NSDate+Helper.m

//
// NSDate+Helper.h
//
// Created by Billy Gray on 2/26/09.
// Copyright (c) 2009–2012, ZETETIC LLC
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//     * Neither the name of the ZETETIC LLC nor the
//       names of its contributors may be used to endorse or promote products
//       derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY ZETETIC LLC ''AS IS'' AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL ZETETIC LLC BE LIABLE FOR ANY
// DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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//

#import "NSDate+Helper.h"

static NSString *kNSDateHelperFormatFullDateWithTime    = