custom monthly: by weekday and offset (e.g. "the second Tuesday")
+		echo '
 							<dt class="clear">
 								<label>
 									', Lang::$txt['calendar_repeat_byday_label'], '
@@ -253,42 +286,42 @@ function template_event_options()
 							<dd id="month_byday_options">
 								<div class="rrule_input clear">';
 
-	foreach (Utils::$context['event']->byday_items as $byday_item_key => $byday_item) {
-		echo '
+		foreach (Utils::$context['event']->byday_items as $byday_item_key => $byday_item) {
+			echo '
 									<div>
 										<select id="byday_num_select_', $byday_item_key, '" name="BYDAY_num[', $byday_item_key, ']" class="rrule_input byday_num_select" disabled>';
 
-		foreach (Utils::$context['event']->byday_num_options as $num => $ordinal) {
-			if (isset($prev_num) && ($num < 0) !== ($prev_num < 0)) {
-				echo '
+			foreach (Utils::$context['event']->byday_num_options as $num => $ordinal) {
+				if (isset($prev_num) && ($num < 0) !== ($prev_num < 0)) {
+					echo '
 											<option disabled>------</option>';
-		}
+			}
 
-		echo '
+			echo '
 											<option value="', $num, '" class="byday_num_', ($num < 0 ? 'neg' : '') . abs($num), '"', $num == $byday_item['num'] ? ' selected' : '', '>', $ordinal, '</option>';
 
-			$prev_num = $num;
-		}
-		unset($prev_num);
+				$prev_num = $num;
+			}
+			unset($prev_num);
 
-		echo '
+			echo '
 										</select>
 										<select id="byday_name_select_', $byday_item_key, '" name="BYDAY_name[', $byday_item_key, ']" class="rrule_input byday_name_select" disabled>';
 
-		foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
-			echo '
+			foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
+				echo '
 											<option value="', $weekday['abbrev'], '" class="byday_name_', $weekday['abbrev'], '"', $weekday['abbrev'] == $byday_item['name'] ? ' selected' : '', '>', $weekday['long'], '</option>';
-		}
+			}
 
-		echo '
+			echo '
 											<option disabled>------</option>
 											<option value="MO,TU,WE,TH,FR">', Lang::$txt['calendar_repeat_weekday'], '</option>
 											<option value="SA,SU">', Lang::$txt['calendar_repeat_weekend_day'], '</option>
 										</select>
 									</div>';
-	}
+		}
 
-	echo '
+		echo '
 								</div>
 								<div>
 									<a id="event_add_byday" class="rrule_input button floatnone">', Lang::$txt['calendar_repeat_add_condition'], '</a>
@@ -297,29 +330,29 @@ function template_event_options()
 									<div>
 										<select name="BYDAY_num[-1]" class="rrule_input byday_num_select">';
 
-	foreach (Utils::$context['event']->byday_num_options as $num => $ordinal) {
-		if (isset($prev_num) && ($num < 0) !== ($prev_num < 0)) {
-			echo '
+		foreach (Utils::$context['event']->byday_num_options as $num => $ordinal) {
+			if (isset($prev_num) && ($num < 0) !== ($prev_num < 0)) {
+				echo '
 											<option disabled>------</option>';
-	}
+		}
 
-	echo '
+		echo '
 											<option value="', $num, '" class="byday_num_', ($num < 0 ? 'neg' : '') . abs($num), '">', $ordinal, '</option>';
 
-		$prev_num = $num;
-	}
-	unset($prev_num);
+			$prev_num = $num;
+		}
+		unset($prev_num);
 
-	echo '
+		echo '
 										</select>
 										<select name="BYDAY_name[-1]" class="rrule_input byday_name_select">';
 
-	foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
-		echo '
+		foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
+			echo '
 											<option value="', $weekday['abbrev'], '" class="byday_name_', $weekday['abbrev'], '">', $weekday['long'], '</option>';
-	}
+		}
 
-	echo '
+		echo '
 											<option disabled>------</option>
 											<option value="MO,TU,WE,TH,FR">', Lang::$txt['calendar_repeat_weekday'], '</option>
 											<option value="SA,SU">', Lang::$txt['calendar_repeat_weekend_day'], '</option>
@@ -329,25 +362,26 @@ function template_event_options()
 							</dd>
 						</dl>';
 
-	// Custom weekly options.
-	echo '
+		// Custom weekly options.
+		echo '
 						<dl id="weekly_options" class="rrule_input_wrapper">
 							<dt class="clear">
 								<label>', Lang::$txt['calendar_repeat_byday_label'], '</label>
 							</dt>
 							<dd class="rrule_input_row">';
 
-	foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
-		echo '
+		foreach (Utils::$context['event']->sorted_weekdays as $weekday) {
+			echo '
 									<label class="byday_label">
 										<input type="checkbox" name="BYDAY[]" id="byday_', $weekday['abbrev'], '" value="', $weekday['abbrev'], '"  class="rrule_input"', in_array($weekday['abbrev'], Utils::$context['event']->recurrence_iterator->getRRule()->byday ?? []) ? ' checked' : '', ' disabled>
 										<span>', $weekday['short'], '</span>
 									</label>';
-	}
+		}
 
-	echo '
+		echo '
 							</dd>
 						</dl>';
+	}
 
 	// Advanced options.
 	echo '
diff --git a/Themes/default/ManageCalendar.template.php b/Themes/default/ManageCalendar.template.php
index e9c61259b9..0c1005dd42 100644
--- a/Themes/default/ManageCalendar.template.php
+++ b/Themes/default/ManageCalendar.template.php
@@ -25,59 +25,20 @@ function template_edit_holiday()
 			<div class="cat_bar">
 				<h3 class="catbg">', Utils::$context['page_title'], '</h3>
 			</div>
-			<div class="windowbg">
-				<dl class="settings">
-					<dt>
-						<strong>', Lang::$txt['holidays_title_label'], ':</strong>
-					</dt>
-					<dd>
-						<input type="text" name="title" value="', Utils::$context['holiday']['title'], '" size="55" maxlength="60">
-					</dd>
-					<dt>
-						<strong>', Lang::$txt['calendar_year'], '</strong>
-					</dt>
-					<dd>
-						<select name="year" id="year" onchange="generateDays();">
-							<option value="0000"', Utils::$context['holiday']['year'] == '0000' ? ' selected' : '', '>', Lang::$txt['every_year'], '</option>';
+			<div class="windowbg">';
 
-	// Show a list of all the years we allow...
-	for ($year = Config::$modSettings['cal_minyear']; $year <= Config::$modSettings['cal_maxyear']; $year++)
-		echo '
-							<option value="', $year, '"', $year == Utils::$context['holiday']['year'] ? ' selected' : '', '>', $year, '</option>';
-
-	echo '
-						</select>
-						<label for="month">', Lang::$txt['calendar_month'], '</label>
-						<select name="month" id="month" onchange="generateDays();">';
-
-	// There are 12 months per year - ensure that they all get listed.
-	for ($month = 1; $month <= 12; $month++)
-		echo '
-							<option value="', $month, '"', $month == Utils::$context['holiday']['month'] ? ' selected' : '', '>', Lang::$txt['months'][$month], '</option>';
-
-	echo '
-						</select>
-						<label for="day">', Lang::$txt['calendar_day'], '</label>
-						<select name="day" id="day" onchange="generateDays();">';
-
-	// This prints out all the days in the current month - this changes dynamically as we switch months.
-	for ($day = 1; $day <= Utils::$context['holiday']['last_day']; $day++)
-		echo '
-							<option value="', $day, '"', $day == Utils::$context['holiday']['day'] ? ' selected' : '', '>', $day, '</option>';
+	template_event_options();
 
-	echo '
-						</select>
-					</dd>
-				</dl>';
-
-	if (Utils::$context['is_new'])
+	if (Utils::$context['is_new']) {
 		echo '
 				<input type="submit" value="', Lang::$txt['holidays_button_add'], '" class="button">';
-	else
+	} else {
 		echo '
 				<input type="submit" name="edit" value="', Lang::$txt['holidays_button_edit'], '" class="button">
 				<input type="submit" name="delete" value="', Lang::$txt['holidays_button_remove'], '" class="button">
-				<input type="hidden" name="holiday" value="', Utils::$context['holiday']['id'], '">';
+				<input type="hidden" name="holiday" value="', Utils::$context['event']['id'], '">';
+	}
+
 	echo '
 				<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
 				<input type="hidden" name="' . Utils::$context['admin-eh_token_var'] . '" value="' . Utils::$context['admin-eh_token'] . '">
diff --git a/Themes/default/css/calendar.css b/Themes/default/css/calendar.css
index 63d1148af9..5837fbb6f3 100644
--- a/Themes/default/css/calendar.css
+++ b/Themes/default/css/calendar.css
@@ -173,6 +173,13 @@ td.days:hover {
 #main_grid tr:not(.days_wrapper) td {
 	min-height: 30px;
 }
+p.inline.holidays {
+	display: flex;
+	flex-flow: row wrap;
+}
+p.inline.holidays > span {
+	width: 300px;
+}
 #calendar_range,
 #calendar_navigation {
 	padding: 5px 0;
diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index 77e4ef4000..9f9f8fe6e8 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -557,9 +557,18 @@ strong[id^='child_list_']::after {
 	color: #078907;
 }
 
-.holiday > span {
+.holiday > span.label {
 	color: #025dff;
 }
+.holiday_wrapper > span:first-of-type::before {
+	content: '(';
+}
+.holiday_wrapper > span:first-of-type::after {
+	content: ',';
+}
+.holiday_wrapper > span:last-of-type::after {
+	content: ')';
+}
 /* Events that are currently selected on the calendar. Won't see it much, probably. */
 .sel_event {
 	font-weight: bold;
diff --git a/Themes/default/scripts/event.js b/Themes/default/scripts/event.js
index 16b65adacc..9493177246 100644
--- a/Themes/default/scripts/event.js
+++ b/Themes/default/scripts/event.js
@@ -31,9 +31,10 @@ function updateEventUI()
 	let weekday = getWeekday(start_date);
 
 	// Disable or enable the time-related fields as necessary.
-	document.getElementById("start_time").disabled = document.getElementById("allday").checked;
-	document.getElementById("end_time").disabled = document.getElementById("allday").checked;
-	document.getElementById("tz").disabled = document.getElementById("allday").checked;
+	document.getElementById("start_time").disabled = document.getElementById("start_time").dataset.forceDisabled;
+	document.getElementById("start_time").disabled = document.getElementById("allday").checked || document.getElementById("start_time").dataset.forceDisabled;
+	document.getElementById("end_time").disabled = document.getElementById("allday").checked || document.getElementById("end_time").dataset.forceDisabled;
+	document.getElementById("tz").disabled = document.getElementById("allday").checked || document.getElementById("tz").dataset.forceDisabled;
 
 	// Reset the recurring event options to be hidden and disabled.
 	// We'll turn the appropriate ones back on below.
@@ -422,6 +423,21 @@ function updateEventUI()
 		}
 	}
 
+	if (
+		document.getElementById("rrule")
+		&& document.getElementById("special_rrule_modifier")
+		&& typeof special_rrules !== "undefined"
+		&& Array.isArray(special_rrules)
+	) {
+		if (special_rrules.includes(document.getElementById("rrule").value)) {
+			document.getElementById("special_rrule_options").style.display = "";
+			document.getElementById("special_rrule_modifier").disabled = false;
+		} else {
+			document.getElementById("special_rrule_options").style.display = "none";
+			document.getElementById("special_rrule_modifier").disabled = true;
+		}
+	}
+
 	end_date = updateEndDate(start_date, end_date);
 
 	// Show the basic RRule select menu.
@@ -434,7 +450,7 @@ function updateEventUI()
 	}
 
 	// If necessary, show the options for RRule end.
-	if (document.getElementById("rrule").value !== "never") {
+	if (document.getElementById("rrule").value === "custom" || document.getElementById("rrule").value.substring(0, 5) === "FREQ=") {
 		const end_option = document.getElementById("end_option");
 		const until = document.getElementById("until");
 		const count = document.getElementById("count");
diff --git a/other/install_3-0_MySQL.sql b/other/install_3-0_MySQL.sql
index 875b8ec083..d46dd8f61b 100644
--- a/other/install_3-0_MySQL.sql
+++ b/other/install_3-0_MySQL.sql
@@ -181,24 +181,13 @@ CREATE TABLE {$db_prefix}calendar (
 	sequence SMALLINT UNSIGNED NOT NULL DEFAULT '0';
 	uid VARCHAR(255) NOT NULL DEFAULT '',
 	type TINYINT UNSIGNED NOT NULL DEFAULT '0';
+	enabled TINYINT UNSIGNED NOT NULL DEFAULT '1';
 	PRIMARY KEY (id_event),
 	INDEX idx_start_date (start_date),
 	INDEX idx_end_date (end_date),
 	INDEX idx_topic (id_topic, id_member)
 ) ENGINE={$engine};
 
-#
-# Table structure for table `calendar_holidays`
-#
-
-CREATE TABLE {$db_prefix}calendar_holidays (
-	id_holiday SMALLINT UNSIGNED AUTO_INCREMENT,
-	event_date date NOT NULL DEFAULT '1004-01-01',
-	title VARCHAR(255) NOT NULL DEFAULT '',
-	PRIMARY KEY (id_holiday),
-	INDEX idx_event_date (event_date)
-) ENGINE={$engine};
-
 #
 # Table structure for table `categories`
 #
@@ -1575,217 +1564,39 @@ VALUES (-1,1,0), (0,1,0), (2,1,0);
 # --------------------------------------------------------
 
 #
-# Dumping data for table `calendar_holidays`
-#
-
-INSERT INTO {$db_prefix}calendar_holidays
-	(title, event_date)
-VALUES ('New Year''s', '1004-01-01'),
-	('Christmas', '1004-12-25'),
-	('Valentine''s Day', '1004-02-14'),
-	('St. Patrick''s Day', '1004-03-17'),
-	('April Fools', '1004-04-01'),
-	('Earth Day', '1004-04-22'),
-	('United Nations Day', '1004-10-24'),
-	('Halloween', '1004-10-31'),
-	('Mother''s Day', '2010-05-09'),
-	('Mother''s Day', '2011-05-08'),
-	('Mother''s Day', '2012-05-13'),
-	('Mother''s Day', '2013-05-12'),
-	('Mother''s Day', '2014-05-11'),
-	('Mother''s Day', '2015-05-10'),
-	('Mother''s Day', '2016-05-08'),
-	('Mother''s Day', '2017-05-14'),
-	('Mother''s Day', '2018-05-13'),
-	('Mother''s Day', '2019-05-12'),
-	('Mother''s Day', '2020-05-10'),
-	('Mother''s Day', '2021-05-09'),
-	('Mother''s Day', '2022-05-08'),
-	('Mother''s Day', '2023-05-14'),
-	('Mother''s Day', '2024-05-12'),
-	('Mother''s Day', '2025-05-11'),
-	('Mother''s Day', '2026-05-10'),
-	('Mother''s Day', '2027-05-09'),
-	('Mother''s Day', '2028-05-14'),
-	('Mother''s Day', '2029-05-13'),
-	('Mother''s Day', '2030-05-12'),
-	('Father''s Day', '2010-06-20'),
-	('Father''s Day', '2011-06-19'),
-	('Father''s Day', '2012-06-17'),
-	('Father''s Day', '2013-06-16'),
-	('Father''s Day', '2014-06-15'),
-	('Father''s Day', '2015-06-21'),
-	('Father''s Day', '2016-06-19'),
-	('Father''s Day', '2017-06-18'),
-	('Father''s Day', '2018-06-17'),
-	('Father''s Day', '2019-06-16'),
-	('Father''s Day', '2020-06-21'),
-	('Father''s Day', '2021-06-20'),
-	('Father''s Day', '2022-06-19'),
-	('Father''s Day', '2023-06-18'),
-	('Father''s Day', '2024-06-16'),
-	('Father''s Day', '2025-06-15'),
-	('Father''s Day', '2026-06-21'),
-	('Father''s Day', '2027-06-20'),
-	('Father''s Day', '2028-06-18'),
-	('Father''s Day', '2029-06-17'),
-	('Father''s Day', '2030-06-16'),
-	('Summer Solstice', '2010-06-21'),
-	('Summer Solstice', '2011-06-21'),
-	('Summer Solstice', '2012-06-20'),
-	('Summer Solstice', '2013-06-21'),
-	('Summer Solstice', '2014-06-21'),
-	('Summer Solstice', '2015-06-21'),
-	('Summer Solstice', '2016-06-20'),
-	('Summer Solstice', '2017-06-20'),
-	('Summer Solstice', '2018-06-21'),
-	('Summer Solstice', '2019-06-21'),
-	('Summer Solstice', '2020-06-20'),
-	('Summer Solstice', '2021-06-21'),
-	('Summer Solstice', '2022-06-21'),
-	('Summer Solstice', '2023-06-21'),
-	('Summer Solstice', '2024-06-20'),
-	('Summer Solstice', '2025-06-21'),
-	('Summer Solstice', '2026-06-21'),
-	('Summer Solstice', '2027-06-21'),
-	('Summer Solstice', '2028-06-20'),
-	('Summer Solstice', '2029-06-21'),
-	('Summer Solstice', '2030-06-21'),
-	('Vernal Equinox', '2010-03-20'),
-	('Vernal Equinox', '2011-03-20'),
-	('Vernal Equinox', '2012-03-20'),
-	('Vernal Equinox', '2013-03-20'),
-	('Vernal Equinox', '2014-03-20'),
-	('Vernal Equinox', '2015-03-20'),
-	('Vernal Equinox', '2016-03-20'),
-	('Vernal Equinox', '2017-03-20'),
-	('Vernal Equinox', '2018-03-20'),
-	('Vernal Equinox', '2019-03-20'),
-	('Vernal Equinox', '2020-03-20'),
-	('Vernal Equinox', '2021-03-20'),
-	('Vernal Equinox', '2022-03-20'),
-	('Vernal Equinox', '2023-03-20'),
-	('Vernal Equinox', '2024-03-20'),
-	('Vernal Equinox', '2025-03-20'),
-	('Vernal Equinox', '2026-03-20'),
-	('Vernal Equinox', '2027-03-20'),
-	('Vernal Equinox', '2028-03-20'),
-	('Vernal Equinox', '2029-03-20'),
-	('Vernal Equinox', '2030-03-20'),
-	('Winter Solstice', '2010-12-21'),
-	('Winter Solstice', '2011-12-22'),
-	('Winter Solstice', '2012-12-21'),
-	('Winter Solstice', '2013-12-21'),
-	('Winter Solstice', '2014-12-21'),
-	('Winter Solstice', '2015-12-22'),
-	('Winter Solstice', '2016-12-21'),
-	('Winter Solstice', '2017-12-21'),
-	('Winter Solstice', '2018-12-21'),
-	('Winter Solstice', '2019-12-22'),
-	('Winter Solstice', '2020-12-21'),
-	('Winter Solstice', '2021-12-21'),
-	('Winter Solstice', '2022-12-21'),
-	('Winter Solstice', '2023-12-22'),
-	('Winter Solstice', '2024-12-21'),
-	('Winter Solstice', '2025-12-21'),
-	('Winter Solstice', '2026-12-21'),
-	('Winter Solstice', '2027-12-22'),
-	('Winter Solstice', '2028-12-21'),
-	('Winter Solstice', '2029-12-21'),
-	('Winter Solstice', '2030-12-21'),
-	('Autumnal Equinox', '2010-09-23'),
-	('Autumnal Equinox', '2011-09-23'),
-	('Autumnal Equinox', '2012-09-22'),
-	('Autumnal Equinox', '2013-09-22'),
-	('Autumnal Equinox', '2014-09-23'),
-	('Autumnal Equinox', '2015-09-23'),
-	('Autumnal Equinox', '2016-09-22'),
-	('Autumnal Equinox', '2017-09-22'),
-	('Autumnal Equinox', '2018-09-23'),
-	('Autumnal Equinox', '2019-09-23'),
-	('Autumnal Equinox', '2020-09-22'),
-	('Autumnal Equinox', '2021-09-22'),
-	('Autumnal Equinox', '2022-09-23'),
-	('Autumnal Equinox', '2023-09-23'),
-	('Autumnal Equinox', '2024-09-22'),
-	('Autumnal Equinox', '2025-09-22'),
-	('Autumnal Equinox', '2026-09-23'),
-	('Autumnal Equinox', '2027-09-23'),
-	('Autumnal Equinox', '2028-09-22'),
-	('Autumnal Equinox', '2029-09-22'),
-	('Autumnal Equinox', '2030-09-22');
-
-INSERT INTO {$db_prefix}calendar_holidays
-	(title, event_date)
-VALUES ('Independence Day', '1004-07-04'),
-	('Cinco de Mayo', '1004-05-05'),
-	('Flag Day', '1004-06-14'),
-	('Veterans Day', '1004-11-11'),
-	('Groundhog Day', '1004-02-02'),
-	('Thanksgiving', '2010-11-25'),
-	('Thanksgiving', '2011-11-24'),
-	('Thanksgiving', '2012-11-22'),
-	('Thanksgiving', '2013-11-28'),
-	('Thanksgiving', '2014-11-27'),
-	('Thanksgiving', '2015-11-26'),
-	('Thanksgiving', '2016-11-24'),
-	('Thanksgiving', '2017-11-23'),
-	('Thanksgiving', '2018-11-22'),
-	('Thanksgiving', '2019-11-28'),
-	('Thanksgiving', '2020-11-26'),
-	('Thanksgiving', '2021-11-25'),
-	('Thanksgiving', '2022-11-24'),
-	('Thanksgiving', '2023-11-23'),
-	('Thanksgiving', '2024-11-28'),
-	('Thanksgiving', '2025-11-27'),
-	('Thanksgiving', '2026-11-26'),
-	('Thanksgiving', '2027-11-25'),
-	('Thanksgiving', '2028-11-23'),
-	('Thanksgiving', '2029-11-22'),
-	('Thanksgiving', '2030-11-28'),
-	('Memorial Day', '2010-05-31'),
-	('Memorial Day', '2011-05-30'),
-	('Memorial Day', '2012-05-28'),
-	('Memorial Day', '2013-05-27'),
-	('Memorial Day', '2014-05-26'),
-	('Memorial Day', '2015-05-25'),
-	('Memorial Day', '2016-05-30'),
-	('Memorial Day', '2017-05-29'),
-	('Memorial Day', '2018-05-28'),
-	('Memorial Day', '2019-05-27'),
-	('Memorial Day', '2020-05-25'),
-	('Memorial Day', '2021-05-31'),
-	('Memorial Day', '2022-05-30'),
-	('Memorial Day', '2023-05-29'),
-	('Memorial Day', '2024-05-27'),
-	('Memorial Day', '2025-05-26'),
-	('Memorial Day', '2026-05-25'),
-	('Memorial Day', '2027-05-31'),
-	('Memorial Day', '2028-05-29'),
-	('Memorial Day', '2029-05-28'),
-	('Memorial Day', '2030-05-27'),
-	('Labor Day', '2010-09-06'),
-	('Labor Day', '2011-09-05'),
-	('Labor Day', '2012-09-03'),
-	('Labor Day', '2013-09-02'),
-	('Labor Day', '2014-09-01'),
-	('Labor Day', '2015-09-07'),
-	('Labor Day', '2016-09-05'),
-	('Labor Day', '2017-09-04'),
-	('Labor Day', '2018-09-03'),
-	('Labor Day', '2019-09-02'),
-	('Labor Day', '2020-09-07'),
-	('Labor Day', '2021-09-06'),
-	('Labor Day', '2022-09-05'),
-	('Labor Day', '2023-09-04'),
-	('Labor Day', '2024-09-02'),
-	('Labor Day', '2025-09-01'),
-	('Labor Day', '2026-09-07'),
-	('Labor Day', '2027-09-06'),
-	('Labor Day', '2028-09-04'),
-	('Labor Day', '2029-09-03'),
-	('Labor Day', '2030-09-02'),
-	('D-Day', '1004-06-06');
+# Dumping data for table `calendar`
+#
+
+INSERT INTO {$db_prefix}calendar
+	(title, start_date, end_date, start_time, timezone, location, duration, rrule, rdates, type, enabled)
+VALUES
+	('April Fools\' Day', '2000-04-01', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Christmas', '2000-12-25', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Cinco de Mayo', '2000-05-05', '9999-12-31', NULL, NULL, 'Mexico, USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('D-Day', '2000-06-06', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Easter', '2000-04-23', '9999-12-31', NULL, NULL, '', 'P1D', 'EASTER_W', '', 1, 1),
+	('Earth Day', '2000-04-22', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Father\'s Day', '2000-06-19', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY;BYMONTH=6;BYDAY=3SU', '', 1, 1),
+	('Flag Day', '2000-06-14', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Good Friday', '2000-04-21', '9999-12-31', NULL, NULL, '', 'P1D', 'EASTER_W-P2D', '', 1, 1),
+	('Groundhog Day', '2000-02-02', '9999-12-31', NULL, NULL, 'Canada, USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Halloween', '2000-10-31', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Independence Day', '2000-07-04', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Labor Day', '2000-09-03', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO', '', 1, 1),
+	('Labour Day', '2000-09-03', '9999-12-31', NULL, NULL, 'Canada', 'P1D', 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO', '', 1, 1),
+	('Memorial Day', '2000-05-31', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY;BYMONTH=5;BYDAY=-1MO', '', 1, 1),
+	('Mother\'s Day', '2000-05-08', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY;BYMONTH=5;BYDAY=2SU', '', 1, 1),
+	('New Year\'s Day', '2000-01-01', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Remembrance Day', '2000-11-11', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('St. Patrick\'s Day', '2000-03-17', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Thanksgiving', '2000-11-26', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY;BYMONTH=11;BYDAY=4TH', '', 1, 1),
+	('United Nations Day', '2000-10-24', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Valentine\'s Day', '2000-02-14', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Veterans Day', '2000-11-11', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Vernal Equinox', '2000-03-20', '9999-12-31', '07:30:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20000320T073000Z,20010320T131900Z,20020320T190800Z,20030321T005800Z,20040320T064700Z,20050320T123600Z,20060320T182500Z,20070321T001400Z,20080320T060400Z,20090320T115300Z,20100320T174200Z,20110320T233100Z,20120320T052000Z,20130320T111000Z,20140320T165900Z,20150320T224800Z,20160320T043700Z,20170320T102600Z,20180320T161600Z,20190320T220500Z,20200320T035400Z,20210320T094300Z,20220320T153200Z,20230320T212200Z,20240320T031100Z,20250320T090000Z,20260320T144900Z,20270320T203800Z,20280320T022800Z,20290320T081700Z,20300320T140600Z,20310320T195500Z,20320320T014400Z,20330320T073400Z,20340320T132300Z,20350320T191200Z,20360320T010100Z,20370320T065000Z,20380320T124000Z,20390320T182900Z,20400320T001800Z,20410320T060700Z,20420320T115600Z,20430320T174600Z,20440319T233500Z,20450320T052400Z,20460320T111300Z,20470320T170200Z,20480319T225200Z,20490320T044100Z,20500320T103000Z,20510320T161900Z,20520319T220800Z,20530320T035800Z,20540320T094700Z,20550320T153600Z,20560319T212500Z,20570320T031400Z,20580320T090400Z,20590320T145300Z,20600319T204200Z,20610320T023100Z,20620320T082000Z,20630320T141000Z,20640319T195900Z,20650320T014800Z,20660320T073700Z,20670320T132600Z,20680319T191600Z,20690320T010500Z,20700320T065400Z,20710320T124300Z,20720319T183200Z,20730320T002200Z,20740320T061100Z,20750320T120000Z,20760319T174900Z,20770319T233800Z,20780320T052800Z,20790320T111700Z,20800319T170600Z,20810319T225500Z,20820320T044400Z,20830320T103400Z,20840319T162300Z,20850319T221200Z,20860320T040100Z,20870320T095000Z,20880319T154000Z,20890319T212900Z,20900320T031800Z,20910320T090700Z,20920319T145600Z,20930319T204600Z,20940320T023500Z,20950320T082400Z,20960319T141300Z,20970319T200200Z,20980320T015200Z,20990320T074100Z', 1, 1),
+	('Summer Solstice', '2000-06-21', '9999-12-31', '01:44:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20000621T014400Z,20010621T073200Z,20020621T132000Z,20030621T190800Z,20040621T005600Z,20050621T064400Z,20060621T123200Z,20070621T182100Z,20080621T000900Z,20090621T055700Z,20100621T114500Z,20110621T173300Z,20120620T232100Z,20130621T050900Z,20140621T105700Z,20150621T164600Z,20160620T223400Z,20170621T042200Z,20180621T101000Z,20190621T155800Z,20200620T214600Z,20210621T033400Z,20220621T092300Z,20230621T151100Z,20240620T205900Z,20250621T024700Z,20260621T083500Z,20270621T142300Z,20280620T201100Z,20290621T015900Z,20300621T074800Z,20310621T133600Z,20320620T192400Z,20330621T011200Z,20340621T070000Z,20350621T124800Z,20360620T183600Z,20370621T002400Z,20380621T061300Z,20390621T120100Z,20400620T174900Z,20410620T233700Z,20420621T052500Z,20430621T111300Z,20440620T170100Z,20450620T224900Z,20460621T043700Z,20470621T102600Z,20480620T161400Z,20490620T220200Z,20500621T035000Z,20510621T093800Z,20520620T152600Z,20530620T211400Z,20540621T030200Z,20550621T085100Z,20560620T143900Z,20570620T202700Z,20580621T021500Z,20590621T080300Z,20600620T135100Z,20610620T193900Z,20620621T012700Z,20630621T071600Z,20640620T130400Z,20650620T185200Z,20660621T004000Z,20670621T062800Z,20680620T121600Z,20690620T180400Z,20700620T235200Z,20710621T054100Z,20720620T112900Z,20730620T171700Z,20740620T230500Z,20750621T045300Z,20760620T104100Z,20770620T162900Z,20780620T221700Z,20790621T040500Z,20800620T095400Z,20810620T154200Z,20820620T213000Z,20830621T031800Z,20840620T090600Z,20850620T145400Z,20860620T204200Z,20870621T023000Z,20880620T081900Z,20890620T140700Z,20900620T195500Z,20910621T014300Z,20920620T073100Z,20930620T131900Z,20940620T190700Z,20950621T005500Z,20960620T064300Z,20970620T123200Z,20980620T182000Z,20990621T000800Z', 1, 1),
+	('Autumnal Equinox', '2000-09-22', '9999-12-31', '17:16:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20000922T171600Z,20010922T230500Z,20020923T045400Z,20030923T104200Z,20040922T163100Z,20050922T222000Z,20060923T040800Z,20070923T095700Z,20080922T154600Z,20090922T213400Z,20100923T032300Z,20110923T091200Z,20120922T150100Z,20130922T204900Z,20140923T023800Z,20150923T082700Z,20160922T141500Z,20170922T200400Z,20180923T015300Z,20190923T074100Z,20200922T133000Z,20210922T191900Z,20220923T010700Z,20230923T065600Z,20240922T124500Z,20250922T183300Z,20260923T002200Z,20270923T061100Z,20280922T115900Z,20290922T174800Z,20300922T233700Z,20310923T052600Z,20320922T111400Z,20330922T170300Z,20340922T225200Z,20350923T044000Z,20360922T102900Z,20370922T161800Z,20380922T220600Z,20390923T035500Z,20400922T094400Z,20410922T153200Z,20420922T212100Z,20430923T031000Z,20440922T085800Z,20450922T144700Z,20460922T203600Z,20470923T022400Z,20480922T081300Z,20490922T140200Z,20500922T195000Z,20510923T013900Z,20520922T072800Z,20530922T131600Z,20540922T190500Z,20550923T005400Z,20560922T064200Z,20570922T123100Z,20580922T182000Z,20590923T000800Z,20600922T055700Z,20610922T114600Z,20620922T173400Z,20630922T232300Z,20640922T051200Z,20650922T110000Z,20660922T164900Z,20670922T223800Z,20680922T042600Z,20690922T101500Z,20700922T160400Z,20710922T215200Z,20720922T034100Z,20730922T093000Z,20740922T151800Z,20750922T210700Z,20760922T025600Z,20770922T084400Z,20780922T143300Z,20790922T202200Z,20800922T021000Z,20810922T075900Z,20820922T134800Z,20830922T193600Z,20840922T012500Z,20850922T071400Z,20860922T130200Z,20870922T185100Z,20880922T003900Z,20890922T062800Z,20900922T121700Z,20910922T180500Z,20920921T235400Z,20930922T054300Z,20940922T113100Z,20950922T172000Z,20960921T230900Z,20970922T045700Z,20980922T104600Z,20990922T163500Z', 1, 1),
+	('Winter Solstice', '2000-12-21', '9999-12-31', '13:27:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20001221T132700Z,20011221T191600Z,20021222T010600Z,20031222T065600Z,20041221T124600Z,20051221T183500Z,20061222T002500Z,20071222T061500Z,20081221T120400Z,20091221T175400Z,20101221T234400Z,20111222T053400Z,20121221T112300Z,20131221T171300Z,20141221T230300Z,20151222T045300Z,20161221T104200Z,20171221T163200Z,20181221T222200Z,20191222T041100Z,20201221T100100Z,20211221T155100Z,20221221T214100Z,20231222T033000Z,20241221T092000Z,20251221T151000Z,20261221T205900Z,20271222T024900Z,20281221T083900Z,20291221T142900Z,20301221T201800Z,20311222T020800Z,20321221T075800Z,20331221T134800Z,20341221T193700Z,20351222T012700Z,20361221T071700Z,20371221T130600Z,20381221T185600Z,20391222T004600Z,20401221T063600Z,20411221T122500Z,20421221T181500Z,20431222T000500Z,20441221T055400Z,20451221T114400Z,20461221T173400Z,20471221T232400Z,20481221T051300Z,20491221T110300Z,20501221T165300Z,20511221T224200Z,20521221T043200Z,20531221T102200Z,20541221T161200Z,20551221T220100Z,20561221T035100Z,20571221T094100Z,20581221T153000Z,20591221T212000Z,20601221T031000Z,20611221T090000Z,20621221T144900Z,20631221T203900Z,20641221T022900Z,20651221T081800Z,20661221T140800Z,20671221T195800Z,20681221T014700Z,20691221T073700Z,20701221T132700Z,20711221T191700Z,20721221T010600Z,20731221T065600Z,20741221T124600Z,20751221T183500Z,20761221T002500Z,20771221T061500Z,20781221T120500Z,20791221T175400Z,20801220T234400Z,20811221T053400Z,20821221T112300Z,20831221T171300Z,20841220T230300Z,20851221T045200Z,20861221T104200Z,20871221T163200Z,20881220T222200Z,20891221T041100Z,20901221T100100Z,20911221T155100Z,20921220T214000Z,20931221T033000Z,20941221T092000Z,20951221T150900Z,20961220T205900Z,20971221T024900Z,20981221T083900Z,20991221T142800Z', 1, 1)
 # --------------------------------------------------------
 
 #
diff --git a/other/install_3-0_PostgreSQL.sql b/other/install_3-0_PostgreSQL.sql
index 3165afe740..a36779d9c5 100644
--- a/other/install_3-0_PostgreSQL.sql
+++ b/other/install_3-0_PostgreSQL.sql
@@ -342,6 +342,7 @@ CREATE TABLE {$db_prefix}calendar (
 	sequence smallint NOT NULL DEFAULT '0';
 	uid VARCHAR(255) NOT NULL DEFAULT '',
 	type smallint NOT NULL DEFAULT '0';
+	enabled smallint NOT NULL DEFAULT '1';
 	PRIMARY KEY (id_event)
 );
 
@@ -353,29 +354,6 @@ CREATE INDEX {$db_prefix}calendar_start_date ON {$db_prefix}calendar (start_date
 CREATE INDEX {$db_prefix}calendar_end_date ON {$db_prefix}calendar (end_date);
 CREATE INDEX {$db_prefix}calendar_topic ON {$db_prefix}calendar (id_topic, id_member);
 
-#
-# Sequence for table `calendar_holidays`
-#
-
-CREATE SEQUENCE {$db_prefix}calendar_holidays_seq;
-
-#
-# Table structure for table `calendar_holidays`
-#
-
-CREATE TABLE {$db_prefix}calendar_holidays (
-	id_holiday smallint DEFAULT nextval('{$db_prefix}calendar_holidays_seq'),
-	event_date date NOT NULL DEFAULT '1004-01-01',
-	title varchar(255) NOT NULL DEFAULT '',
-	PRIMARY KEY (id_holiday)
-);
-
-#
-# Indexes for table `calendar_holidays`
-#
-
-CREATE INDEX {$db_prefix}calendar_holidays_event_date ON {$db_prefix}calendar_holidays (event_date);
-
 #
 # Sequence for table `categories`
 #
@@ -2131,217 +2109,39 @@ VALUES (-1,1,0), (0,1,0), (2,1,0);
 # --------------------------------------------------------
 
 #
-# Dumping data for table `calendar_holidays`
-#
-
-INSERT INTO {$db_prefix}calendar_holidays
-	(title, event_date)
-VALUES ('New Year''s', '1004-01-01'),
-	('Christmas', '1004-12-25'),
-	('Valentine''s Day', '1004-02-14'),
-	('St. Patrick''s Day', '1004-03-17'),
-	('April Fools', '1004-04-01'),
-	('Earth Day', '1004-04-22'),
-	('United Nations Day', '1004-10-24'),
-	('Halloween', '1004-10-31'),
-	('Mother''s Day', '2010-05-09'),
-	('Mother''s Day', '2011-05-08'),
-	('Mother''s Day', '2012-05-13'),
-	('Mother''s Day', '2013-05-12'),
-	('Mother''s Day', '2014-05-11'),
-	('Mother''s Day', '2015-05-10'),
-	('Mother''s Day', '2016-05-08'),
-	('Mother''s Day', '2017-05-14'),
-	('Mother''s Day', '2018-05-13'),
-	('Mother''s Day', '2019-05-12'),
-	('Mother''s Day', '2020-05-10'),
-	('Mother''s Day', '2021-05-09'),
-	('Mother''s Day', '2022-05-08'),
-	('Mother''s Day', '2023-05-14'),
-	('Mother''s Day', '2024-05-12'),
-	('Mother''s Day', '2025-05-11'),
-	('Mother''s Day', '2026-05-10'),
-	('Mother''s Day', '2027-05-09'),
-	('Mother''s Day', '2028-05-14'),
-	('Mother''s Day', '2029-05-13'),
-	('Mother''s Day', '2030-05-12'),
-	('Father''s Day', '2010-06-20'),
-	('Father''s Day', '2011-06-19'),
-	('Father''s Day', '2012-06-17'),
-	('Father''s Day', '2013-06-16'),
-	('Father''s Day', '2014-06-15'),
-	('Father''s Day', '2015-06-21'),
-	('Father''s Day', '2016-06-19'),
-	('Father''s Day', '2017-06-18'),
-	('Father''s Day', '2018-06-17'),
-	('Father''s Day', '2019-06-16'),
-	('Father''s Day', '2020-06-21'),
-	('Father''s Day', '2021-06-20'),
-	('Father''s Day', '2022-06-19'),
-	('Father''s Day', '2023-06-18'),
-	('Father''s Day', '2024-06-16'),
-	('Father''s Day', '2025-06-15'),
-	('Father''s Day', '2026-06-21'),
-	('Father''s Day', '2027-06-20'),
-	('Father''s Day', '2028-06-18'),
-	('Father''s Day', '2029-06-17'),
-	('Father''s Day', '2030-06-16'),
-	('Summer Solstice', '2010-06-21'),
-	('Summer Solstice', '2011-06-21'),
-	('Summer Solstice', '2012-06-20'),
-	('Summer Solstice', '2013-06-21'),
-	('Summer Solstice', '2014-06-21'),
-	('Summer Solstice', '2015-06-21'),
-	('Summer Solstice', '2016-06-20'),
-	('Summer Solstice', '2017-06-20'),
-	('Summer Solstice', '2018-06-21'),
-	('Summer Solstice', '2019-06-21'),
-	('Summer Solstice', '2020-06-20'),
-	('Summer Solstice', '2021-06-21'),
-	('Summer Solstice', '2022-06-21'),
-	('Summer Solstice', '2023-06-21'),
-	('Summer Solstice', '2024-06-20'),
-	('Summer Solstice', '2025-06-21'),
-	('Summer Solstice', '2026-06-21'),
-	('Summer Solstice', '2027-06-21'),
-	('Summer Solstice', '2028-06-20'),
-	('Summer Solstice', '2029-06-21'),
-	('Summer Solstice', '2030-06-21'),
-	('Vernal Equinox', '2010-03-20'),
-	('Vernal Equinox', '2011-03-20'),
-	('Vernal Equinox', '2012-03-20'),
-	('Vernal Equinox', '2013-03-20'),
-	('Vernal Equinox', '2014-03-20'),
-	('Vernal Equinox', '2015-03-20'),
-	('Vernal Equinox', '2016-03-20'),
-	('Vernal Equinox', '2017-03-20'),
-	('Vernal Equinox', '2018-03-20'),
-	('Vernal Equinox', '2019-03-20'),
-	('Vernal Equinox', '2020-03-20'),
-	('Vernal Equinox', '2021-03-20'),
-	('Vernal Equinox', '2022-03-20'),
-	('Vernal Equinox', '2023-03-20'),
-	('Vernal Equinox', '2024-03-20'),
-	('Vernal Equinox', '2025-03-20'),
-	('Vernal Equinox', '2026-03-20'),
-	('Vernal Equinox', '2027-03-20'),
-	('Vernal Equinox', '2028-03-20'),
-	('Vernal Equinox', '2029-03-20'),
-	('Vernal Equinox', '2030-03-20'),
-	('Winter Solstice', '2010-12-21'),
-	('Winter Solstice', '2011-12-22'),
-	('Winter Solstice', '2012-12-21'),
-	('Winter Solstice', '2013-12-21'),
-	('Winter Solstice', '2014-12-21'),
-	('Winter Solstice', '2015-12-22'),
-	('Winter Solstice', '2016-12-21'),
-	('Winter Solstice', '2017-12-21'),
-	('Winter Solstice', '2018-12-21'),
-	('Winter Solstice', '2019-12-22'),
-	('Winter Solstice', '2020-12-21'),
-	('Winter Solstice', '2021-12-21'),
-	('Winter Solstice', '2022-12-21'),
-	('Winter Solstice', '2023-12-22'),
-	('Winter Solstice', '2024-12-21'),
-	('Winter Solstice', '2025-12-21'),
-	('Winter Solstice', '2026-12-21'),
-	('Winter Solstice', '2027-12-22'),
-	('Winter Solstice', '2028-12-21'),
-	('Winter Solstice', '2029-12-21'),
-	('Winter Solstice', '2030-12-21'),
-	('Autumnal Equinox', '2010-09-23'),
-	('Autumnal Equinox', '2011-09-23'),
-	('Autumnal Equinox', '2012-09-22'),
-	('Autumnal Equinox', '2013-09-22'),
-	('Autumnal Equinox', '2014-09-23'),
-	('Autumnal Equinox', '2015-09-23'),
-	('Autumnal Equinox', '2016-09-22'),
-	('Autumnal Equinox', '2017-09-22'),
-	('Autumnal Equinox', '2018-09-23'),
-	('Autumnal Equinox', '2019-09-23'),
-	('Autumnal Equinox', '2020-09-22'),
-	('Autumnal Equinox', '2021-09-22'),
-	('Autumnal Equinox', '2022-09-23'),
-	('Autumnal Equinox', '2023-09-23'),
-	('Autumnal Equinox', '2024-09-22'),
-	('Autumnal Equinox', '2025-09-22'),
-	('Autumnal Equinox', '2026-09-23'),
-	('Autumnal Equinox', '2027-09-23'),
-	('Autumnal Equinox', '2028-09-22'),
-	('Autumnal Equinox', '2029-09-22'),
-	('Autumnal Equinox', '2030-09-22');
-
-INSERT INTO {$db_prefix}calendar_holidays
-	(title, event_date)
-VALUES ('Independence Day', '1004-07-04'),
-	('Cinco de Mayo', '1004-05-05'),
-	('Flag Day', '1004-06-14'),
-	('Veterans Day', '1004-11-11'),
-	('Groundhog Day', '1004-02-02'),
-	('Thanksgiving', '2010-11-25'),
-	('Thanksgiving', '2011-11-24'),
-	('Thanksgiving', '2012-11-22'),
-	('Thanksgiving', '2013-11-28'),
-	('Thanksgiving', '2014-11-27'),
-	('Thanksgiving', '2015-11-26'),
-	('Thanksgiving', '2016-11-24'),
-	('Thanksgiving', '2017-11-23'),
-	('Thanksgiving', '2018-11-22'),
-	('Thanksgiving', '2019-11-28'),
-	('Thanksgiving', '2020-11-26'),
-	('Thanksgiving', '2021-11-25'),
-	('Thanksgiving', '2022-11-24'),
-	('Thanksgiving', '2023-11-23'),
-	('Thanksgiving', '2024-11-28'),
-	('Thanksgiving', '2025-11-27'),
-	('Thanksgiving', '2026-11-26'),
-	('Thanksgiving', '2027-11-25'),
-	('Thanksgiving', '2028-11-23'),
-	('Thanksgiving', '2029-11-22'),
-	('Thanksgiving', '2030-11-28'),
-	('Memorial Day', '2010-05-31'),
-	('Memorial Day', '2011-05-30'),
-	('Memorial Day', '2012-05-28'),
-	('Memorial Day', '2013-05-27'),
-	('Memorial Day', '2014-05-26'),
-	('Memorial Day', '2015-05-25'),
-	('Memorial Day', '2016-05-30'),
-	('Memorial Day', '2017-05-29'),
-	('Memorial Day', '2018-05-28'),
-	('Memorial Day', '2019-05-27'),
-	('Memorial Day', '2020-05-25'),
-	('Memorial Day', '2021-05-31'),
-	('Memorial Day', '2022-05-30'),
-	('Memorial Day', '2023-05-29'),
-	('Memorial Day', '2024-05-27'),
-	('Memorial Day', '2025-05-26'),
-	('Memorial Day', '2026-05-25'),
-	('Memorial Day', '2027-05-31'),
-	('Memorial Day', '2028-05-29'),
-	('Memorial Day', '2029-05-28'),
-	('Memorial Day', '2030-05-27'),
-	('Labor Day', '2010-09-06'),
-	('Labor Day', '2011-09-05'),
-	('Labor Day', '2012-09-03'),
-	('Labor Day', '2013-09-02'),
-	('Labor Day', '2014-09-01'),
-	('Labor Day', '2015-09-07'),
-	('Labor Day', '2016-09-05'),
-	('Labor Day', '2017-09-04'),
-	('Labor Day', '2018-09-03'),
-	('Labor Day', '2019-09-02'),
-	('Labor Day', '2020-09-07'),
-	('Labor Day', '2021-09-06'),
-	('Labor Day', '2022-09-05'),
-	('Labor Day', '2023-09-04'),
-	('Labor Day', '2024-09-02'),
-	('Labor Day', '2025-09-01'),
-	('Labor Day', '2026-09-07'),
-	('Labor Day', '2027-09-06'),
-	('Labor Day', '2028-09-04'),
-	('Labor Day', '2029-09-03'),
-	('Labor Day', '2030-09-02'),
-	('D-Day', '1004-06-06');
+# Dumping data for table `calendar`
+#
+
+INSERT INTO {$db_prefix}calendar
+	(title, start_date, end_date, start_time, timezone, location, duration, rrule, rdates, type, enabled)
+VALUES
+	('April Fools\' Day', '2000-04-01', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Christmas', '2000-12-25', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Cinco de Mayo', '2000-05-05', '9999-12-31', NULL, NULL, 'Mexico, USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('D-Day', '2000-06-06', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Easter', '2000-04-23', '9999-12-31', NULL, NULL, '', 'P1D', 'EASTER_W', '', 1, 1),
+	('Earth Day', '2000-04-22', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Father\'s Day', '2000-06-19', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY;BYMONTH=6;BYDAY=3SU', '', 1, 1),
+	('Flag Day', '2000-06-14', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Good Friday', '2000-04-21', '9999-12-31', NULL, NULL, '', 'P1D', 'EASTER_W-P2D', '', 1, 1),
+	('Groundhog Day', '2000-02-02', '9999-12-31', NULL, NULL, 'Canada, USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Halloween', '2000-10-31', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Independence Day', '2000-07-04', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Labor Day', '2000-09-03', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO', '', 1, 1),
+	('Labour Day', '2000-09-03', '9999-12-31', NULL, NULL, 'Canada', 'P1D', 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO', '', 1, 1),
+	('Memorial Day', '2000-05-31', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY;BYMONTH=5;BYDAY=-1MO', '', 1, 1),
+	('Mother\'s Day', '2000-05-08', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY;BYMONTH=5;BYDAY=2SU', '', 1, 1),
+	('New Year\'s Day', '2000-01-01', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Remembrance Day', '2000-11-11', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('St. Patrick\'s Day', '2000-03-17', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Thanksgiving', '2000-11-26', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY;BYMONTH=11;BYDAY=4TH', '', 1, 1),
+	('United Nations Day', '2000-10-24', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Valentine\'s Day', '2000-02-14', '9999-12-31', NULL, NULL, '', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Veterans Day', '2000-11-11', '9999-12-31', NULL, NULL, 'USA', 'P1D', 'FREQ=YEARLY', '', 1, 1),
+	('Vernal Equinox', '2000-03-20', '9999-12-31', '07:30:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20000320T073000Z,20010320T131900Z,20020320T190800Z,20030321T005800Z,20040320T064700Z,20050320T123600Z,20060320T182500Z,20070321T001400Z,20080320T060400Z,20090320T115300Z,20100320T174200Z,20110320T233100Z,20120320T052000Z,20130320T111000Z,20140320T165900Z,20150320T224800Z,20160320T043700Z,20170320T102600Z,20180320T161600Z,20190320T220500Z,20200320T035400Z,20210320T094300Z,20220320T153200Z,20230320T212200Z,20240320T031100Z,20250320T090000Z,20260320T144900Z,20270320T203800Z,20280320T022800Z,20290320T081700Z,20300320T140600Z,20310320T195500Z,20320320T014400Z,20330320T073400Z,20340320T132300Z,20350320T191200Z,20360320T010100Z,20370320T065000Z,20380320T124000Z,20390320T182900Z,20400320T001800Z,20410320T060700Z,20420320T115600Z,20430320T174600Z,20440319T233500Z,20450320T052400Z,20460320T111300Z,20470320T170200Z,20480319T225200Z,20490320T044100Z,20500320T103000Z,20510320T161900Z,20520319T220800Z,20530320T035800Z,20540320T094700Z,20550320T153600Z,20560319T212500Z,20570320T031400Z,20580320T090400Z,20590320T145300Z,20600319T204200Z,20610320T023100Z,20620320T082000Z,20630320T141000Z,20640319T195900Z,20650320T014800Z,20660320T073700Z,20670320T132600Z,20680319T191600Z,20690320T010500Z,20700320T065400Z,20710320T124300Z,20720319T183200Z,20730320T002200Z,20740320T061100Z,20750320T120000Z,20760319T174900Z,20770319T233800Z,20780320T052800Z,20790320T111700Z,20800319T170600Z,20810319T225500Z,20820320T044400Z,20830320T103400Z,20840319T162300Z,20850319T221200Z,20860320T040100Z,20870320T095000Z,20880319T154000Z,20890319T212900Z,20900320T031800Z,20910320T090700Z,20920319T145600Z,20930319T204600Z,20940320T023500Z,20950320T082400Z,20960319T141300Z,20970319T200200Z,20980320T015200Z,20990320T074100Z', 1, 1),
+	('Summer Solstice', '2000-06-21', '9999-12-31', '01:44:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20000621T014400Z,20010621T073200Z,20020621T132000Z,20030621T190800Z,20040621T005600Z,20050621T064400Z,20060621T123200Z,20070621T182100Z,20080621T000900Z,20090621T055700Z,20100621T114500Z,20110621T173300Z,20120620T232100Z,20130621T050900Z,20140621T105700Z,20150621T164600Z,20160620T223400Z,20170621T042200Z,20180621T101000Z,20190621T155800Z,20200620T214600Z,20210621T033400Z,20220621T092300Z,20230621T151100Z,20240620T205900Z,20250621T024700Z,20260621T083500Z,20270621T142300Z,20280620T201100Z,20290621T015900Z,20300621T074800Z,20310621T133600Z,20320620T192400Z,20330621T011200Z,20340621T070000Z,20350621T124800Z,20360620T183600Z,20370621T002400Z,20380621T061300Z,20390621T120100Z,20400620T174900Z,20410620T233700Z,20420621T052500Z,20430621T111300Z,20440620T170100Z,20450620T224900Z,20460621T043700Z,20470621T102600Z,20480620T161400Z,20490620T220200Z,20500621T035000Z,20510621T093800Z,20520620T152600Z,20530620T211400Z,20540621T030200Z,20550621T085100Z,20560620T143900Z,20570620T202700Z,20580621T021500Z,20590621T080300Z,20600620T135100Z,20610620T193900Z,20620621T012700Z,20630621T071600Z,20640620T130400Z,20650620T185200Z,20660621T004000Z,20670621T062800Z,20680620T121600Z,20690620T180400Z,20700620T235200Z,20710621T054100Z,20720620T112900Z,20730620T171700Z,20740620T230500Z,20750621T045300Z,20760620T104100Z,20770620T162900Z,20780620T221700Z,20790621T040500Z,20800620T095400Z,20810620T154200Z,20820620T213000Z,20830621T031800Z,20840620T090600Z,20850620T145400Z,20860620T204200Z,20870621T023000Z,20880620T081900Z,20890620T140700Z,20900620T195500Z,20910621T014300Z,20920620T073100Z,20930620T131900Z,20940620T190700Z,20950621T005500Z,20960620T064300Z,20970620T123200Z,20980620T182000Z,20990621T000800Z', 1, 1),
+	('Autumnal Equinox', '2000-09-22', '9999-12-31', '17:16:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20000922T171600Z,20010922T230500Z,20020923T045400Z,20030923T104200Z,20040922T163100Z,20050922T222000Z,20060923T040800Z,20070923T095700Z,20080922T154600Z,20090922T213400Z,20100923T032300Z,20110923T091200Z,20120922T150100Z,20130922T204900Z,20140923T023800Z,20150923T082700Z,20160922T141500Z,20170922T200400Z,20180923T015300Z,20190923T074100Z,20200922T133000Z,20210922T191900Z,20220923T010700Z,20230923T065600Z,20240922T124500Z,20250922T183300Z,20260923T002200Z,20270923T061100Z,20280922T115900Z,20290922T174800Z,20300922T233700Z,20310923T052600Z,20320922T111400Z,20330922T170300Z,20340922T225200Z,20350923T044000Z,20360922T102900Z,20370922T161800Z,20380922T220600Z,20390923T035500Z,20400922T094400Z,20410922T153200Z,20420922T212100Z,20430923T031000Z,20440922T085800Z,20450922T144700Z,20460922T203600Z,20470923T022400Z,20480922T081300Z,20490922T140200Z,20500922T195000Z,20510923T013900Z,20520922T072800Z,20530922T131600Z,20540922T190500Z,20550923T005400Z,20560922T064200Z,20570922T123100Z,20580922T182000Z,20590923T000800Z,20600922T055700Z,20610922T114600Z,20620922T173400Z,20630922T232300Z,20640922T051200Z,20650922T110000Z,20660922T164900Z,20670922T223800Z,20680922T042600Z,20690922T101500Z,20700922T160400Z,20710922T215200Z,20720922T034100Z,20730922T093000Z,20740922T151800Z,20750922T210700Z,20760922T025600Z,20770922T084400Z,20780922T143300Z,20790922T202200Z,20800922T021000Z,20810922T075900Z,20820922T134800Z,20830922T193600Z,20840922T012500Z,20850922T071400Z,20860922T130200Z,20870922T185100Z,20880922T003900Z,20890922T062800Z,20900922T121700Z,20910922T180500Z,20920921T235400Z,20930922T054300Z,20940922T113100Z,20950922T172000Z,20960921T230900Z,20970922T045700Z,20980922T104600Z,20990922T163500Z', 1, 1),
+	('Winter Solstice', '2000-12-21', '9999-12-31', '13:27:00', 'UTC', '', 'PT1M', 'FREQ=YEARLY;COUNT=1', '20001221T132700Z,20011221T191600Z,20021222T010600Z,20031222T065600Z,20041221T124600Z,20051221T183500Z,20061222T002500Z,20071222T061500Z,20081221T120400Z,20091221T175400Z,20101221T234400Z,20111222T053400Z,20121221T112300Z,20131221T171300Z,20141221T230300Z,20151222T045300Z,20161221T104200Z,20171221T163200Z,20181221T222200Z,20191222T041100Z,20201221T100100Z,20211221T155100Z,20221221T214100Z,20231222T033000Z,20241221T092000Z,20251221T151000Z,20261221T205900Z,20271222T024900Z,20281221T083900Z,20291221T142900Z,20301221T201800Z,20311222T020800Z,20321221T075800Z,20331221T134800Z,20341221T193700Z,20351222T012700Z,20361221T071700Z,20371221T130600Z,20381221T185600Z,20391222T004600Z,20401221T063600Z,20411221T122500Z,20421221T181500Z,20431222T000500Z,20441221T055400Z,20451221T114400Z,20461221T173400Z,20471221T232400Z,20481221T051300Z,20491221T110300Z,20501221T165300Z,20511221T224200Z,20521221T043200Z,20531221T102200Z,20541221T161200Z,20551221T220100Z,20561221T035100Z,20571221T094100Z,20581221T153000Z,20591221T212000Z,20601221T031000Z,20611221T090000Z,20621221T144900Z,20631221T203900Z,20641221T022900Z,20651221T081800Z,20661221T140800Z,20671221T195800Z,20681221T014700Z,20691221T073700Z,20701221T132700Z,20711221T191700Z,20721221T010600Z,20731221T065600Z,20741221T124600Z,20751221T183500Z,20761221T002500Z,20771221T061500Z,20781221T120500Z,20791221T175400Z,20801220T234400Z,20811221T053400Z,20821221T112300Z,20831221T171300Z,20841220T230300Z,20851221T045200Z,20861221T104200Z,20871221T163200Z,20881220T222200Z,20891221T041100Z,20901221T100100Z,20911221T155100Z,20921220T214000Z,20931221T033000Z,20941221T092000Z,20951221T150900Z,20961220T205900Z,20971221T024900Z,20981221T083900Z,20991221T142800Z', 1, 1)
 # --------------------------------------------------------
 
 #
diff --git a/other/upgrade_3-0_MySQL.sql b/other/upgrade_3-0_MySQL.sql
index 5763d05165..3d4bae8d71 100644
--- a/other/upgrade_3-0_MySQL.sql
+++ b/other/upgrade_3-0_MySQL.sql
@@ -106,6 +106,7 @@ ADD COLUMN adjustments JSON DEFAULT NULL;
 ADD COLUMN sequence SMALLINT UNSIGNED NOT NULL DEFAULT '0';
 ADD COLUMN uid VARCHAR(255) NOT NULL DEFAULT '',
 ADD COLUMN type TINYINT UNSIGNED NOT NULL DEFAULT '0';
+ADD COLUMN enabled TINYINT UNSIGNED NOT NULL DEFAULT '1';
 ---#
 
 ---# Set duration and rrule values and change end_date
@@ -169,4 +170,629 @@ ADD COLUMN type TINYINT UNSIGNED NOT NULL DEFAULT '0';
 ---# Drop end_time column from calendar table
 ALTER TABLE {$db_prefix}calendar
 DROP COLUMN end_time;
+---#
+
+---# Migrate holidays to events
+---{
+	$known_holidays = [
+		'April Fools' => [
+			'title' => "April Fools' Day",
+			'start_date' => '2000-04-01',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Christmas' => [
+			'start_date' => '2000-12-25',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Cinco de Mayo' => [
+			'start_date' => '2000-05-05',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'Mexico, USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'D-Day' => [
+			'start_date' => '2000-06-06',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Easter' => [
+			'start_date' => '2000-04-23',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'EASTER_W',
+		],
+		'Earth Day' => [
+			'start_date' => '2000-04-22',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		"Father's Day" => [
+			'start_date' => '2000-06-19',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=6;BYDAY=3SU',
+		],
+		'Flag Day' => [
+			'start_date' => '2000-06-14',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Good Friday' => [
+			'start_date' => '2000-04-21',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'EASTER_W-P2D',
+		],
+		'Groundhog Day' => [
+			'start_date' => '2000-02-02',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'Canada, USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Halloween' => [
+			'start_date' => '2000-10-31',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Independence Day' => [
+			'start_date' => '2000-07-04',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Labor Day' => [
+			'start_date' => '2000-09-03',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO',
+		],
+		'Labour Day' => [
+			'start_date' => '2000-09-03',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'Canada',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO',
+		],
+		'Memorial Day' => [
+			'start_date' => '2000-05-31',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=5;BYDAY=-1MO',
+		],
+		"Mother's Day" => [
+			'start_date' => '2000-05-08',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=5;BYDAY=2SU',
+		],
+		"New Year's" => [
+			'title' => "New Year's Day",
+			'start_date' => '2000-01-01',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Remembrance Day' => [
+			'start_date' => '2000-11-11',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		"St. Patrick's Day" => [
+			'start_date' => '2000-03-17',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Thanksgiving' => [
+			'start_date' => '2000-11-26',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=11;BYDAY=4TH',
+		],
+		'United Nations Day' => [
+			'start_date' => '2000-10-24',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		"Valentine's Day" => [
+			'start_date' => '2000-02-14',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Veterans Day' => [
+			'start_date' => '2000-11-11',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+
+		// Astronomical events
+		'Vernal Equinox' => [
+			'start_date' => '2000-03-20',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '07:30:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20000320T073000Z',
+				'20010320T131900Z',
+				'20020320T190800Z',
+				'20030321T005800Z',
+				'20040320T064700Z',
+				'20050320T123600Z',
+				'20060320T182500Z',
+				'20070321T001400Z',
+				'20080320T060400Z',
+				'20090320T115300Z',
+				'20100320T174200Z',
+				'20110320T233100Z',
+				'20120320T052000Z',
+				'20130320T111000Z',
+				'20140320T165900Z',
+				'20150320T224800Z',
+				'20160320T043700Z',
+				'20170320T102600Z',
+				'20180320T161600Z',
+				'20190320T220500Z',
+				'20200320T035400Z',
+				'20210320T094300Z',
+				'20220320T153200Z',
+				'20230320T212200Z',
+				'20240320T031100Z',
+				'20250320T090000Z',
+				'20260320T144900Z',
+				'20270320T203800Z',
+				'20280320T022800Z',
+				'20290320T081700Z',
+				'20300320T140600Z',
+				'20310320T195500Z',
+				'20320320T014400Z',
+				'20330320T073400Z',
+				'20340320T132300Z',
+				'20350320T191200Z',
+				'20360320T010100Z',
+				'20370320T065000Z',
+				'20380320T124000Z',
+				'20390320T182900Z',
+				'20400320T001800Z',
+				'20410320T060700Z',
+				'20420320T115600Z',
+				'20430320T174600Z',
+				'20440319T233500Z',
+				'20450320T052400Z',
+				'20460320T111300Z',
+				'20470320T170200Z',
+				'20480319T225200Z',
+				'20490320T044100Z',
+				'20500320T103000Z',
+				'20510320T161900Z',
+				'20520319T220800Z',
+				'20530320T035800Z',
+				'20540320T094700Z',
+				'20550320T153600Z',
+				'20560319T212500Z',
+				'20570320T031400Z',
+				'20580320T090400Z',
+				'20590320T145300Z',
+				'20600319T204200Z',
+				'20610320T023100Z',
+				'20620320T082000Z',
+				'20630320T141000Z',
+				'20640319T195900Z',
+				'20650320T014800Z',
+				'20660320T073700Z',
+				'20670320T132600Z',
+				'20680319T191600Z',
+				'20690320T010500Z',
+				'20700320T065400Z',
+				'20710320T124300Z',
+				'20720319T183200Z',
+				'20730320T002200Z',
+				'20740320T061100Z',
+				'20750320T120000Z',
+				'20760319T174900Z',
+				'20770319T233800Z',
+				'20780320T052800Z',
+				'20790320T111700Z',
+				'20800319T170600Z',
+				'20810319T225500Z',
+				'20820320T044400Z',
+				'20830320T103400Z',
+				'20840319T162300Z',
+				'20850319T221200Z',
+				'20860320T040100Z',
+				'20870320T095000Z',
+				'20880319T154000Z',
+				'20890319T212900Z',
+				'20900320T031800Z',
+				'20910320T090700Z',
+				'20920319T145600Z',
+				'20930319T204600Z',
+				'20940320T023500Z',
+				'20950320T082400Z',
+				'20960319T141300Z',
+				'20970319T200200Z',
+				'20980320T015200Z',
+				'20990320T074100Z',
+			],
+		],
+		'Summer Solstice' => [
+			'start_date' => '2000-06-21',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '01:44:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20000621T014400Z',
+				'20010621T073200Z',
+				'20020621T132000Z',
+				'20030621T190800Z',
+				'20040621T005600Z',
+				'20050621T064400Z',
+				'20060621T123200Z',
+				'20070621T182100Z',
+				'20080621T000900Z',
+				'20090621T055700Z',
+				'20100621T114500Z',
+				'20110621T173300Z',
+				'20120620T232100Z',
+				'20130621T050900Z',
+				'20140621T105700Z',
+				'20150621T164600Z',
+				'20160620T223400Z',
+				'20170621T042200Z',
+				'20180621T101000Z',
+				'20190621T155800Z',
+				'20200620T214600Z',
+				'20210621T033400Z',
+				'20220621T092300Z',
+				'20230621T151100Z',
+				'20240620T205900Z',
+				'20250621T024700Z',
+				'20260621T083500Z',
+				'20270621T142300Z',
+				'20280620T201100Z',
+				'20290621T015900Z',
+				'20300621T074800Z',
+				'20310621T133600Z',
+				'20320620T192400Z',
+				'20330621T011200Z',
+				'20340621T070000Z',
+				'20350621T124800Z',
+				'20360620T183600Z',
+				'20370621T002400Z',
+				'20380621T061300Z',
+				'20390621T120100Z',
+				'20400620T174900Z',
+				'20410620T233700Z',
+				'20420621T052500Z',
+				'20430621T111300Z',
+				'20440620T170100Z',
+				'20450620T224900Z',
+				'20460621T043700Z',
+				'20470621T102600Z',
+				'20480620T161400Z',
+				'20490620T220200Z',
+				'20500621T035000Z',
+				'20510621T093800Z',
+				'20520620T152600Z',
+				'20530620T211400Z',
+				'20540621T030200Z',
+				'20550621T085100Z',
+				'20560620T143900Z',
+				'20570620T202700Z',
+				'20580621T021500Z',
+				'20590621T080300Z',
+				'20600620T135100Z',
+				'20610620T193900Z',
+				'20620621T012700Z',
+				'20630621T071600Z',
+				'20640620T130400Z',
+				'20650620T185200Z',
+				'20660621T004000Z',
+				'20670621T062800Z',
+				'20680620T121600Z',
+				'20690620T180400Z',
+				'20700620T235200Z',
+				'20710621T054100Z',
+				'20720620T112900Z',
+				'20730620T171700Z',
+				'20740620T230500Z',
+				'20750621T045300Z',
+				'20760620T104100Z',
+				'20770620T162900Z',
+				'20780620T221700Z',
+				'20790621T040500Z',
+				'20800620T095400Z',
+				'20810620T154200Z',
+				'20820620T213000Z',
+				'20830621T031800Z',
+				'20840620T090600Z',
+				'20850620T145400Z',
+				'20860620T204200Z',
+				'20870621T023000Z',
+				'20880620T081900Z',
+				'20890620T140700Z',
+				'20900620T195500Z',
+				'20910621T014300Z',
+				'20920620T073100Z',
+				'20930620T131900Z',
+				'20940620T190700Z',
+				'20950621T005500Z',
+				'20960620T064300Z',
+				'20970620T123200Z',
+				'20980620T182000Z',
+				'20990621T000800Z',
+			],
+		],
+		'Autumnal Equinox' => [
+			'start_date' => '2000-09-22',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '17:16:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20000922T171600Z',
+				'20010922T230500Z',
+				'20020923T045400Z',
+				'20030923T104200Z',
+				'20040922T163100Z',
+				'20050922T222000Z',
+				'20060923T040800Z',
+				'20070923T095700Z',
+				'20080922T154600Z',
+				'20090922T213400Z',
+				'20100923T032300Z',
+				'20110923T091200Z',
+				'20120922T150100Z',
+				'20130922T204900Z',
+				'20140923T023800Z',
+				'20150923T082700Z',
+				'20160922T141500Z',
+				'20170922T200400Z',
+				'20180923T015300Z',
+				'20190923T074100Z',
+				'20200922T133000Z',
+				'20210922T191900Z',
+				'20220923T010700Z',
+				'20230923T065600Z',
+				'20240922T124500Z',
+				'20250922T183300Z',
+				'20260923T002200Z',
+				'20270923T061100Z',
+				'20280922T115900Z',
+				'20290922T174800Z',
+				'20300922T233700Z',
+				'20310923T052600Z',
+				'20320922T111400Z',
+				'20330922T170300Z',
+				'20340922T225200Z',
+				'20350923T044000Z',
+				'20360922T102900Z',
+				'20370922T161800Z',
+				'20380922T220600Z',
+				'20390923T035500Z',
+				'20400922T094400Z',
+				'20410922T153200Z',
+				'20420922T212100Z',
+				'20430923T031000Z',
+				'20440922T085800Z',
+				'20450922T144700Z',
+				'20460922T203600Z',
+				'20470923T022400Z',
+				'20480922T081300Z',
+				'20490922T140200Z',
+				'20500922T195000Z',
+				'20510923T013900Z',
+				'20520922T072800Z',
+				'20530922T131600Z',
+				'20540922T190500Z',
+				'20550923T005400Z',
+				'20560922T064200Z',
+				'20570922T123100Z',
+				'20580922T182000Z',
+				'20590923T000800Z',
+				'20600922T055700Z',
+				'20610922T114600Z',
+				'20620922T173400Z',
+				'20630922T232300Z',
+				'20640922T051200Z',
+				'20650922T110000Z',
+				'20660922T164900Z',
+				'20670922T223800Z',
+				'20680922T042600Z',
+				'20690922T101500Z',
+				'20700922T160400Z',
+				'20710922T215200Z',
+				'20720922T034100Z',
+				'20730922T093000Z',
+				'20740922T151800Z',
+				'20750922T210700Z',
+				'20760922T025600Z',
+				'20770922T084400Z',
+				'20780922T143300Z',
+				'20790922T202200Z',
+				'20800922T021000Z',
+				'20810922T075900Z',
+				'20820922T134800Z',
+				'20830922T193600Z',
+				'20840922T012500Z',
+				'20850922T071400Z',
+				'20860922T130200Z',
+				'20870922T185100Z',
+				'20880922T003900Z',
+				'20890922T062800Z',
+				'20900922T121700Z',
+				'20910922T180500Z',
+				'20920921T235400Z',
+				'20930922T054300Z',
+				'20940922T113100Z',
+				'20950922T172000Z',
+				'20960921T230900Z',
+				'20970922T045700Z',
+				'20980922T104600Z',
+				'20990922T163500Z',
+			],
+		],
+		'Winter Solstice' => [
+			'start_date' => '2000-12-21',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '13:27:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20001221T132700Z',
+				'20011221T191600Z',
+				'20021222T010600Z',
+				'20031222T065600Z',
+				'20041221T124600Z',
+				'20051221T183500Z',
+				'20061222T002500Z',
+				'20071222T061500Z',
+				'20081221T120400Z',
+				'20091221T175400Z',
+				'20101221T234400Z',
+				'20111222T053400Z',
+				'20121221T112300Z',
+				'20131221T171300Z',
+				'20141221T230300Z',
+				'20151222T045300Z',
+				'20161221T104200Z',
+				'20171221T163200Z',
+				'20181221T222200Z',
+				'20191222T041100Z',
+				'20201221T100100Z',
+				'20211221T155100Z',
+				'20221221T214100Z',
+				'20231222T033000Z',
+				'20241221T092000Z',
+				'20251221T151000Z',
+				'20261221T205900Z',
+				'20271222T024900Z',
+				'20281221T083900Z',
+				'20291221T142900Z',
+				'20301221T201800Z',
+				'20311222T020800Z',
+				'20321221T075800Z',
+				'20331221T134800Z',
+				'20341221T193700Z',
+				'20351222T012700Z',
+				'20361221T071700Z',
+				'20371221T130600Z',
+				'20381221T185600Z',
+				'20391222T004600Z',
+				'20401221T063600Z',
+				'20411221T122500Z',
+				'20421221T181500Z',
+				'20431222T000500Z',
+				'20441221T055400Z',
+				'20451221T114400Z',
+				'20461221T173400Z',
+				'20471221T232400Z',
+				'20481221T051300Z',
+				'20491221T110300Z',
+				'20501221T165300Z',
+				'20511221T224200Z',
+				'20521221T043200Z',
+				'20531221T102200Z',
+				'20541221T161200Z',
+				'20551221T220100Z',
+				'20561221T035100Z',
+				'20571221T094100Z',
+				'20581221T153000Z',
+				'20591221T212000Z',
+				'20601221T031000Z',
+				'20611221T090000Z',
+				'20621221T144900Z',
+				'20631221T203900Z',
+				'20641221T022900Z',
+				'20651221T081800Z',
+				'20661221T140800Z',
+				'20671221T195800Z',
+				'20681221T014700Z',
+				'20691221T073700Z',
+				'20701221T132700Z',
+				'20711221T191700Z',
+				'20721221T010600Z',
+				'20731221T065600Z',
+				'20741221T124600Z',
+				'20751221T183500Z',
+				'20761221T002500Z',
+				'20771221T061500Z',
+				'20781221T120500Z',
+				'20791221T175400Z',
+				'20801220T234400Z',
+				'20811221T053400Z',
+				'20821221T112300Z',
+				'20831221T171300Z',
+				'20841220T230300Z',
+				'20851221T045200Z',
+				'20861221T104200Z',
+				'20871221T163200Z',
+				'20881220T222200Z',
+				'20891221T041100Z',
+				'20901221T100100Z',
+				'20911221T155100Z',
+				'20921220T214000Z',
+				'20931221T033000Z',
+				'20941221T092000Z',
+				'20951221T150900Z',
+				'20961220T205900Z',
+				'20971221T024900Z',
+				'20981221T083900Z',
+				'20991221T142800Z',
+			],
+		],
+	];
+
+	$request = Db::$db->query(
+		'',
+		'SELECT title, GROUP_CONCAT(event_date) as rdates
+		FROM {db_prefix}calendar_holidays
+		GROUP BY title',
+		[]
+	);
+
+	while ($row = Db::$db->fetch_assoc($request)) {
+		if (isset($known_holidays[$row['title']])) {
+			$holiday = &$known_holidays[$row['title']];
+
+			$holiday['type'] = 1;
+			$holiday['title'] = $holiday['title'] ?? $row['title'];
+			$holiday['allday'] = !isset($holiday['start_time']) || !isset($holiday['timezone']) || !in_array($holiday['timezone'], timezone_identifiers_list(\DateTimeZone::ALL_WITH_BC));
+			$holiday['start'] = new \SMF\Time($holiday['start_date'] . (!$holiday['allday'] ? ' ' . $holiday['start_time'] . ' ' . $holiday['timezone'] : ''));
+			$holiday['duration'] = new \DateInterval($holiday['duration'] ?? 'P1D');
+			$holiday['recurrence_end'] = new \SMF\Time($holiday['recurrence_end']);
+			unset($holiday['start_date'], $holiday['start_time'], $holiday['timezone']);
+
+			$event = new \SMF\Calendar\Event(0, $known_holidays[$row['title']]);
+		} else {
+			$row['type'] = 1;
+			$row['allday'] = true;
+			$row['recurrence_end'] = new \SMF\Time('9999-12-31');
+			$row['duration'] = new \DateInterval('P1D');
+			$row['rdates'] = explode(',', $row['rdates']);
+
+			$row['start'] = array_shift($row['rdates']);
+
+			if (preg_match('/^100\d-/', $row['start'])) {
+				$row['start'] = new \SMF\Time(preg_replace('/^100\d-/', '2000-', $row['start']));
+				$row['rrule'] = 'FREQ=YEARLY';
+			} else {
+				$row['start'] = new \SMF\Time($row['start']);
+				$row['rrule'] = 'FREQ=DAILY;COUNT=1';
+			}
+
+			$event = new \SMF\Calendar\Event(0, $row);
+		}
+
+		$event->save();
+	}
+
+	Db::$db->free_result($request);
+---}
+---#
+
+---# Dropping "calendar_holidays"
+DROP TABLE IF EXISTS {$db_prefix}calendar_holidays;
 ---#
\ No newline at end of file
diff --git a/other/upgrade_3-0_PostgreSQL.sql b/other/upgrade_3-0_PostgreSQL.sql
index 38f6527175..06f5602f3f 100644
--- a/other/upgrade_3-0_PostgreSQL.sql
+++ b/other/upgrade_3-0_PostgreSQL.sql
@@ -104,7 +104,7 @@ ADD COLUMN IF NOT EXISTS adjustments jsonb DEFAULT NULL;
 ADD COLUMN IF NOT EXISTS sequence smallint NOT NULL DEFAULT '0';
 ADD COLUMN IF NOT EXISTS uid varchar(255) NOT NULL DEFAULT '',
 ADD COLUMN IF NOT EXISTS type smallint NOT NULL DEFAULT '0';
-
+ADD COLUMN IF NOT EXISTS enabled smallint NOT NULL DEFAULT '1';
 ---#
 
 ---# Set duration and rrule values and change end_date
@@ -168,4 +168,629 @@ ADD COLUMN IF NOT EXISTS type smallint NOT NULL DEFAULT '0';
 ---# Drop end_time column from calendar table
 ALTER TABLE {$db_prefix}calendar
 DROP COLUMN end_time;
+---#
+
+---# Migrate holidays to events
+---{
+	$known_holidays = [
+		'April Fools' => [
+			'title' => "April Fools' Day",
+			'start_date' => '2000-04-01',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Christmas' => [
+			'start_date' => '2000-12-25',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Cinco de Mayo' => [
+			'start_date' => '2000-05-05',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'Mexico, USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'D-Day' => [
+			'start_date' => '2000-06-06',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Easter' => [
+			'start_date' => '2000-04-23',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'EASTER_W',
+		],
+		'Earth Day' => [
+			'start_date' => '2000-04-22',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		"Father's Day" => [
+			'start_date' => '2000-06-19',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=6;BYDAY=3SU',
+		],
+		'Flag Day' => [
+			'start_date' => '2000-06-14',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Good Friday' => [
+			'start_date' => '2000-04-21',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'EASTER_W-P2D',
+		],
+		'Groundhog Day' => [
+			'start_date' => '2000-02-02',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'Canada, USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Halloween' => [
+			'start_date' => '2000-10-31',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Independence Day' => [
+			'start_date' => '2000-07-04',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Labor Day' => [
+			'start_date' => '2000-09-03',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO',
+		],
+		'Labour Day' => [
+			'start_date' => '2000-09-03',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'Canada',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=9;BYDAY=1MO',
+		],
+		'Memorial Day' => [
+			'start_date' => '2000-05-31',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=5;BYDAY=-1MO',
+		],
+		"Mother's Day" => [
+			'start_date' => '2000-05-08',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=5;BYDAY=2SU',
+		],
+		"New Year's" => [
+			'title' => "New Year's Day",
+			'start_date' => '2000-01-01',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Remembrance Day' => [
+			'start_date' => '2000-11-11',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		"St. Patrick's Day" => [
+			'start_date' => '2000-03-17',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Thanksgiving' => [
+			'start_date' => '2000-11-26',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY;BYMONTH=11;BYDAY=4TH',
+		],
+		'United Nations Day' => [
+			'start_date' => '2000-10-24',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		"Valentine's Day" => [
+			'start_date' => '2000-02-14',
+			'recurrence_end' => '9999-12-31',
+			'rrule' => 'FREQ=YEARLY',
+		],
+		'Veterans Day' => [
+			'start_date' => '2000-11-11',
+			'recurrence_end' => '9999-12-31',
+			'location' => 'USA',
+			'rrule' => 'FREQ=YEARLY',
+		],
+
+		// Astronomical events
+		'Vernal Equinox' => [
+			'start_date' => '2000-03-20',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '07:30:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20000320T073000Z',
+				'20010320T131900Z',
+				'20020320T190800Z',
+				'20030321T005800Z',
+				'20040320T064700Z',
+				'20050320T123600Z',
+				'20060320T182500Z',
+				'20070321T001400Z',
+				'20080320T060400Z',
+				'20090320T115300Z',
+				'20100320T174200Z',
+				'20110320T233100Z',
+				'20120320T052000Z',
+				'20130320T111000Z',
+				'20140320T165900Z',
+				'20150320T224800Z',
+				'20160320T043700Z',
+				'20170320T102600Z',
+				'20180320T161600Z',
+				'20190320T220500Z',
+				'20200320T035400Z',
+				'20210320T094300Z',
+				'20220320T153200Z',
+				'20230320T212200Z',
+				'20240320T031100Z',
+				'20250320T090000Z',
+				'20260320T144900Z',
+				'20270320T203800Z',
+				'20280320T022800Z',
+				'20290320T081700Z',
+				'20300320T140600Z',
+				'20310320T195500Z',
+				'20320320T014400Z',
+				'20330320T073400Z',
+				'20340320T132300Z',
+				'20350320T191200Z',
+				'20360320T010100Z',
+				'20370320T065000Z',
+				'20380320T124000Z',
+				'20390320T182900Z',
+				'20400320T001800Z',
+				'20410320T060700Z',
+				'20420320T115600Z',
+				'20430320T174600Z',
+				'20440319T233500Z',
+				'20450320T052400Z',
+				'20460320T111300Z',
+				'20470320T170200Z',
+				'20480319T225200Z',
+				'20490320T044100Z',
+				'20500320T103000Z',
+				'20510320T161900Z',
+				'20520319T220800Z',
+				'20530320T035800Z',
+				'20540320T094700Z',
+				'20550320T153600Z',
+				'20560319T212500Z',
+				'20570320T031400Z',
+				'20580320T090400Z',
+				'20590320T145300Z',
+				'20600319T204200Z',
+				'20610320T023100Z',
+				'20620320T082000Z',
+				'20630320T141000Z',
+				'20640319T195900Z',
+				'20650320T014800Z',
+				'20660320T073700Z',
+				'20670320T132600Z',
+				'20680319T191600Z',
+				'20690320T010500Z',
+				'20700320T065400Z',
+				'20710320T124300Z',
+				'20720319T183200Z',
+				'20730320T002200Z',
+				'20740320T061100Z',
+				'20750320T120000Z',
+				'20760319T174900Z',
+				'20770319T233800Z',
+				'20780320T052800Z',
+				'20790320T111700Z',
+				'20800319T170600Z',
+				'20810319T225500Z',
+				'20820320T044400Z',
+				'20830320T103400Z',
+				'20840319T162300Z',
+				'20850319T221200Z',
+				'20860320T040100Z',
+				'20870320T095000Z',
+				'20880319T154000Z',
+				'20890319T212900Z',
+				'20900320T031800Z',
+				'20910320T090700Z',
+				'20920319T145600Z',
+				'20930319T204600Z',
+				'20940320T023500Z',
+				'20950320T082400Z',
+				'20960319T141300Z',
+				'20970319T200200Z',
+				'20980320T015200Z',
+				'20990320T074100Z',
+			],
+		],
+		'Summer Solstice' => [
+			'start_date' => '2000-06-21',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '01:44:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20000621T014400Z',
+				'20010621T073200Z',
+				'20020621T132000Z',
+				'20030621T190800Z',
+				'20040621T005600Z',
+				'20050621T064400Z',
+				'20060621T123200Z',
+				'20070621T182100Z',
+				'20080621T000900Z',
+				'20090621T055700Z',
+				'20100621T114500Z',
+				'20110621T173300Z',
+				'20120620T232100Z',
+				'20130621T050900Z',
+				'20140621T105700Z',
+				'20150621T164600Z',
+				'20160620T223400Z',
+				'20170621T042200Z',
+				'20180621T101000Z',
+				'20190621T155800Z',
+				'20200620T214600Z',
+				'20210621T033400Z',
+				'20220621T092300Z',
+				'20230621T151100Z',
+				'20240620T205900Z',
+				'20250621T024700Z',
+				'20260621T083500Z',
+				'20270621T142300Z',
+				'20280620T201100Z',
+				'20290621T015900Z',
+				'20300621T074800Z',
+				'20310621T133600Z',
+				'20320620T192400Z',
+				'20330621T011200Z',
+				'20340621T070000Z',
+				'20350621T124800Z',
+				'20360620T183600Z',
+				'20370621T002400Z',
+				'20380621T061300Z',
+				'20390621T120100Z',
+				'20400620T174900Z',
+				'20410620T233700Z',
+				'20420621T052500Z',
+				'20430621T111300Z',
+				'20440620T170100Z',
+				'20450620T224900Z',
+				'20460621T043700Z',
+				'20470621T102600Z',
+				'20480620T161400Z',
+				'20490620T220200Z',
+				'20500621T035000Z',
+				'20510621T093800Z',
+				'20520620T152600Z',
+				'20530620T211400Z',
+				'20540621T030200Z',
+				'20550621T085100Z',
+				'20560620T143900Z',
+				'20570620T202700Z',
+				'20580621T021500Z',
+				'20590621T080300Z',
+				'20600620T135100Z',
+				'20610620T193900Z',
+				'20620621T012700Z',
+				'20630621T071600Z',
+				'20640620T130400Z',
+				'20650620T185200Z',
+				'20660621T004000Z',
+				'20670621T062800Z',
+				'20680620T121600Z',
+				'20690620T180400Z',
+				'20700620T235200Z',
+				'20710621T054100Z',
+				'20720620T112900Z',
+				'20730620T171700Z',
+				'20740620T230500Z',
+				'20750621T045300Z',
+				'20760620T104100Z',
+				'20770620T162900Z',
+				'20780620T221700Z',
+				'20790621T040500Z',
+				'20800620T095400Z',
+				'20810620T154200Z',
+				'20820620T213000Z',
+				'20830621T031800Z',
+				'20840620T090600Z',
+				'20850620T145400Z',
+				'20860620T204200Z',
+				'20870621T023000Z',
+				'20880620T081900Z',
+				'20890620T140700Z',
+				'20900620T195500Z',
+				'20910621T014300Z',
+				'20920620T073100Z',
+				'20930620T131900Z',
+				'20940620T190700Z',
+				'20950621T005500Z',
+				'20960620T064300Z',
+				'20970620T123200Z',
+				'20980620T182000Z',
+				'20990621T000800Z',
+			],
+		],
+		'Autumnal Equinox' => [
+			'start_date' => '2000-09-22',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '17:16:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20000922T171600Z',
+				'20010922T230500Z',
+				'20020923T045400Z',
+				'20030923T104200Z',
+				'20040922T163100Z',
+				'20050922T222000Z',
+				'20060923T040800Z',
+				'20070923T095700Z',
+				'20080922T154600Z',
+				'20090922T213400Z',
+				'20100923T032300Z',
+				'20110923T091200Z',
+				'20120922T150100Z',
+				'20130922T204900Z',
+				'20140923T023800Z',
+				'20150923T082700Z',
+				'20160922T141500Z',
+				'20170922T200400Z',
+				'20180923T015300Z',
+				'20190923T074100Z',
+				'20200922T133000Z',
+				'20210922T191900Z',
+				'20220923T010700Z',
+				'20230923T065600Z',
+				'20240922T124500Z',
+				'20250922T183300Z',
+				'20260923T002200Z',
+				'20270923T061100Z',
+				'20280922T115900Z',
+				'20290922T174800Z',
+				'20300922T233700Z',
+				'20310923T052600Z',
+				'20320922T111400Z',
+				'20330922T170300Z',
+				'20340922T225200Z',
+				'20350923T044000Z',
+				'20360922T102900Z',
+				'20370922T161800Z',
+				'20380922T220600Z',
+				'20390923T035500Z',
+				'20400922T094400Z',
+				'20410922T153200Z',
+				'20420922T212100Z',
+				'20430923T031000Z',
+				'20440922T085800Z',
+				'20450922T144700Z',
+				'20460922T203600Z',
+				'20470923T022400Z',
+				'20480922T081300Z',
+				'20490922T140200Z',
+				'20500922T195000Z',
+				'20510923T013900Z',
+				'20520922T072800Z',
+				'20530922T131600Z',
+				'20540922T190500Z',
+				'20550923T005400Z',
+				'20560922T064200Z',
+				'20570922T123100Z',
+				'20580922T182000Z',
+				'20590923T000800Z',
+				'20600922T055700Z',
+				'20610922T114600Z',
+				'20620922T173400Z',
+				'20630922T232300Z',
+				'20640922T051200Z',
+				'20650922T110000Z',
+				'20660922T164900Z',
+				'20670922T223800Z',
+				'20680922T042600Z',
+				'20690922T101500Z',
+				'20700922T160400Z',
+				'20710922T215200Z',
+				'20720922T034100Z',
+				'20730922T093000Z',
+				'20740922T151800Z',
+				'20750922T210700Z',
+				'20760922T025600Z',
+				'20770922T084400Z',
+				'20780922T143300Z',
+				'20790922T202200Z',
+				'20800922T021000Z',
+				'20810922T075900Z',
+				'20820922T134800Z',
+				'20830922T193600Z',
+				'20840922T012500Z',
+				'20850922T071400Z',
+				'20860922T130200Z',
+				'20870922T185100Z',
+				'20880922T003900Z',
+				'20890922T062800Z',
+				'20900922T121700Z',
+				'20910922T180500Z',
+				'20920921T235400Z',
+				'20930922T054300Z',
+				'20940922T113100Z',
+				'20950922T172000Z',
+				'20960921T230900Z',
+				'20970922T045700Z',
+				'20980922T104600Z',
+				'20990922T163500Z',
+			],
+		],
+		'Winter Solstice' => [
+			'start_date' => '2000-12-21',
+			'recurrence_end' => '2100-01-01',
+			'start_time' => '13:27:00',
+			'timezone' => 'UTC',
+			'duration' => 'PT1M',
+			'rrule' => 'FREQ=YEARLY;COUNT=1',
+			'rdates' => [
+				'20001221T132700Z',
+				'20011221T191600Z',
+				'20021222T010600Z',
+				'20031222T065600Z',
+				'20041221T124600Z',
+				'20051221T183500Z',
+				'20061222T002500Z',
+				'20071222T061500Z',
+				'20081221T120400Z',
+				'20091221T175400Z',
+				'20101221T234400Z',
+				'20111222T053400Z',
+				'20121221T112300Z',
+				'20131221T171300Z',
+				'20141221T230300Z',
+				'20151222T045300Z',
+				'20161221T104200Z',
+				'20171221T163200Z',
+				'20181221T222200Z',
+				'20191222T041100Z',
+				'20201221T100100Z',
+				'20211221T155100Z',
+				'20221221T214100Z',
+				'20231222T033000Z',
+				'20241221T092000Z',
+				'20251221T151000Z',
+				'20261221T205900Z',
+				'20271222T024900Z',
+				'20281221T083900Z',
+				'20291221T142900Z',
+				'20301221T201800Z',
+				'20311222T020800Z',
+				'20321221T075800Z',
+				'20331221T134800Z',
+				'20341221T193700Z',
+				'20351222T012700Z',
+				'20361221T071700Z',
+				'20371221T130600Z',
+				'20381221T185600Z',
+				'20391222T004600Z',
+				'20401221T063600Z',
+				'20411221T122500Z',
+				'20421221T181500Z',
+				'20431222T000500Z',
+				'20441221T055400Z',
+				'20451221T114400Z',
+				'20461221T173400Z',
+				'20471221T232400Z',
+				'20481221T051300Z',
+				'20491221T110300Z',
+				'20501221T165300Z',
+				'20511221T224200Z',
+				'20521221T043200Z',
+				'20531221T102200Z',
+				'20541221T161200Z',
+				'20551221T220100Z',
+				'20561221T035100Z',
+				'20571221T094100Z',
+				'20581221T153000Z',
+				'20591221T212000Z',
+				'20601221T031000Z',
+				'20611221T090000Z',
+				'20621221T144900Z',
+				'20631221T203900Z',
+				'20641221T022900Z',
+				'20651221T081800Z',
+				'20661221T140800Z',
+				'20671221T195800Z',
+				'20681221T014700Z',
+				'20691221T073700Z',
+				'20701221T132700Z',
+				'20711221T191700Z',
+				'20721221T010600Z',
+				'20731221T065600Z',
+				'20741221T124600Z',
+				'20751221T183500Z',
+				'20761221T002500Z',
+				'20771221T061500Z',
+				'20781221T120500Z',
+				'20791221T175400Z',
+				'20801220T234400Z',
+				'20811221T053400Z',
+				'20821221T112300Z',
+				'20831221T171300Z',
+				'20841220T230300Z',
+				'20851221T045200Z',
+				'20861221T104200Z',
+				'20871221T163200Z',
+				'20881220T222200Z',
+				'20891221T041100Z',
+				'20901221T100100Z',
+				'20911221T155100Z',
+				'20921220T214000Z',
+				'20931221T033000Z',
+				'20941221T092000Z',
+				'20951221T150900Z',
+				'20961220T205900Z',
+				'20971221T024900Z',
+				'20981221T083900Z',
+				'20991221T142800Z',
+			],
+		],
+	];
+
+	$request = Db::$db->query(
+		'',
+		'SELECT title, GROUP_CONCAT(event_date) as rdates
+		FROM {db_prefix}calendar_holidays
+		GROUP BY title',
+		[]
+	);
+
+	while ($row = Db::$db->fetch_assoc($request)) {
+		if (isset($known_holidays[$row['title']])) {
+			$holiday = &$known_holidays[$row['title']];
+
+			$holiday['type'] = 1;
+			$holiday['title'] = $holiday['title'] ?? $row['title'];
+			$holiday['allday'] = !isset($holiday['start_time']) || !isset($holiday['timezone']) || !in_array($holiday['timezone'], timezone_identifiers_list(\DateTimeZone::ALL_WITH_BC));
+			$holiday['start'] = new \SMF\Time($holiday['start_date'] . (!$holiday['allday'] ? ' ' . $holiday['start_time'] . ' ' . $holiday['timezone'] : ''));
+			$holiday['duration'] = new \DateInterval($holiday['duration'] ?? 'P1D');
+			$holiday['recurrence_end'] = new \SMF\Time($holiday['recurrence_end']);
+			unset($holiday['start_date'], $holiday['start_time'], $holiday['timezone']);
+
+			$event = new \SMF\Calendar\Event(0, $known_holidays[$row['title']]);
+		} else {
+			$row['type'] = 1;
+			$row['allday'] = true;
+			$row['recurrence_end'] = new \SMF\Time('9999-12-31');
+			$row['duration'] = new \DateInterval('P1D');
+			$row['rdates'] = explode(',', $row['rdates']);
+
+			$row['start'] = array_shift($row['rdates']);
+
+			if (preg_match('/^100\d-/', $row['start'])) {
+				$row['start'] = new \SMF\Time(preg_replace('/^100\d-/', '2000-', $row['start']));
+				$row['rrule'] = 'FREQ=YEARLY';
+			} else {
+				$row['start'] = new \SMF\Time($row['start']);
+				$row['rrule'] = 'FREQ=DAILY;COUNT=1';
+			}
+
+			$event = new \SMF\Calendar\Event(0, $row);
+		}
+
+		$event->save();
+	}
+
+	Db::$db->free_result($request);
+---}
+---#
+
+---# Dropping "calendar_holidays"
+DROP TABLE IF EXISTS {$db_prefix}calendar_holidays;
 ---#
\ No newline at end of file

From 88efeefc2f3cd765c7ab3e4e24edc8ba6b76b036 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Sat, 16 Dec 2023 15:27:48 -0700
Subject: [PATCH 12/22] Implements SMF\Calendar\Birthday

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Actions/Calendar.php         |  75 +----
 Sources/Calendar/Birthday.php        | 392 +++++++++++++++++++++++++++
 Sources/Calendar/Event.php           |   2 +-
 Sources/Calendar/EventOccurrence.php |   8 +
 Themes/default/Calendar.template.php |   8 +-
 5 files changed, 415 insertions(+), 70 deletions(-)
 create mode 100644 Sources/Calendar/Birthday.php

diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index ac9cb9a29f..dab79be4b6 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -18,6 +18,7 @@
 use SMF\Board;
 use SMF\BrowserDetector;
 use SMF\Cache\CacheApi;
+use SMF\Calendar\Birthday;
 use SMF\Calendar\Event;
 use SMF\Calendar\Holiday;
 use SMF\Config;
@@ -675,78 +676,22 @@ public static function call(): void
 	 */
 	public static function getBirthdayRange(string $low_date, string $high_date): array
 	{
-		// We need to search for any birthday in this range, and whatever year that birthday is on.
-		$year_low = (int) substr($low_date, 0, 4);
-		$year_high = (int) substr($high_date, 0, 4);
-
-		if (Db::$db->title !== POSTGRE_TITLE) {
-			// Collect all of the birthdays for this month.  I know, it's a painful query.
-			$result = Db::$db->query(
-				'',
-				'SELECT id_member, real_name, YEAR(birthdate) AS birth_year, birthdate
-				FROM {db_prefix}members
-				WHERE birthdate != {date:no_birthdate}
-					AND (
-						DATE_FORMAT(birthdate, {string:year_low}) BETWEEN {date:low_date} AND {date:high_date}' . ($year_low == $year_high ? '' : '
-						OR DATE_FORMAT(birthdate, {string:year_high}) BETWEEN {date:low_date} AND {date:high_date}') . '
-					)
-					AND is_activated = {int:is_activated}',
-				[
-					'is_activated' => 1,
-					'no_birthdate' => '1004-01-01',
-					'year_low' => $year_low . '-%m-%d',
-					'year_high' => $year_high . '-%m-%d',
-					'low_date' => $low_date,
-					'high_date' => $high_date,
-				],
-			);
-		} else {
-			$result = Db::$db->query(
-				'',
-				'SELECT id_member, real_name, YEAR(birthdate) AS birth_year, birthdate
-				FROM {db_prefix}members
-				WHERE birthdate != {date:no_birthdate}
-					AND (
-						indexable_month_day(birthdate) BETWEEN indexable_month_day({date:year_low_low_date}) AND indexable_month_day({date:year_low_high_date})' . ($year_low == $year_high ? '' : '
-						OR indexable_month_day(birthdate) BETWEEN indexable_month_day({date:year_high_low_date}) AND indexable_month_day({date:year_high_high_date})') . '
-					)
-					AND is_activated = {int:is_activated}',
-				[
-					'is_activated' => 1,
-					'no_birthdate' => '1004-01-01',
-					'year_low_low_date' => $low_date,
-					'year_low_high_date' => $year_low == $year_high ? $high_date : $year_low . '-12-31',
-					'year_high_low_date' => $year_low == $year_high ? $low_date : $year_high . '-01-01',
-					'year_high_high_date' => $high_date,
-				],
-			);
-		}
-		$bday = [];
-
-		while ($row = Db::$db->fetch_assoc($result)) {
-			if ($year_low != $year_high) {
-				$age_year = substr($row['birthdate'], 5) <= substr($high_date, 5) ? $year_high : $year_low;
-			} else {
-				$age_year = $year_low;
-			}
+		$birthdays = [];
+		$high_date = (new \DateTimeImmutable($high_date . ' +1 day'))->format('Y-m-d');
 
-			$bday[$age_year . substr($row['birthdate'], 4)][] = [
-				'id' => $row['id_member'],
-				'name' => $row['real_name'],
-				'age' => $row['birth_year'] > 1004 && $row['birth_year'] <= $age_year ? $age_year - $row['birth_year'] : null,
-				'is_last' => false,
-			];
+		foreach(Birthday::getOccurrencesInRange($low_date, $high_date) as $occurrence) {
+			$birthdays[$occurrence->start->format('Y-m-d')][$occurrence->member] = $occurrence;
 		}
-		Db::$db->free_result($result);
 
-		ksort($bday);
+		ksort($birthdays);
 
 		// Set is_last, so the themes know when to stop placing separators.
-		foreach ($bday as $mday => $array) {
-			$bday[$mday][count($array) - 1]['is_last'] = true;
+		foreach ($birthdays as $date => $bdays) {
+			ksort($birthdays[$date]);
+			$birthdays[$date][array_key_last($birthdays[$date])]['is_last'] = true;
 		}
 
-		return $bday;
+		return $birthdays;
 	}
 
 	/**
diff --git a/Sources/Calendar/Birthday.php b/Sources/Calendar/Birthday.php
new file mode 100644
index 0000000000..e81ef91478
--- /dev/null
+++ b/Sources/Calendar/Birthday.php
@@ -0,0 +1,392 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF\Calendar;
+
+use SMF\Db\DatabaseApi as Db;
+use SMF\Time;
+use SMF\User;
+
+/**
+ * Represents a member's birthday.
+ */
+class Birthday extends Event
+{
+	/*****************
+	 * Class constants
+	 *****************/
+
+	/**
+	 * @var int
+	 *
+	 * A value to add to the ID in order to avoid conflicts with regular events.
+	 */
+	public const ID_MODIFIER = 10 ** 6;
+
+	/*******************
+	 * Public properties
+	 *******************/
+
+	/**
+	 * @var int
+	 *
+	 * This event's type.
+	 * Value must be one of the parent class's TYPE_* constants.
+	 */
+	public int $type = self::TYPE_BIRTHDAY;
+
+	/****************************
+	 * Internal static properties
+	 ****************************/
+
+	/**
+	 * @var bool
+	 *
+	 * If true, Birthday::get() will not destroy instances after yielding them.
+	 * This is used internally by Birthday::getOccurrencesInRange().
+	 */
+	protected static bool $keep_all = false;
+
+	/****************
+	 * Public methods
+	 ****************/
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 */
+	public function save(): void
+	{
+	}
+
+	/**
+	 * Sets custom properties.
+	 *
+	 * @param string $prop The property name.
+	 * @param mixed $value The value to set.
+	 */
+	public function __set(string $prop, $value): void
+	{
+		parent::__set($prop, $value);
+	}
+
+	/**
+	 * Gets custom property values.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __get(string $prop): mixed
+	{
+		return parent::__get($prop);
+	}
+
+	/**
+	 * Checks whether a custom property has been set.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __isset(string $prop): bool
+	{
+		return parent::__isset($prop);
+	}
+
+	/**
+	 * Unsets custom properties.
+	 *
+	 * @param string $prop The property name.
+	 */
+	public function __unset(string $prop): void
+	{
+		parent::__unset($prop);
+	}
+
+	/***********************
+	 * Public static methods
+	 ***********************/
+
+	/**
+	 * Loads a member's birthday.
+	 *
+	 * @param int|array $id ID number of the member.
+	 * @param bool $is_topic Ignored.
+	 * @param bool $use_permissions Ignored.
+	 * @return array Instances of this class for the loaded events.
+	 */
+	public static function load(int $id, bool $is_topic = false, bool $use_permissions = true): array
+	{
+		if ($id <= 0) {
+			return [];
+		}
+
+		$loaded = [];
+
+		$selects = [
+			'm.id_member',
+			'm.real_name',
+			'm.birthdate',
+		];
+		$where = [
+			'm.id_member = {int:id}',
+		];
+		$params = [
+			'id' => $id,
+		];
+
+		foreach(self::queryData($selects, $params, [], $where) as $row) {
+			// Add a value to the ID in order to avoid conflicts with regular events.
+			$id = self::ID_MODIFIER + (int) $row['id_member'];
+
+			$row['view_start'] = \DateTimeImmutable::createFromInterface($row['view_start']);
+			$row['view_end'] = $row['view_start']->add(new \DateInterval('P1D'));
+
+			$loaded[] = new self($id, $row);
+		}
+
+		return $loaded;
+	}
+
+	/**
+	 * Generator that yields instances of this class.
+	 *
+	 * @param string $low_date The low end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param string $high_date The high end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param bool $use_permissions Ignored.
+	 * @param array $query_customizations Customizations to the SQL query.
+	 * @return Generator<Event> Iterating over result gives Event instances.
+	 */
+	public static function get(string $low_date, string $high_date, bool $use_permissions = true, array $query_customizations = []): \Generator
+	{
+		$low_date = !empty($low_date) ? $low_date : (new \DateTime('first day of this month, midnight'))->format('Y-m-d');
+		$high_date = !empty($high_date) ? $high_date : (new \DateTime('first day of next month, midnight'))->format('Y-m-d');
+
+		// We need to search for any birthday in this range, and whatever year that birthday is on.
+		$year_low = (int) substr($low_date, 0, 4);
+		$year_high = (int) substr($high_date, 0, 4);
+
+		$selects = $query_customizations['selects'] ?? [
+			'm.id_member',
+			'm.real_name',
+			'm.birthdate',
+		];
+		$joins = $query_customizations['joins'] ?? [];
+		$order = $query_customizations['order'] ?? [];
+		$group = $query_customizations['group'] ?? [];
+		$limit = $query_customizations['limit'] ?? 0;
+
+		switch (Db::$db->title) {
+			case POSTGRE_TITLE:
+				$where = $query_customizations['where'] ?? [
+					'birthdate != {date:no_birthdate}',
+					'is_activated = {int:is_activated}',
+					'(
+						indexable_month_day(birthdate) BETWEEN indexable_month_day({date:year_low_low_date}) AND indexable_month_day({date:year_low_high_date})' . ($year_low == $year_high ? '' : '
+						OR indexable_month_day(birthdate) BETWEEN indexable_month_day({date:year_high_low_date}) AND indexable_month_day({date:year_high_high_date})') . '
+					)',
+				];
+				$params = $query_customizations['params'] ?? [
+					'is_activated' => 1,
+					'no_birthdate' => '1004-01-01',
+					'year_low_low_date' => $low_date,
+					'year_low_high_date' => $year_low == $year_high ? $high_date : $year_low . '-12-31',
+					'year_high_low_date' => $year_low == $year_high ? $low_date : $year_high . '-01-01',
+					'year_high_high_date' => $high_date,
+				];
+				break;
+
+			default:
+				$where = $query_customizations['where'] ?? [
+					'birthdate != {date:no_birthdate}',
+					'is_activated = {int:is_activated}',
+					'(
+						DATE_FORMAT(birthdate, {string:year_low}) BETWEEN {date:low_date} AND {date:high_date}' . ($year_low == $year_high ? '' : '
+						OR DATE_FORMAT(birthdate, {string:year_high}) BETWEEN {date:low_date} AND {date:high_date}') . '
+					)',
+				];
+				$params = $query_customizations['params'] ?? [
+					'is_activated' => 1,
+					'no_birthdate' => '1004-01-01',
+					'year_low' => $year_low . '-%m-%d',
+					'year_high' => $year_high . '-%m-%d',
+					'low_date' => $low_date,
+					'high_date' => $high_date,
+				];
+				break;
+		}
+
+		foreach(self::queryData($selects, $params, $joins, $where, $order, $group, $limit) as $row) {
+			// Add a value to the ID in order to avoid conflicts with regular events.
+			$id = self::ID_MODIFIER + (int) $row['id_member'];
+
+			$row['view_start'] = new \DateTimeImmutable($low_date);
+			$row['view_end'] = new \DateTimeImmutable($high_date);
+
+			yield (new self($id, $row));
+
+			if (!self::$keep_all) {
+				unset(self::$loaded[$id]);
+			}
+		}
+	}
+
+	/**
+	 * Gets events within the given date range, and returns a generator that
+	 * yields all occurrences of those events within that range.
+	 *
+	 * @param string $low_date The low end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param string $high_date The high end of the range, inclusive, in YYYY-MM-DD format.
+	 * @param bool $use_permissions Whether to use permissions. Default: true.
+	 * @param array $query_customizations Customizations to the SQL query.
+	 * @return Generator<EventOccurrence> Iterating over result gives
+	 *    EventOccurrence instances.
+	 */
+	public static function getOccurrencesInRange(string $low_date, string $high_date, bool $use_permissions = true, array $query_customizations = []): \Generator
+	{
+		self::$keep_all = true;
+
+		foreach (self::get($low_date, $high_date, $use_permissions, $query_customizations) as $event) {
+			foreach ($event->getAllVisibleOccurrences() as $occurrence) {
+				yield $occurrence;
+			}
+		}
+
+		self::$keep_all = false;
+	}
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 *
+	 * @param array $eventOptions Event data ('title', 'start_date', etc.)
+	 */
+	public static function create(array $eventOptions): void
+	{
+	}
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 *
+	 * @param int $id The ID of the event
+	 * @param array $eventOptions An array of event information.
+	 */
+	public static function modify(int $id, array &$eventOptions): void
+	{
+	}
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 *
+	 * @param int $id The event's ID.
+	 */
+	public static function remove(int $id): void
+	{
+	}
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 *
+	 * @param array $eventOptions An array of optional time and date parameters
+	 *    (span, start_year, end_month, etc., etc.)
+	 */
+	public static function setRequestedStartAndDuration(array &$eventOptions): void
+	{
+	}
+
+	/*************************
+	 * Internal static methods
+	 *************************/
+
+	/**
+	 * Generator that runs queries about event data and yields the result rows.
+	 *
+	 * @param array $selects Table columns to select.
+	 * @param array $params Parameters to substitute into query text.
+	 * @param array $joins Zero or more *complete* JOIN clauses.
+	 *    E.g.: 'LEFT JOIN {db_prefix}categories AS c ON (c.id_cat = b.id_cat)'
+	 *    Note that 'FROM {db_prefix}boards AS b' is always part of the query.
+	 * @param array $where Zero or more conditions for the WHERE clause.
+	 *    Conditions will be placed in parentheses and concatenated with AND.
+	 *    If this is left empty, no WHERE clause will be used.
+	 * @param array $order Zero or more conditions for the ORDER BY clause.
+	 *    If this is left empty, no ORDER BY clause will be used.
+	 * @param array $group Zero or more conditions for the GROUP BY clause.
+	 *    If this is left empty, no GROUP BY clause will be used.
+	 * @param int|string $limit Maximum number of results to retrieve.
+	 *    If this is left empty, all results will be retrieved.
+	 *
+	 * @return Generator<array> Iterating over the result gives database rows.
+	 */
+	protected static function queryData(array $selects, array $params = [], array $joins = [], array $where = [], array $order = [], array $group = [], int|string $limit = 0): \Generator
+	{
+		$request = Db::$db->query(
+			'',
+			'SELECT
+				' . implode(', ', $selects) . '
+			FROM {db_prefix}members AS m' . (empty($joins) ? '' : '
+				' . implode("\n\t\t\t\t", $joins)) . (empty($where) ? '' : '
+			WHERE (' . implode(') AND (', $where) . ')') . (empty($group) ? '' : '
+			GROUP BY ' . implode(', ', $group)) . (empty($order) ? '' : '
+			ORDER BY ' . implode(', ', $order)) . (!empty($limit) ? '
+			LIMIT ' . $limit : ''),
+			$params,
+		);
+
+		while ($row = Db::$db->fetch_assoc($request)) {
+			$row['start'] = new Time($row['birthdate']);
+			unset($row['birthdate']);
+
+			$row['recurrence_end'] = (clone $row['start'])->modify('+ 130 years');
+
+			$row['rrule'] = 'FREQ=YEARLY;INTERVAL=1';
+			$row['duration'] = new \DateInterval('P1D');
+			$row['allday'] = true;
+
+			$row['rdates'] = [];
+			$row['exdates'] = [];
+
+			yield $row;
+		}
+		Db::$db->free_result($request);
+	}
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 *
+	 * @param array $eventOptions An array of optional time and date parameters
+	 *    (span, start_year, end_month, etc., etc.)
+	 */
+	protected static function setRequestedRRule(array &$eventOptions): void
+	{
+	}
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 *
+	 * @param Event $event An event that is being created or modified.
+	 */
+	protected static function setRequestedRDatesAndExDates(Event $event): void
+	{
+	}
+
+	/**
+	 * Not applicable. Birthday info is updated via the user's profile.
+	 *
+	 * @param array $input Array of info about event start and end times.
+	 * @return array Standardized version of $input array.
+	 */
+	protected static function standardizeEventOptions(array $input): array
+	{
+		return $input;
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index 6d9b488c6b..a9194dfbd3 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -45,7 +45,7 @@ class Event implements \ArrayAccess
 
 	public const TYPE_EVENT = 0;
 	public const TYPE_HOLIDAY = 1;
-	public const TYPE_BIRTHDAY = 2; // Not yet implemented.
+	public const TYPE_BIRTHDAY = 2;
 
 	/*******************
 	 * Public properties
diff --git a/Sources/Calendar/EventOccurrence.php b/Sources/Calendar/EventOccurrence.php
index 2914e26731..0fd8dadc6c 100644
--- a/Sources/Calendar/EventOccurrence.php
+++ b/Sources/Calendar/EventOccurrence.php
@@ -350,6 +350,13 @@ public function __get(string $prop): mixed
 			case 'end_iso_gmdate':
 				return $end->{substr($prop, 4)};
 
+			case 'age':
+				if ($this->getParentEvent()->type === Event::TYPE_BIRTHDAY && $this->getParentEvent()->start->format('Y') === 1004) {
+					return null;
+				}
+
+				return date_diff($this->start, $this->getParentEvent()->start)->y;
+
 			// These inherit from the parent event unless overridden for this occurrence.
 			case 'allday':
 			case 'duration':
@@ -431,6 +438,7 @@ public function __isset(string $prop): bool
 				return property_exists($this, 'start');
 
 			case 'uid':
+			case 'age':
 			case 'type':
 			case 'allday':
 			case 'duration':
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index f044a38cf9..63f2387669 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -180,8 +180,8 @@ function template_show_upcoming_list($grid_name)
 
 			$birthdays = array();
 
-			foreach ($date as $member)
-				$birthdays[] = '<a href="' . Config::$scripturl . '?action=profile;u=' . $member['id'] . '">' . $member['name'] . (isset($member['age']) ? ' (' . $member['age'] . ')' : '') . '</a>';
+			foreach ($date as $bday)
+				$birthdays[] = '<a href="' . Config::$scripturl . '?action=profile;u=' . $bday->member . '">' . $bday->name . (isset($bday->age) ? ' (' . $bday->age . ')' : '') . '</a>';
 
 			echo implode(', ', $birthdays);
 
@@ -410,9 +410,9 @@ function template_show_month_grid($grid_name, $is_mini = false)
 							id, name (person), age (if they have one set?), and is_last. (last in list?) */
 						$use_js_hide = empty(Utils::$context['show_all_birthdays']) && count($day['birthdays']) > 15;
 						$birthday_count = 0;
-						foreach ($day['birthdays'] as $member)
+						foreach ($day['birthdays'] as $bday)
 						{
-							echo '<a href="', Config::$scripturl, '?action=profile;u=', $member['id'], '"><span class="fix_rtl_names">', $member['name'], '</span>', isset($member['age']) ? ' (' . $member['age'] . ')' : '', '</a>', $member['is_last'] || ($count == 10 && $use_js_hide) ? '' : ', ';
+							echo '<a href="', Config::$scripturl, '?action=profile;u=', $bday['member'], '"><span class="fix_rtl_names">', $bday['name'], '</span>', isset($bday['age']) ? ' (' . $bday['age'] . ')' : '', '</a>', $bday['is_last'] || ($count == 10 && $use_js_hide) ? '' : ', ';
 
 							// 9...10! Let's stop there.
 							if ($birthday_count == 10 && $use_js_hide)

From c5d55cf86140f3ec7f6d2c3d1ef0a6712d1f4e97 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Wed, 27 Dec 2023 16:47:21 -0700
Subject: [PATCH 13/22] Adds support for altering event occurrences

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/General.php             |   7 +
 Sources/Actions/Calendar.php            |  39 ++-
 Sources/Actions/Post.php                |  19 +-
 Sources/Actions/Post2.php               |  23 +-
 Sources/Calendar/Event.php              | 411 +++++++++++++++---------
 Sources/Calendar/EventAdjustment.php    | 162 ++++++++++
 Sources/Calendar/EventOccurrence.php    | 209 +++++++++++-
 Themes/default/Calendar.template.php    |  16 +-
 Themes/default/Display.template.php     |   2 +-
 Themes/default/EventEditor.template.php |  78 ++++-
 Themes/default/Post.template.php        |  10 +-
 Themes/default/scripts/event.js         |  28 +-
 Themes/default/scripts/script.js        |   4 +
 13 files changed, 790 insertions(+), 218 deletions(-)
 create mode 100644 Sources/Calendar/EventAdjustment.php

diff --git a/Languages/en_US/General.php b/Languages/en_US/General.php
index 0236ddc308..bb97af5bf4 100644
--- a/Languages/en_US/General.php
+++ b/Languages/en_US/General.php
@@ -759,6 +759,13 @@
 $txt['calendar_repeat_special'] = 'Special';
 $txt['calendar_repeat_special_rrule_modifier'] = 'Offset';
 $txt['calendar_repeat_offset_examples'] = 'e.g.: +P1D, -PT2H';
+$txt['calendar_repeat_adjustment_label'] = 'Apply changes to';
+$txt['calendar_repeat_adjustment_this_only'] = 'Only this occurrence';
+$txt['calendar_repeat_adjustment_this_and_future'] = 'This and future occurrences';
+$txt['calendar_repeat_adjustment_confirm'] = 'Are you sure you want to apply these changes to all future occurrences?-n--n-WARNING: if you select both &quot;Delete&quot; and &quot;This and future occurrences&quot;, you will delete this and all future occurrences.';
+$txt['calendar_repeat_delete_label'] = 'Delete';
+$txt['calendar_confirm_occurrence_delete'] = 'Are you sure you want to delete this occurrence of the event?-n--n-WARNING: if you select both &quot;Delete&quot; and &quot;This and future occurrences&quot;, you will delete this and all future occurrences.';
+$txt['calendar_repeat_adjustment_edit_first'] = 'Edit original event';
 
 $txt['movetopic_change_subject'] = 'Change the topic’s subject';
 $txt['movetopic_new_subject'] = 'New subject';
diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index dab79be4b6..1d4f2221e8 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -20,6 +20,7 @@
 use SMF\Cache\CacheApi;
 use SMF\Calendar\Birthday;
 use SMF\Calendar\Event;
+use SMF\Calendar\EventOccurrence;
 use SMF\Calendar\Holiday;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
@@ -123,7 +124,7 @@ public function show(): void
 		Theme::loadJavaScriptFile('calendar.js', ['defer' => true], 'smf_calendar');
 
 		// Did they specify an individual event ID? If so, let's splice the year/month in to what we would otherwise be doing.
-		if (isset($_GET['event'])) {
+		if (isset($_GET['event']) && !isset($_REQUEST['start_date'])) {
 			$evid = (int) $_GET['event'];
 
 			if ($evid > 0) {
@@ -387,7 +388,11 @@ public function post(): void
 			}
 			// Deleting...
 			elseif (isset($_REQUEST['deleteevent'])) {
-				Event::remove($_REQUEST['eventid']);
+				if (isset($_REQUEST['recurrenceid'])) {
+					EventOccurrence::remove($_REQUEST['eventid'], $_REQUEST['recurrenceid'], !empty($_REQUEST['affects_future']));
+				} else {
+					Event::remove($_REQUEST['eventid']);
+				}
 			}
 			// ... or just update it?
 			else {
@@ -395,6 +400,15 @@ public function post(): void
 					'title' => Utils::entitySubstr($_REQUEST['evtitle'], 0, 100),
 					'location' => Utils::entitySubstr($_REQUEST['event_location'], 0, 255),
 				];
+
+				if (!empty($_REQUEST['recurrenceid'])) {
+					$eventOptions['recurrenceid'] = $_REQUEST['recurrenceid'];
+				}
+
+				if (!empty($_REQUEST['affects_future'])) {
+					$eventOptions['affects_future'] = $_REQUEST['affects_future'];
+				}
+
 				Event::modify($_REQUEST['eventid'], $eventOptions);
 			}
 
@@ -434,6 +448,7 @@ public function post(): void
 		// New?
 		if (!isset($_REQUEST['eventid'])) {
 			Utils::$context['event'] = new Event(-1);
+			Utils::$context['event']->selected_occurrence = Utils::$context['event']->getFirstOccurrence();
 		} else {
 			list(Utils::$context['event']) = Event::load($_REQUEST['eventid']);
 
@@ -454,21 +469,31 @@ public function post(): void
 			} elseif (!User::$me->allowedTo('calendar_edit_any')) {
 				User::$me->isAllowedTo('calendar_edit_own');
 			}
+
+			if (isset($_REQUEST['recurrenceid'])) {
+				$selected_occurrence = Utils::$context['event']->getOccurrence($_REQUEST['recurrenceid']);
+			}
+
+			if (empty($selected_occurrence)) {
+				$selected_occurrence = Utils::$context['event']->getFirstOccurrence();
+			}
+
+			Utils::$context['event']->selected_occurrence = $selected_occurrence;
 		}
 
 		// An all day event? Set up some nice defaults in case the user wants to change that
-		if (Utils::$context['event']->allday == true) {
+		if (Utils::$context['event']->allday) {
 			$now = Time::create('now');
-			Utils::$context['event']->tz = User::getTimezone();
-			Utils::$context['event']->start->modify(Time::create('now')->format('H:i:s'));
-			Utils::$context['event']->duration = new TimeInterval('PT' . ($now->format('H') < 23 ? '1H' : (59 - $now->format('i')) . 'M'));
+			Utils::$context['event']->selected_occurrence->tz = User::getTimezone();
+			Utils::$context['event']->selected_occurrence->start->modify($now->format('H:i:s'));
+			Utils::$context['event']->selected_occurrence->duration = new TimeInterval('PT' . ($now->format('H') < 23 ? '1H' : (59 - $now->format('i')) . 'M'));
 		}
 
 		// Need this so the user can select a timezone for the event.
 		Utils::$context['all_timezones'] = TimeZone::list(Utils::$context['event']->start_datetime);
 
 		// If the event's timezone is not in SMF's standard list of time zones, try to fix it.
-		Utils::$context['event']->fixTimezone();
+		Utils::$context['event']->selected_occurrence->fixTimezone();
 
 		// Get list of boards that can be posted in.
 		$boards = User::$me->boardsAllowedTo('post_new');
diff --git a/Sources/Actions/Post.php b/Sources/Actions/Post.php
index e11942ce33..51ad42b3d8 100644
--- a/Sources/Actions/Post.php
+++ b/Sources/Actions/Post.php
@@ -737,6 +737,17 @@ protected function initiateEvent(): void
 
 		if (!isset(Utils::$context['event']) || !(Utils::$context['event'] instanceof Event)) {
 			Utils::$context['event'] = new Event(-1);
+			Utils::$context['event']->selected_occurrence = Utils::$context['event']->getFirstOccurrence();
+		} else {
+			if (isset($_REQUEST['recurrenceid'])) {
+				$selected_occurrence = Utils::$context['event']->getOccurrence($_REQUEST['recurrenceid']);
+			}
+
+			if (empty($selected_occurrence)) {
+				$selected_occurrence = Utils::$context['event']->getFirstOccurrence();
+			}
+
+			Utils::$context['event']->selected_occurrence = $selected_occurrence;
 		}
 
 		// Permissions check!
@@ -770,16 +781,16 @@ protected function initiateEvent(): void
 
 		// An all day event? Set up some nice defaults in case the user wants to change that
 		if (Utils::$context['event']->allday == true) {
-			Utils::$context['event']->tz = User::getTimezone();
-			Utils::$context['event']->start->modify(Time::create('now')->format('%H:%M:%S'));
-			Utils::$context['event']->end->modify(Time::create('now + 1 hour')->format('%H:%M:%S'));
+			Utils::$context['event']->selected_occurrence->tz = User::getTimezone();
+			Utils::$context['event']->selected_occurrence->start->modify(Time::create('now')->format('%H:%M:%S'));
+			Utils::$context['event']->selected_occurrence->end->modify(Time::create('now + 1 hour')->format('%H:%M:%S'));
 		}
 
 		// Need this so the user can select a timezone for the event.
 		Utils::$context['all_timezones'] = TimeZone::list(Utils::$context['event']->timestamp);
 
 		// If the event's timezone is not in SMF's standard list of time zones, try to fix it.
-		Utils::$context['event']->fixTimezone();
+		Utils::$context['event']->selected_occurrence->fixTimezone();
 
 		Theme::loadTemplate('EventEditor');
 		Theme::addJavaScriptVar('monthly_byday_items', (string) (count(Utils::$context['event']->byday_items) - 1));
diff --git a/Sources/Actions/Post2.php b/Sources/Actions/Post2.php
index 86eb07f19a..780af2488d 100644
--- a/Sources/Actions/Post2.php
+++ b/Sources/Actions/Post2.php
@@ -21,6 +21,7 @@
 use SMF\BrowserDetector;
 use SMF\Cache\CacheApi;
 use SMF\Calendar\Event;
+use SMF\Calendar\EventOccurrence;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
 use SMF\Draft;
@@ -535,14 +536,11 @@ public function submit(): void
 
 			// Delete it?
 			if (isset($_REQUEST['deleteevent'])) {
-				Db::$db->query(
-					'',
-					'DELETE FROM {db_prefix}calendar
-					WHERE id_event = {int:id_event}',
-					[
-						'id_event' => $_REQUEST['eventid'],
-					],
-				);
+				if (isset($_REQUEST['recurrenceid'])) {
+					EventOccurrence::remove($_REQUEST['eventid'], $_REQUEST['recurrenceid'], !empty($_REQUEST['affects_future']));
+				} else {
+					Event::remove($_REQUEST['eventid']);
+				}
 			}
 			// ... or just update it?
 			else {
@@ -554,6 +552,15 @@ public function submit(): void
 					'location' => $_POST['event_location'],
 					'member' => User::$me->id,
 				];
+
+				if (!empty($_REQUEST['recurrenceid'])) {
+					$eventOptions['recurrenceid'] = $_REQUEST['recurrenceid'];
+				}
+
+				if (!empty($_REQUEST['affects_future'])) {
+					$eventOptions['affects_future'] = $_REQUEST['affects_future'];
+				}
+
 				Event::modify($_REQUEST['eventid'], $eventOptions);
 			}
 		}
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index a9194dfbd3..498e2d8df9 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -33,7 +33,16 @@
 /**
  * Represents a (possibly recurring) calendar event.
  *
- * @todo Add support for editing specific instances as exceptions to the RRule.
+ * Overview the process by which the complete recurrence set is built:
+ *
+ *  1. The $start and $duration values are used to determine when the first
+ *     occurrence happens.
+ *  2. A RecurrenceIterator is constructed using the RRule, RDates, and ExDates.
+ *  3. The RecurrenceIterator generates the list of occurrences.
+ *  4. Individual occurrences are instantiated as EventOccurrence objects when
+ *     needed.
+ *  5. When an EventOccurrence is instantiated, it may have adjustments applied
+ *     to it via an EventAdjustment object.
  */
 class Event implements \ArrayAccess
 {
@@ -242,6 +251,23 @@ class Event implements \ArrayAccess
 	 */
 	public array $special_rrule;
 
+	/**
+	 * @var array
+	 *
+	 * Info about adjustments to apply to subsets of occurrences of this event.
+	 *
+	 * Keys are the IDs of EventOccurrence objects.
+	 * Values are EventAdjustment objects.
+	 */
+	public array $adjustments = [];
+
+	/**
+	 * @var EventOccurrence
+	 *
+	 * When editing an event, this is the occurrence being edited.
+	 */
+	public EventOccurrence $selected_occurrence;
+
 	/**************************
 	 * Public static properties
 	 **************************/
@@ -291,6 +317,13 @@ class Event implements \ArrayAccess
 	 * Internal properties
 	 *********************/
 
+	/**
+	 * @var int
+	 *
+	 * Increments every time the event is modified.
+	 */
+	protected int $sequence = 0;
+
 	/**
 	 * @var bool
 	 *
@@ -317,7 +350,6 @@ class Event implements \ArrayAccess
 		'id_board' => 'board',
 		'id_topic' => 'topic',
 		'id_first_msg' => 'msg',
-		'sequence' => 'modified_time',
 		'id_member' => 'member',
 		'poster' => 'member',
 		'real_name' => 'name',
@@ -489,6 +521,10 @@ public function __construct(int $id = 0, array $props = [])
 			}
 		}
 
+		if ((string) ($props['adjustments'] ?? '') !== '') {
+			$this->adjustments = EventAdjustment::createBatch($props['adjustments']);
+		}
+
 		unset(
 			$props['rrule'],
 			$props['start'],
@@ -610,6 +646,49 @@ public function save(): void
 
 		$rrule = !empty($this->special_rrule) ? implode('', $this->special_rrule) : (string) $this->recurrence_iterator->getRRule();
 
+		$rdates = array_unique($this->recurrence_iterator->getRDates());
+		$exdates = array_unique($this->recurrence_iterator->getExDates());
+
+		$rdates = array_diff($rdates, $exdates);
+		$exdates = array_intersect($exdates, $this->recurrence_iterator->getRRuleOccurrences());
+
+		foreach ($exdates as $key => $exdate) {
+			if (new Time($exdate) > $recurrence_end) {
+				unset($exdates[$key]);
+			}
+		}
+
+		foreach ($this->adjustments as $recurrence_id => $adjustment) {
+			if (new Time((string) $recurrence_id) > $recurrence_end) {
+				unset($this->adjustments[$recurrence_id]);
+
+				continue;
+			}
+
+			if (
+				(
+					!isset($adjustment->offset)
+					|| (string) $adjustment->offset === 'PT0S'
+				)
+				&& (
+					!isset($adjustment->duration)
+					|| (string) $adjustment->duration === (string) $this->duration
+				)
+				&& (
+					!isset($adjustment->location)
+					|| $adjustment->location === $this->location
+				)
+				&& (
+					!isset($adjustment->title)
+					|| $adjustment->title === $this->title
+				)
+			) {
+				unset($this->adjustments[$recurrence_id]);
+			}
+		}
+
+		ksort($this->adjustments);
+
 		// Saving a new event.
 		if (!$is_edit) {
 			$columns = [
@@ -624,6 +703,8 @@ public function save(): void
 				'rrule' => 'string',
 				'rdates' => 'string',
 				'exdates' => 'string',
+				'adjustments' => 'string',
+				'sequence' => 'int',
 				'uid' => 'string-255',
 				'type' => 'int',
 				'enabled' => 'int',
@@ -639,8 +720,10 @@ public function save(): void
 				Utils::truncate($this->location, 255),
 				(string) $this->duration,
 				$rrule,
-				implode(',', $this->recurrence_iterator->getRDates()),
-				implode(',', $this->recurrence_iterator->getExDates()),
+				implode(',', $rdates),
+				implode(',', $exdates),
+				json_encode($this->adjustments),
+				0,
 				$this->uid,
 				$this->type,
 				(int) $this->enabled,
@@ -684,6 +767,8 @@ public function save(): void
 				'rrule = {string:rrule}',
 				'rdates = {string:rdates}',
 				'exdates = {string:exdates}',
+				'adjustments = {string:adjustments}',
+				'sequence = {int:sequence}',
 				'uid = {string:uid}',
 				'type = {int:type}',
 				'enabled = {int:enabled}',
@@ -699,8 +784,10 @@ public function save(): void
 				'id_topic' => $this->topic,
 				'duration' => (string) $this->duration,
 				'rrule' => $rrule,
-				'rdates' => implode(',', $this->recurrence_iterator->getRDates()),
-				'exdates' => implode(',', $this->recurrence_iterator->getExDates()),
+				'rdates' => implode(',', $rdates),
+				'exdates' => implode(',', $exdates),
+				'adjustments' => json_encode($this->adjustments),
+				'sequence' => ++$this->sequence,
 				'uid' => $this->uid,
 				'type' => $this->type,
 				'enabled' => (int) $this->enabled,
@@ -906,6 +993,29 @@ public function getOccurrence(string $id): EventOccurrence|false
 		return $occurrence ?? false;
 	}
 
+	/**
+	 * Updates the RRule to set a new UNTIL date.
+	 *
+	 * This is somewhat complicated because it requires updating the recurrence
+	 * iterator and its underlying RRule.
+	 */
+	public function changeUntil(\DateTimeInterface $until): void
+	{
+		if ($until < $this->start) {
+			throw new \ValueError();
+		}
+
+		$rrule = $this->recurrence_iterator->getRRule();
+
+		unset($rrule->count);
+		$rrule->until = Time::createFromInterface($until);
+		$rrule->until_type = $rrule->until_type ?? ($this->allday ? RecurrenceIterator::TYPE_ALLDAY : RecurrenceIterator::TYPE_ABSOLUTE);
+
+		$this->rrule = (string) $rrule;
+
+		$this->createRecurrenceIterator();
+	}
+
 	/**
 	 * Sets custom properties.
 	 *
@@ -999,7 +1109,7 @@ public function __set(string $prop, mixed $value): void
 						break;
 					}
 				}
-				$this->duration = $this->start->diff($value);
+				$this->duration = TimeInterval::createFromDateInterval($this->start->diff($value));
 				break;
 
 			case 'end_datetime':
@@ -1370,41 +1480,6 @@ public function __isset(string $prop): bool
 		}
 	}
 
-	/**
-	 *
-	 */
-	public function fixTimezone(): void
-	{
-		$all_timezones = TimeZone::list($this->start->date);
-
-		if (!isset($all_timezones[$this->start->timezone])) {
-			$later = strtotime('@' . $this->start->timestamp . ' + 1 year');
-			$tzinfo = (new \DateTimeZone($this->start->timezone))->getTransitions($this->start->timestamp, $later);
-
-			$found = false;
-
-			foreach ($all_timezones as $possible_tzid => $dummy) {
-				// Ignore the "-----" option
-				if (empty($possible_tzid)) {
-					continue;
-				}
-
-				$possible_tzinfo = (new \DateTimeZone($possible_tzid))->getTransitions($this->start->timestamp, $later);
-
-				if ($tzinfo === $possible_tzinfo) {
-					$this->start->timezone = $possible_tzid;
-					$found = true;
-					break;
-				}
-			}
-
-			// Hm. That's weird. Well, just prepend it to the list and let the user deal with it.
-			if (!$found) {
-				$all_timezones = [$this->start->timezone => '[UTC' . $this->start->format('P') . '] - ' . $this->start->timezone] + $all_timezones;
-			}
-		}
-	}
-
 	/***********************
 	 * Public static methods
 	 ***********************/
@@ -1662,6 +1737,23 @@ public static function create(array $eventOptions): void
 	 */
 	public static function modify(int $id, array &$eventOptions): void
 	{
+		list($event) = self::load($id);
+
+		// If request was to modify a specific occurrence, do that instead.
+		if (
+			!empty($eventOptions['recurrenceid'])
+			&& $event->getFirstOccurrence()->id != $eventOptions['recurrenceid']
+		) {
+			$rid = $eventOptions['recurrenceid'];
+			unset($eventOptions['recurrenceid']);
+
+			EventOccurrence::modify($id, $rid, $eventOptions);
+
+			return;
+		}
+
+		unset($eventOptions['recurrenceid']);
+
 		// Sanitize the title and location.
 		foreach (['title', 'location'] as $key) {
 			$eventOptions[$key] = Utils::htmlspecialchars($eventOptions[$key] ?? '', ENT_QUOTES);
@@ -1675,7 +1767,6 @@ public static function modify(int $id, array &$eventOptions): void
 
 		self::setRequestedRRule($eventOptions);
 
-		list($event) = self::load($id);
 		$event->set($eventOptions);
 
 		self::setRequestedRDatesAndExDates($event);
@@ -1710,6 +1801,115 @@ public static function remove(int $id): void
 		unset(self::$loaded[$id]);
 	}
 
+	/**
+	 * Set the start and end dates and times for a posted event for insertion
+	 * into the database.
+	 *
+	 *  - Validates all date and times given to it.
+	 *  - Makes sure events do not exceed the maximum allowed duration (if any).
+	 *  - If passed an array that defines any time or date parameters, they will
+	 *    be used. Otherwise, gets the values from $_POST.
+	 *
+	 * @param array $eventOptions An array of optional time and date parameters
+	 *    (span, start_year, end_month, etc., etc.)
+	 */
+	public static function setRequestedStartAndDuration(array &$eventOptions): void
+	{
+		// Convert unprefixed time unit parameters to start_* parameters.
+		foreach (['year', 'month', 'day', 'hour', 'minute', 'second'] as $key) {
+			foreach ([$eventOptions, $_POST] as &$array) {
+				if (isset($array[$key])) {
+					$array['start_' . $key] = $array[$key];
+					unset($array[$key]);
+				}
+			}
+		}
+
+		// Try to fill missing values in $eventOptions with values from $_POST.
+		foreach (['year', 'month', 'day', 'hour', 'minute', 'second', 'date', 'time', 'datetime'] as $key) {
+			$eventOptions['start_' . $key] = $eventOptions['start_' . $key] ?? ($_POST['start_' . $key] ?? null);
+
+			$eventOptions['end_' . $key] = $eventOptions['end_' . $key] ?? ($_POST['end_' . $key] ?? null);
+		}
+
+		foreach (['allday', 'timezone'] as $key) {
+			$eventOptions[$key] = $eventOptions[$key] ?? ($_POST[$key] ?? null);
+		}
+
+		// Standardize the input.
+		$eventOptions = self::standardizeEventOptions($eventOptions);
+
+		// Create our two Time objects.
+		$eventOptions['start'] = new Time(implode(' ', [$eventOptions['start_date'], $eventOptions['start_time'], $eventOptions['timezone']]));
+
+		$eventOptions['end'] = new Time(implode(' ', [$eventOptions['end_date'], $eventOptions['end_time'], $eventOptions['timezone']]));
+
+		// Make sure the two dates have a sane relationship.
+		if ($eventOptions['end']->getTimestamp() < $eventOptions['start']->getTimestamp()) {
+			$eventOptions['end']->setTimestamp($eventOptions['start']->getTimestamp());
+		}
+
+		// Ensure 'allday' is a boolean.
+		$eventOptions['allday'] = !empty($eventOptions['allday']);
+
+		// Now replace 'end' with 'duration'.
+		if ($eventOptions['allday']) {
+			$eventOptions['end']->modify('+1 day');
+		}
+		$eventOptions['duration'] = TimeInterval::createFromDateInterval($eventOptions['start']->diff($eventOptions['end']));
+		unset($eventOptions['end']);
+
+		// Unset all null values and all scalar date/time parameters.
+		$scalars = [
+			'year',
+			'month',
+			'day',
+			'hour',
+			'minute',
+			'second',
+			'start_datetime',
+			'start_date',
+			'start_time',
+			'start_year',
+			'start_month',
+			'start_day',
+			'start_hour',
+			'start_minute',
+			'start_second',
+			'start_date_local',
+			'start_date_orig',
+			'start_time_local',
+			'start_time_orig',
+			'start_timestamp',
+			'start_iso_gmdate',
+			'end_datetime',
+			'end_date',
+			'end_time',
+			'end_year',
+			'end_month',
+			'end_day',
+			'end_hour',
+			'end_minute',
+			'end_second',
+			'end_date_local',
+			'end_date_orig',
+			'end_time_local',
+			'end_time_orig',
+			'end_timestamp',
+			'end_iso_gmdate',
+			'timezone',
+			'tz',
+			'tzid',
+			'tz_abbrev',
+		];
+
+		foreach($eventOptions as $key => $value) {
+			if (is_null($value) || in_array($key, $scalars)) {
+				unset($eventOptions[$key]);
+			}
+		}
+	}
+
 	/******************
 	 * Internal methods
 	 ******************/
@@ -1835,6 +2035,7 @@ protected function createRecurrenceIterator(): bool
 	 */
 	protected function createOccurrence(\DateTimeInterface $start, ?TimeInterval $duration = null): EventOccurrence
 	{
+		// Set up the basic properties for the occurrence.
 		$props = [
 			'start' => Time::createFromInterface($start),
 		];
@@ -1845,6 +2046,19 @@ protected function createOccurrence(\DateTimeInterface $start, ?TimeInterval $du
 
 		$props['id'] = $this->allday ? $props['start']->format('Ymd') : (clone $props['start'])->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\\THis\\Z');
 
+		// Are their any adjustments to apply?
+		foreach ($this->adjustments as $adjustment) {
+			if ($adjustment->id > $props['id']) {
+				break;
+			}
+
+			if (!$adjustment->affects_future && $adjustment->id < $props['id']) {
+				continue;
+			}
+
+			$props['adjustment'] = $adjustment;
+		}
+
 		return new EventOccurrence($this->id, $props);
 	}
 
@@ -1898,7 +2112,7 @@ protected static function queryData(array $selects, array $params = [], array $j
 			$row['start'] = new Time($row['start_date'] . (!$row['allday'] ? ' ' . $row['start_time'] . ' ' . $row['timezone'] : ' ' . User::getTimezone()));
 			unset($row['start_date'], $row['start_time'], $row['timezone']);
 
-			// Replace duration string with a DateInterval object.
+			// Replace duration string with a TimeInterval object.
 			$row['duration'] = new TimeInterval($row['duration']);
 
 			// end_date is only used for narrowing the query.
@@ -1916,115 +2130,6 @@ protected static function queryData(array $selects, array $params = [], array $j
 		Db::$db->free_result($request);
 	}
 
-	/**
-	 * Set the start and end dates and times for a posted event for insertion
-	 * into the database.
-	 *
-	 *  - Validates all date and times given to it.
-	 *  - Makes sure events do not exceed the maximum allowed duration (if any).
-	 *  - If passed an array that defines any time or date parameters, they will
-	 *    be used. Otherwise, gets the values from $_POST.
-	 *
-	 * @param array $eventOptions An array of optional time and date parameters
-	 *    (span, start_year, end_month, etc., etc.)
-	 */
-	protected static function setRequestedStartAndDuration(array &$eventOptions): void
-	{
-		// Convert unprefixed time unit parameters to start_* parameters.
-		foreach (['year', 'month', 'day', 'hour', 'minute', 'second'] as $key) {
-			foreach ([$eventOptions, $_POST] as &$array) {
-				if (isset($array[$key])) {
-					$array['start_' . $key] = $array[$key];
-					unset($array[$key]);
-				}
-			}
-		}
-
-		// Try to fill missing values in $eventOptions with values from $_POST.
-		foreach (['year', 'month', 'day', 'hour', 'minute', 'second', 'date', 'time', 'datetime'] as $key) {
-			$eventOptions['start_' . $key] = $eventOptions['start_' . $key] ?? ($_POST['start_' . $key] ?? null);
-
-			$eventOptions['end_' . $key] = $eventOptions['end_' . $key] ?? ($_POST['end_' . $key] ?? null);
-		}
-
-		foreach (['allday', 'timezone'] as $key) {
-			$eventOptions[$key] = $eventOptions[$key] ?? ($_POST[$key] ?? null);
-		}
-
-		// Standardize the input.
-		$eventOptions = self::standardizeEventOptions($eventOptions);
-
-		// Create our two Time objects.
-		$eventOptions['start'] = new Time(implode(' ', [$eventOptions['start_date'], $eventOptions['start_time'], $eventOptions['timezone']]));
-
-		$eventOptions['end'] = new Time(implode(' ', [$eventOptions['end_date'], $eventOptions['end_time'], $eventOptions['timezone']]));
-
-		// Make sure the two dates have a sane relationship.
-		if ($eventOptions['end']->getTimestamp() < $eventOptions['start']->getTimestamp()) {
-			$eventOptions['end']->setTimestamp($eventOptions['start']->getTimestamp());
-		}
-
-		// Ensure 'allday' is a boolean.
-		$eventOptions['allday'] = !empty($eventOptions['allday']);
-
-		// Now replace 'end' with 'duration'.
-		if ($eventOptions['allday']) {
-			$eventOptions['end']->modify('+1 day');
-		}
-		$eventOptions['duration'] = $eventOptions['start']->diff($eventOptions['end']);
-		unset($eventOptions['end']);
-
-		// Unset all null values and all scalar date/time parameters.
-		$scalars = [
-			'year',
-			'month',
-			'day',
-			'hour',
-			'minute',
-			'second',
-			'start_datetime',
-			'start_date',
-			'start_time',
-			'start_year',
-			'start_month',
-			'start_day',
-			'start_hour',
-			'start_minute',
-			'start_second',
-			'start_date_local',
-			'start_date_orig',
-			'start_time_local',
-			'start_time_orig',
-			'start_timestamp',
-			'start_iso_gmdate',
-			'end_datetime',
-			'end_date',
-			'end_time',
-			'end_year',
-			'end_month',
-			'end_day',
-			'end_hour',
-			'end_minute',
-			'end_second',
-			'end_date_local',
-			'end_date_orig',
-			'end_time_local',
-			'end_time_orig',
-			'end_timestamp',
-			'end_iso_gmdate',
-			'timezone',
-			'tz',
-			'tzid',
-			'tz_abbrev',
-		];
-
-		foreach($eventOptions as $key => $value) {
-			if (is_null($value) || in_array($key, $scalars)) {
-				unset($eventOptions[$key]);
-			}
-		}
-	}
-
 	/**
 	 * Set the RRule for a posted event for insertion into the database.
 	 *
diff --git a/Sources/Calendar/EventAdjustment.php b/Sources/Calendar/EventAdjustment.php
new file mode 100644
index 0000000000..8591a2a0ac
--- /dev/null
+++ b/Sources/Calendar/EventAdjustment.php
@@ -0,0 +1,162 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2023 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF\Calendar;
+
+use SMF\TimeInterval;
+
+/**
+ * Used to apply adjustments to properties of EventOccurrence objects.
+ */
+class EventAdjustment
+{
+	/*******************
+	 * Public properties
+	 *******************/
+
+	/**
+	 * @var string
+	 *
+	 * The ID of the first affected occurrence of the event.
+	 */
+	public string $id;
+
+	/**
+	 * @var bool
+	 *
+	 * Determines whether future event occurrences are affected or not.
+	 */
+	public bool $affects_future = false;
+
+	/**
+	 * @var SMF\TimeInterval
+	 *
+	 * A TimeInterval object representing how much to the adjust the start of
+	 * the affected occurrences compared to their original start date.
+	 */
+	public ?TimeInterval $offset;
+
+	/**
+	 * @var SMF\TimeInterval
+	 *
+	 * A TimeInterval object representing the duration of the affected
+	 * occurrences of the event.
+	 */
+	public ?TimeInterval $duration;
+
+	/**
+	 * @var string
+	 *
+	 * Location for the affected occurrences of this event.
+	 */
+	public ?string $location;
+
+	/**
+	 * @var string
+	 *
+	 * Title for the affected occurrences of the event.
+	 */
+	public ?string $title;
+
+	/****************
+	 * Public methods
+	 ****************/
+
+	/**
+	 * Constructor.
+	 *
+	 * @param int $id The ID string of the first affected event occurrence.
+	 * @param bool $affects_future Whether future occurrences are also affected.
+	 *    Default: false.
+	 * @param ?array $offset Array representation of SMF\TimeInterval data.
+	 * @param ?array $duration Array representation of SMF\TimeInterval data.
+	 * @param ?string $location Location string.
+	 * @param ?string $title Title string.
+	 */
+	public function __construct(
+		string $id,
+		bool $affects_future = false,
+		?array $offset = null,
+		?array $duration = null,
+		?string $location = null,
+		?string $title = null,
+	) {
+		$this->id = $id;
+		$this->affects_future = $affects_future;
+
+		foreach (['offset', 'duration'] as $prop) {
+			if (!isset(${$prop})) {
+				continue;
+			}
+
+			if (!empty(${$prop}['f'])) {
+				${$prop}['s'] += ${$prop}['f'];
+				unset(${$prop}['f']);
+			}
+
+			$string = 'P';
+
+			foreach (['y', 'm', 'd', 'h', 'i', 's'] as $key) {
+				if ($key === 'h') {
+					$string .= 'T';
+				}
+
+				if (!empty(${$prop}[$key])) {
+					$string .= ${$prop}[$key] . ($key === 'i' ? 'M' : strtoupper($key));
+				}
+			}
+
+			$this->{$prop} = new TimeInterval(rtrim($string, 'PT'));
+			$this->{$prop}->invert = (int) ${$prop}['invert'];
+		}
+
+		$this->location = $location;
+		$this->title = $title;
+	}
+
+	/***********************
+	 * Public static methods
+	 ***********************/
+
+	/**
+	 * Creates a batch of EventAdjustment instances from JSON data.
+	 *
+	 * @param string $json JSON string containing a batch of adjustment data.
+	 * @return array Instances of this class.
+	 */
+	public static function createBatch(string $json): array
+	{
+		$adjustments = [];
+
+		foreach (json_decode($json, true) as $key => $value) {
+			$key = $value['id'] ?? $key;
+
+			$adjustments[$key] = new self(
+				$key,
+				$value['affects_future'] ?? false,
+				$value['offset'] ?? null,
+				$value['duration'] ?? null,
+				$value['location'] ?? null,
+				$value['title'] ?? null,
+			);
+		}
+
+		ksort($adjustments);
+
+		return $adjustments;
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/Sources/Calendar/EventOccurrence.php b/Sources/Calendar/EventOccurrence.php
index 0fd8dadc6c..af19e980c6 100644
--- a/Sources/Calendar/EventOccurrence.php
+++ b/Sources/Calendar/EventOccurrence.php
@@ -19,6 +19,9 @@
 use SMF\ArrayAccessHelper;
 use SMF\Config;
 use SMF\Time;
+use SMF\TimeInterval;
+use SMF\TimeZone;
+use SMF\Utils;
 
 /**
  * Represents a single occurrence of a calendar event.
@@ -56,6 +59,14 @@ class EventOccurrence implements \ArrayAccess
 	 */
 	public Time $start;
 
+	/**
+	 * @var SMF\Time
+	 *
+	 * An EventAdjustment object representing changes made to this occurrence of
+	 * the event, if any.
+	 */
+	public EventAdjustment $adjustment;
+
 	/*********************
 	 * Internal properties
 	 *********************/
@@ -66,11 +77,11 @@ class EventOccurrence implements \ArrayAccess
 	 * Alternate names for some object properties.
 	 */
 	protected array $prop_aliases = [
+		'recurrenceid' => 'id',
 		'eventid' => 'id_event',
 		'id_board' => 'board',
 		'id_topic' => 'topic',
 		'id_first_msg' => 'msg',
-		'sequence' => 'modified_time',
 		'id_member' => 'member',
 		'poster' => 'member',
 		'real_name' => 'name',
@@ -81,6 +92,13 @@ class EventOccurrence implements \ArrayAccess
 		'end_object' => 'end',
 	];
 
+	/**
+	 * @var SMF\Time
+	 *
+	 * A Time object representing the unadjusted start of this occurrence.
+	 */
+	protected Time $unadjusted_start;
+
 	/****************
 	 * Public methods
 	 ****************/
@@ -100,11 +118,79 @@ public function __construct(int $id_event = 0, array $props = [])
 			throw new \ValueError();
 		}
 
+		$this->unadjusted_start = clone $props['start'];
+		$this->start = clone $props['start'];
+		unset($props['start']);
+
+		$this->id = $props['id'] ?? ($this->allday ? $this->start->format('Ymd') : (clone $this->start)->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\\THis\\Z'));
+		unset($props['id']);
+
+		if (isset($props['adjustment'])) {
+			$this->adjustment = $props['adjustment'];
+			unset($props['adjustment']);
+		}
+
+		// Set any other properties we were given.
 		$this->set($props);
 
-		if (!isset($this->id)) {
-			$this->id = $this->allday ? $this->start->format('Ymd') : (clone $this->start)->setTimezone(new \DateTimeZone('UTC'))->format('Ymd\\THis\\Z');
+		// Apply any adjustments.
+		if (isset($this->adjustment)) {
+			if (isset($this->adjustment->offset)) {
+				$this->start->add($this->adjustment->offset);
+			}
+
+			if (isset($this->adjustment->duration)) {
+				$this->duration = clone $this->adjustment->duration;
+			}
+
+			if (isset($this->adjustment->location)) {
+				$this->location = $this->adjustment->location;
+			}
+
+			if (isset($this->adjustment->title)) {
+				$this->title = $this->adjustment->title;
+			}
+		}
+	}
+
+	/**
+	 * Saving an individual occurrence means updating the parent event's
+	 * adjustments property and then saving the parent event.
+	 */
+	public function save()
+	{
+		// Just in case...
+		ksort($this->getParentEvent()->adjustments);
+
+		foreach ($this->getParentEvent()->adjustments as $adjustment) {
+			// Adjustment takes effect after this occurrence, so stop.
+			if ($adjustment->id > $this->id) {
+				break;
+			}
+
+			// Adjustment takes effect before this occurrence but doesn't
+			// affect it, so skip.
+			if (!$adjustment->affects_future && $adjustment->id < $this->id) {
+				continue;
+			}
+
+			// If the found adjustment has all the same values that this
+			// occurrence's current adjustment also has, then there's nothing
+			// that needs to change.
+			if (
+				(string) ($this->adjustment->offset ?? '') === (string) ($adjustment->offset ?? '')
+				&& (string) ($this->adjustment->duration ?? '') === (string) ($adjustment->duration ?? '')
+				&& (string) ($this->adjustment->location ?? '') === (string) ($adjustment->location ?? '')
+				&& (string) ($this->adjustment->title ?? '') === (string) ($adjustment->title ?? '')
+			) {
+				return;
+			}
 		}
+
+		// Add a new entry to the parent event's list of adjustments.
+		$this->adjustment->id = $this->id;
+		$this->getParentEvent()->adjustments[$this->id] = clone $this->adjustment;
+		$this->getParentEvent()->save();
 	}
 
 	/**
@@ -222,10 +308,12 @@ public function __set(string $prop, $value): void
 			case 'duration':
 				if (!($value instanceof \DateInterval)) {
 					try {
-						$value = new \DateInterval((string) $value);
+						$value = new TimeInterval((string) $value);
 					} catch (\Throwable $e) {
 						break;
 					}
+				} elseif (!($value instanceof TimeInterval)) {
+					$value = TimeInterval::createFromDateInterval($value);
 				}
 				$this->custom['duration'] = $value;
 				break;
@@ -264,6 +352,7 @@ public function __set(string $prop, $value): void
 			case 'age':
 			case 'uid':
 			case 'tz_abbrev':
+			case 'sequence':
 			case 'new':
 			case 'is_selected':
 			case 'href':
@@ -357,6 +446,19 @@ public function __get(string $prop): mixed
 
 				return date_diff($this->start, $this->getParentEvent()->start)->y;
 
+			case 'is_first':
+				return $this->unadjusted_start == $this->getParentEvent()->start;
+
+			case 'can_affect_future':
+				return !isset($this->adjustment) || $this->adjustment->affects_future === true;
+
+			// These are set separately for each occurrence.
+			case 'modify_href':
+				return Config::$scripturl . '?action=' . ($this->getParentEvent()->board == 0 ? 'calendar;sa=post;' : 'post;msg=' . $this->getParentEvent()->msg . ';topic=' . $this->getParentEvent()->topic . '.0;calendar;') . 'eventid=' . $this->id_event . ';recurrenceid=' . $this->id . ';' . Utils::$context['session_var'] . '=' . Utils::$context['session_id'];
+
+			case 'export_href':
+				return Config::$scripturl . '?action=calendar;sa=ical;eventid=' . $this->id_event . ';recurrenceid=' . $this->id . ';' . Utils::$context['session_var'] . '=' . Utils::$context['session_id'];
+
 			// These inherit from the parent event unless overridden for this occurrence.
 			case 'allday':
 			case 'duration':
@@ -374,14 +476,13 @@ public function __get(string $prop): mixed
 			case 'member':
 			case 'name':
 			case 'groups':
+			case 'sequence':
 			case 'new':
 			case 'is_selected':
 			case 'href':
 			case 'link':
 			case 'can_edit':
-			case 'modify_href':
 			case 'can_export':
-			case 'export_href':
 				return $this->getParentEvent()->{$prop};
 
 			default:
@@ -451,6 +552,7 @@ public function __isset(string $prop): bool
 			case 'member':
 			case 'name':
 			case 'groups':
+			case 'sequence':
 			case 'new':
 			case 'is_selected':
 			case 'href':
@@ -466,6 +568,41 @@ public function __isset(string $prop): bool
 		}
 	}
 
+	/**
+	 *
+	 */
+	public function fixTimezone(): void
+	{
+		$all_timezones = TimeZone::list($this->start->date);
+
+		if (!isset($all_timezones[$this->start->timezone])) {
+			$later = strtotime('@' . $this->start->timestamp . ' + 1 year');
+			$tzinfo = (new \DateTimeZone($this->start->timezone))->getTransitions($this->start->timestamp, $later);
+
+			$found = false;
+
+			foreach ($all_timezones as $possible_tzid => $dummy) {
+				// Ignore the "-----" option
+				if (empty($possible_tzid)) {
+					continue;
+				}
+
+				$possible_tzinfo = (new \DateTimeZone($possible_tzid))->getTransitions($this->start->timestamp, $later);
+
+				if ($tzinfo === $possible_tzinfo) {
+					$this->start->timezone = $possible_tzid;
+					$found = true;
+					break;
+				}
+			}
+
+			// Hm. That's weird. Well, just prepend it to the list and let the user deal with it.
+			if (!$found) {
+				$all_timezones = [$this->start->timezone => '[UTC' . $this->start->format('P') . '] - ' . $this->start->timezone] + $all_timezones;
+			}
+		}
+	}
+
 	/**
 	 * Retrieves the Event that this EventOccurrence is an occurrence of.
 	 *
@@ -477,7 +614,65 @@ public function getParentEvent(): Event
 			Event::load($this->id_event);
 		}
 
-		return Event::$loaded[$this->id_event];
+		return Event::$loaded[$this->id_event] ?? new Event(-1);
+	}
+
+	/***********************
+	 * Public static methods
+	 ***********************/
+
+	/**
+	 * Modifies an individual occurrence of an event.
+	 *
+	 * @param int $id_event The ID of the parent event.
+	 * @param string $id The recurrence ID of the occurrence.
+	 * @param array $eventOptions An array of event information.
+	 */
+	public static function modify(int $id_event, string $id, array &$eventOptions): void
+	{
+		// Set the new start date and duration.
+		Event::setRequestedStartAndDuration($eventOptions);
+
+		$eventOptions['view_start'] = \DateTimeImmutable::createFromInterface($eventOptions['start']);
+		$eventOptions['view_end'] = $eventOptions['view_start']->add(new TimeInterval('P1D'));
+
+		list($event) = Event::load($id_event);
+
+		$occurrence = $event->getOccurrence($id);
+
+		$offset = TimeInterval::createFromDateInterval(date_diff($occurrence->unadjusted_start, $eventOptions['start']));
+
+		$occurrence->adjustment = new EventAdjustment(
+			$id,
+			isset($occurrence->adjustment) && $occurrence->adjustment->affects_future ? !empty($eventOptions['affects_future']) : false,
+			(string) $offset !== 'PT0S' ? (array) $offset : null,
+			(string) $eventOptions['duration'] !== (string) $occurrence->getParentEvent()->duration ? (array) $eventOptions['duration'] : null,
+			isset($eventOptions['location']) && $eventOptions['location'] !== $occurrence->getParentEvent()->location ? Utils::htmlspecialchars($eventOptions['location'], ENT_QUOTES) : null,
+			isset($eventOptions['title']) && $eventOptions['title'] !== $occurrence->getParentEvent()->title ? Utils::htmlspecialchars($eventOptions['title'], ENT_QUOTES) : null,
+		);
+
+		$occurrence->save();
+	}
+
+	/**
+	 * Removes an event occurrence from the recurrence set.
+	 *
+	 * @param int $id_event The parent event's ID.
+	 * @param string $id The recurrence ID.
+	 */
+	public static function remove(int $id_event, string $id, bool $affects_future = false): void
+	{
+		list($event) = Event::load($id_event);
+
+		if ($event->getFirstOccurrence()->id === $id) {
+			Event::remove($id_event);
+		} elseif ($affects_future) {
+			$event->changeUntil(new Time($id));
+			$event->save();
+		} else {
+			$event->removeOccurrence(new Time($id));
+			$event->save();
+		}
 	}
 }
 
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index 63f2387669..5c8de13156 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -831,9 +831,10 @@ function template_event_post()
 	echo '
 		<form action="', Config::$scripturl, '?action=calendar;sa=post" method="post" name="postevent" accept-charset="', Utils::$context['character_set'], '" onsubmit="submitonce(this);">';
 
-	if (!empty(Utils::$context['event']['new']))
+	if (!empty(Utils::$context['event']->new))
 		echo '
-			<input type="hidden" name="eventid" value="', Utils::$context['event']['eventid'], '">';
+			<input type="hidden" name="eventid" value="', Utils::$context['event']->id, '">
+			<input type="hidden" name="recurrenceid" value="', Utils::$context['event']->selected_occurrence->id, '">';
 
 	// Start the main table.
 	echo '
@@ -863,17 +864,8 @@ function template_event_post()
 	template_event_options();
 
 	echo '
-					<input type="submit" value="', empty(Utils::$context['event']['new']) ? Lang::$txt['save'] : Lang::$txt['post'], '" class="button">';
-
-	// Delete button?
-	if (empty(Utils::$context['event']['new']))
-		echo '
-					<input type="submit" name="deleteevent" value="', Lang::$txt['event_delete'], '" data-confirm="', Lang::$txt['calendar_confirm_delete'], '" class="button you_sure">';
-
-	echo '
+					<input type="submit" value="', empty(Utils::$context['event']->new) ? Lang::$txt['save'] : Lang::$txt['post'], '" class="button">
 					<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
-					<input type="hidden" name="eventid" value="', Utils::$context['event']['eventid'], '">
-
 				</div><!-- .roundframe -->
 			</div><!-- #post_event -->
 		</form>';
diff --git a/Themes/default/Display.template.php b/Themes/default/Display.template.php
index 56864dc583..5204e5033d 100644
--- a/Themes/default/Display.template.php
+++ b/Themes/default/Display.template.php
@@ -187,7 +187,7 @@ function template_main()
 		{
 			echo '
 				<li>
-					<strong class="event_title"><a href="', Config::$scripturl, '?action=calendar;event=', $event['id'], '">', $event['title'], '</a></strong>';
+					<strong class="event_title"><a href="', Config::$scripturl, '?action=calendar;event=', $event['id_event'], (!$event->is_first ? ';start_date=' . $event['start_date'] : ''), '">', $event['title'], '</a></strong>';
 
 			if ($event['can_edit'])
 				echo ' <a href="' . $event['modify_href'] . '"><span class="main_icons calendar_modify" title="', Lang::$txt['calendar_edit'], '"></span></a>';
diff --git a/Themes/default/EventEditor.template.php b/Themes/default/EventEditor.template.php
index 2f2cf7b797..81aa475831 100644
--- a/Themes/default/EventEditor.template.php
+++ b/Themes/default/EventEditor.template.php
@@ -65,14 +65,14 @@ function template_event_options()
 								<label', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>', Lang::$txt['calendar_event_title'], '</label>
 							</dt>
 							<dd>
-								<input type="text" id="evtitle" name="evtitle" maxlength="255" value="', Utils::$context['event']->title, '"', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>
+								<input type="text" id="evtitle" name="evtitle" maxlength="255" value="', Utils::$context['event']->selected_occurrence->title, '"', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>
 							</dd>
 
 							<dt class="clear">
 								<label>', Lang::$txt['location'], '</label>
 							</dt>
 							<dd>
-								<input type="text" name="event_location" id="event_location" maxlength="255" value="', Utils::$context['event']->location, '">
+								<input type="text" name="event_location" id="event_location" maxlength="255" value="', Utils::$context['event']->selected_occurrence->location, '">
 							</dd>
 						</dl>';
 
@@ -84,7 +84,7 @@ function template_event_options()
 								<label for="allday">', Lang::$txt['calendar_allday'], '</label>
 							</dt>
 							<dd>
-								<input type="checkbox" name="allday" id="allday"', !empty(Utils::$context['event']->allday) ? ' checked' : '', !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', '>
+								<input type="checkbox" name="allday" id="allday"', !empty(Utils::$context['event']->allday) ? ' checked' : '', !empty(Utils::$context['event']->special_rrule) || (!Utils::$context['event']->new && !Utils::$context['event']->selected_occurrence->is_first) ? ' disabled' : '', '>
 
 							</dd>
 
@@ -92,16 +92,16 @@ function template_event_options()
 								<label>', Lang::$txt['start'], '</label>
 							</dt>
 							<dd>
-								<input type="date" name="start_date" id="start_date" value="', Utils::$context['event']->start->format('Y-m-d'), '" class="date_input start"', !empty(Utils::$context['event']->special_rrule) ? ' disabled data-force-disabled' : '', '>
-								<input type="time" name="start_time" id="start_time" value="', Utils::$context['event']->start->format('H:i'), '" class="time_input start"', !empty(Utils::$context['event']->allday) || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
+								<input type="date" name="start_date" id="start_date" value="', Utils::$context['event']->selected_occurrence->start->format('Y-m-d'), '" class="date_input start"', !empty(Utils::$context['event']->special_rrule) ? ' disabled data-force-disabled' : '', '>
+								<input type="time" name="start_time" id="start_time" value="', Utils::$context['event']->selected_occurrence->start->format('H:i'), '" class="time_input start"', !empty(Utils::$context['event']->allday) || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
 							</dd>
 
 							<dt class="clear">
 								<label>', Lang::$txt['end'], '</label>
 							</dt>
 							<dd>
-								<input type="date" name="end_date" id="end_date" value="', Utils::$context['event']->end->format('Y-m-d'), '" class="date_input end"', Config::$modSettings['cal_maxspan'] == 1 || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
-								<input type="time" name="end_time" id="end_time" value="', Utils::$context['event']->end->format('H:i'), '" class="time_input end"', !empty(Utils::$context['event']->allday) || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
+								<input type="date" name="end_date" id="end_date" value="', Utils::$context['event']->selected_occurrence->end->format('Y-m-d'), '" class="date_input end"', Config::$modSettings['cal_maxspan'] == 1 || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
+								<input type="time" name="end_time" id="end_time" value="', Utils::$context['event']->selected_occurrence->end->format('H:i'), '" class="time_input end"', !empty(Utils::$context['event']->allday) || !empty(Utils::$context['event']->special_rrule) ? ' disabled' : '', !empty(Utils::$context['event']->special_rrule) ? ' data-force-disabled' : '', '>
 							</dd>
 
 							<dt id="tz_dt" class="clear">
@@ -116,7 +116,7 @@ function template_event_options()
 
 	foreach (Utils::$context['all_timezones'] as $tz => $tzname) {
 		echo '
-									<option', is_numeric($tz) ? ' value="" disabled' : ' value="' . $tz . '"', $tz === Utils::$context['event']->tz ? ' selected' : '', '>', $tzname, '</option>';
+									<option', is_numeric($tz) ? ' value="" disabled' : ' value="' . $tz . '"', $tz === Utils::$context['event']->selected_occurrence->tz ? ' selected' : '', '>', $tzname, '</option>';
 	}
 
 	echo '
@@ -124,6 +124,63 @@ function template_event_options()
 							</dd>
 						</dl>';
 
+	// If this is a new event or the first occurrence of an existing event, show the RRULE stuff.
+	if (Utils::$context['event']->new || Utils::$context['event']->selected_occurrence->is_first) {
+		template_rrule();
+	} else {
+		template_occurrence_options();
+	}
+
+	echo '
+					</fieldset>';
+}
+
+/**
+ * Template used when editing a single occurrence of an event.
+ */
+function template_occurrence_options()
+{
+	if (Utils::$context['event']->selected_occurrence->can_affect_future) {
+		echo '
+						<dl id="occurrence_options">
+							<dt class="clear">
+								<label for="deleteevent">', Lang::$txt['calendar_repeat_delete_label'], '</label>
+							</dt>
+							<dd>
+									<input type="checkbox" name="deleteevent" id="deleteevent" class="you_sure" data-confirm="' . Lang::$txt['calendar_confirm_occurrence_delete'] . '">
+							</dd>
+
+							<dt class="clear">
+								', Lang::$txt['calendar_repeat_adjustment_label'], '
+							</dt>
+							<dd>
+								<label>
+									<input type="radio" name="affects_future" value="0" required checked>
+									<span>', Lang::$txt['calendar_repeat_adjustment_this_only'], '</span>
+								</label>
+								<br>
+								<label>
+									<input type="radio" name="affects_future" value="1" required class="you_sure" data-confirm="' . Lang::$txt['calendar_repeat_adjustment_confirm'] . '">
+									<span>', Lang::$txt['calendar_repeat_adjustment_this_and_future'], '</span>
+								</label>
+							</dd>
+						</dl>';
+	}
+
+	echo '
+						<dl>
+							<dt class="clear"></dt>
+							<dd>
+								<a href="', Utils::$context['event']->modify_href, '" class="smalltext bbc_link">', Lang::$txt['calendar_repeat_adjustment_edit_first'], '</a>
+							</dd>
+						</dl>';
+}
+
+/**
+ * Template for the recurrence rule options for events.
+ */
+function template_rrule()
+{
 	// Recurring event options.
 	echo '
 						<dl id="rrule_options">';
@@ -428,11 +485,13 @@ function template_event_options()
 
 	foreach (Utils::$context['event']->recurrence_iterator->getExDates() as $key => $exdate) {
 		$exdate = new SMF\Time($exdate);
+		$exdate->setTimezone(Utils::$context['event']->start->getTimezone());
 
 		echo '
 										<div>
 											<input type="date" name="EXDATE_date[', $key, ']" value="', $exdate->format('Y-m-d'), '" class="date_input">
 											<input type="time" name="EXDATE_time[', $key, ']" value="', $exdate->format('H:i'), '" class="time_input">
+											<a class="main_icons delete"></a>
 										</div>';
 	}
 
@@ -452,8 +511,7 @@ function template_event_options()
 							</dl>';
 
 	echo '
-						</details>
-					</fieldset>';
+						</details>';
 }
 
 ?>
\ No newline at end of file
diff --git a/Themes/default/Post.template.php b/Themes/default/Post.template.php
index 5cccc71d1e..e5055b4346 100644
--- a/Themes/default/Post.template.php
+++ b/Themes/default/Post.template.php
@@ -88,9 +88,10 @@ function addPollOption()
 			</div>
 			<br>';
 
-	if (Utils::$context['make_event'] && (!Utils::$context['event']['new'] || !empty(Utils::$context['current_board'])))
+	if (Utils::$context['make_event'] && (!Utils::$context['event']->new || !empty(Utils::$context['current_board'])))
 		echo '
-			<input type="hidden" name="eventid" value="', Utils::$context['event']['id'], '">';
+			<input type="hidden" name="eventid" value="', Utils::$context['event']->id, '">
+			<input type="hidden" name="recurrenceid" value="', Utils::$context['event']->selected_occurrence->id, '">';
 
 	// Start the main table.
 	echo '
@@ -437,11 +438,6 @@ function addPollOption()
 					<span id="post_confirm_buttons">
 						', template_control_richedit_buttons(Utils::$context['post_box_name']);
 
-	// Option to delete an event if user is editing one.
-	if (Utils::$context['make_event'] && !Utils::$context['event']['new'])
-		echo '
-						<input type="submit" name="deleteevent" value="', Lang::$txt['event_delete'], '" data-confirm="', Lang::$txt['event_delete_confirm'], '" class="button you_sure">';
-
 	echo '
 					</span>
 				</div><!-- .roundframe -->
diff --git a/Themes/default/scripts/event.js b/Themes/default/scripts/event.js
index 9493177246..b3043ffa1a 100644
--- a/Themes/default/scripts/event.js
+++ b/Themes/default/scripts/event.js
@@ -4,7 +4,9 @@ for (const elem of document.querySelectorAll("#start_date, #start_time, #end_dat
 	elem.addEventListener("change", updateEventUI);
 }
 
-document.getElementById("event_add_byday").addEventListener("click", addByDayItem);
+for (const elem of document.querySelectorAll("#event_add_byday")) {
+	elem.addEventListener("click", addByDayItem);
+}
 
 for (const elem of document.querySelectorAll("#event_add_rdate, #event_add_exdate")) {
 	elem.addEventListener("click", addRDateOrExDate);
@@ -47,7 +49,7 @@ function updateEventUI()
 	}
 
 	// If using a custom RRule, show the relevant options.
-	if (document.getElementById("rrule").value === "custom") {
+	if (document.getElementById("rrule") && document.getElementById("rrule").value === "custom") {
 		// Show select menu for FREQ options.
 		document.getElementById("freq_interval_options").style.display = "";
 
@@ -403,8 +405,10 @@ function updateEventUI()
 
 		}
 	} else {
-		document.getElementById("freq_interval_options").style.display = "none";
-		document.getElementById("freq").value = "DAILY";
+		if (document.getElementById("freq_interval_options")) {
+			document.getElementById("freq_interval_options").style.display = "none";
+			document.getElementById("freq").value = "DAILY";
+		}
 
 		for (const elem of document.querySelectorAll(".rrule_input_wrapper")) {
 			elem.style.display = "none";
@@ -450,7 +454,7 @@ function updateEventUI()
 	}
 
 	// If necessary, show the options for RRule end.
-	if (document.getElementById("rrule").value === "custom" || document.getElementById("rrule").value.substring(0, 5) === "FREQ=") {
+	if (document.getElementById("rrule") && (document.getElementById("rrule").value === "custom" || document.getElementById("rrule").value.substring(0, 5) === "FREQ=")) {
 		const end_option = document.getElementById("end_option");
 		const until = document.getElementById("until");
 		const count = document.getElementById("count");
@@ -533,12 +537,14 @@ function updateEndDate(start_date, end_date)
 	}
 
 	// If necessary, also update the UNTIL field.
-	let until = new Date(document.getElementById("until").value + "T23:59:59.999");
+	if (document.getElementById("until")) {
+		let until = new Date(document.getElementById("until").value + "T23:59:59.999");
 
-	document.getElementById("until").min = document.getElementById("start_date").value;
+		document.getElementById("until").min = document.getElementById("start_date").value;
 
-	if (start_date.getTime() > until.getTime()) {
-		document.getElementById("until").value = document.getElementById("end_date").value;
+		if (start_date.getTime() > until.getTime()) {
+			document.getElementById("until").value = document.getElementById("end_date").value;
+		}
 	}
 
 	// Remember any changes to start and end dates.
@@ -593,6 +599,10 @@ function getNewStartDateByDay(start_date, end_of_month, byday_num, selected_days
 // Determine whether the BYDAY_num select menu's "fifth" option should be enabled or not.
 function enableOrDisableFifth()
 {
+	if (!document.getElementById("byday_name_select_0")) {
+		return;
+	}
+
 	const start_date = new Date(document.getElementById("start_date").value + 'T' + document.getElementById("start_time").value);
 
 	const end_of_month = new Date(
diff --git a/Themes/default/scripts/script.js b/Themes/default/scripts/script.js
index 9397aad431..f21d45710b 100644
--- a/Themes/default/scripts/script.js
+++ b/Themes/default/scripts/script.js
@@ -1732,6 +1732,10 @@ $(function() {
 
 	// Generic confirmation message.
 	$(document).on('click', '.you_sure', function() {
+		if (!this.checked) {
+			return true;
+		}
+
 		var custom_message = $(this).attr('data-confirm');
 		var timeBefore = new Date();
 		var result = confirm(custom_message ? custom_message.replace(/-n-/g, "\n") : smf_you_sure);

From b5a38255eaf8d97980cbaa615a3f2b6497fd0336 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Sun, 7 Jan 2024 03:26:34 -0700
Subject: [PATCH 14/22] Adds support for importing calendar data from iCal
 files

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/Admin.php                  |   1 +
 Languages/en_US/ManageCalendar.php         |   9 ++
 Sources/Actions/Admin/ACP.php              |   4 +
 Sources/Actions/Admin/Calendar.php         |  42 +++++++
 Sources/Calendar/Event.php                 | 126 +++++++++++++++++++++
 Sources/Calendar/Holiday.php               |  17 +++
 Themes/default/ManageCalendar.template.php |  42 +++++++
 7 files changed, 241 insertions(+)

diff --git a/Languages/en_US/Admin.php b/Languages/en_US/Admin.php
index 96c42b340d..878bf98b4f 100644
--- a/Languages/en_US/Admin.php
+++ b/Languages/en_US/Admin.php
@@ -711,6 +711,7 @@
 $txt['boards_edit'] = 'Modify Boards';
 $txt['mboards_new_cat'] = 'Create new category';
 $txt['manage_holidays'] = 'Manage Holidays';
+$txt['calendar_import'] = 'Import Calendar Data';
 $txt['calendar_settings'] = 'Calendar Settings';
 $txt['search_weights'] = 'Weights';
 $txt['search_method'] = 'Search Method';
diff --git a/Languages/en_US/ManageCalendar.php b/Languages/en_US/ManageCalendar.php
index 800cc2dee9..59ea04e774 100644
--- a/Languages/en_US/ManageCalendar.php
+++ b/Languages/en_US/ManageCalendar.php
@@ -55,4 +55,13 @@
 $txt['holidays_date_varies'] = 'Date varies';
 $txt['every_year'] = 'Every Year';
 
+// Importing calendar data
+$txt['calendar_import_desc'] = 'Here you can import holidays and events from iCalendar files.';
+$txt['calendar_import_url'] = 'URL of iCalendar data';
+$txt['calendar_import_url_desc'] = 'This should be the URL of an .ics file.';
+$txt['calendar_import_type'] = 'Import events as';
+$txt['calendar_import_type_holiday'] = 'Holidays';
+$txt['calendar_import_type_event'] = 'Events';
+$txt['calendar_import_button'] = 'Import';
+
 ?>
\ No newline at end of file
diff --git a/Sources/Actions/Admin/ACP.php b/Sources/Actions/Admin/ACP.php
index 26d03f8bb9..5e7f94298c 100644
--- a/Sources/Actions/Admin/ACP.php
+++ b/Sources/Actions/Admin/ACP.php
@@ -305,6 +305,10 @@ class ACP implements ActionInterface
 							'label' => 'manage_holidays',
 							'permission' => 'admin_forum',
 						],
+						'import' => [
+							'label' => 'calendar_import',
+							'permission' => 'admin_forum',
+						],
 						'settings' => [
 							'label' => 'calendar_settings',
 							'permission' => 'admin_forum',
diff --git a/Sources/Actions/Admin/Calendar.php b/Sources/Actions/Admin/Calendar.php
index 846c0bc477..6f679e32bd 100644
--- a/Sources/Actions/Admin/Calendar.php
+++ b/Sources/Actions/Admin/Calendar.php
@@ -32,8 +32,10 @@
 use SMF\Time;
 use SMF\TimeInterval;
 use SMF\TimeZone;
+use SMF\Url;
 use SMF\User;
 use SMF\Utils;
+use SMF\WebFetch\WebFetchApi;
 
 /**
  * This class allows you to manage the calendar.
@@ -66,6 +68,7 @@ class Calendar implements ActionInterface
 	public static array $subactions = [
 		'holidays' => 'holidays',
 		'editholiday' => 'edit',
+		'import' => 'import',
 		'settings' => 'settings',
 	];
 
@@ -302,6 +305,42 @@ public function edit(): void
 		Theme::loadJavaScriptFile('event.js', ['defer' => true], 'smf_event');
 	}
 
+	/**
+	 * Handles importing events and holidays from iCalendar files.
+	 */
+	public function import(): void
+	{
+		Theme::loadTemplate('ManageCalendar');
+		Utils::$context['sub_template'] = 'import';
+		Utils::$context['page_title'] = Lang::$txt['calendar_import'];
+
+		// Submitting?
+		if (isset($_POST[Utils::$context['session_var']], $_POST['ics_url'], $_POST['type'])) {
+			User::$me->checkSession();
+			SecurityToken::validate('admin-calendarimport');
+
+			$ics_url = new Url($_POST['ics_url'], true);
+
+			if ($ics_url->isValid()) {
+				$ics_data = WebFetchApi::fetch($ics_url);
+			}
+
+			if (!empty($ics_data)) {
+				switch ($_POST['type']) {
+					case 'holiday':
+						Holiday::import($ics_data);
+						break;
+
+					case 'event':
+						Event::import($ics_data);
+						break;
+				}
+			}
+		}
+
+		SecurityToken::create('admin-calendarimport');
+	}
+
 	/**
 	 * Handles showing and changing calendar settings.
 	 */
@@ -474,6 +513,9 @@ protected function __construct()
 				'holidays' => [
 					'description' => Lang::$txt['manage_holidays_desc'],
 				],
+				'import' => [
+					'description' => Lang::$txt['calendar_import_desc'],
+				],
 				'settings' => [
 					'description' => Lang::$txt['calendar_settings_desc'],
 				],
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index 498e2d8df9..e580d02873 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -1801,6 +1801,132 @@ public static function remove(int $id): void
 		unset(self::$loaded[$id]);
 	}
 
+	/**
+	 * Imports events from iCalendar data and saves them to the database.
+	 *
+	 * @param string $ics Some iCalendar data (e.g. the content of an ICS file).
+	 * @return array An array of instances of this class.
+	 */
+	public static function import(string $ics): array
+	{
+		$events = self::constructFromICal($ics, self::TYPE_EVENT);
+
+		foreach ($events as $event) {
+			$event->save();
+		}
+
+		return $events;
+	}
+
+	/**
+	 * Constructs instances of this class from iCalendar data.
+	 *
+	 * @param string $ics Some iCalendar data (e.g. the content of an ICS file).
+	 * @param ?int $type Forces all events to be imported as the specified type.
+	 *    Values can be one of this class's TYPE_* constants, or null for auto.
+	 * @return array An array of instances of this class.
+	 */
+	public static function constructFromICal(string $ics, ?int $type = null): array
+	{
+		$events = [];
+
+		$ics = preg_replace('/\R\h/', '', $ics);
+
+		$lines = preg_split('/\R/', $ics);
+
+		$in_event = false;
+		$props = [];
+
+		foreach ($lines as $line) {
+			if ($line === 'BEGIN:VEVENT') {
+				$in_event = true;
+			}
+
+			if ($line === 'END:VEVENT') {
+				if (
+					isset(
+						$props['start'],
+						$props['duration'],
+						$props['title'],
+					)
+				) {
+					if (isset($type)) {
+						$props['type'] = $type;
+					}
+
+					if (isset($props['type']) && $props['type'] === self::TYPE_HOLIDAY) {
+						$events[] = new Holiday(0, $props);
+					} else {
+						unset($props['type']);
+						$events[] = new self(0, $props);
+					}
+				}
+
+				$in_event = false;
+				$props = [];
+			}
+
+			if (!$in_event) {
+				continue;
+			}
+
+			if (strpos($line, 'DTSTART') === 0) {
+				if (preg_match('/;TZID=([^:;]+)[^:]*:(\d+T\d+)/', $line, $matches)) {
+					$props['start'] = new Time($matches[2] . ' ' . $matches[1]);
+					$props['allday'] = false;
+				} elseif (preg_match('/:(\d+T\d+)(Z?)/', $line, $matches)) {
+					$props['start'] = new Time($matches[1] . ($matches[2] === 'Z' ? ' UTC' : ''));
+					$props['allday'] = false;
+				} elseif (preg_match('/:(\d+)/', $line, $matches)) {
+					$props['start'] = new Time($matches[1] . ' ' . User::getTimezone());
+					$props['allday'] = true;
+				}
+			}
+
+			if (strpos($line, 'DTEND') === 0) {
+				if (preg_match('/;TZID=([^:;]+)[^:]*:(\d+T\d+)/', $line, $matches)) {
+					$end = new Time($matches[2] . ' ' . $matches[1]);
+				} elseif (preg_match('/:(\d+T\d+)(Z?)/', $line, $matches)) {
+					$end = new Time($matches[1] . ($matches[2] === 'Z' ? ' UTC' : ''));
+				} elseif (preg_match('/:(\d+)/', $line, $matches)) {
+					$end = new Time($matches[1] . ' ' . User::getTimezone());
+				}
+
+				$props['duration'] = TimeInterval::createFromDateInterval($props['start']->diff($end));
+			}
+
+			if (strpos($line, 'DURATION') === 0) {
+				$props['duration'] = new TimeInterval(substr($line, strpos($line, ':') + 1));
+			}
+
+			if (!isset($type) && strpos($line, 'CATEGORIES') === 0) {
+				$props['type'] = str_contains(strtolower($line), 'holiday') ? self::TYPE_HOLIDAY : self::TYPE_EVENT;
+			}
+
+			if (strpos($line, 'SUMMARY') === 0) {
+				$props['title'] = substr($line, strpos($line, ':') + 1);
+			}
+
+			if (strpos($line, 'LOCATION') === 0) {
+				$props['location'] = substr($line, strpos($line, ':') + 1);
+			}
+
+			if (strpos($line, 'RRULE') === 0) {
+				$props['rrule'] = substr($line, strpos($line, ':') + 1);
+			}
+
+			if (strpos($line, 'RDATE') === 0) {
+				$props['rdates'] = explode(',', substr($line, strpos($line, ':') + 1));
+			}
+
+			if (strpos($line, 'EXDATE') === 0) {
+				$props['exdates'] = explode(',', substr($line, strpos($line, ':') + 1));
+			}
+		}
+
+		return $events;
+	}
+
 	/**
 	 * Set the start and end dates and times for a posted event for insertion
 	 * into the database.
diff --git a/Sources/Calendar/Holiday.php b/Sources/Calendar/Holiday.php
index 05fdb2f88a..3148fbe15a 100644
--- a/Sources/Calendar/Holiday.php
+++ b/Sources/Calendar/Holiday.php
@@ -424,6 +424,23 @@ public static function remove(int $id): void
 		parent::remove($id);
 	}
 
+	/**
+	 * Imports holidays from iCalendar data and saves them to the database.
+	 *
+	 * @param string $ics Some iCalendar data (e.g. the content of an ICS file).
+	 * @return array An array of instances of this class.
+	 */
+	public static function import(string $ics): array
+	{
+		$holidays = self::constructFromICal($ics, self::TYPE_HOLIDAY);
+
+		foreach ($holidays as $holiday) {
+			$holiday->save();
+		}
+
+		return $holidays;
+	}
+
 	/**
 	 * Computes the Western and Eastern dates of Easter for the given year.
 	 *
diff --git a/Themes/default/ManageCalendar.template.php b/Themes/default/ManageCalendar.template.php
index 0c1005dd42..7303851c72 100644
--- a/Themes/default/ManageCalendar.template.php
+++ b/Themes/default/ManageCalendar.template.php
@@ -46,4 +46,46 @@ function template_edit_holiday()
 		</form>';
 }
 
+/**
+ * Importing iCalendar data.
+ */
+function template_import()
+{
+	// Show a form for all the holiday information.
+	echo '
+		<form action="', Config::$scripturl, '?action=admin;area=managecalendar;sa=import" method="post" accept-charset="', Utils::$context['character_set'], '">
+			<div class="cat_bar">
+				<h3 class="catbg">', Utils::$context['page_title'], '</h3>
+			</div>
+			<div class="windowbg">
+				<dl class="settings">
+					<dt>
+						<label for="">', Lang::$txt['calendar_import_url'], '</label>
+						<br>
+						<span class="smalltext">', Lang::$txt['calendar_import_url_desc'], '</span>
+					</dt>
+					<dd>
+						<input type="url" name="ics_url" id="ics_url">
+					</dd>
+					<dt>
+						<label>', Lang::$txt['calendar_import_type'], '</label>
+					</dt>
+					<dd>
+						<label>
+							<input type="radio" name="type" value="holiday" checked>
+							', Lang::$txt['calendar_import_type_holiday'], '
+						</label>
+						<label>
+							<input type="radio" name="type" value="event">
+							', Lang::$txt['calendar_import_type_event'], '
+						</label>
+					</dd>
+				</dl>
+				<input type="submit" name="import" value="', Lang::$txt['calendar_import_button'], '" class="button">
+				<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
+				<input type="hidden" name="' . Utils::$context['admin-calendarimport_token_var'] . '" value="' . Utils::$context['admin-calendarimport_token'] . '">
+			</div><!-- .windowbg -->
+		</form>';
+}
+
 ?>
\ No newline at end of file

From 6db7551f4126658d04d622ce4f28174783593918 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Sun, 7 Jan 2024 23:58:14 -0700
Subject: [PATCH 15/22] Improves the code to export events in iCal format

1. Fixes problems where we weren't conforming to the spec.
2. Adds support for exporting recurring events.
Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Actions/Calendar.php         |  7 ++-
 Sources/Calendar/Event.php           | 90 ++++++++++++++++++++++++----
 Sources/Calendar/EventOccurrence.php | 48 ++++++---------
 3 files changed, 101 insertions(+), 44 deletions(-)

diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index 1d4f2221e8..eb154d6d68 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -546,7 +546,7 @@ public function export(): void
 		}
 
 		// Load up the event in question and check it is valid.
-		list($event) = Event::load($_REQUEST['eventid']);
+		$event = current(Event::load((int) $_REQUEST['eventid']));
 
 		if (!($event instanceof Event)) {
 			ErrorHandler::fatalLang('no_access', false);
@@ -559,7 +559,7 @@ public function export(): void
 		$filecontents[] = 'PRODID:-//SimpleMachines//' . SMF_FULL_VERSION . '//EN';
 		$filecontents[] = 'VERSION:2.0';
 
-		$filecontents[] = $event->getVEvent();
+		$filecontents[] = $event->export();
 
 		$filecontents[] = 'END:VCALENDAR';
 
@@ -586,7 +586,8 @@ public function export(): void
 		header('connection: close');
 		header('content-disposition: attachment; filename="' . $event->title . '.ics"');
 
-		$calevent = implode("\n", $filecontents);
+		// RFC 5545 requires "\r\n", not just "\n".
+		$calevent = implode("\r\n", $filecontents);
 
 		if (empty(Config::$modSettings['enableCompressedOutput'])) {
 			// todo: correctly handle $filecontents before passing to string function
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index e580d02873..517ebffb29 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -821,16 +821,60 @@ public function save(): void
 		]);
 	}
 
-	// /**
-	//  * @todo Builds an iCalendar document for the event, including all
-	//  * recurrence info.
-	//  *
-	//  * @return string An iCalendar VEVENT document.
-	//  */
-	// public function getVEvent(): string
-	// {
-	// 	return '';
-	// }
+	/**
+	 * Builds iCalendar components for events, including recurrence info.
+	 *
+	 * @return string One or more VEVENT components for an iCalendar document.
+	 */
+	public function export(): string
+	{
+		$filecontents = [];
+		$filecontents[] = 'BEGIN:VEVENT';
+
+		$filecontents[] = 'SUMMARY:' . $this->title;
+
+		if (!empty($this->location)) {
+			$filecontents[] = 'LOCATION:' . str_replace(',', '\\,', $this->location);
+		}
+
+		if (!empty($this->topic)) {
+			$filecontents[] = 'URL:' . Config::$scripturl . '?topic=' . $this->topic . '.0';
+		}
+
+		$filecontents[] = 'UID:' . $this->uid;
+		$filecontents[] = 'SEQUENCE:' . $this->sequence;
+
+		$filecontents[] = 'DTSTAMP:' . date('Ymd\\THis\\Z', $this->modified_time ?? time());
+		$filecontents[] = 'DTSTART' . ($this->allday ? ';VALUE=DATE' : (!in_array($this->tz, RRule::UTC_SYNONYMS) ? ';TZID=' . $this->tz : '')) . ':' . $this->start->format('Ymd' . ($this->allday ? '' : '\\THis' . (in_array($this->tz, RRule::UTC_SYNONYMS) ? '\\Z' : '')));
+		$filecontents[] = 'DURATION:' . (string) $this->duration;
+
+		if ((string) $this->recurrence_iterator->getRRule() !== 'FREQ=YEARLY;COUNT=1') {
+			$filecontents[] = 'RRULE:' . (string) $this->recurrence_iterator->getRRule();
+		}
+
+		if ($this->recurrence_iterator->getRDates() !== []) {
+			$filecontents[] = 'RDATE' . ($this->allday ? ';VALUE=DATE' : '') . ':' . implode(",\r\n ", $this->recurrence_iterator->getRDates());
+		}
+
+		if ($this->recurrence_iterator->getExDates() !== []) {
+			$filecontents[] = 'EXDATE' . ($this->allday ? ';VALUE=DATE' : '') . ':' . implode(",\r\n ", $this->recurrence_iterator->getExDates());
+		}
+
+		$filecontents[] = 'END:VEVENT';
+
+		// Fit all lines within iCalendar's line width restraint.
+		foreach ($filecontents as $line_num => $line) {
+			$filecontents[$line_num] = self::foldICalLine($line);
+		}
+
+		// Adjusted occurrences need their own VEVENTs.
+		foreach ($this->adjustments as $recurrence_id => $adjustment) {
+			$occurrence = $this->getOccurrence($recurrence_id);
+			$filecontents[] = $occurrence->export();
+		}
+
+		return implode("\r\n", $filecontents);
+	}
 
 	/**
 	 * Adds an arbitrary date to the recurrence set.
@@ -1927,6 +1971,32 @@ public static function constructFromICal(string $ics, ?int $type = null): array
 		return $events;
 	}
 
+	/**
+	 * Folds lines of text to fit within the iCalendar line width restraint.
+	 *
+	 * @param string $line The line of text to fold.
+	 * @return string $line The folded version of $line.
+	 */
+	public static function foldICalLine(string $line): string
+	{
+		$folded = [];
+
+		$temp = '';
+
+		foreach (mb_str_split($line) as $char) {
+			if (strlen($temp . $char) > 75) {
+				$folded[] = $temp;
+				$temp = '';
+			}
+
+			$temp .= $char;
+		}
+
+		$folded[] = $temp;
+
+		return implode("\r\n ", $folded);
+	}
+
 	/**
 	 * Set the start and end dates and times for a posted event for insertion
 	 * into the database.
diff --git a/Sources/Calendar/EventOccurrence.php b/Sources/Calendar/EventOccurrence.php
index af19e980c6..55a233fe05 100644
--- a/Sources/Calendar/EventOccurrence.php
+++ b/Sources/Calendar/EventOccurrence.php
@@ -22,6 +22,7 @@
 use SMF\TimeInterval;
 use SMF\TimeZone;
 use SMF\Utils;
+use SMF\Uuid;
 
 /**
  * Represents a single occurrence of a calendar event.
@@ -194,51 +195,36 @@ public function save()
 	}
 
 	/**
-	 * Builds an iCalendar document for this occurrence of the event.
+	 * Builds an iCalendar component for this occurrence of the event.
 	 *
-	 * @return string An iCalendar VEVENT document.
+	 * @return string A VEVENT component for an iCalendar document.
 	 */
-	public function getVEvent(): string
+	public function export(): string
 	{
-		// Check the title isn't too long - iCal requires some formatting if so.
-		$title = str_split($this->title, 30);
-
-		foreach ($title as $id => $line) {
-			if ($id != 0) {
-				$title[$id] = ' ' . $title[$id];
-			}
-		}
-
-		// This is what we will be sending later.
 		$filecontents = [];
 		$filecontents[] = 'BEGIN:VEVENT';
-		$filecontents[] = 'ORGANIZER;CN="' . $this->name . '":MAILTO:' . Config::$webmaster_email;
-		$filecontents[] = 'DTSTAMP:' . date('Ymd\\THis\\Z', time());
-		$filecontents[] = 'DTSTART' . ($this->allday ? ';VALUE=DATE' : (!in_array($this->tz, RRule::UTC_SYNONYMS) ? ';TZID=' . $this->tz : '')) . ':' . $this->start->format('Ymd' . ($this->allday ? '' : '\\THis' . (in_array($this->tz, RRule::UTC_SYNONYMS) ? '\\Z' : '')));
 
-		// Event has a duration/
-		if (
-			(!$this->allday && $this->start_iso_gmdate != $this->end_iso_gmdate)
-			|| ($this->allday && $this->start_date != $this->end_date)
-		) {
-			$filecontents[] = 'DTEND' . ($this->allday ? ';VALUE=DATE' : (!in_array($this->tz, RRule::UTC_SYNONYMS) ? ';TZID=' . $this->tz : '')) . ':' . $this->end->format('Ymd' . ($this->allday ? '' : '\\THis' . (in_array($this->tz, RRule::UTC_SYNONYMS) ? '\\Z' : '')));
-		}
-
-		// Event has changed? Advance the sequence for this UID.
-		if ($this->sequence > 0) {
-			$filecontents[] = 'SEQUENCE:' . $this->sequence;
-		}
+		$filecontents[] = 'SUMMARY:' . $this->title;
 
 		if (!empty($this->location)) {
 			$filecontents[] = 'LOCATION:' . str_replace(',', '\\,', $this->location);
 		}
 
-		$filecontents[] = 'SUMMARY:' . implode('', $title);
 		$filecontents[] = 'UID:' . $this->uid;
-		$filecontents[] = 'RECURRENCE-ID' . ($this->allday ? ';VALUE=DATE' : '') . ':' . $this->id;
+		$filecontents[] = 'SEQUENCE:' . $this->sequence;
+		$filecontents[] = 'RECURRENCE-ID' . (isset($this->adjustment) && $this->adjustment->affects_future ? ';RANGE=THISANDFUTURE' : '') . ($this->allday ? ';VALUE=DATE' : '') . ':' . $this->id;
+
+		$filecontents[] = 'DTSTAMP:' . date('Ymd\\THis\\Z', $this->modified_time ?? time());
+		$filecontents[] = 'DTSTART' . ($this->allday ? ';VALUE=DATE' : (!in_array($this->tz, RRule::UTC_SYNONYMS) ? ';TZID=' . $this->tz : '')) . ':' . $this->start->format('Ymd' . ($this->allday ? '' : '\\THis' . (in_array($this->tz, RRule::UTC_SYNONYMS) ? '\\Z' : '')));
+		$filecontents[] = 'DURATION:' . (string) $this->duration;
+
 		$filecontents[] = 'END:VEVENT';
 
-		return implode("\n", $filecontents);
+		foreach ($filecontents as $line_num => $line) {
+			$filecontents[$line_num] = Event::foldICalLine($line);
+		}
+
+		return implode("\r\n", $filecontents);
 	}
 
 	/**

From e95676992702e8251847aa392e906b46757bf24e Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Sat, 10 Feb 2024 00:57:14 -0700
Subject: [PATCH 16/22] Shows human-readable recurrence rule descriptions for
 recurring events

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/General.php          | 139 +++++++
 Sources/Calendar/RRule.php           | 550 +++++++++++++++++++++++++++
 Themes/default/Calendar.template.php |  15 +
 Themes/default/Display.template.php  |   7 +
 Themes/default/css/index.css         |   2 +-
 5 files changed, 712 insertions(+), 1 deletion(-)

diff --git a/Languages/en_US/General.php b/Languages/en_US/General.php
index bb97af5bf4..3e4d4f4e70 100644
--- a/Languages/en_US/General.php
+++ b/Languages/en_US/General.php
@@ -767,6 +767,145 @@
 $txt['calendar_confirm_occurrence_delete'] = 'Are you sure you want to delete this occurrence of the event?-n--n-WARNING: if you select both &quot;Delete&quot; and &quot;This and future occurrences&quot;, you will delete this and all future occurrences.';
 $txt['calendar_repeat_adjustment_edit_first'] = 'Edit original event';
 
+// Used to show a human-readable explanation of the recurrence rule for a repeating event.
+$txt['calendar_rrule_desc'] = 'Repeats {rrule_description}{start_date, select,
+	false {}
+	other {, starting {start_date}}
+}.';
+// 'freq' will be one of YEARLY, MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY, or SECONDLY, or else a named month day (e.g. "Friday the 13th").
+$txt['calendar_rrule_desc_frequency_interval'] = 'every {freq, select,
+	YEARLY {{interval, plural,
+		=1 {year}
+		one {# year}
+		other {# years}
+	}}
+	MONTHLY {{interval, plural,
+		=1 {month}
+		one {# month}
+		other {# months}
+	}}
+	WEEKLY {{interval, plural,
+		=1 {week}
+		one {# week}
+		other {# weeks}
+	}}
+	DAILY {{interval, plural,
+		=1 {day}
+		one {# day}
+		other {# days}
+	}}
+	HOURLY {{interval, plural,
+		=1 {hour}
+		one {# hour}
+		other {# hours}
+	}}
+	MINUTELY {{interval, plural,
+		=1 {minute}
+		one {# minute}
+		other {# minutes}
+	}}
+	SECONDLY {{interval, plural,
+		=1 {second}
+		one {# second}
+		other {# seconds}
+	}}
+	other {{freq}}
+}';
+// 'freq' will be one of YEARLY, MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY, or SECONDLY, or else a named month day (e.g. "Friday the 13th").
+$txt['calendar_rrule_desc_frequency_interval_ordinal'] = 'every {freq, select,
+	YEARLY {{interval, selectordinal,
+		=1 {year}
+		one {#st year}
+		two {#nd year}
+		few {#rd year}
+		other {#th year}
+	}}
+	MONTHLY {{interval, selectordinal,
+		=1 {month}
+		one {#st month}
+		two {#nd month}
+		few {#rd month}
+		other {#th month}
+	}}
+	WEEKLY {{interval, selectordinal,
+		=1 {week}
+		one {#st week}
+		two {#nd week}
+		few {#rd week}
+		other {#th week}
+	}}
+	DAILY {{interval, selectordinal,
+		=1 {day}
+		one {#st day}
+		two {#nd day}
+		few {#rd day}
+		other {#th day}
+	}}
+	HOURLY {{interval, selectordinal,
+		=1 {hour}
+		one {#st hour}
+		two {#nd hour}
+		few {#rd hour}
+		other {#th hour}
+	}}
+	MINUTELY {{interval, selectordinal,
+		=1 {minute}
+		one {#st minute}
+		two {#nd minute}
+		few {#rd minute}
+		other {#th minute}
+	}}
+	SECONDLY {{interval, selectordinal,
+		=1 {second}
+		one {#st second}
+		two {#nd second}
+		few {#rd second}
+		other {#th second}
+	}}
+	other {{freq}}
+}';
+// 'months_titles' is a list of month names, using the forms from $txt['months_titles'].
+$txt['calendar_rrule_desc_bymonth'] = 'in {months_titles}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_byweekno'] = '{count, plural,
+	one {in the {ordinal_list} week of the year}
+	other {in the {ordinal_list} weeks of the year}
+}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_byyearday'] = '{count, plural,
+	one {on the {ordinal_list} day of the year}
+	other {on the {ordinal_list} days of the year}
+}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_bymonthday'] = '{count, plural,
+	one {on the {ordinal_list} day of the month}
+	other {on the {ordinal_list} days of the month}
+}';
+// Translators can replace 'ordinal_month_day' with 'cardinal_month_day' in this string if the target language prefers cardinal numbers instead of ordinal numbers for this form. For example, '{day_name} the {ordinal_month_day}' will produce 'Friday the 13th', whereas '{cardinal_month_day} {day_name}' will produce '13 Friday'.
+$txt['calendar_rrule_desc_named_monthday'] = '{day_name} the {ordinal_month_day}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, or 3rd").
+$txt['calendar_rrule_desc_named_monthdays'] = 'the first {day_name} that is the {ordinal_list} day of the month';
+// E.g. "the 2nd Thursday"
+$txt['calendar_rrule_desc_ordinal_day_name'] = 'the {ordinal} {day_name}';
+// E.g. "on Monday", "on Tuesday and Thursday"
+$txt['calendar_rrule_desc_byday'] = 'on {day_names}';
+// E.g. "on every Monday", "on every Tuesday and Thursday"
+$txt['calendar_rrule_desc_byday_every'] = 'on every {day_names}';
+$txt['calendar_rrule_desc_byminute'] = '{minute_list} past the hour';
+$txt['calendar_rrule_desc_bytime'] = 'at {times_list}';
+$txt['calendar_rrule_desc_bygeneric'] = 'of {list}';
+$txt['calendar_rrule_desc_between'] = 'between {min} and {max}';
+$txt['calendar_rrule_desc_until'] = 'until {date}';
+$txt['calendar_rrule_desc_count'] = '{count, plural,
+	one {for # occurrence}
+	other {for # occurrences}
+}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_bysetpos'] = '{count, plural,
+	one {on each {ordinal_list} occurrence}
+	other {on each {ordinal_list} occurrences}
+} of {rrule_description}';
+
 $txt['movetopic_change_subject'] = 'Change the topic’s subject';
 $txt['movetopic_new_subject'] = 'New subject';
 $txt['movetopic_change_all_subjects'] = 'Change every message’s subject';
diff --git a/Sources/Calendar/RRule.php b/Sources/Calendar/RRule.php
index 79ccdcc68f..1b64c30123 100644
--- a/Sources/Calendar/RRule.php
+++ b/Sources/Calendar/RRule.php
@@ -15,6 +15,11 @@
 
 namespace SMF\Calendar;
 
+use SMF\Config;
+use SMF\Lang;
+use SMF\Time;
+use SMF\Utils;
+
 /**
  * Represents a recurrence rule from RFC 5545.
  */
@@ -515,6 +520,551 @@ public function __toString(): string
 
 		return implode(';', $rrule);
 	}
+
+	/**
+	 * Builds a human-readable description of this RRule.
+	 *
+	 * @param EventOccurrence $occurrence The event occurrence that is currently
+	 *    being viewed.
+	 * @param ?bool $show_start Whether to show the start date in the description.
+	 *    If not set, will be determined automatically.
+	 */
+	public function getDescription(EventOccurrence $occurrence, ?bool $show_start = null): string
+	{
+		if (($this->count ?? 0) === 1) {
+			return '';
+		}
+
+		// Just in case...
+		Lang::load('General+Modifications');
+
+		if (!empty($this->bysetpos)) {
+			$description = $this->getDescriptionBySetPos($occurrence->getParentEvent()->start);
+		} else {
+			$description = $this->getDescriptionNormal($occurrence->getParentEvent()->start);
+		}
+
+		// When the repetition ends.
+		if (isset($this->until)) {
+			if (
+				!in_array($this->freq, ['HOURLY', 'MINUTELY', 'SECONDLY'])
+				&& empty($this->byhour)
+				&& empty($this->byminute)
+				&& empty($this->bysecond)
+			) {
+				$until = Time::createFromInterface($this->until)->format(Time::getDateFormat());
+			} else {
+				$until = Time::createFromInterface($this->until)->format();
+			}
+
+			$description .= ' ' . Lang::getTxt('calendar_rrule_desc_until', ['date' => $until]);
+		} elseif (!empty($this->count)) {
+			$description .= ' ' . Lang::getTxt('calendar_rrule_desc_count', ['count' => $this->count]);
+		}
+
+		$description = Lang::getTxt(
+			'calendar_rrule_desc',
+			[
+				'rrule_description' => $description,
+				'start_date' => ($show_start ?? !$occurrence->is_first) ? '<a href="' . Config::$scripturl . '?action=calendar;event=' . $occurrence->id_event . '" class="bbc_link">' . Time::createFromInterface($occurrence->getParentEvent()->start)->format($occurrence->allday ? Time::getDateFormat() : null, false) . '</a>' : 'false',
+			],
+		);
+
+		return Utils::normalizeSpaces(
+			$description,
+			true,
+			true,
+			[
+				'no_breaks' => true,
+				'collapse_hspace' => true,
+			],
+		);
+	}
+
+	/******************
+	 * Internal methods
+	 ******************/
+
+	/**
+	 * Gets the description without any BYSETPOS considerations.
+	 *
+	 * @param \DateTimeInterface $start
+	 */
+	protected function getDescriptionNormal(\DateTimeInterface $start): string
+	{
+		$description = [];
+
+		// Basic frequency interval (e.g. "Every year", "Every 3 weeks", etc.)
+		$description['frequency_interval'] = Lang::getTxt('calendar_rrule_desc_frequency_interval', ['freq' => $this->freq, 'interval' => $this->interval]);
+
+		$this->getDescriptionByDay($start, $description);
+		$this->getDescriptionByMonth($start, $description);
+		$this->getDescriptionByWeekNo($start, $description);
+		$this->getDescriptionByYearDay($start, $description);
+		$this->getDescriptionByMonthDay($start, $description);
+		$this->getDescriptionByTime($start, $description);
+
+		return implode(' ', $description);
+	}
+
+	/**
+	 * Gets the description with BYSETPOS considerations.
+	 *
+	 * @param \DateTimeInterface $start
+	 */
+	protected function getDescriptionBySetPos(\DateTimeInterface $start): string
+	{
+		$description = [];
+
+		// BYSETPOS can theoretically be used with any RRule, but it only really
+		// makes much sense to use it with BYDAY and BYMONTH (and that is the
+		// only way it will ever be used in events created by SMF). For that
+		// reason, it is really awkward to build a custom BYSETPOS description
+		// for RRules that contain any BY* values besides BYDAY and BYMONTH.
+		// So in the rare case that we are given such an RRule, we just use
+		// 'the nth instance of "<normal description>"' and call it good enough.
+		if (
+			empty($byweekno)
+			&& empty($byyearday)
+			&& empty($bymonthday)
+			&& empty($byhour)
+			&& empty($byminute)
+			&& empty($bysecond)
+		) {
+			if (!empty($this->byday)) {
+				$days_long_or_short = count($this->byday) > 3 ? 'days_short' : 'days';
+
+				$day_names = [];
+
+				foreach ($this->byday as $day) {
+					if (in_array($day, self::WEEKDAYS)) {
+						$day_names[] = Lang::$txt[$days_long_or_short][(array_search($day, self::WEEKDAYS) + 1) % 7];
+					} else {
+						$desc_byday = 'calendar_rrule_desc_byday';
+
+						list($num, $name) = preg_split('/(?=MO|TU|WE|TH|FR|SA|SU)/', $day);
+						$num = empty($num) ? 1 : (int) $num;
+
+						$nth = Lang::getTxt($num < 0 ? 'ordinal_spellout_last' : 'ordinal_spellout', [abs($num)]);
+						$day_name = Lang::$txt[$days_long_or_short][(array_search($name, self::WEEKDAYS) + 1) % 7];
+
+						$day_names[] = Lang::getTxt('calendar_rrule_desc_ordinal_day_name', ['ordinal' => $nth, 'day_name' => $day_name]);
+					}
+				}
+
+				$description['byday'] = Lang::sentenceList($day_names, 'xor');
+			}
+
+			if (!empty($this->bymonth)) {
+				if (($this->freq === 'MONTHLY' || $this->freq === 'YEARLY') && ($this->interval ?? 1) === 1) {
+					unset($description['frequency_interval']);
+				}
+
+				$months_titles = [];
+
+				foreach ($this->bymonth as $month_num) {
+					$months_titles[] = Lang::$txt['month_titles'][$month_num];
+				}
+
+				$description['bymonth'] = Lang::getTxt('calendar_rrule_desc_bymonth', ['months_titles' => Lang::sentenceList($months_titles)]);
+			}
+
+			// Basic frequency interval (e.g. "Every year", "Every 3 weeks", etc.)
+			$frequency_interval = Lang::getTxt('calendar_rrule_desc_frequency_interval', ['freq' => $this->freq, 'interval' => $this->interval]);
+		} else {
+			$description[] = '<q>' . $this->getDescriptionNormal($start) . '</q>';
+		}
+
+		$ordinals = array_map(fn ($n) => Lang::getTxt($n < 0 ? 'ordinal_spellout_last' : 'ordinal_spellout', [abs($n)]), $this->bysetpos);
+
+		return (isset($frequency_interval) ? $frequency_interval . ' ' : '') . Lang::getTxt(
+			'calendar_rrule_desc_bysetpos',
+			[
+				'ordinal_list' => Lang::sentenceList($ordinals),
+				'count' => count($this->bysetpos),
+				'rrule_description' => implode(' ', $description),
+			],
+		);
+	}
+
+	/**
+	 * Day of week (e.g. "on Monday", "on Monday and Tuesday", "on the 3rd Monday")
+	 *
+	 * @param \DateTimeInterface $start
+	 * @param array &$description
+	 */
+	protected function getDescriptionByDay(\DateTimeInterface $start, array &$description): void
+	{
+		if (empty($this->byday)) {
+			return;
+		}
+
+		if (($this->freq === 'DAILY' || $this->freq === 'WEEKLY') && ($this->interval ?? 1) === 1) {
+			unset($description['frequency_interval']);
+		}
+
+		$desc_byday = ($this->freq === 'YEARLY' && empty($this->byweekno)) || $this->freq === 'MONTHLY' ? 'calendar_rrule_desc_byday_every' : 'calendar_rrule_desc_byday';
+
+		$days_long_or_short = count($this->byday) > 3 ? 'days_short' : 'days';
+
+		$day_names = [];
+
+		foreach ($this->byday as $day) {
+			if (in_array($day, self::WEEKDAYS)) {
+				$day_names[] = Lang::$txt[$days_long_or_short][(array_search($day, self::WEEKDAYS) + 1) % 7];
+			} else {
+				$desc_byday = 'calendar_rrule_desc_byday';
+
+				list($num, $name) = preg_split('/(?=MO|TU|WE|TH|FR|SA|SU)/', $day);
+				$num = empty($num) ? 1 : (int) $num;
+
+				$nth = Lang::getTxt($num < 0 ? 'ordinal_spellout_last' : 'ordinal_spellout', [abs($num)]);
+				$day_name = Lang::$txt[$days_long_or_short][(array_search($name, self::WEEKDAYS) + 1) % 7];
+
+				$day_names[] = Lang::getTxt('calendar_rrule_desc_ordinal_day_name', ['ordinal' => $nth, 'day_name' => $day_name]);
+			}
+		}
+
+		$description['byday'] = Lang::getTxt($desc_byday, ['day_names' => Lang::sentenceList($day_names)]);
+
+		if (
+			$desc_byday === 'calendar_rrule_desc_byday_every'
+			&& ($this->interval ?? 1) > 1
+			&& (
+				$this->freq === 'MONTHLY'
+				|| (
+					$this->freq === 'YEARLY'
+					&& empty($this->bymonth)
+					&& empty($this->byweekno)
+					&& empty($this->byyearday)
+					&& empty($this->bymonthday)
+				)
+			)
+		) {
+			$description['bymonth'] = Lang::getTxt(
+				'calendar_rrule_desc_bygeneric',
+				[
+					'list' => Lang::getTxt(
+						'calendar_rrule_desc_frequency_interval_ordinal',
+						[
+							'freq' => $this->freq,
+							'interval' => $this->interval,
+						],
+					),
+				],
+			);
+
+			unset($description['frequency_interval']);
+		}
+	}
+
+	/**
+	 * Months (e.g. "in January", "in March and April")
+	 *
+	 * @param \DateTimeInterface $start
+	 * @param array &$description
+	 */
+	protected function getDescriptionByMonth(\DateTimeInterface $start, array &$description): void
+	{
+		if (empty($this->bymonth)) {
+			return;
+		}
+
+		if (($this->freq === 'MONTHLY' || $this->freq === 'YEARLY') && ($this->interval ?? 1) === 1) {
+			unset($description['frequency_interval']);
+		}
+
+		$months_titles = [];
+
+		foreach ($this->bymonth as $month_num) {
+			$months_titles[] = Lang::$txt['months_titles'][$month_num];
+		}
+
+		$description['bymonth'] = Lang::getTxt('calendar_rrule_desc_bymonth', ['months_titles' => Lang::sentenceList($months_titles)]);
+	}
+
+	/**
+	 * Week number (e.g. "in the 3rd week of the year")
+	 *
+	 * @param \DateTimeInterface $start
+	 * @param array &$description
+	 */
+	protected function getDescriptionByWeekNo(\DateTimeInterface $start, array &$description): void
+	{
+		if (empty($this->byweekno)) {
+			return;
+		}
+
+		if ($this->freq === 'YEARLY' && ($this->interval ?? 1) === 1) {
+			unset($description['frequency_interval']);
+		}
+
+		$ordinals = array_map(fn ($n) => Lang::getTxt('ordinal_spellout', [$n]), $this->byweekno);
+		$description['byweekno'] = Lang::getTxt('calendar_rrule_desc_byweekno', ['ordinal_list' => Lang::sentenceList($ordinals), 'count' => count($ordinals)]);
+	}
+
+	/**
+	 * Day of year (e.g. "on the 3rd day of the year")
+	 *
+	 * @param \DateTimeInterface $start
+	 * @param array &$description
+	 */
+	protected function getDescriptionByYearDay(\DateTimeInterface $start, array &$description): void
+	{
+		if (empty($this->byyearday)) {
+			return;
+		}
+
+		if ($this->freq === 'YEARLY' && ($this->interval ?? 1) === 1) {
+			unset($description['frequency_interval']);
+		}
+
+		$ordinals = array_map(fn ($n) => Lang::getTxt('ordinal_spellout', [$n]), $this->byyearday);
+		$description['byeyarday'] = Lang::getTxt('calendar_rrule_desc_byyearday', ['ordinal_list' => Lang::sentenceList($ordinals), 'count' => count($ordinals)]);
+	}
+
+	/**
+	 * Day of month (e.g. "on the 3rd day of the month")
+	 *
+	 * @param \DateTimeInterface $start
+	 * @param array &$description
+	 */
+	protected function getDescriptionByMonthDay(\DateTimeInterface $start, array &$description): void
+	{
+		if (empty($this->bymonthday)) {
+			return;
+		}
+
+		if ($this->freq === 'MONTHLY' && ($this->interval ?? 1) === 1) {
+			unset($description['frequency_interval']);
+		}
+
+		// Special cases for when we have both day names and month days.
+		if (
+			count($this->byday ?? []) >= 1
+			&& array_intersect($this->byday, self::WEEKDAYS) === $this->byday
+		) {
+			$days_long_or_short = count($this->byday) > 3 ? 'days_short' : 'days';
+
+			// "Friday the 13th"
+			if (count($this->bymonthday) === 1 && count($this->byday) === 1) {
+				$named_monthday = Lang::getTxt(
+					'calendar_rrule_desc_named_monthday',
+					[
+						'day_name' => Lang::$txt[$days_long_or_short][(array_search($this->byday[0], self::WEEKDAYS) + 1) % 7],
+						'ordinal_month_day' => Lang::getTxt('ordinal', $this->bymonthday),
+						'cardinal_month_day' => $this->bymonthday[0],
+					],
+				);
+
+				if ($this->freq === 'MONTHLY') {
+					$description['frequency_interval'] = Lang::getTxt(
+						'calendar_rrule_desc_frequency_interval',
+						[
+							'freq' => $named_monthday,
+						],
+					);
+
+					unset($description['byday']);
+				} else {
+					$description['byday'] = Lang::getTxt(
+						'calendar_rrule_desc_byday',
+						[
+							'day_names' => $named_monthday,
+						],
+					);
+				}
+			}
+			// "the first Tuesday or Thursday that is the second, third, or fourth day of the month"
+			else {
+				foreach ($this->byday as $day_abbrev) {
+					$day_names[] = Lang::$txt[$days_long_or_short][(array_search($day_abbrev, self::WEEKDAYS) + 1) % 7];
+				}
+
+				$ordinal_form = max(array_map('abs', $this->bymonthday)) < 10 && count($this->bymonthday) <= 3 ? 'ordinal_spellout' : 'ordinal';
+
+				$ordinals = array_map(fn ($n) => Lang::getTxt($n < 0 ? $ordinal_form . '_last' : $ordinal_form, [abs($n)]), $this->bymonthday);
+
+				$description['byday'] = Lang::getTxt(
+					'calendar_rrule_desc_byday',
+					[
+						'day_names' => Lang::getTxt(
+							'calendar_rrule_desc_named_monthdays',
+							[
+								'ordinal_list' => Lang::sentenceList($ordinals, 'or'),
+								'day_name' => Lang::sentenceList($day_names, 'or'),
+							],
+						),
+					],
+				);
+			}
+		}
+		// Normal case.
+		else {
+			$ordinals = array_map(fn ($n) => Lang::getTxt($n < 0 ? 'ordinal_spellout_last' : 'ordinal_spellout', [abs($n)]), $this->bymonthday);
+			$description['bymonthday'] = Lang::getTxt('calendar_rrule_desc_bymonthday', ['ordinal_list' => Lang::sentenceList($ordinals), 'count' => count($ordinals)]);
+		}
+	}
+
+	/**
+	 * Hour, minute, and second.
+	 *
+	 * @param \DateTimeInterface $start
+	 * @param array &$description
+	 */
+	protected function getDescriptionByTime(\DateTimeInterface $start, array &$description): void
+	{
+		// Hour, minute, and second.
+		$time_format = Time::getTimeFormat();
+
+		// Do we need to show seconds?
+		if (!empty($this->bysecond) || $this->freq === 'SECONDLY') {
+			if (Time::isStrftimeFormat($time_format)) {
+				if (!str_contains($time_format, '%S')) {
+					if (str_contains($time_format, '%M')) {
+						$time_format = str_replace('%M', '%M:%S', $time_format);
+					} else {
+						if (str_contains($time_format, '%I')) {
+							$time_format = str_replace('%I', '%I:%M:%S', $time_format);
+						} elseif (str_contains($time_format, '%l')) {
+							$time_format = str_replace('%l', '%l:%M:%S', $time_format);
+						} elseif (str_contains($time_format, '%H')) {
+							$time_format = str_replace('%H', '%H:%M:%S', $time_format);
+						} elseif (str_contains($time_format, '%k')) {
+							$time_format = str_replace('%k', '%k:%M:%S', $time_format);
+						} else {
+							$time_format = '%H:%M:%S';
+						}
+					}
+				}
+			} else {
+				if (!str_contains($time_format, 's')) {
+					if (str_contains($time_format, 'i')) {
+						$time_format = str_replace('i', 'i:s', $time_format);
+					} else {
+						if (str_contains($time_format, 'h')) {
+							$time_format = str_replace('h', 'h:i:s', $time_format);
+						} elseif (str_contains($time_format, 'g')) {
+							$time_format = str_replace('g', 'g:i:s', $time_format);
+						} elseif (str_contains($time_format, 'H')) {
+							$time_format = str_replace('H', 'H:i:s', $time_format);
+						} elseif (str_contains($time_format, 'G')) {
+							$time_format = str_replace('G', 'G:i:s', $time_format);
+						} else {
+							$time_format = 'H:i:s';
+						}
+					}
+				}
+			}
+		}
+
+		$min = Time::createFromInterface($start);
+
+		$max = Time::createFromInterface($start)->setTime(
+			(int) (isset($this->byhour) ? max($this->byhour) : $start->format('H')),
+			(int) (isset($this->byminute) ? max($this->byminute) : $start->format('i')),
+			(int) (isset($this->bysecond) ? max($this->bysecond) : $start->format('s')),
+		);
+
+		// Seconds.
+		if (!empty($this->bysecond)) {
+			if ($this->freq === 'SECONDLY' && ($this->interval ?? 1) === 1) {
+				unset($description['frequency_interval']);
+			}
+
+			if (range(min($this->bysecond), max($this->bysecond)) === $this->bysecond) {
+				$list = Lang::getTxt(
+					'calendar_rrule_desc_between',
+					[
+						'min' => $min->format('s'),
+						'max' => Lang::getTxt('number_of_seconds', [$max->format('s')]),
+					],
+				);
+			} else {
+				$list = $this->bysecond;
+
+				sort($list);
+				$list[array_key_last($list)] = Lang::getTxt('number_of_seconds', [$list[array_key_last($list)]]);
+				$list = Lang::sentenceList($list);
+			}
+
+			$description['bytime'] = Lang::getTxt('calendar_rrule_desc_bytime', ['times_list' => $list]);
+		}
+
+		// Minutes.
+		if (!empty($this->byminute)) {
+			if ($this->freq === 'MINUTELY' && ($this->interval ?? 1) === 1) {
+				unset($description['frequency_interval']);
+			}
+
+			if (range(min($this->byminute), max($this->byminute)) === $this->byminute) {
+				$list = Lang::getTxt(
+					'calendar_rrule_desc_between',
+					[
+						'min' => $min->format('i'),
+						'max' => Lang::getTxt('number_of_minutes', [$max->format('i')]),
+					],
+				);
+
+				if (!isset($description['bytime'])) {
+					$description['bytime'] = Lang::getTxt('calendar_rrule_desc_byminute', ['minute_list' => $list]);
+				} else {
+					$description['bytime'] .= ' ' . Lang::getTxt('calendar_rrule_desc_byminute', ['minute_list' => $list]);
+				}
+			} else {
+				$list = $this->byminute;
+
+				sort($list);
+				$list[array_key_last($list)] = Lang::getTxt('number_of_minutes', [$list[array_key_last($list)]]);
+				$list = Lang::sentenceList($list);
+
+				if (!isset($description['bytime'])) {
+					$description['bytime'] = Lang::getTxt('calendar_rrule_desc_bytime', ['times_list' => Lang::getTxt('calendar_rrule_desc_byminute', ['minute_list' => $list])]);
+				} else {
+					$description['bytime'] .= ' ' . Lang::getTxt('calendar_rrule_desc_bygeneric', ['list' => Lang::getTxt('calendar_rrule_desc_byminute', ['minute_list' => $list])]);
+				}
+			}
+		} elseif (!empty($this->bysecond)) {
+			$description['bytime'] .= ' ' . Lang::getTxt('calendar_rrule_desc_bygeneric', ['list' => Lang::getTxt('calendar_rrule_desc_frequency_interval', ['freq' => 'MINUTELY', 'interval' => 1])]);
+		}
+
+		// Hours.
+		if (!empty($this->byhour)) {
+			if ($this->freq === 'HOURLY' && ($this->interval ?? 1) === 1) {
+				unset($description['frequency_interval']);
+			}
+
+			if (range(min($this->byhour), max($this->byhour)) === $this->byhour) {
+				$list = Lang::getTxt(
+					'calendar_rrule_desc_between',
+					[
+						'min' => $min->format($time_format),
+						'max' => $max->format($time_format),
+					],
+				);
+
+				if (!isset($description['bytime'])) {
+					$description['bytime'] = $list;
+				} else {
+					$description['bytime'] .= ' ' . $list;
+				}
+			} else {
+				$list = $this->byhour;
+
+				sort($list);
+				$list[array_key_last($list)] = Lang::getTxt('number_of_hours', [$list[array_key_last($list)]]);
+				$list = Lang::sentenceList($list);
+
+				if (!isset($description['bytime'])) {
+					$description['bytime'] = Lang::getTxt('calendar_rrule_desc_bytime', ['times_list' => $list]);
+				} else {
+					$description['bytime'] .= ' ' . Lang::getTxt('calendar_rrule_desc_bygeneric', ['list' => $list]);
+				}
+			}
+		} elseif (!empty($this->byminute)) {
+			$description['bytime'] .= ' ' . Lang::getTxt('calendar_rrule_desc_bygeneric', ['list' => Lang::getTxt('calendar_rrule_desc_frequency_interval', ['freq' => 'HOURLY', 'interval' => 1])]);
+		}
+	}
 }
 
 ?>
\ No newline at end of file
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index 5c8de13156..f8801742c8 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -96,6 +96,8 @@ function template_show_upcoming_list($grid_name)
 				</div>
 				<ul>';
 
+		$first_shown = [];
+
 		foreach ($calendar_data['events'] as $date => $date_events)
 		{
 			foreach ($date_events as $event)
@@ -150,6 +152,19 @@ function template_show_upcoming_list($grid_name)
 				if (!empty($event['location']))
 					echo '<br>', $event['location'];
 
+				// If the first occurrence is not visible on the current page,
+				// we mention it in the RRULE description.
+				if ($event->is_first) {
+					$first_shown[] = $event->id_event;
+				}
+
+				$rrule_description = $event->getParentEvent()->recurrence_iterator->getRRule()->getDescription($event, !in_array($event->id_event, $first_shown));
+
+				if (!empty($rrule_description)) {
+					echo '
+						<br>', $rrule_description;
+				}
+
 				echo '
 					</li>';
 			}
diff --git a/Themes/default/Display.template.php b/Themes/default/Display.template.php
index 5204e5033d..f06452c3e6 100644
--- a/Themes/default/Display.template.php
+++ b/Themes/default/Display.template.php
@@ -236,6 +236,13 @@ function template_main()
 				echo '
 					<br>', $event['location'];
 
+			$rrule_description = $event->getParentEvent()->recurrence_iterator->getRRule()->getDescription($event);
+
+			if (!empty($rrule_description)) {
+				echo '
+					<br>', $rrule_description;
+			}
+
 			echo '
 				</li>';
 		}
diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index 9f9f8fe6e8..4567ed603b 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -3826,7 +3826,7 @@ h3.titlebg, h4.titlebg, .titlebg, h3.subbg, h4.subbg, .subbg {
 .generic_list_wrapper .information div {
 	background: none;
 }
-.information a:not(.button) {
+.information a:not(.button):not(.bbc_link) {
 	font-weight: bold;
 }
 p.information img {

From eaff03b04cda506fcfda17639cde124530d2bb61 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Thu, 7 Mar 2024 23:46:16 -0700
Subject: [PATCH 17/22] Moves calendar strings to their own file

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/Calendar.php       | 211 +++++++++++++++++++++++++++++
 Languages/en_US/General.php        | 210 +---------------------------
 Sources/Actions/Admin/Calendar.php |   2 +-
 Sources/Actions/BoardIndex.php     |   2 +
 Sources/Actions/Calendar.php       |   2 +
 Sources/Actions/Display.php        |   3 +
 Sources/Actions/Post.php           |   2 +-
 Sources/Calendar/Event.php         |   2 +
 Sources/Calendar/RRule.php         |   2 +-
 Sources/ServerSideIncludes.php     |   5 +-
 Sources/Theme.php                  |   2 +
 11 files changed, 232 insertions(+), 211 deletions(-)
 create mode 100644 Languages/en_US/Calendar.php

diff --git a/Languages/en_US/Calendar.php b/Languages/en_US/Calendar.php
new file mode 100644
index 0000000000..c57d5bcb01
--- /dev/null
+++ b/Languages/en_US/Calendar.php
@@ -0,0 +1,211 @@
+<?php
+
+// Version: 3.0 Alpha 1; General
+
+$txt['birthdays'] = 'Birthdays:';
+$txt['events'] = 'Events:';
+$txt['birthdays_upcoming'] = 'Upcoming Birthdays:';
+$txt['events_upcoming'] = 'Upcoming Events:';
+// Prompt for holidays in the calendar, leave blank to just display the holiday's name.
+$txt['calendar_prompt'] = 'Holidays:';
+$txt['calendar_month'] = 'Month';
+$txt['calendar_year'] = 'Year';
+$txt['calendar_day'] = 'Day';
+$txt['calendar_event_title'] = 'Title';
+$txt['calendar_event_options'] = 'Event Options';
+$txt['calendar_post_in'] = 'Post in';
+$txt['calendar_edit'] = 'Edit Event';
+$txt['calendar_export'] = 'Export Event';
+$txt['calendar_view_week'] = 'View Week';
+$txt['event_delete_confirm'] = 'Delete this event?';
+$txt['event_delete'] = 'Delete Event';
+$txt['calendar_post_event'] = 'Post Event';
+$txt['calendar'] = 'Calendar';
+$txt['calendar_link'] = 'Link to Calendar';
+$txt['calendar_upcoming'] = 'Upcoming Calendar';
+$txt['calendar_today'] = 'Today’s Calendar';
+$txt['calendar_week'] = 'Week';
+$txt['calendar_week_beginning'] = 'Week beginning {date}';
+$txt['calendar_numb_days'] = 'Number of Days';
+$txt['calendar_how_edit'] = 'how do you edit these events?';
+$txt['calendar_link_event'] = 'Link Event To Post';
+$txt['calendar_confirm_delete'] = 'Are you sure you want to delete this event?';
+$txt['calendar_linked_events'] = 'Linked Events';
+$txt['calendar_click_all'] = 'Show all';
+$txt['calendar_allday'] = 'All day';
+$txt['calendar_timezone'] = 'Time zone';
+$txt['calendar_list'] = 'List';
+$txt['calendar_empty'] = 'There are no events to display.';
+
+$txt['calendar_repeat_recurrence_label'] = 'Repeats';
+$txt['calendar_repeat_interval_label'] = 'Every';
+$txt['calendar_repeat_bymonthday_label'] = 'On';
+$txt['calendar_repeat_byday_label'] = 'On';
+$txt['calendar_repeat_bymonth_label'] = 'In';
+$txt['calendar_repeat_rrule_presets'] = ['never' => 'Never', 'FREQ=DAILY' => 'Every day', 'FREQ=WEEKLY' => 'Every week', 'FREQ=MONTHLY' => 'Every month', 'FREQ=YEARLY' => 'Every year', 'custom' => 'Custom...'];
+$txt['calendar_repeat_frequency_units'] = ['YEARLY' => 'year(s)', 'MONTHLY' => 'month(s)', 'WEEKLY' => 'week(s)', 'DAILY' => 'day(s)', 'HOURLY' => 'hour(s)', 'MINUTELY' => 'minute(s)', 'SECONDLY' => 'second(s)'];
+$txt['calendar_repeat_until_options'] = ['forever' => 'Forever', 'until' => 'Until', 'count' => 'Number of times'];
+$txt['calendar_repeat_byday_num_options'] = [1 => 'the first', 2 => 'the second', 3 => 'the third', 4 => 'the fourth', 5 => 'the fifth', -1 => 'the last', -2 => 'the second last'];
+$txt['calendar_repeat_weekday'] = 'weekday';
+$txt['calendar_repeat_weekend_day'] = 'weekend day';
+$txt['calendar_repeat_add_condition'] = 'Add Another';
+$txt['calendar_repeat_advanced_options_label'] = 'More options...';
+$txt['calendar_repeat_rdates_label'] = 'Additional dates';
+$txt['calendar_repeat_exdates_label'] = 'Skipped dates';
+$txt['calendar_repeat_easter_w'] = 'Easter (Western)';
+$txt['calendar_repeat_easter_e'] = 'Easter (Eastern)';
+$txt['calendar_repeat_vernal_equinox'] = 'Vernal Equinox';
+$txt['calendar_repeat_summer_solstice'] = 'Summer Solstice';
+$txt['calendar_repeat_autumnal_equinox'] = 'Autumnal Equinox';
+$txt['calendar_repeat_winter_solstice'] = 'Winter Solstice';
+$txt['calendar_repeat_special'] = 'Special';
+$txt['calendar_repeat_special_rrule_modifier'] = 'Offset';
+$txt['calendar_repeat_offset_examples'] = 'e.g.: +P1D, -PT2H';
+$txt['calendar_repeat_adjustment_label'] = 'Apply changes to';
+$txt['calendar_repeat_adjustment_this_only'] = 'Only this occurrence';
+$txt['calendar_repeat_adjustment_this_and_future'] = 'This and future occurrences';
+$txt['calendar_repeat_adjustment_confirm'] = 'Are you sure you want to apply these changes to all future occurrences?-n--n-WARNING: if you select both &quot;Delete&quot; and &quot;This and future occurrences&quot;, you will delete this and all future occurrences.';
+$txt['calendar_repeat_delete_label'] = 'Delete';
+$txt['calendar_confirm_occurrence_delete'] = 'Are you sure you want to delete this occurrence of the event?-n--n-WARNING: if you select both &quot;Delete&quot; and &quot;This and future occurrences&quot;, you will delete this and all future occurrences.';
+$txt['calendar_repeat_adjustment_edit_first'] = 'Edit original event';
+
+// Used to show a human-readable explanation of the recurrence rule for a repeating event.
+$txt['calendar_rrule_desc'] = 'Repeats {rrule_description}{start_date, select,
+	false {}
+	other {, starting {start_date}}
+}.';
+// 'freq' will be one of YEARLY, MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY, or SECONDLY, or else a named month day (e.g. "Friday the 13th").
+$txt['calendar_rrule_desc_frequency_interval'] = 'every {freq, select,
+	YEARLY {{interval, plural,
+		=1 {year}
+		one {# year}
+		other {# years}
+	}}
+	MONTHLY {{interval, plural,
+		=1 {month}
+		one {# month}
+		other {# months}
+	}}
+	WEEKLY {{interval, plural,
+		=1 {week}
+		one {# week}
+		other {# weeks}
+	}}
+	DAILY {{interval, plural,
+		=1 {day}
+		one {# day}
+		other {# days}
+	}}
+	HOURLY {{interval, plural,
+		=1 {hour}
+		one {# hour}
+		other {# hours}
+	}}
+	MINUTELY {{interval, plural,
+		=1 {minute}
+		one {# minute}
+		other {# minutes}
+	}}
+	SECONDLY {{interval, plural,
+		=1 {second}
+		one {# second}
+		other {# seconds}
+	}}
+	other {{freq}}
+}';
+// 'freq' will be one of YEARLY, MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY, or SECONDLY, or else a named month day (e.g. "Friday the 13th").
+$txt['calendar_rrule_desc_frequency_interval_ordinal'] = 'every {freq, select,
+	YEARLY {{interval, selectordinal,
+		=1 {year}
+		one {#st year}
+		two {#nd year}
+		few {#rd year}
+		other {#th year}
+	}}
+	MONTHLY {{interval, selectordinal,
+		=1 {month}
+		one {#st month}
+		two {#nd month}
+		few {#rd month}
+		other {#th month}
+	}}
+	WEEKLY {{interval, selectordinal,
+		=1 {week}
+		one {#st week}
+		two {#nd week}
+		few {#rd week}
+		other {#th week}
+	}}
+	DAILY {{interval, selectordinal,
+		=1 {day}
+		one {#st day}
+		two {#nd day}
+		few {#rd day}
+		other {#th day}
+	}}
+	HOURLY {{interval, selectordinal,
+		=1 {hour}
+		one {#st hour}
+		two {#nd hour}
+		few {#rd hour}
+		other {#th hour}
+	}}
+	MINUTELY {{interval, selectordinal,
+		=1 {minute}
+		one {#st minute}
+		two {#nd minute}
+		few {#rd minute}
+		other {#th minute}
+	}}
+	SECONDLY {{interval, selectordinal,
+		=1 {second}
+		one {#st second}
+		two {#nd second}
+		few {#rd second}
+		other {#th second}
+	}}
+	other {{freq}}
+}';
+// 'months_titles' is a list of month names, using the forms from $txt['months_titles'].
+$txt['calendar_rrule_desc_bymonth'] = 'in {months_titles}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_byweekno'] = '{count, plural,
+	one {in the {ordinal_list} week of the year}
+	other {in the {ordinal_list} weeks of the year}
+}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_byyearday'] = '{count, plural,
+	one {on the {ordinal_list} day of the year}
+	other {on the {ordinal_list} days of the year}
+}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_bymonthday'] = '{count, plural,
+	one {on the {ordinal_list} day of the month}
+	other {on the {ordinal_list} days of the month}
+}';
+// Translators can replace 'ordinal_month_day' with 'cardinal_month_day' in this string if the target language prefers cardinal numbers instead of ordinal numbers for this form. For example, '{day_name} the {ordinal_month_day}' will produce 'Friday the 13th', whereas '{cardinal_month_day} {day_name}' will produce '13 Friday'.
+$txt['calendar_rrule_desc_named_monthday'] = '{day_name} the {ordinal_month_day}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, or 3rd").
+$txt['calendar_rrule_desc_named_monthdays'] = 'the first {day_name} that is the {ordinal_list} day of the month';
+// E.g. "the 2nd Thursday"
+$txt['calendar_rrule_desc_ordinal_day_name'] = 'the {ordinal} {day_name}';
+// E.g. "on Monday", "on Tuesday and Thursday"
+$txt['calendar_rrule_desc_byday'] = 'on {day_names}';
+// E.g. "on every Monday", "on every Tuesday and Thursday"
+$txt['calendar_rrule_desc_byday_every'] = 'on every {day_names}';
+$txt['calendar_rrule_desc_byminute'] = '{minute_list} past the hour';
+$txt['calendar_rrule_desc_bytime'] = 'at {times_list}';
+$txt['calendar_rrule_desc_bygeneric'] = 'of {list}';
+$txt['calendar_rrule_desc_between'] = 'between {min} and {max}';
+$txt['calendar_rrule_desc_until'] = 'until {date}';
+$txt['calendar_rrule_desc_count'] = '{count, plural,
+	one {for # occurrence}
+	other {for # occurrences}
+}';
+// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
+$txt['calendar_rrule_desc_bysetpos'] = '{count, plural,
+	one {on each {ordinal_list} occurrence}
+	other {on each {ordinal_list} occurrences}
+} of {rrule_description}';
+
+?>
\ No newline at end of file
diff --git a/Languages/en_US/General.php b/Languages/en_US/General.php
index 3e4d4f4e70..bb617310c3 100644
--- a/Languages/en_US/General.php
+++ b/Languages/en_US/General.php
@@ -109,10 +109,12 @@
 $txt['days_title'] = 'Days';
 $txt['days'] = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
 $txt['days_short'] = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
-// Months must start with 1 => 'January'. (or translated, of course.)
 $txt['months_title'] = 'Months';
+// Months must start with 1 => 'January' (or translated, of course).
 $txt['months'] = [1 => 'January', 2 => 'February', 3 => 'March', 4 => 'April', 5 => 'May', 6 => 'June', 7 => 'July', 8 => 'August', 9 => 'September', 10 => 'October', 11 => 'November', 12 => 'December'];
+// Months must start with 1 => 'January' (or translated, of course).
 $txt['months_titles'] = [1 => 'January', 2 => 'February', 3 => 'March', 4 => 'April', 5 => 'May', 6 => 'June', 7 => 'July', 8 => 'August', 9 => 'September', 10 => 'October', 11 => 'November', 12 => 'December'];
+// Months must start with 1 => 'Jan' (or translated, of course).
 $txt['months_short'] = [1 => 'Jan', 2 => 'Feb', 3 => 'Mar', 4 => 'Apr', 5 => 'May', 6 => 'Jun', 7 => 'Jul', 8 => 'Aug', 9 => 'Sep', 10 => 'Oct', 11 => 'Nov', 12 => 'Dec'];
 $txt['prev_month'] = 'Previous month';
 $txt['next_month'] = 'Next month';
@@ -700,212 +702,6 @@
 // argument(s): SMF_FULL_VERSION, SMF_SOFTWARE_YEAR, Config::$scripturl
 $forum_copyright = '<a href="{scripturl}?action=credits" title="License" target="_blank" rel="noopener">{version} &copy; {year}</a>, <a href="https://www.simplemachines.org" title="Simple Machines" target="_blank" rel="noopener">Simple Machines</a>';
 
-$txt['birthdays'] = 'Birthdays:';
-$txt['events'] = 'Events:';
-$txt['birthdays_upcoming'] = 'Upcoming Birthdays:';
-$txt['events_upcoming'] = 'Upcoming Events:';
-// Prompt for holidays in the calendar, leave blank to just display the holiday's name.
-$txt['calendar_prompt'] = 'Holidays:';
-$txt['calendar_month'] = 'Month';
-$txt['calendar_year'] = 'Year';
-$txt['calendar_day'] = 'Day';
-$txt['calendar_event_title'] = 'Title';
-$txt['calendar_event_options'] = 'Event Options';
-$txt['calendar_post_in'] = 'Post in';
-$txt['calendar_edit'] = 'Edit Event';
-$txt['calendar_export'] = 'Export Event';
-$txt['calendar_view_week'] = 'View Week';
-$txt['event_delete_confirm'] = 'Delete this event?';
-$txt['event_delete'] = 'Delete Event';
-$txt['calendar_post_event'] = 'Post Event';
-$txt['calendar'] = 'Calendar';
-$txt['calendar_link'] = 'Link to Calendar';
-$txt['calendar_upcoming'] = 'Upcoming Calendar';
-$txt['calendar_today'] = 'Today’s Calendar';
-$txt['calendar_week'] = 'Week';
-$txt['calendar_week_beginning'] = 'Week beginning {date}';
-$txt['calendar_numb_days'] = 'Number of Days';
-$txt['calendar_how_edit'] = 'how do you edit these events?';
-$txt['calendar_link_event'] = 'Link Event To Post';
-$txt['calendar_confirm_delete'] = 'Are you sure you want to delete this event?';
-$txt['calendar_linked_events'] = 'Linked Events';
-$txt['calendar_click_all'] = 'Show all';
-$txt['calendar_allday'] = 'All day';
-$txt['calendar_timezone'] = 'Time zone';
-$txt['calendar_list'] = 'List';
-$txt['calendar_empty'] = 'There are no events to display.';
-
-$txt['calendar_repeat_recurrence_label'] = 'Repeats';
-$txt['calendar_repeat_interval_label'] = 'Every';
-$txt['calendar_repeat_bymonthday_label'] = 'On';
-$txt['calendar_repeat_byday_label'] = 'On';
-$txt['calendar_repeat_bymonth_label'] = 'In';
-$txt['calendar_repeat_rrule_presets'] = ['never' => 'Never', 'FREQ=DAILY' => 'Every day', 'FREQ=WEEKLY' => 'Every week', 'FREQ=MONTHLY' => 'Every month', 'FREQ=YEARLY' => 'Every year', 'custom' => 'Custom...'];
-$txt['calendar_repeat_frequency_units'] = ['YEARLY' => 'year(s)', 'MONTHLY' => 'month(s)', 'WEEKLY' => 'week(s)', 'DAILY' => 'day(s)', 'HOURLY' => 'hour(s)', 'MINUTELY' => 'minute(s)', 'SECONDLY' => 'second(s)'];
-$txt['calendar_repeat_until_options'] = ['forever' => 'Forever', 'until' => 'Until', 'count' => 'Number of times'];
-$txt['calendar_repeat_byday_num_options'] = [1 => 'the first', 2 => 'the second', 3 => 'the third', 4 => 'the fourth', 5 => 'the fifth', -1 => 'the last', -2 => 'the second last'];
-$txt['calendar_repeat_weekday'] = 'weekday';
-$txt['calendar_repeat_weekend_day'] = 'weekend day';
-$txt['calendar_repeat_add_condition'] = 'Add Another';
-$txt['calendar_repeat_advanced_options_label'] = 'More options...';
-$txt['calendar_repeat_rdates_label'] = 'Additional dates';
-$txt['calendar_repeat_exdates_label'] = 'Skipped dates';
-$txt['calendar_repeat_easter_w'] = 'Easter (Western)';
-$txt['calendar_repeat_easter_e'] = 'Easter (Eastern)';
-$txt['calendar_repeat_vernal_equinox'] = 'Vernal Equinox';
-$txt['calendar_repeat_summer_solstice'] = 'Summer Solstice';
-$txt['calendar_repeat_autumnal_equinox'] = 'Autumnal Equinox';
-$txt['calendar_repeat_winter_solstice'] = 'Winter Solstice';
-$txt['calendar_repeat_special'] = 'Special';
-$txt['calendar_repeat_special_rrule_modifier'] = 'Offset';
-$txt['calendar_repeat_offset_examples'] = 'e.g.: +P1D, -PT2H';
-$txt['calendar_repeat_adjustment_label'] = 'Apply changes to';
-$txt['calendar_repeat_adjustment_this_only'] = 'Only this occurrence';
-$txt['calendar_repeat_adjustment_this_and_future'] = 'This and future occurrences';
-$txt['calendar_repeat_adjustment_confirm'] = 'Are you sure you want to apply these changes to all future occurrences?-n--n-WARNING: if you select both &quot;Delete&quot; and &quot;This and future occurrences&quot;, you will delete this and all future occurrences.';
-$txt['calendar_repeat_delete_label'] = 'Delete';
-$txt['calendar_confirm_occurrence_delete'] = 'Are you sure you want to delete this occurrence of the event?-n--n-WARNING: if you select both &quot;Delete&quot; and &quot;This and future occurrences&quot;, you will delete this and all future occurrences.';
-$txt['calendar_repeat_adjustment_edit_first'] = 'Edit original event';
-
-// Used to show a human-readable explanation of the recurrence rule for a repeating event.
-$txt['calendar_rrule_desc'] = 'Repeats {rrule_description}{start_date, select,
-	false {}
-	other {, starting {start_date}}
-}.';
-// 'freq' will be one of YEARLY, MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY, or SECONDLY, or else a named month day (e.g. "Friday the 13th").
-$txt['calendar_rrule_desc_frequency_interval'] = 'every {freq, select,
-	YEARLY {{interval, plural,
-		=1 {year}
-		one {# year}
-		other {# years}
-	}}
-	MONTHLY {{interval, plural,
-		=1 {month}
-		one {# month}
-		other {# months}
-	}}
-	WEEKLY {{interval, plural,
-		=1 {week}
-		one {# week}
-		other {# weeks}
-	}}
-	DAILY {{interval, plural,
-		=1 {day}
-		one {# day}
-		other {# days}
-	}}
-	HOURLY {{interval, plural,
-		=1 {hour}
-		one {# hour}
-		other {# hours}
-	}}
-	MINUTELY {{interval, plural,
-		=1 {minute}
-		one {# minute}
-		other {# minutes}
-	}}
-	SECONDLY {{interval, plural,
-		=1 {second}
-		one {# second}
-		other {# seconds}
-	}}
-	other {{freq}}
-}';
-// 'freq' will be one of YEARLY, MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY, or SECONDLY, or else a named month day (e.g. "Friday the 13th").
-$txt['calendar_rrule_desc_frequency_interval_ordinal'] = 'every {freq, select,
-	YEARLY {{interval, selectordinal,
-		=1 {year}
-		one {#st year}
-		two {#nd year}
-		few {#rd year}
-		other {#th year}
-	}}
-	MONTHLY {{interval, selectordinal,
-		=1 {month}
-		one {#st month}
-		two {#nd month}
-		few {#rd month}
-		other {#th month}
-	}}
-	WEEKLY {{interval, selectordinal,
-		=1 {week}
-		one {#st week}
-		two {#nd week}
-		few {#rd week}
-		other {#th week}
-	}}
-	DAILY {{interval, selectordinal,
-		=1 {day}
-		one {#st day}
-		two {#nd day}
-		few {#rd day}
-		other {#th day}
-	}}
-	HOURLY {{interval, selectordinal,
-		=1 {hour}
-		one {#st hour}
-		two {#nd hour}
-		few {#rd hour}
-		other {#th hour}
-	}}
-	MINUTELY {{interval, selectordinal,
-		=1 {minute}
-		one {#st minute}
-		two {#nd minute}
-		few {#rd minute}
-		other {#th minute}
-	}}
-	SECONDLY {{interval, selectordinal,
-		=1 {second}
-		one {#st second}
-		two {#nd second}
-		few {#rd second}
-		other {#th second}
-	}}
-	other {{freq}}
-}';
-// 'months_titles' is a list of month names, using the forms from $txt['months_titles'].
-$txt['calendar_rrule_desc_bymonth'] = 'in {months_titles}';
-// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
-$txt['calendar_rrule_desc_byweekno'] = '{count, plural,
-	one {in the {ordinal_list} week of the year}
-	other {in the {ordinal_list} weeks of the year}
-}';
-// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
-$txt['calendar_rrule_desc_byyearday'] = '{count, plural,
-	one {on the {ordinal_list} day of the year}
-	other {on the {ordinal_list} days of the year}
-}';
-// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
-$txt['calendar_rrule_desc_bymonthday'] = '{count, plural,
-	one {on the {ordinal_list} day of the month}
-	other {on the {ordinal_list} days of the month}
-}';
-// Translators can replace 'ordinal_month_day' with 'cardinal_month_day' in this string if the target language prefers cardinal numbers instead of ordinal numbers for this form. For example, '{day_name} the {ordinal_month_day}' will produce 'Friday the 13th', whereas '{cardinal_month_day} {day_name}' will produce '13 Friday'.
-$txt['calendar_rrule_desc_named_monthday'] = '{day_name} the {ordinal_month_day}';
-// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, or 3rd").
-$txt['calendar_rrule_desc_named_monthdays'] = 'the first {day_name} that is the {ordinal_list} day of the month';
-// E.g. "the 2nd Thursday"
-$txt['calendar_rrule_desc_ordinal_day_name'] = 'the {ordinal} {day_name}';
-// E.g. "on Monday", "on Tuesday and Thursday"
-$txt['calendar_rrule_desc_byday'] = 'on {day_names}';
-// E.g. "on every Monday", "on every Tuesday and Thursday"
-$txt['calendar_rrule_desc_byday_every'] = 'on every {day_names}';
-$txt['calendar_rrule_desc_byminute'] = '{minute_list} past the hour';
-$txt['calendar_rrule_desc_bytime'] = 'at {times_list}';
-$txt['calendar_rrule_desc_bygeneric'] = 'of {list}';
-$txt['calendar_rrule_desc_between'] = 'between {min} and {max}';
-$txt['calendar_rrule_desc_until'] = 'until {date}';
-$txt['calendar_rrule_desc_count'] = '{count, plural,
-	one {for # occurrence}
-	other {for # occurrences}
-}';
-// 'ordinal_list' is a list of ordinal numbers (e.g. "1st, 2nd, and 3rd"). 'count' is the number of items in 'ordinal_list'.
-$txt['calendar_rrule_desc_bysetpos'] = '{count, plural,
-	one {on each {ordinal_list} occurrence}
-	other {on each {ordinal_list} occurrences}
-} of {rrule_description}';
-
 $txt['movetopic_change_subject'] = 'Change the topic’s subject';
 $txt['movetopic_new_subject'] = 'New subject';
 $txt['movetopic_change_all_subjects'] = 'Change every message’s subject';
diff --git a/Sources/Actions/Admin/Calendar.php b/Sources/Actions/Admin/Calendar.php
index 6f679e32bd..bdbbdf20f1 100644
--- a/Sources/Actions/Admin/Calendar.php
+++ b/Sources/Actions/Admin/Calendar.php
@@ -494,7 +494,7 @@ public static function getConfigVars(): array
 	protected function __construct()
 	{
 		// Everything's gonna need this.
-		Lang::load('ManageCalendar');
+		Lang::load('Calendar+ManageCalendar');
 
 		if (empty(Config::$modSettings['cal_enabled'])) {
 			unset(self::$subactions['holidays'], self::$subactions['editholiday']);
diff --git a/Sources/Actions/BoardIndex.php b/Sources/Actions/BoardIndex.php
index 01afe3e07e..3ef7eef4fd 100644
--- a/Sources/Actions/BoardIndex.php
+++ b/Sources/Actions/BoardIndex.php
@@ -605,6 +605,8 @@ public static function get(array $board_index_options): array
 	 */
 	protected function __construct()
 	{
+		Lang::load('Calendar');
+
 		Theme::loadTemplate('BoardIndex');
 		Utils::$context['template_layers'][] = 'boardindex_outer';
 
diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index eb154d6d68..3c2dfab477 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -1540,6 +1540,8 @@ public static function convertDateToEnglish(string $date): string
 	 */
 	protected function __construct()
 	{
+		Lang::load('Calendar');
+
 		if ($_GET['action'] === 'clock') {
 			$this->subaction = 'clock';
 		} elseif (!empty($_GET['sa']) && isset(self::$subactions[$_GET['sa']])) {
diff --git a/Sources/Actions/Display.php b/Sources/Actions/Display.php
index a2f840a9d6..a63851f27a 100644
--- a/Sources/Actions/Display.php
+++ b/Sources/Actions/Display.php
@@ -1064,6 +1064,8 @@ protected function loadEvents(): void
 			&& !empty(Config::$modSettings['cal_showInTopic'])
 			&& !empty(Config::$modSettings['cal_enabled'])
 		) {
+			Lang::load('Calendar');
+
 			foreach(Event::load(Topic::$info->id, true) as $event) {
 				if (($occurrence = $event->getUpcomingOccurrence()) === false) {
 					$occurrence = $event->getLastOccurrence();
@@ -1348,6 +1350,7 @@ protected function buildButtons(): void
 		}
 
 		if (Topic::$info->permissions['calendar_post']) {
+			Lang::load('Calendar');
 			Utils::$context['mod_buttons']['calendar'] = ['text' => 'calendar_link', 'url' => Config::$scripturl . '?action=post;calendar;msg=' . Topic::$info->id_first_msg . ';topic=' . Utils::$context['current_topic'] . '.0'];
 		}
 
diff --git a/Sources/Actions/Post.php b/Sources/Actions/Post.php
index 51ad42b3d8..451ed1f165 100644
--- a/Sources/Actions/Post.php
+++ b/Sources/Actions/Post.php
@@ -234,7 +234,7 @@ public function execute(): void
 	 */
 	public function show(): void
 	{
-		Lang::load('Post');
+		Lang::load('Post+Calendar');
 
 		if (!empty(Config::$modSettings['drafts_post_enabled'])) {
 			Lang::load('Drafts');
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index 517ebffb29..a4d57eb26c 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -407,6 +407,8 @@ class Event implements \ArrayAccess
 	 */
 	public function __construct(int $id = 0, array $props = [])
 	{
+		Lang::load('Calendar');
+
 		// Just in case someone passes -2 or something.
 		$id = max(-1, $id);
 
diff --git a/Sources/Calendar/RRule.php b/Sources/Calendar/RRule.php
index 1b64c30123..2e48c23164 100644
--- a/Sources/Calendar/RRule.php
+++ b/Sources/Calendar/RRule.php
@@ -536,7 +536,7 @@ public function getDescription(EventOccurrence $occurrence, ?bool $show_start =
 		}
 
 		// Just in case...
-		Lang::load('General+Modifications');
+		Lang::load('General+Calendar');
 
 		if (!empty($this->bysetpos)) {
 			$description = $this->getDescriptionBySetPos($occurrence->getParentEvent()->start);
diff --git a/Sources/ServerSideIncludes.php b/Sources/ServerSideIncludes.php
index 212a75a206..2a4c7d5b52 100644
--- a/Sources/ServerSideIncludes.php
+++ b/Sources/ServerSideIncludes.php
@@ -1883,7 +1883,6 @@ public static function news(string $output_method = 'echo'): ?string
 	 */
 	public static function todaysBirthdays(string $output_method = 'echo'): ?array
 	{
-
 		if (!self::$setup_done) {
 			new self();
 		}
@@ -2034,6 +2033,8 @@ public static function todaysCalendar(string $output_method = 'echo'): array|str
 			return $return;
 		}
 
+		Lang::load('Calendar');
+
 		if (!empty($return['calendar_holidays'])) {
 			echo '
 				<span class="holiday">' . Lang::$txt['calendar_prompt'] . ' ' . implode(', ', (array) $return['calendar_holidays']) . '<br></span>';
@@ -2435,6 +2436,8 @@ public static function recentEvents(int $max_events = 7, string $output_method =
 			return $return;
 		}
 
+		Lang::load('Calendar');
+
 		// Well the output method is echo.
 		echo '
 				<span class="event">' . Lang::$txt['events'] . '</span> ';
diff --git a/Sources/Theme.php b/Sources/Theme.php
index dbfb623ec9..cd0f430d85 100644
--- a/Sources/Theme.php
+++ b/Sources/Theme.php
@@ -931,6 +931,8 @@ public static function setupMenuContext(): void
 
 		$cacheTime = (int) Config::$modSettings['lastActive'] * 60;
 
+		Lang::load('Calendar');
+
 		// Initial "can you post an event in the calendar" option - but this might have been set in the calendar already.
 		if (!isset(Utils::$context['allow_calendar_event'])) {
 			Utils::$context['allow_calendar_event'] = Utils::$context['allow_calendar'] && User::$me->allowedTo('calendar_post');

From f06c38ad90b1a0567e7135faacc27537df5dfeff Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Sun, 10 Mar 2024 00:01:44 -0700
Subject: [PATCH 18/22] Allow linking existing topics and events

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/Calendar.php            |  10 +-
 Languages/en_US/Errors.php              |   1 +
 Sources/Actions/Calendar.php            | 114 ++++++----
 Sources/Actions/Display.php             |  14 +-
 Sources/Actions/Post.php                |  17 +-
 Sources/Actions/Post2.php               | 125 +++++++----
 Sources/Topic.php                       |  22 ++
 Themes/default/Calendar.template.php    |   4 +-
 Themes/default/Display.template.php     |  74 +------
 Themes/default/EventEditor.template.php | 277 ++++++++++++++++++++++--
 Themes/default/Post.template.php        |   5 +-
 Themes/default/css/index.css            |  19 +-
 Themes/default/css/responsive.css       |  29 +--
 Themes/default/scripts/event.js         |  63 +++++-
 Themes/default/scripts/script.js        |   5 -
 15 files changed, 568 insertions(+), 211 deletions(-)

diff --git a/Languages/en_US/Calendar.php b/Languages/en_US/Calendar.php
index c57d5bcb01..e9ced65673 100644
--- a/Languages/en_US/Calendar.php
+++ b/Languages/en_US/Calendar.php
@@ -21,7 +21,15 @@
 $txt['event_delete'] = 'Delete Event';
 $txt['calendar_post_event'] = 'Post Event';
 $txt['calendar'] = 'Calendar';
-$txt['calendar_link'] = 'Link to Calendar';
+$txt['calendar_link'] = 'Add Event';
+$txt['calendar_unlink'] = 'Unlink event';
+$txt['calendar_link_to'] = 'Link to';
+$txt['calendar_only'] = 'Calendar only';
+$txt['calendar_event_new'] = 'New event';
+$txt['calendar_event_existing'] = 'Existing event';
+$txt['calendar_topic_existing'] = 'Existing topic';
+$txt['calendar_link_event_id'] = 'Event ID';
+$txt['calendar_link_topic_id'] = 'Topic ID';
 $txt['calendar_upcoming'] = 'Upcoming Calendar';
 $txt['calendar_today'] = 'Today’s Calendar';
 $txt['calendar_week'] = 'Week';
diff --git a/Languages/en_US/Errors.php b/Languages/en_US/Errors.php
index ac3e38c935..047846f817 100644
--- a/Languages/en_US/Errors.php
+++ b/Languages/en_US/Errors.php
@@ -161,6 +161,7 @@
 $txt['invalid_date'] = 'Invalid date.';
 $txt['missing_event_id'] = 'Missing event ID.';
 $txt['cant_edit_event'] = 'You do not have permission to edit this event.';
+$txt['event_already_linked'] = 'This event is already linked to another topic.';
 $txt['missing_board_id'] = 'Board ID is missing.';
 $txt['missing_topic_id'] = 'Topic ID is missing.';
 $txt['topic_doesnt_exist'] = 'Topic does not exist.';
diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index 3c2dfab477..7d504e599c 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -359,7 +359,7 @@ public function post(): void
 			User::$me->checkSession();
 
 			// Validate the post...
-			if (!isset($_POST['link_to_board'])) {
+			if (!in_array($_POST['link_to'] ?? '', ['board', 'topic'])) {
 				self::validateEventPost();
 			}
 
@@ -369,8 +369,15 @@ public function post(): void
 			}
 
 			// New - and directing?
-			if (isset($_POST['link_to_board']) || empty(Config::$modSettings['cal_allow_unlinked'])) {
+			if (in_array($_POST['link_to'] ?? '', ['board', 'topic']) || empty(Config::$modSettings['cal_allow_unlinked'])) {
 				$_REQUEST['calendar'] = 1;
+
+				if (empty($_POST['topic'])) {
+					unset($_POST['topic']);
+				} elseif (isset($_POST['link_to']) && $_POST['link_to'] === 'topic') {
+					$_REQUEST['msg'] = Topic::load((int) $_POST['topic'])->id_first_msg;
+				}
+
 				Post::call();
 
 				return;
@@ -784,53 +791,82 @@ public static function getHolidayRange(string $low_date, string $high_date): arr
 	}
 
 	/**
-	 * Does permission checks to see if an event can be linked to a board/topic.
+	 * Does permission checks to see if the current user can link the current
+	 * topic to a calendar event.
+	 *
+	 * To succeed, the following conditions must be met:
+	 *
+	 * 1. The calendar must be enabled.
 	 *
-	 * Checks if the current user can link the current topic to the calendar, permissions et al.
-	 * This requires the calendar_post permission, a forum moderator, or a topic starter.
-	 * Expects the Topic::$topic_id and Board::$info->id variables to be set.
-	 * If the user doesn't have proper permissions, an error will be shown.
+	 * 2. If an event is passed to the $event parameter, the current user must
+	 *    be able to edit that event. Otherwise, the current user must be able
+	 *    to create new events.
+	 *
+	 * 3. There must be a current topic (i.e. Topic::$topic_id must be set).
+	 *
+	 * 4. The current user must be able to edit the first post in the current
+	 *    topic.
+	 *
+	 * @param bool $trigger_error Whether to trigger an error if the user cannot
+	 *    link an event to this topic. Default: true.
+	 * @param ?Event $event The event that the user wants to link to the current
+	 *    topic, or null if the user wants to create a new event.
+	 * @return bool Whether the user can link an event to the current topic.
 	 */
-	public static function canLinkEvent(): void
+	public static function canLinkEvent(bool $trigger_error = true, ?Event $event = null): bool
 	{
-		// If you can't post, you can't link.
-		User::$me->isAllowedTo('calendar_post');
+		// Is the calendar enabled?
+		if (empty(Config::$modSettings['cal_enabled'])) {
+			if ($trigger_error) {
+				ErrorHandler::fatalLang('calendar_off', false);
+			}
+
+			return false;
+		}
+
+		// Can the user create or edit the event?
+		$perm = !isset($event) ? 'calendar_post' : ($event->member === User::$me->id ? 'calendar_edit_own' : 'calendar_edit_any');
+
+		if (!User::$me->allowedTo($perm)) {
+			if ($trigger_error) {
+				User::$me->isAllowedTo($perm);
+			}
 
-		// No board?  No topic?!?
-		if (empty(Board::$info->id)) {
-			ErrorHandler::fatalLang('missing_board_id', false);
+			return false;
 		}
 
+		// Are we in a topic?
 		if (empty(Topic::$topic_id)) {
-			ErrorHandler::fatalLang('missing_topic_id', false);
-		}
-
-		// Administrator, Moderator, or owner.  Period.
-		if (!User::$me->allowedTo('admin_forum') && !User::$me->allowedTo('moderate_board')) {
-			// Not admin or a moderator of this board. You better be the owner - or else.
-			$result = Db::$db->query(
-				'',
-				'SELECT id_member_started
-				FROM {db_prefix}topics
-				WHERE id_topic = {int:current_topic}
-				LIMIT 1',
-				[
-					'current_topic' => Topic::$topic_id,
-				],
-			);
-
-			if ($row = Db::$db->fetch_assoc($result)) {
-				// Not the owner of the topic.
-				if ($row['id_member_started'] != User::$me->id) {
-					ErrorHandler::fatalLang('not_your_topic', 'user');
-				}
+			if ($trigger_error) {
+				ErrorHandler::fatalLang('missing_topic_id', false);
 			}
-			// Topic/Board doesn't exist.....
-			else {
-				ErrorHandler::fatalLang('calendar_no_topic', 'general');
+
+			return false;
+		}
+
+		// Don't let guests edit the posts of other guests.
+		if (User::$me->is_guest) {
+			if ($trigger_error) {
+				ErrorHandler::fatalLang('not_your_topic', false);
 			}
-			Db::$db->free_result($result);
+
+			return false;
 		}
+
+		// Linking an event counts as modifying the first post.
+		Topic::load();
+
+		$perm = User::$me->started ? ['modify_own', 'modify_any'] : 'modify_any';
+
+		if (!User::$me->allowedTo($perm, Topic::$info->id_board, true)) {
+			if ($trigger_error) {
+				User::$me->isAllowedTo($perm, Topic::$info->id_board, true);
+			}
+
+			return false;
+		}
+
+		return true;
 	}
 
 	/**
diff --git a/Sources/Actions/Display.php b/Sources/Actions/Display.php
index a63851f27a..7458aa55f4 100644
--- a/Sources/Actions/Display.php
+++ b/Sources/Actions/Display.php
@@ -1066,7 +1066,7 @@ protected function loadEvents(): void
 		) {
 			Lang::load('Calendar');
 
-			foreach(Event::load(Topic::$info->id, true) as $event) {
+			foreach (Topic::$info->getLinkedEvents() as $event) {
 				if (($occurrence = $event->getUpcomingOccurrence()) === false) {
 					$occurrence = $event->getLastOccurrence();
 				}
@@ -1075,6 +1075,8 @@ protected function loadEvents(): void
 			}
 
 			if (!empty(Utils::$context['linked_calendar_events'])) {
+				Theme::loadTemplate('EventEditor');
+
 				Utils::$context['linked_calendar_events'][count(Utils::$context['linked_calendar_events']) - 1]['is_last'] = true;
 			}
 		}
@@ -1293,6 +1295,11 @@ protected function buildButtons(): void
 			Utils::$context['normal_buttons']['add_poll'] = ['text' => 'add_poll', 'url' => Config::$scripturl . '?action=editpoll;add;topic=' . Utils::$context['current_topic'] . '.' . Utils::$context['start']];
 		}
 
+		if (Calendar::canLinkEvent(false)) {
+			Lang::load('Calendar');
+			Utils::$context['normal_buttons']['calendar'] = ['text' => 'calendar_link', 'url' => Config::$scripturl . '?action=post;calendar;msg=' . Topic::$info->id_first_msg . ';topic=' . Utils::$context['current_topic'] . '.0'];
+		}
+
 		if (Topic::$info->permissions['can_mark_unread']) {
 			Utils::$context['normal_buttons']['mark_unread'] = ['text' => 'mark_unread', 'url' => Config::$scripturl . '?action=markasread;sa=topic;t=' . Utils::$context['mark_unread_time'] . ';topic=' . Utils::$context['current_topic'] . '.' . Utils::$context['start'] . ';' . Utils::$context['session_var'] . '=' . Utils::$context['session_id']];
 		}
@@ -1349,11 +1356,6 @@ protected function buildButtons(): void
 			Utils::$context['mod_buttons']['merge'] = ['text' => 'merge', 'url' => Config::$scripturl . '?action=mergetopics;board=' . Utils::$context['current_board'] . '.0;from=' . Utils::$context['current_topic']];
 		}
 
-		if (Topic::$info->permissions['calendar_post']) {
-			Lang::load('Calendar');
-			Utils::$context['mod_buttons']['calendar'] = ['text' => 'calendar_link', 'url' => Config::$scripturl . '?action=post;calendar;msg=' . Topic::$info->id_first_msg . ';topic=' . Utils::$context['current_topic'] . '.0'];
-		}
-
 		// Restore topic. eh?  No monkey business.
 		if (Topic::$info->permissions['can_restore_topic']) {
 			Utils::$context['mod_buttons']['restore_topic'] = ['text' => 'restore_topic', 'url' => Config::$scripturl . '?action=restoretopic;topics=' . Utils::$context['current_topic'] . ';' . Utils::$context['session_var'] . '=' . Utils::$context['session_id']];
diff --git a/Sources/Actions/Post.php b/Sources/Actions/Post.php
index 451ed1f165..d82d082e7e 100644
--- a/Sources/Actions/Post.php
+++ b/Sources/Actions/Post.php
@@ -753,6 +753,19 @@ protected function initiateEvent(): void
 		// Permissions check!
 		User::$me->isAllowedTo('calendar_post');
 
+		// Are there any other linked events besides this one?
+		foreach (Event::load(Topic::$topic_id, true) as $event) {
+			if ($event->id === Utils::$context['event']->id) {
+				continue;
+			}
+
+			if (($occurrence = $event->getUpcomingOccurrence()) === false) {
+				$occurrence = $event->getLastOccurrence();
+			}
+
+			Utils::$context['linked_calendar_events'][] = $occurrence;
+		}
+
 		// We want a fairly compact version of the time, but as close as possible to the user's settings.
 		$time_string = Time::getShortTimeFormat();
 
@@ -796,8 +809,8 @@ protected function initiateEvent(): void
 		Theme::addJavaScriptVar('monthly_byday_items', (string) (count(Utils::$context['event']->byday_items) - 1));
 		Theme::loadJavaScriptFile('event.js', ['defer' => true], 'smf_event');
 
-		Utils::$context['event']->board = !empty(Board::$info->id) ? Board::$info->id : (int) Config::$modSettings['cal_defaultboard'];
-		Utils::$context['event']->topic = !empty(Topic::$info->id) ? Topic::$info->id : 0;
+		Utils::$context['event']->board = !empty(Utils::$context['event']->board) ? Utils::$context['event']->board : (Board::$info->id ?? (int) Config::$modSettings['cal_defaultboard']);
+		Utils::$context['event']->topic = !empty(Utils::$context['event']->topic) ? Utils::$context['event']->topic : -1;
 	}
 
 	/**
diff --git a/Sources/Actions/Post2.php b/Sources/Actions/Post2.php
index 780af2488d..89c048db40 100644
--- a/Sources/Actions/Post2.php
+++ b/Sources/Actions/Post2.php
@@ -276,7 +276,7 @@ public function submit(): void
 			}
 		}
 
-		if (isset($_POST['calendar']) && !isset($_REQUEST['deleteevent']) && Utils::htmlTrim($_POST['evtitle']) === '') {
+		if (isset($_POST['calendar']) && !isset($_REQUEST['deleteevent']) && !isset($_REQUEST['event_id_to_link']) && Utils::htmlTrim($_POST['evtitle']) === '') {
 			$this->errors[] = 'no_event';
 		}
 
@@ -510,58 +510,91 @@ public function submit(): void
 		}
 
 		// Editing or posting an event?
-		if (isset($_POST['calendar']) && (!isset($_REQUEST['eventid']) || $_REQUEST['eventid'] == -1)) {
-			// Make sure they can link an event to this post.
-			Calendar::canLinkEvent();
-
-			// Insert the event.
-			$eventOptions = [
-				'board' => Board::$info->id,
-				'topic' => Topic::$topic_id,
-				'title' => $_POST['evtitle'],
-				'location' => $_POST['event_location'],
-				'member' => User::$me->id,
-			];
-			Event::create($eventOptions);
-		} elseif (isset($_POST['calendar'])) {
-			$_REQUEST['eventid'] = (int) $_REQUEST['eventid'];
-
-			// Validate the post...
-			Calendar::validateEventPost();
-
-			// If you're not allowed to edit any and all events, you have to be the poster.
-			if (!User::$me->allowedTo('calendar_edit_any')) {
-				User::$me->isAllowedTo('calendar_edit_' . (!empty(User::$me->id) && Calendar::getEventPoster($_REQUEST['eventid']) == User::$me->id ? 'own' : 'any'));
-			}
+		if (isset($_POST['calendar'])) {
+			if (!isset($_REQUEST['eventid']) || $_REQUEST['eventid'] == -1) {
+				// Linking an existing event.
+				if (
+					isset($_REQUEST['event_id_to_link'], $_REQUEST['event_link_to'])
+					&& $_REQUEST['event_link_to'] === 'existing'
+					&& Event::load((int) $_REQUEST['event_id_to_link']) !== []
+				) {
+					$event = Event::$loaded[(int) $_REQUEST['event_id_to_link']];
+
+					Calendar::canLinkEvent(true, $event);
+
+					if (!empty($event->topic)) {
+						ErrorHandler::fatalLang('event_already_linked', 'user');
+					}
 
-			// Delete it?
-			if (isset($_REQUEST['deleteevent'])) {
-				if (isset($_REQUEST['recurrenceid'])) {
-					EventOccurrence::remove($_REQUEST['eventid'], $_REQUEST['recurrenceid'], !empty($_REQUEST['affects_future']));
-				} else {
-					Event::remove($_REQUEST['eventid']);
+					$event->board = Board::$info->id;
+					$event->topic = Topic::$topic_id;
+					$event->save();
 				}
-			}
-			// ... or just update it?
-			else {
-				// Set up our options
-				$eventOptions = [
-					'board' => Board::$info->id,
-					'topic' => Topic::$topic_id,
-					'title' => $_POST['evtitle'],
-					'location' => $_POST['event_location'],
-					'member' => User::$me->id,
-				];
+				// Creating a new event.
+				else {
+					// Make sure they can link an event to this post.
+					Calendar::canLinkEvent(true);
+
+					$eventOptions = [
+						'board' => Board::$info->id,
+						'topic' => Topic::$topic_id,
+						'title' => $_POST['evtitle'],
+						'location' => $_POST['event_location'],
+						'member' => User::$me->id,
+					];
+					Event::create($eventOptions);
+				}
+			} else {
+				$_REQUEST['eventid'] = (int) $_REQUEST['eventid'];
 
-				if (!empty($_REQUEST['recurrenceid'])) {
-					$eventOptions['recurrenceid'] = $_REQUEST['recurrenceid'];
+				// Validate the post...
+				Calendar::validateEventPost();
+
+				// If you're not allowed to edit any and all events, you have to be the poster.
+				if (!User::$me->allowedTo('calendar_edit_any')) {
+					User::$me->isAllowedTo('calendar_edit_' . (!empty(User::$me->id) && Calendar::getEventPoster($_REQUEST['eventid']) == User::$me->id ? 'own' : 'any'));
 				}
 
-				if (!empty($_REQUEST['affects_future'])) {
-					$eventOptions['affects_future'] = $_REQUEST['affects_future'];
+				// Delete it?
+				if (isset($_REQUEST['deleteevent'])) {
+					if (isset($_REQUEST['recurrenceid'])) {
+						EventOccurrence::remove($_REQUEST['eventid'], $_REQUEST['recurrenceid'], !empty($_REQUEST['affects_future']));
+					} else {
+						Event::remove($_REQUEST['eventid']);
+					}
 				}
+				// Unlink it from the topic?
+				elseif (isset($_REQUEST['unlink'])) {
+					$eventOptions = [
+						'board' => 0,
+						'topic' => 0,
+						'title' => $_POST['evtitle'],
+						'location' => $_POST['event_location'],
+					];
+
+					Event::modify($_REQUEST['eventid'], $eventOptions);
+				}
+				// ... or just update it?
+				else {
+					// Set up our options
+					$eventOptions = [
+						'board' => Board::$info->id,
+						'topic' => Topic::$topic_id,
+						'title' => $_POST['evtitle'],
+						'location' => $_POST['event_location'],
+						'member' => User::$me->id,
+					];
+
+					if (!empty($_REQUEST['recurrenceid'])) {
+						$eventOptions['recurrenceid'] = $_REQUEST['recurrenceid'];
+					}
+
+					if (!empty($_REQUEST['affects_future'])) {
+						$eventOptions['affects_future'] = $_REQUEST['affects_future'];
+					}
 
-				Event::modify($_REQUEST['eventid'], $eventOptions);
+					Event::modify($_REQUEST['eventid'], $eventOptions);
+				}
 			}
 		}
 
diff --git a/Sources/Topic.php b/Sources/Topic.php
index cdcc492f6d..ecb9ccf112 100644
--- a/Sources/Topic.php
+++ b/Sources/Topic.php
@@ -18,6 +18,7 @@
 use SMF\Actions\Moderation\ReportedContent;
 use SMF\Actions\Notify;
 use SMF\Cache\CacheApi;
+use SMF\Calendar\Event;
 use SMF\Db\DatabaseApi as Db;
 use SMF\Search\SearchApi;
 
@@ -312,6 +313,13 @@ class Topic implements \ArrayAccess
 		'topic_started_time' => 'started_time',
 	];
 
+	/**
+	 * @var array
+	 *
+	 * IDs of any events that are linked to this topic.
+	 */
+	protected array $events;
+
 	/****************************
 	 * Internal static properties
 	 ****************************/
@@ -529,6 +537,20 @@ public function getLikedMsgs(): array
 		return $liked_messages;
 	}
 
+	/**
+	 * Returns any calendar events that are linked to this topic.
+	 */
+	public function getLinkedEvents(): array
+	{
+		if (!isset($this->events)) {
+			foreach(Event::load($this->id, true) as $event) {
+				$this->events[] = $event->id;
+			}
+		}
+
+		return array_intersect_key(Event::$loaded, array_flip($this->events ?? []));
+	}
+
 	/***********************
 	 * Public static methods
 	 ***********************/
diff --git a/Themes/default/Calendar.template.php b/Themes/default/Calendar.template.php
index f8801742c8..058892e4d5 100644
--- a/Themes/default/Calendar.template.php
+++ b/Themes/default/Calendar.template.php
@@ -879,7 +879,9 @@ function template_event_post()
 	template_event_options();
 
 	echo '
-					<input type="submit" value="', empty(Utils::$context['event']->new) ? Lang::$txt['save'] : Lang::$txt['post'], '" class="button">
+					<div class="buttonlist">
+						<input type="submit" value="', empty(Utils::$context['event']->new) ? Lang::$txt['save'] : Lang::$txt['post'], '" class="button floatright">
+					</div>
 					<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
 				</div><!-- .roundframe -->
 			</div><!-- #post_event -->
diff --git a/Themes/default/Display.template.php b/Themes/default/Display.template.php
index f06452c3e6..2d95d94a41 100644
--- a/Themes/default/Display.template.php
+++ b/Themes/default/Display.template.php
@@ -174,81 +174,13 @@ function template_main()
 	}
 
 	// Does this topic have some events linked to it?
-	if (!empty(Utils::$context['linked_calendar_events']))
-	{
+	if (!empty(Utils::$context['linked_calendar_events'])) {
 		echo '
 		<div class="title_bar">
 			<h3 class="titlebg">', Lang::$txt['calendar_linked_events'], '</h3>
-		</div>
-		<div class="information events">
-			<ul>';
-
-		foreach (Utils::$context['linked_calendar_events'] as $event)
-		{
-			echo '
-				<li>
-					<strong class="event_title"><a href="', Config::$scripturl, '?action=calendar;event=', $event['id_event'], (!$event->is_first ? ';start_date=' . $event['start_date'] : ''), '">', $event['title'], '</a></strong>';
-
-			if ($event['can_edit'])
-				echo ' <a href="' . $event['modify_href'] . '"><span class="main_icons calendar_modify" title="', Lang::$txt['calendar_edit'], '"></span></a>';
-
-			if ($event['can_export'])
-				echo ' <a href="' . $event['export_href'] . '"><span class="main_icons calendar_export" title="', Lang::$txt['calendar_export'], '"></span></a>';
-
-			echo '
-					<br>';
-
-			if (!empty($event['allday']))
-			{
-				echo '<time datetime="' . $event['start_iso_gmdate'] . '">', trim($event['start_date_local']), '</time>', ($event['start_date'] != $event['end_date']) ? ' &ndash; <time datetime="' . $event['end_iso_gmdate'] . '">' . trim($event['end_date_local']) . '</time>' : '';
-			}
-			else
-			{
-				// Display event info relative to user's local timezone
-				echo '<time datetime="' . $event['start_iso_gmdate'] . '">', trim($event['start_date_local']), ', ', trim($event['start_time_local']), '</time> &ndash; <time datetime="' . $event['end_iso_gmdate'] . '">';
-
-				if ($event['start_date_local'] != $event['end_date_local'])
-					echo trim($event['end_date_local']) . ', ';
-
-				echo trim($event['end_time_local']);
-
-				// Display event info relative to original timezone
-				if ($event['start_date_local'] . $event['start_time_local'] != $event['start_date_orig'] . $event['start_time_orig'])
-				{
-					echo '</time> (<time datetime="' . $event['start_iso_gmdate'] . '">';
-
-					if ($event['start_date_orig'] != $event['start_date_local'] || $event['end_date_orig'] != $event['end_date_local'] || $event['start_date_orig'] != $event['end_date_orig'])
-						echo trim($event['start_date_orig']), ', ';
-
-					echo trim($event['start_time_orig']), '</time> &ndash; <time datetime="' . $event['end_iso_gmdate'] . '">';
-
-					if ($event['start_date_orig'] != $event['end_date_orig'])
-						echo trim($event['end_date_orig']) . ', ';
-
-					echo trim($event['end_time_orig']), ' ', $event['tz_abbrev'], '</time>)';
-				}
-				// Event is scheduled in the user's own timezone? Let 'em know, just to avoid confusion
-				else
-					echo ' ', $event['tz_abbrev'], '</time>';
-			}
-
-			if (!empty($event['location']))
-				echo '
-					<br>', $event['location'];
-
-			$rrule_description = $event->getParentEvent()->recurrence_iterator->getRRule()->getDescription($event);
-
-			if (!empty($rrule_description)) {
-				echo '
-					<br>', $rrule_description;
-			}
+		</div>';
 
-			echo '
-				</li>';
-		}
-		echo '
-			</ul>
-		</div><!-- .information -->';
+		template_linked_events();
 	}
 
 	// Show the page index... "Pages: [1]".
diff --git a/Themes/default/EventEditor.template.php b/Themes/default/EventEditor.template.php
index 81aa475831..0cfad78ac6 100644
--- a/Themes/default/EventEditor.template.php
+++ b/Themes/default/EventEditor.template.php
@@ -14,6 +14,8 @@
 use SMF\Calendar\Event;
 use SMF\Config;
 use SMF\Lang;
+use SMF\Topic;
+use SMF\User;
 use SMF\Utils;
 
 /**
@@ -24,42 +26,194 @@
 function template_event_options()
 {
 	echo '
-					<fieldset id="event_options">
-						<legend>', Lang::$txt['calendar_event_options'], '</legend>
-						<input type="hidden" name="calendar" value="1">';
+				<fieldset id="event_options">
+					<legend>', Lang::$txt['calendar_event_options'], '</legend>
+					<input type="hidden" name="calendar" value="1">
+					<input type="hidden" name="eventid" value="', Utils::$context['event']->id, '">
+					<input type="hidden" name="recurrenceid" value="', Utils::$context['event']->selected_occurrence->id, '">';
+
+	// Allow the user to link events to topics.
+	if (
+		Utils::$context['event']->type === Event::TYPE_EVENT
+		&& (
+			Utils::$context['event']->new
+			|| Utils::$context['event']->selected_occurrence->is_first
+		)
+	) {
+		if (empty(Utils::$context['event']->topic)) {
+			template_event_board();
+		} elseif (Utils::$context['event']->topic === (Topic::$topic_id ?? NAN)) {
+			template_event_unlink();
+		} elseif (Utils::$context['event']->new) {
+			template_event_link_to();
+		}
+	}
 
-	// If this is a new event let the user specify which board they want the linked post to be put into.
-	if (!empty(Utils::$context['event']->new) && !empty(Utils::$context['event']->categories)) {
+	template_event_new();
+
+	echo '
+				</fieldset>';
+}
+
+/**
+ * Template for linking an existing topic to an event.
+ */
+function template_event_link_to()
+{
+	// If user cannot edit existing events, we don't need to bother showing these options at all.
+	if (!User::$me->allowedTo('calendar_edit_any') && !User::$me->allowedTo('calendar_edit_own')) {
+		return;
+	}
+
+	// If user can both create and edit events, show both options.
+	if (User::$me->allowedTo('calendar_post')) {
 		echo '
-						<dl id="event_board">
-							<dt class="clear">
-								<label>', Lang::$txt['calendar_post_in'], '</label>
-							</dt>
-							<dd>
-								<input type="checkbox" name="link_to_board"', (!empty(Utils::$context['event']->board) ? ' checked' : ''), ' onclick="toggleLinked(this.form);">
-								<select name="board"', empty(Utils::$context['event']->board) ? ' disabled' : '', '>';
+					<dl id="event_link_to">
+						<dt class="clear">
+							' . Lang::$txt['calendar_link_to'] . '
+						</dt>
+						<dd>
+							<label>
+								<input type="radio" id="event_link_to_new" name="event_link_to" value="new" checked>
+								<span>' . Lang::$txt['calendar_event_new'] . '</span>
+							</label>
+							<label>
+								<input type="radio" name="event_link_to" value="existing">
+								<span>' . Lang::$txt['calendar_event_existing'] . '</span>
+							</label>
+						</dd>
+					</dl>';
+	}
+
+	// Let the user specify an existing event to link to.
+	echo '
+					<dl id="event_id_to_link">
+						<dt class="clear">
+							' . Lang::$txt['calendar_link_event_id'] . '
+						</dt>
+						<dd>
+							<input type="text" name="event_id_to_link">
+						</dd>
+					</dl>';
+}
+
+/**
+ * Template for unlinking a topic and an event.
+ */
+function template_event_unlink()
+{
+	if (empty(Utils::$context['event']->topic) || empty(Config::$modSettings['cal_allow_unlinked'])) {
+		return;
+	}
+
+	echo '
+					<dl>
+						<dt class="clear">
+							' . Lang::$txt['calendar_unlink'] . '
+						</dt>
+						<dd>
+							<input type="checkbox" name="unlink">
+						</dd>
+					</dl>
+					<hr class="clear">';
+}
+
+/**
+ * Template for choosing a board to create a linked topic in.
+ */
+function template_event_board()
+{
+	// If user cannot create new events, skip this.
+	if (!User::$me->allowedTo('calendar_post')) {
+		return;
+	}
+
+	echo '
+					<dl id="topic_link_to">
+						<dt class="clear">
+							' . Lang::$txt['calendar_post_in'] . '
+						</dt>
+						<dd>';
+
+	if (!empty(Config::$modSettings['cal_allow_unlinked'])) {
+		echo '
+							<label>
+								<input type="radio" id="link_to_none" name="link_to" value="none"' . (empty(Utils::$context['event']->topic) ? ' checked' : '') . '>
+								' . Lang::$txt['calendar_only'] . '
+							</label>';
+	}
+
+	if (!empty(Utils::$context['event']->categories)) {
+		echo '
+							<label>
+								<input type="radio" id="link_to_board" name="link_to" value="board"' . (empty(Utils::$context['event']->topic) && empty(Config::$modSettings['cal_allow_unlinked']) ? ' checked' : '') . '>
+								' . Lang::$txt['new_topic'] . '
+							</label>';
+	}
+
+	echo '
+							<label>
+								<input type="radio" id="link_to_topic" name="link_to" value="topic"' . (!empty(Utils::$context['event']->topic) ? ' checked' : '') . '>
+								' . Lang::$txt['calendar_topic_existing'] . '
+							</label>
+						</dd>
+					</dl>';
+
+
+	if (!empty(Utils::$context['event']->categories)) {
+		echo '
+					<dl id="event_board">
+						<dt class="clear">
+							<label>' . Lang::$txt['board_name'] . '</label>
+						</dt>
+						<dd>';
+		echo '
+							<select name="board"', empty(Utils::$context['event']->board) ? ' disabled' : '', '>';
 
 		foreach (Utils::$context['event']->categories as $category) {
 			echo '
-									<optgroup label="', $category['name'], '">';
+								<optgroup label="', $category['name'], '">';
 
 			foreach ($category['boards'] as $board) {
 				echo '
-										<option value="', $board['id'], '"', $board['selected'] ? ' selected' : '', '>', $board['child_level'] > 0 ? str_repeat('==', $board['child_level'] - 1) . '=&gt;' : '', ' ', $board['name'], '</option>';
+									<option value="', $board['id'], '"', $board['id'] == Utils::$context['event']->board ? ' selected' : '', '>', $board['child_level'] > 0 ? str_repeat('==', $board['child_level'] - 1) . '=&gt;' : '', ' ', $board['name'], '</option>';
 			}
 
 			echo '
-									</optgroup>';
+								</optgroup>';
 		}
 
 		echo '
-								</select>
-							</dd>
-						</dl>';
+							</select>
+						</dd>
+					</dl>';
+	}
+
+	echo '
+					<dl id="event_topic">
+						<dt class="clear">
+							<label>' . Lang::$txt['calendar_link_topic_id'] . '</label>
+						</dt>
+						<dd>
+							<input type="text" name="topic" value="' . (!empty(Utils::$context['event']->topic) ? Utils::$context['event']->topic : '') . '">
+						</dd>
+					</dl>
+					<hr class="clear">';
+}
+
+/**
+ * Template for entering info about a new event.
+ */
+function template_event_new()
+{
+	// If user cannot create new events, skip this.
+	if (!User::$me->allowedTo('calendar_post')) {
+		return;
 	}
 
 	// Basic event info
 	echo '
+					<div id="event_new">
 						<dl id="event_basic_info">
 							<dt class="clear">
 								<label', isset(Utils::$context['post_error']['no_event']) ? ' class="error"' : '', '>', Lang::$txt['calendar_event_title'], '</label>
@@ -132,7 +286,8 @@ function template_event_options()
 	}
 
 	echo '
-					</fieldset>';
+					</div>';
+
 }
 
 /**
@@ -514,4 +669,88 @@ function template_rrule()
 						</details>';
 }
 
+/**
+ * Template to show linked events.
+ */
+function template_linked_events()
+{
+	if (empty(Utils::$context['linked_calendar_events'])) {
+		return;
+	}
+
+	echo '
+				<div class="information events">
+					<ul>';
+
+	foreach (Utils::$context['linked_calendar_events'] as $event) {
+		echo '
+						<li>
+							<strong class="event_title"><a href="', Config::$scripturl, '?action=calendar;event=', $event['id_event'], (!$event->is_first ? ';start_date=' . $event['start_date'] : ''), '">', $event['title'], '</a></strong>';
+
+		if ($event['can_edit']) {
+			echo ' <a href="' . $event['modify_href'] . '"><span class="main_icons calendar_modify" title="', Lang::$txt['calendar_edit'], '"></span></a>';
+		}
+
+		if ($event['can_export']) {
+			echo ' <a href="' . $event['export_href'] . '"><span class="main_icons calendar_export" title="', Lang::$txt['calendar_export'], '"></span></a>';
+		}
+
+		echo '
+							<br>';
+
+		if (!empty($event['allday'])) {
+			echo '<time datetime="' . $event['start_iso_gmdate'] . '">', trim($event['start_date_local']), '</time>', ($event['start_date'] != $event['end_date']) ? ' &ndash; <time datetime="' . $event['end_iso_gmdate'] . '">' . trim($event['end_date_local']) . '</time>' : '';
+		} else {
+			// Display event info relative to user's local timezone
+			echo '<time datetime="' . $event['start_iso_gmdate'] . '">', trim($event['start_date_local']), ', ', trim($event['start_time_local']), '</time> &ndash; <time datetime="' . $event['end_iso_gmdate'] . '">';
+
+			if ($event['start_date_local'] != $event['end_date_local']) {
+				echo trim($event['end_date_local']) . ', ';
+			}
+
+			echo trim($event['end_time_local']);
+
+			// Display event info relative to original timezone
+			if ($event['start_date_local'] . $event['start_time_local'] != $event['start_date_orig'] . $event['start_time_orig']) {
+				echo '</time> (<time datetime="' . $event['start_iso_gmdate'] . '">';
+
+				if ($event['start_date_orig'] != $event['start_date_local'] || $event['end_date_orig'] != $event['end_date_local'] || $event['start_date_orig'] != $event['end_date_orig']) {
+					echo trim($event['start_date_orig']), ', ';
+				}
+
+				echo trim($event['start_time_orig']), '</time> &ndash; <time datetime="' . $event['end_iso_gmdate'] . '">';
+
+				if ($event['start_date_orig'] != $event['end_date_orig']) {
+					echo trim($event['end_date_orig']) . ', ';
+				}
+
+				echo trim($event['end_time_orig']), ' ', $event['tz_abbrev'], '</time>)';
+			}
+			// Event is scheduled in the user's own timezone? Let 'em know, just to avoid confusion
+			else {
+				echo ' ', $event['tz_abbrev'], '</time>';
+			}
+		}
+
+		if (!empty($event['location'])) {
+			echo '
+							<br>', $event['location'];
+		}
+
+		$rrule_description = $event->getParentEvent()->recurrence_iterator->getRRule()->getDescription($event);
+
+		if (!empty($rrule_description)) {
+			echo '
+							<br>', $rrule_description;
+		}
+
+		echo '
+						</li>';
+	}
+
+	echo '
+					</ul>
+				</div>';
+}
+
 ?>
\ No newline at end of file
diff --git a/Themes/default/Post.template.php b/Themes/default/Post.template.php
index e5055b4346..6d10eb6206 100644
--- a/Themes/default/Post.template.php
+++ b/Themes/default/Post.template.php
@@ -144,11 +144,14 @@ function addPollOption()
 	if (Utils::$context['make_event'])
 	{
 		echo '
-					<hr class="clear">
 					<div id="post_event">';
 
 		template_event_options();
 
+		if (!empty(Utils::$context['linked_calendar_events'])) {
+			template_linked_events();
+		}
+
 		echo '
 					</div><!-- #post_event -->';
 	}
diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index 4567ed603b..0f5926a122 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -143,6 +143,9 @@ fieldset legend {
 	box-shadow: none;
 	border: none;
 }
+fieldset legend a {
+	font-weight: normal;
+}
 summary {
 	margin: 5px 0;
 }
@@ -1464,13 +1467,22 @@ ul li.greeting {
 
 /* Styles for edit event section
 ---------------------------------------------------- */
+#post_header + #post_event {
+	margin: 1em 0 2em;
+}
 #post_event .roundframe {
 	padding: 12px 12%;
 	overflow: auto;
 }
 #post_event fieldset {
-	padding: 6px;
+	padding: 6px 12px;
 	clear: both;
+	margin-bottom: 12px;
+}
+#post_event fieldset:not(:last-child) {
+	margin-bottom: 0;
+	border-bottom-left-radius: 0;
+	border-bottom-right-radius: 0;
 }
 #post_event span.label {
 	margin: 0 0.5em 0 2px;
@@ -1558,6 +1570,11 @@ ul li.greeting {
 .bymonthday_label input:disabled + span {
 	opacity: 0.5;
 }
+#event_link_to label,
+#topic_link_to label {
+	margin-right: 2ch;
+	display: inline-block;
+}
 
 /* Styles for the recent messages section.
 ---------------------------------------------------- */
diff --git a/Themes/default/css/responsive.css b/Themes/default/css/responsive.css
index abe23147e3..d35d27724f 100644
--- a/Themes/default/css/responsive.css
+++ b/Themes/default/css/responsive.css
@@ -42,21 +42,7 @@
 	#member_list .ip, #member_list .last_active, #member_list .user_name {
 		display: none !important;
 	}
-}
-
-@media (min-width: 720px) and (max-width: 799px) {
-	#top_info .welcome {
-		display: none;
-	}
-}
 
-/* We have shared things... */
-@media screen and (max-width: 720px) {
-	/* Remove some content from the hooks table */
-	#list_integration_hooks th#header_list_integration_hooks_function_name, #list_integration_hooks td.function_name,
-	#list_integration_hooks th#header_list_integration_hooks_remove, #list_integration_hooks td.remove {
-		display: none;
-	}
 	/* New Mobile Action/Mod Pop (Test) */
 	.moderationbuttons_check {
 		display: none;
@@ -106,6 +92,21 @@
 	.mobile_buttons {
 		display: block;
 	}
+}
+
+@media (min-width: 720px) and (max-width: 799px) {
+	#top_info .welcome {
+		display: none;
+	}
+}
+
+/* We have shared things... */
+@media screen and (max-width: 720px) {
+	/* Remove some content from the hooks table */
+	#list_integration_hooks th#header_list_integration_hooks_function_name, #list_integration_hooks td.function_name,
+	#list_integration_hooks th#header_list_integration_hooks_remove, #list_integration_hooks td.remove {
+		display: none;
+	}
 
 	/* Stuff */
 	#top_info {
diff --git a/Themes/default/scripts/event.js b/Themes/default/scripts/event.js
index b3043ffa1a..7b8c1e9950 100644
--- a/Themes/default/scripts/event.js
+++ b/Themes/default/scripts/event.js
@@ -1,6 +1,6 @@
 window.addEventListener("DOMContentLoaded", updateEventUI);
 
-for (const elem of document.querySelectorAll("#start_date, #start_time, #end_date, #end_time, #allday, #tz, #rrule, #freq, #end_option, #monthly_option_type_bymonthday, #monthly_option_type_byday, #byday_num_select_0, #byday_name_select_0, #weekly_options .rrule_input[name=\'BYDAY\[\]\'], #monthly_options .rrule_input[name=\'BYDAY_num\[\]\'], #monthly_options .rrule_input[name=\'BYDAY_name\[\]\'], #monthly_options .rrule_input[name=\'BYMONTHDAY\[\]\']")) {
+for (const elem of document.querySelectorAll("#start_date, #start_time, #end_date, #end_time, #allday, #tz, #rrule, #freq, #end_option, #monthly_option_type_bymonthday, #monthly_option_type_byday, #byday_num_select_0, #byday_name_select_0, #weekly_options .rrule_input[name=\'BYDAY\[\]\'], #monthly_options .rrule_input[name=\'BYDAY_num\[\]\'], #monthly_options .rrule_input[name=\'BYDAY_name\[\]\'], #monthly_options .rrule_input[name=\'BYMONTHDAY\[\]\'], #event_link_to label, #event_link_to input, #topic_link_to label, #topic_link_to input")) {
 	elem.addEventListener("change", updateEventUI);
 }
 
@@ -19,16 +19,19 @@ for (const elem of document.querySelectorAll("#rdate_list a, #exdate_list a")) {
 let rdates_count = document.querySelectorAll("#rdate_list input[type='date']").length;
 let exdates_count = document.querySelectorAll("#exdate_list input[type='date']").length;
 
-let current_start_date = new Date(document.getElementById("start_date").value + 'T' + document.getElementById("start_time").value);
-let current_end_date = new Date(document.getElementById("end_date").value + 'T' + document.getElementById("end_time").value);
+let current_start_date = new Date(document.getElementById("start_date").value + 'T' + (document.getElementById("allday").checked ? '12:00:00' : document.getElementById("start_time").value));
+let current_end_date = new Date(document.getElementById("end_date").value + 'T' + (document.getElementById("allday").checked ? '12:00:00' : document.getElementById("end_time").value));
 
 const weekday_abbrevs = ["SU", "MO", "TU", "WE", "TH", "FR", "SA"];
 
 // Update all the parts of the event editing UI.
 function updateEventUI()
 {
-	let start_date = new Date(document.getElementById("start_date").value + 'T' + document.getElementById("start_time").value);
-	let end_date = new Date(document.getElementById("end_date").value + 'T' + document.getElementById("end_time").value);
+	toggleNewOrExistingEvent();
+	toggleNewOrExistingTopic();
+
+	let start_date = new Date(document.getElementById("start_date").value + 'T' + (document.getElementById("allday").checked ? '12:00:00' : document.getElementById("start_time").value));
+	let end_date = new Date(document.getElementById("end_date").value + 'T' + (document.getElementById("allday").checked ? '12:00:00' : document.getElementById("end_time").value));
 
 	let weekday = getWeekday(start_date);
 
@@ -705,4 +708,54 @@ function removeRDateOrExDate()
 	}
 
 	this.parentElement.remove();
+}
+
+function toggleNewOrExistingEvent()
+{
+	if (!document.getElementById("event_link_to")) {
+		return;
+	}
+
+	if (document.getElementById("event_link_to_new").checked === true) {
+		document.getElementById("event_new").style.display = '';
+		document.getElementById("event_id_to_link").style.display = 'none';
+		document.querySelector("#event_id_to_link input").disabled = true;
+	} else {
+		document.getElementById("event_new").style.display = 'none';
+		document.getElementById("event_id_to_link").style.display = '';
+		document.querySelector("#event_id_to_link input").disabled = false;
+	}
+}
+
+function toggleNewOrExistingTopic()
+{
+	if (!document.getElementById("topic_link_to")) {
+		return;
+	}
+
+	if (document.getElementById("event_board")) {
+		document.getElementById("event_board").style.display = 'none';
+		document.querySelector("#event_board select").disabled = true;
+	}
+
+	if (document.getElementById("event_topic")) {
+		document.getElementById("event_topic").style.display = 'none';
+		document.querySelector("#event_topic input").disabled = true;
+	}
+
+	if (
+		document.getElementById("event_board")
+		&& document.getElementById("link_to_board")
+		&& document.getElementById("link_to_board").checked === true
+	) {
+		document.getElementById("event_board").style.display = '';
+		document.querySelector("#event_board select").disabled = false;
+	} else if (
+		document.getElementById("event_topic")
+		&& document.getElementById("link_to_topic")
+		&& document.getElementById("link_to_topic").checked === true
+	) {
+		document.getElementById("event_topic").style.display = '';
+		document.querySelector("#event_topic input").disabled = false;
+	}
 }
\ No newline at end of file
diff --git a/Themes/default/scripts/script.js b/Themes/default/scripts/script.js
index f21d45710b..9601a920e6 100644
--- a/Themes/default/scripts/script.js
+++ b/Themes/default/scripts/script.js
@@ -1591,11 +1591,6 @@ function generateDays(offset)
 		dayElement.selectedIndex = selected;
 }
 
-function toggleLinked(form)
-{
-	form.board.disabled = !form.link_to_board.checked;
-}
-
 function initSearch()
 {
 	if (document.forms.searchform.search.value.indexOf("%u") != -1)

From 1c0c52ee6dca98aa88747713c4e407304097c080 Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Thu, 25 Apr 2024 19:21:41 -0600
Subject: [PATCH 19/22] Adds support for subscribing to external calendars

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/ManageCalendar.php           |   4 +
 Languages/en_US/ManageScheduledTasks.php     |   2 +
 Sources/Actions/Admin/Calendar.php           | 194 +++++++++++++++++--
 Sources/TaskRunner.php                       |   3 +
 Sources/Tasks/FetchCalendarSubscriptions.php |  62 ++++++
 Themes/default/ManageCalendar.template.php   |  12 ++
 6 files changed, 265 insertions(+), 12 deletions(-)
 create mode 100644 Sources/Tasks/FetchCalendarSubscriptions.php

diff --git a/Languages/en_US/ManageCalendar.php b/Languages/en_US/ManageCalendar.php
index 59ea04e774..5003131d1f 100644
--- a/Languages/en_US/ManageCalendar.php
+++ b/Languages/en_US/ManageCalendar.php
@@ -63,5 +63,9 @@
 $txt['calendar_import_type_holiday'] = 'Holidays';
 $txt['calendar_import_type_event'] = 'Events';
 $txt['calendar_import_button'] = 'Import';
+$txt['calendar_import_subscribe'] = 'Subscribe to this calendar';
+$txt['calendar_import_subscribe_desc'] = 'Calendars you subscribe to will be reimported regularly.';
+$txt['calendar_import_manage_subscriptions'] = 'Subscribed calendars';
+$txt['calendar_import_unsubscribe'] = 'Unsubscribe';
 
 ?>
\ No newline at end of file
diff --git a/Languages/en_US/ManageScheduledTasks.php b/Languages/en_US/ManageScheduledTasks.php
index 9e41742ea6..c2f586a5e3 100644
--- a/Languages/en_US/ManageScheduledTasks.php
+++ b/Languages/en_US/ManageScheduledTasks.php
@@ -25,6 +25,8 @@
 $txt['scheduled_task_desc_weekly_digest'] = 'Emails out the weekly digest for notification subscribers.';
 $txt['scheduled_task_fetchSMfiles'] = 'Fetch Simple Machines files';
 $txt['scheduled_task_desc_fetchSMfiles'] = 'Retrieves javascript files containing notifications of updates and other information.';
+$txt['scheduled_task_fetch_calendar_subs'] = 'Fetch updates from subscribed calendars';
+$txt['scheduled_task_desc_fetch_calendar_subs'] = 'Updates SMF’s calendar with data from external calendars that you have subscribed to.';
 $txt['scheduled_task_birthdayemails'] = 'Send Birthday emails';
 $txt['scheduled_task_desc_birthdayemails'] = 'Sends out emails wishing members a happy birthday.';
 $txt['scheduled_task_weekly_maintenance'] = 'Weekly Maintenance';
diff --git a/Sources/Actions/Admin/Calendar.php b/Sources/Actions/Admin/Calendar.php
index bdbbdf20f1..81e29c2f22 100644
--- a/Sources/Actions/Admin/Calendar.php
+++ b/Sources/Actions/Admin/Calendar.php
@@ -20,6 +20,7 @@
 use SMF\Actions\ActionInterface;
 use SMF\Actions\BackwardCompatibility;
 use SMF\Board;
+use SMF\Calendar\Event;
 use SMF\Calendar\Holiday;
 use SMF\Config;
 use SMF\Db\DatabaseApi as Db;
@@ -28,6 +29,7 @@
 use SMF\Lang;
 use SMF\Menu;
 use SMF\SecurityToken;
+use SMF\TaskRunner;
 use SMF\Theme;
 use SMF\Time;
 use SMF\TimeInterval;
@@ -315,30 +317,198 @@ public function import(): void
 		Utils::$context['page_title'] = Lang::$txt['calendar_import'];
 
 		// Submitting?
-		if (isset($_POST[Utils::$context['session_var']], $_POST['ics_url'], $_POST['type'])) {
+		if (isset($_POST[Utils::$context['session_var']])) {
 			User::$me->checkSession();
 			SecurityToken::validate('admin-calendarimport');
 
-			$ics_url = new Url($_POST['ics_url'], true);
+			if (isset($_POST['ics_url'], $_POST['type'])) {
+				$ics_url = new Url($_POST['ics_url'], true);
 
-			if ($ics_url->isValid()) {
-				$ics_data = WebFetchApi::fetch($ics_url);
+				if ($ics_url->isValid()) {
+					$ics_data = WebFetchApi::fetch($ics_url);
+				}
+
+				if (!empty($ics_data)) {
+					switch ($_POST['type']) {
+						case 'holiday':
+							Holiday::import($ics_data);
+							break;
+
+						case 'event':
+							Event::import($ics_data);
+							break;
+					}
+				}
+
+				// Subscribing to this calendar?
+				if (isset($_POST['subscribe'])) {
+					$subscribed = Utils::jsonDecode(Config::$modSettings['calendar_subscriptions'] ?? '[]', true);
+
+					$subscribed[(string) $ics_url] = $_POST['type'] === 'holiday' ? Event::TYPE_HOLIDAY : Event::TYPE_EVENT;
+
+					Config::updateModSettings(['calendar_subscriptions' => Utils::jsonEncode($subscribed)]);
+
+					$request = Db::$db->query(
+						'',
+						'SELECT id_task
+						FROM {db_prefix}scheduled_tasks
+						WHERE task = {string:task}',
+						[
+							'task' => 'fetch_calendar_subs',
+						],
+					);
+
+					$exists = Db::$db->num_rows($request) > 0;
+					Db::$db->free_result($request);
+
+					if (!$exists) {
+						$id_task = Db::$db->insert(
+							'',
+							'{db_prefix}scheduled_tasks',
+							[
+								'next_time' => 'int',
+								'time_offset' => 'int',
+								'time_regularity' => 'int',
+								'time_unit' => 'string-1',
+								'disabled' => 'int',
+								'task' => 'string-24',
+							],
+							[
+								'next_time' => 0,
+								'time_offset' => 0,
+								'time_regularity' => 1,
+								'time_unit' => 'd',
+								'disabled' => 0,
+								'task' => 'fetch_calendar_subs',
+							],
+							['id_task'],
+						);
+
+						TaskRunner::calculateNextTrigger((string) $id_task, true);
+					}
+				}
 			}
 
-			if (!empty($ics_data)) {
-				switch ($_POST['type']) {
-					case 'holiday':
-						Holiday::import($ics_data);
-						break;
+			// Unsubscribing from some calendars?
+			if (isset($_POST['unsubscribe'], $_POST['subscribed'])) {
+				$subscribed = Utils::jsonDecode(Config::$modSettings['calendar_subscriptions'] ?? '[]', true);
+
+				foreach ($subscribed as $url => $type) {
+					$hashes[md5($url)] = $url;
+				}
 
-					case 'event':
-						Event::import($ics_data);
-						break;
+				foreach ($_POST['subscribed'] as $hash => $value) {
+					unset($subscribed[$hashes[$hash]]);
 				}
+
+				Config::updateModSettings(['calendar_subscriptions' => Utils::jsonEncode($subscribed)]);
 			}
 		}
 
 		SecurityToken::create('admin-calendarimport');
+
+		// List the current calendar subscriptions.
+		$subscribed = Utils::jsonDecode(Config::$modSettings['calendar_subscriptions'] ?? '[]', true);
+
+		if (!empty($subscribed)) {
+			foreach ($subscribed as $url => $type) {
+				Utils::$context['calendar_subscriptions'][] = [
+					'hash' => md5($url),
+					'url' => $url,
+					'type' => $type === Event::TYPE_HOLIDAY ? Lang::$txt['calendar_import_type_holiday'] : Lang::$txt['calendar_import_type_event'],
+				];
+			}
+
+			$listOptions = [
+				'id' => 'calendar_subscriptions',
+				'title' => Lang::$txt['calendar_import_manage_subscriptions'],
+				'items_per_page' => Config::$modSettings['defaultMaxListItems'],
+				'base_href' => Config::$scripturl . '?action=admin;area=managecalendar;sa=import',
+				// 'default_sort_col' => 'url',
+				'get_items' => [
+					'value' => Utils::$context['calendar_subscriptions'],
+				],
+				'get_count' => [
+					'value' => count(Utils::$context['calendar_subscriptions']),
+				],
+				'no_items_label' => Lang::$txt['none'],
+				'columns' => [
+					'url' => [
+						'header' => [
+							'value' => Lang::$txt['url'],
+						],
+						'data' => [
+							'sprintf' => [
+								'format' => '%1$s',
+								'params' => [
+									'url' => true,
+								],
+							],
+						],
+						'sort' => [
+							'default' => '',
+							'reverse' => '',
+						],
+					],
+					'type' => [
+						'header' => [
+							'value' => Lang::sentenceList(
+								[
+									Lang::$txt['calendar_import_type_event'],
+									Lang::$txt['calendar_import_type_holiday'],
+								],
+								'or',
+							),
+						],
+						'data' => [
+							'sprintf' => [
+								'format' => '%1$s',
+								'params' => [
+									'type' => false,
+								],
+							],
+						],
+						'sort' => [
+							'default' => 'cal.start_date',
+							'reverse' => 'cal.start_date DESC',
+						],
+					],
+					'check' => [
+						'header' => [
+							'value' => '<input type="checkbox" onclick="invertAll(this, this.form);">',
+							'class' => 'centercol',
+						],
+						'data' => [
+							'sprintf' => [
+								'format' => '<input type="checkbox" name="subscribed[%1$s]">',
+								'params' => [
+									'hash' => false,
+								],
+							],
+							'class' => 'centercol',
+						],
+					],
+				],
+				'form' => [
+					'href' => Config::$scripturl . '?action=admin;area=managecalendar;sa=import',
+					'token' => 'admin-calendarimport',
+				],
+				'additional_rows' => [
+					// [
+					// 	'position' => 'above_column_headers',
+					// 	'value' => '<input type="submit" name="unsubscribe" value="' . Lang::$txt['calendar_import_unsubscribe'] . '" class="button">',
+					// ],
+					[
+						'position' => 'below_table_data',
+						'value' => '<input type="submit" name="unsubscribe" value="' . Lang::$txt['calendar_import_unsubscribe'] . '" class="button">',
+					],
+				],
+			];
+
+			new ItemList($listOptions);
+
+			Theme::loadTemplate('GenericList');
+		}
 	}
 
 	/**
diff --git a/Sources/TaskRunner.php b/Sources/TaskRunner.php
index b50d604715..1f622bd4d4 100644
--- a/Sources/TaskRunner.php
+++ b/Sources/TaskRunner.php
@@ -86,6 +86,9 @@ class TaskRunner
 		'fetchSMfiles' => [
 			'class' => 'SMF\\Tasks\\FetchSMFiles',
 		],
+		'fetch_calendar_subs' => [
+			'class' => 'SMF\\Tasks\\FetchCalendarSubscriptions',
+		],
 		'birthdayemails' => [
 			'class' => 'SMF\\Tasks\\Birthday_Notify',
 		],
diff --git a/Sources/Tasks/FetchCalendarSubscriptions.php b/Sources/Tasks/FetchCalendarSubscriptions.php
new file mode 100644
index 0000000000..f046dffb9f
--- /dev/null
+++ b/Sources/Tasks/FetchCalendarSubscriptions.php
@@ -0,0 +1,62 @@
+<?php
+
+/**
+ * Simple Machines Forum (SMF)
+ *
+ * @package SMF
+ * @author Simple Machines https://www.simplemachines.org
+ * @copyright 2024 Simple Machines and individual contributors
+ * @license https://www.simplemachines.org/about/smf/license.php BSD
+ *
+ * @version 3.0 Alpha 1
+ */
+
+declare(strict_types=1);
+
+namespace SMF\Tasks;
+
+use SMF\Calendar\Event;
+use SMF\Calendar\Holiday;
+use SMF\Config;
+use SMF\Url;
+use SMF\Utils;
+use SMF\WebFetch\WebFetchApi;
+
+/**
+ * Imports updates from subscribed calendars into SMF's calendar.
+ */
+class FetchCalendarSubscriptions extends ScheduledTask
+{
+	/**
+	 * This executes the task.
+	 *
+	 * @return bool Always returns true.
+	 * @todo PHP 8.2: This can be changed to return type: true.
+	 */
+	public function execute(): bool
+	{
+		foreach (Utils::jsonDecode(Config::$modSettings['calendar_subscriptions'] ?? '[]', true) as $url => $type) {
+			$url = new Url($url, true);
+
+			if ($url->isValid()) {
+				$ics_data = WebFetchApi::fetch($url);
+			}
+
+			if (!empty($ics_data)) {
+				switch ($type) {
+					case 'holiday':
+						Holiday::import($ics_data);
+						break;
+
+					case 'event':
+						Event::import($ics_data);
+						break;
+				}
+			}
+		}
+
+		return true;
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/Themes/default/ManageCalendar.template.php b/Themes/default/ManageCalendar.template.php
index 7303851c72..cd6eeb6347 100644
--- a/Themes/default/ManageCalendar.template.php
+++ b/Themes/default/ManageCalendar.template.php
@@ -80,12 +80,24 @@ function template_import()
 							', Lang::$txt['calendar_import_type_event'], '
 						</label>
 					</dd>
+					<dt>
+						<label>', Lang::$txt['calendar_import_subscribe'], '</label>
+						<br>
+						<span class="smalltext">', Lang::$txt['calendar_import_subscribe_desc'], '</span>
+					</dt>
+					<dd>
+						<input type="checkbox" name="subscribe" id="subscribe">
+					</dd>
 				</dl>
 				<input type="submit" name="import" value="', Lang::$txt['calendar_import_button'], '" class="button">
 				<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
 				<input type="hidden" name="' . Utils::$context['admin-calendarimport_token_var'] . '" value="' . Utils::$context['admin-calendarimport_token'] . '">
 			</div><!-- .windowbg -->
 		</form>';
+
+	if (!empty(Utils::$context['calendar_subscriptions'])) {
+		template_show_list('calendar_subscriptions');
+	}
 }
 
 ?>
\ No newline at end of file

From 253e41571d8a378d2e3c20ca10b648e50e7478bb Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Mon, 29 Apr 2024 16:05:14 -0600
Subject: [PATCH 20/22] Further improves the code for exporting events

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Languages/en_US/Calendar.php         |   5 +
 Sources/Actions/Calendar.php         | 244 +++++++++++++++++++++------
 Sources/Calendar/Event.php           |  82 +++++----
 Themes/default/css/index.css         |   6 +
 Themes/default/images/icons/feed.svg |   4 +
 5 files changed, 264 insertions(+), 77 deletions(-)
 create mode 100644 Themes/default/images/icons/feed.svg

diff --git a/Languages/en_US/Calendar.php b/Languages/en_US/Calendar.php
index e9ced65673..e3d4e09785 100644
--- a/Languages/en_US/Calendar.php
+++ b/Languages/en_US/Calendar.php
@@ -16,6 +16,11 @@
 $txt['calendar_post_in'] = 'Post in';
 $txt['calendar_edit'] = 'Edit Event';
 $txt['calendar_export'] = 'Export Event';
+$txt['calendar_subscribe'] = 'Subscribe';
+$txt['calendar_subscribe_desc'] = 'Shows upcoming events in your calendar app.';
+$txt['calendar_subscribe_url_copied'] = 'The calendar subscription URL has been copied to the clipboard. Paste it into your calendar app to subscribe.';
+$txt['calendar_download'] = 'Download';
+$txt['calendar_download_desc'] = 'Exports a copy of the currently visible events.';
 $txt['calendar_view_week'] = 'View Week';
 $txt['event_delete_confirm'] = 'Delete this event?';
 $txt['event_delete'] = 'Delete Event';
diff --git a/Sources/Actions/Calendar.php b/Sources/Actions/Calendar.php
index 9ba444e240..ac6c15701c 100644
--- a/Sources/Actions/Calendar.php
+++ b/Sources/Actions/Calendar.php
@@ -320,7 +320,64 @@ public function show(): void
 		Utils::$context['calendar_buttons'] = [];
 
 		if (Utils::$context['can_post']) {
-			Utils::$context['calendar_buttons']['post_event'] = ['text' => 'calendar_post_event', 'image' => 'calendarpe.png', 'url' => Config::$scripturl . '?action=calendar;sa=post;month=' . Utils::$context['current_month'] . ';year=' . Utils::$context['current_year'] . ';' . Utils::$context['session_var'] . '=' . Utils::$context['session_id']];
+			Utils::$context['calendar_buttons']['post_event'] = [
+				'text' => 'calendar_post_event',
+				'url' => Config::$scripturl . '?action=calendar;sa=post;month=' . Utils::$context['current_month'] . ';year=' . Utils::$context['current_year'] . ';' . Utils::$context['session_var'] . '=' . Utils::$context['session_id'],
+			];
+		}
+
+		if (!empty(Config::$modSettings['cal_export']) && !User::$me->possibly_robot) {
+			$webcal_url = Config::$scripturl . '?action=calendar;sa=ical' . (!User::$me->is_guest ? ';u=' . User::$me->id . ';token=' . $this->createToken(User::$me) : '');
+
+			if (BrowserDetector::isBrowser('safari') || BrowserDetector::isBrowser('iphone')) {
+				$webcal_url = preg_replace('/^https?/', 'webcal', $webcal_url);
+			} else {
+				$webcal_url = 'javascript:navigator.clipboard.writeText(' . Utils::escapeJavaScript($webcal_url) . ');alert(' . Utils::escapeJavaScript(Lang::$txt['calendar_subscribe_url_copied']) . ')';
+			}
+
+			$ics_url = Config::$scripturl . '?action=calendar;sa=ical';
+
+			switch (Utils::$context['calendar_view']) {
+				case 'viewmonth':
+					$ics_url .= ';start_date=' . $start_object->format('Y-m-01');
+					$ics_url .= ';duration=P1M';
+					break;
+
+				case 'viewweek':
+					$s = clone $start_object;
+
+					while (($s->format('N') % 7) > $calendarOptions['start_day']) {
+						$s->modify('-1 day');
+					}
+
+					$ics_url .= ';start_date=' . $s->format('Y-m-d');
+					$ics_url .= ';duration=P7D';
+					break;
+
+				default:
+					$ics_url .= ';start_date=' . $start_object->format('Y-m-d');
+					$ics_url .= ';duration=' . (string) TimeInterval::createFromDateInterval($start_object->diff($end_object));
+					break;
+			}
+
+			Lang::$txt[''] = '';
+
+			Utils::$context['calendar_buttons']['cal_export'] = [
+				'text' => '',
+				'class' => 'main_icons feed',
+				'custom' => 'title="' . Lang::getTxt('calendar_subscribe') . '"',
+				'url' => $ics_url,
+				'sub_buttons' => [
+					'subscribe' => [
+						'text' => 'calendar_subscribe',
+						'url' => $webcal_url,
+					],
+					'download' => [
+						'text' => 'calendar_download',
+						'url' => $ics_url,
+					],
+				],
+			];
 		}
 
 		// Allow mods to add additional buttons here
@@ -539,68 +596,107 @@ public function export(): void
 			ErrorHandler::fatalLang('calendar_export_off', false);
 		}
 
-		// Goes without saying that this is required.
-		if (!isset($_REQUEST['eventid'])) {
-			ErrorHandler::fatalLang('no_access', false);
-		}
+		$file = [
+			'mime_type' => 'text/calendar',
+			'expires' => time() + 3600,
+			// Will be changed below.
+			'mtime' => 0,
+			// Will be changed below.
+			'filename' => 'event.ics',
+			// More will be added below.
+			'content' => [
+				'BEGIN:VCALENDAR',
+				'METHOD:PUBLISH',
+				'PRODID:-//SimpleMachines//' . SMF_FULL_VERSION . '//EN',
+				'VERSION:2.0',
+			],
+		];
 
-		// Load up the event in question and check it is valid.
-		$event = current(Event::load((int) $_REQUEST['eventid']));
+		if (isset($_REQUEST['eventid'])) {
+			// Load up the event in question and check it is valid.
+			$event = current(Event::load((int) $_REQUEST['eventid']));
 
-		if (!($event instanceof Event)) {
-			ErrorHandler::fatalLang('no_access', false);
-		}
+			if (!($event instanceof Event)) {
+				ErrorHandler::fatalLang('no_access', false);
+			}
 
-		// This is what we will be sending later.
-		$filecontents = [];
-		$filecontents[] = 'BEGIN:VCALENDAR';
-		$filecontents[] = 'METHOD:PUBLISH';
-		$filecontents[] = 'PRODID:-//SimpleMachines//' . SMF_FULL_VERSION . '//EN';
-		$filecontents[] = 'VERSION:2.0';
+			// Was a specific occurrence requested, or the event in general?
+			if (
+				isset($_REQUEST['recurrenceid'])
+				&& ($occurrence = $event->getOccurrence($_REQUEST['recurrenceid'])) !== false
+			) {
+				$file['content'][] = $occurrence->export();
+			} else {
+				$file['content'][] = $event->export();
+			}
 
-		$filecontents[] = $event->export();
+			$file['filename'] = $event->title . '.ics';
+			$file['mtime'] = $event->modified_time;
+		} else {
+			$this->authenticateForExport();
 
-		$filecontents[] = 'END:VCALENDAR';
+			// Get all the visible events within a date range.
+			if (isset($_REQUEST['start_date'])) {
+				$low_date = @(new Time($_REQUEST['start_date']));
+			}
 
-		// Send some standard headers.
-		ob_end_clean();
+			if (!isset($low_date)) {
+				$low_date = new Time('now');
+				$low_date->setDate((int) $low_date->format('Y'), (int) $low_date->format('m'), 1);
+			}
 
-		if (!empty(Config::$modSettings['enableCompressedOutput'])) {
-			@ob_start('ob_gzhandler');
-		} else {
-			ob_start();
-		}
+			if (isset($_REQUEST['duration'])) {
+				$duration = @(new TimeInterval($_REQUEST['duration']));
+			}
 
-		// Send the file headers
-		header('pragma: ');
-		header('cache-control: no-cache');
+			if (!isset($duration)) {
+				$duration = new TimeInterval('P3M');
+			}
 
-		if (!BrowserDetector::isBrowser('gecko')) {
-			header('content-transfer-encoding: binary');
-		}
+			$high_date = (clone $low_date)->add($duration);
 
-		header('expires: ' . gmdate('D, d M Y H:i:s', time() + 3600) . ' GMT');
-		header('last-modified: ' . gmdate('D, d M Y H:i:s', $event->modified_time) . ' GMT');
-		header('accept-ranges: bytes');
-		header('connection: close');
-		header('content-disposition: attachment; filename="' . $event->title . '.ics"');
+			$full_event_uids = [];
 
-		// RFC 5545 requires "\r\n", not just "\n".
-		$calevent = implode("\r\n", $filecontents);
+			foreach (Event::getOccurrencesInRange($low_date->format('Y-m-d'), $high_date->format('Y-m-d'), true) as $occurrence) {
+				$event = $occurrence->getParentEvent();
+
+				// Skip if we already exported the full event.
+				if (in_array($event->uid, $full_event_uids)) {
+					continue;
+				}
+
+				if (
+					// If there was no requested start date, export the full event.
+					!isset($_REQUEST['start_date'])
+					// Or if all occurrences are visible, export the full event.
+					|| (
+						$event->start >= $low_date
+						&& $event->getRecurrenceEnd() <= $high_date
+					)
+				) {
+					$file['content'][] = $event->export();
+					$full_event_ids[] = $event->uid;
+				}
+				// Otherwise, export just this occurrence.
+				else {
+					$file['content'][] = $occurrence->export();
+				}
+
+				$file['mtime'] = max($file['mtime'], $event->modified_time);
+			}
 
-		if (empty(Config::$modSettings['enableCompressedOutput'])) {
-			// todo: correctly handle $filecontents before passing to string function
-			header('content-length: ' . Utils::entityStrlen($calevent));
+			$file['filename'] = implode(' ', [Utils::$context['forum_name'], Lang::$txt['events'], $low_date->format('Y-m-d'), $high_date->format('Y-m-d')]) . '.ics';
 		}
 
-		// This is a calendar item!
-		header('content-type: text/calendar');
+		$file['content'][] = 'END:VCALENDAR';
+
+		// RFC 5545 requires "\r\n", not just "\n".
+		$file['content'] = implode("\r\n", $file['content']);
 
-		// Chuck out the card.
-		echo $calevent;
+		$file['size'] = strlen($file['content']);
 
-		// Off we pop - lovely!
-		Utils::obExit(false);
+		// Send it.
+		Utils::emitFile($file);
 	}
 
 	/**
@@ -1558,8 +1654,26 @@ protected function __construct()
 			return;
 		}
 
+		// Special case for handling calendar subscriptions.
+		if (
+			User::$me->is_guest
+			&& $this->subaction === 'ical'
+			&& isset($_REQUEST['u'], $_REQUEST['token'])
+		) {
+			$user = current(User::load((int) $_REQUEST['u']));
+
+			if (
+				!($user instanceof User)
+				|| !$user->allowedTo('calendar_view')
+				|| $_REQUEST['token'] !== $this->createToken($user)
+			) {
+				exit;
+			}
+		}
 		// Permissions, permissions, permissions.
-		User::$me->isAllowedTo('calendar_view');
+		else {
+			User::$me->isAllowedTo('calendar_view');
+		}
 
 		// Some global template resources.
 		Utils::$context['calendar_resources'] = [
@@ -1567,6 +1681,40 @@ protected function __construct()
 			'max_year' => Config::$modSettings['cal_maxyear'],
 		];
 	}
+
+	/**
+	 * Generates an calendar subscription authentication token.
+	 *
+	 * @param User $user The member that this token is for.
+	 * @return string The authentication token.
+	 */
+	protected function createToken(User $user): string
+	{
+		$token = hash_hmac('sha3-224', (string) $user->id, Config::getAuthSecret(), true);
+
+		return strtr(base64_encode($token), ['+' => '_', '/' => '-', '=' => '']);
+	}
+
+	/**
+	 * Validates the guest-supplided user ID and token combination, and loads
+	 * the requested user if the token is valid.
+	 *
+	 * Does nothing if the user is already logged in.
+	 */
+	protected function authenticateForExport(): void
+	{
+		if (!User::$me->is_guest) {
+			return;
+		}
+
+		if (!empty($_REQUEST['u']) && isset($_REQUEST['token'])) {
+			$user = current(User::load((int) $_REQUEST['u']));
+
+			if (($user instanceof User) && $_REQUEST['token'] === $this->createToken($user)) {
+				User::setMe($user->id);
+			}
+		}
+	}
 }
 
 ?>
\ No newline at end of file
diff --git a/Sources/Calendar/Event.php b/Sources/Calendar/Event.php
index a4d57eb26c..6665fc04bb 100644
--- a/Sources/Calendar/Event.php
+++ b/Sources/Calendar/Event.php
@@ -616,35 +616,7 @@ public function save(): void
 	{
 		$is_edit = ($this->id ?? 0) > 0;
 
-		if (!empty($this->recurrence_iterator->getRRule()->until)) {
-			// When we have an until value, life is easy.
-			$recurrence_end = Time::createFromInterface($this->recurrence_iterator->getRRule()->until)->modify('-1 second');
-		} elseif (!empty($this->recurrence_iterator->getRRule()->count)) {
-			// Save current values.
-			$view_start = clone $this->view_start;
-			$view_end = clone $this->view_end;
-			$recurrence_iterator = clone $this->recurrence_iterator;
-
-			// Make new recurrence iterator that gets all occurrences.
-			$this->rrule = (string) $recurrence_iterator->getRRule();
-			$this->view_start = clone $this->start;
-			$this->view_end = new Time('9999-12-31');
-
-			unset($this->recurrence_iterator);
-			$this->createRecurrenceIterator();
-
-			// Get last occurrence.
-			$this->recurrence_iterator->end();
-			$recurrence_end = Time::createFromInterface($this->recurrence_iterator->current());
-
-			// Put everything back.
-			$this->view_start = $view_start;
-			$this->view_end = $view_end;
-			$this->recurrence_iterator = $recurrence_iterator;
-		} else {
-			// Forever.
-			$recurrence_end = new Time('9999-12-31');
-		}
+		$recurrence_end = $this->getRecurrenceEnd();
 
 		$rrule = !empty($this->special_rrule) ? implode('', $this->special_rrule) : (string) $this->recurrence_iterator->getRRule();
 
@@ -1061,6 +1033,58 @@ public function changeUntil(\DateTimeInterface $until): void
 
 		$this->createRecurrenceIterator();
 	}
+	/**
+	 * Gets the date after which no more occurrences happen.
+	 *
+	 * @return Time When the recurrence ends.
+	 */
+	public function getRecurrenceEnd(): Time
+	{
+		// If there's no recurrence, there's nothing to do.
+		if (!isset($this->recurrence_iterator)) {
+			return $this->start;
+		}
+
+		// When we have an until value, life is easy.
+		if (!empty($this->recurrence_iterator->getRRule()->until)) {
+			return Time::createFromInterface($this->recurrence_iterator->getRRule()->until)->modify('-1 second');
+		}
+
+		// A count value takes more work.
+		if (!empty($this->recurrence_iterator->getRRule()->count)) {
+			// If the count is 1, then the start is the end.
+			if ($this->recurrence_iterator->getRRule()->count == 1) {
+				return $this->start;
+			}
+
+			// Save current values.
+			$view_start = clone $this->view_start;
+			$view_end = clone $this->view_end;
+			$recurrence_iterator = clone $this->recurrence_iterator;
+
+			// Make new recurrence iterator that gets all occurrences.
+			$this->rrule = (string) $recurrence_iterator->getRRule();
+			$this->view_start = clone $this->start;
+			$this->view_end = new Time('9999-12-31');
+
+			unset($this->recurrence_iterator);
+			$this->createRecurrenceIterator();
+
+			// Get last occurrence.
+			$this->recurrence_iterator->end();
+			$value = Time::createFromInterface($this->recurrence_iterator->current());
+
+			// Put everything back.
+			$this->view_start = $view_start;
+			$this->view_end = $view_end;
+			$this->recurrence_iterator = $recurrence_iterator;
+
+			return $value;
+		}
+
+		// Forever.
+		return new Time('9999-12-31');
+	}
 
 	/**
 	 * Sets custom properties.
diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index 0f5926a122..bcfe1918fe 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -1789,6 +1789,12 @@ tr.windowbg td, tr.bg td, .table_grid tr td {
 	background: url(../images/icons/bell.png);
 	background-size: 16px;
 }
+.main_icons.feed::before {
+	background: url(../images/icons/feed.svg);
+	background-size: 16px;}
+a.main_icons.feed::before {
+	margin: -0.2em -0.4em 0;
+}
 /* Load better icons for higher resolution screens */
 @media
 	screen and (-webkit-min-device-pixel-ratio: 1.66),
diff --git a/Themes/default/images/icons/feed.svg b/Themes/default/images/icons/feed.svg
new file mode 100644
index 0000000000..c19b379974
--- /dev/null
+++ b/Themes/default/images/icons/feed.svg
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<svg width="800px" height="800px" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg">
+  <path fill="#000000" d="M 87 87 L 87 257 C 177 257 263.666 274.333 347 309 C 430.333 343.666 503.833 392.833 567.5 456.5 C 631.166 520.166 680.333 593.666 715 677 C 749.666 760.333 767 847 767 937 L 937 937 C 937 824.333 915.5 716 872.5 612 C 829.5 508 768 416.166 688 336.5 C 608 256.833 516 195.333 412 152 C 308 108.666 199.666 87 87 87 Z M 87 374 L 87 539 C 139.666 539 190.5 549.166 239.5 569.5 C 288.5 589.833 331.666 618.666 369 656 C 406.333 693.333 435 736.333 455 785 C 475 833.666 485 884.333 485 937 L 650 937 C 650 862.333 635.833 790.5 607.5 721.5 C 579.166 652.5 538.5 591.666 485.5 539 C 432.5 486.333 371.5 445.666 302.5 417 C 233.5 388.333 161.666 374 87 374 Z M 204 704 C 182.666 704 163 709.333 145 720 C 127 730.666 112.833 744.833 102.5 762.5 C 92.166 780.166 87 799.666 87 821 C 87 842.333 92.166 861.833 102.5 879.5 C 112.833 897.166 127 911.166 145 921.5 C 163 931.833 182.5 937 203.5 937 C 224.5 937 244 931.833 262 921.5 C 280 911.166 294.166 897.166 304.5 879.5 C 314.833 861.833 320 842.333 320 821 C 320 799.666 314.833 780.166 304.5 762.5 C 294.166 744.833 280 730.666 262 720 C 244 709.333 224.666 704 204 704 Z"/>
+</svg>
\ No newline at end of file

From 40c90d66dce222d35c6b670b270321bbad3104cf Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Mon, 29 Apr 2024 16:06:07 -0600
Subject: [PATCH 21/22] Fixes CSS for dropmenu buttons created in
 template_button_strip()

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Themes/default/css/index.css | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/Themes/default/css/index.css b/Themes/default/css/index.css
index bcfe1918fe..da345483bb 100644
--- a/Themes/default/css/index.css
+++ b/Themes/default/css/index.css
@@ -4005,7 +4005,7 @@ h3.profile_hd::before,
 #top_section, .quickbuttons > li,
 .quickbuttons li ul, .quickbuttons li ul li a:hover, .quickbuttons ul li a:focus,
 .inline_mod_check, .popup_window, #inner_section, .post_options ul,
-.post_options ul a:hover, .post_options ul a:focus, .notify_dropdown a:hover, .notify_dropdown a:focus {
+.post_options ul a:hover, .post_options ul a:focus, .dropmenu .viewport .overview a:hover, .dropmenu .viewport .overview a:focus {
 	background: #fff; /* fallback for some browsers */
 	background-image: linear-gradient(#e2e9f3 0%, #fff 70%);
 }
@@ -4021,20 +4021,21 @@ h3.profile_hd::before,
 }
 
 /* Topic/Board follow-alert menu */
-.notify_dropdown strong {
+.dropmenu .viewport .overview strong {
 	font-size: 1.1em;
 }
-.notify_dropdown a {
+.dropmenu .viewport .overview a {
 	display: block;
 	padding: 0.5em;
 	text-decoration: none;
 	border: 1px solid transparent;
 	border-radius: 3px;
 }
-.notify_dropdown a:hover, .notify_dropdown a:focus {
+.dropmenu .viewport .overview a:hover,
+.dropmenu .viewport .overview a:focus {
 	border-color: #ddd;
 }
-.notify_dropdown span {
+.dropmenu .viewport .overview span {
 	font-size: 0.9em;
 }
 

From fc92e92b86bdac83e38db58f3c8515dfd3cab1ae Mon Sep 17 00:00:00 2001
From: Jon Stovell <jonstovell@gmail.com>
Date: Mon, 29 Apr 2024 18:46:37 -0600
Subject: [PATCH 22/22] Fixes a bug in SMF\Tasks\FetchCalendarSubscriptions

Signed-off-by: Jon Stovell <jonstovell@gmail.com>
---
 Sources/Tasks/FetchCalendarSubscriptions.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Sources/Tasks/FetchCalendarSubscriptions.php b/Sources/Tasks/FetchCalendarSubscriptions.php
index f046dffb9f..4dc080be37 100644
--- a/Sources/Tasks/FetchCalendarSubscriptions.php
+++ b/Sources/Tasks/FetchCalendarSubscriptions.php
@@ -44,11 +44,11 @@ public function execute(): bool
 
 			if (!empty($ics_data)) {
 				switch ($type) {
-					case 'holiday':
+					case Event::TYPE_HOLIDAY:
 						Holiday::import($ics_data);
 						break;
 
-					case 'event':
+					case Event::TYPE_EVENT:
 						Event::import($ics_data);
 						break;
 				}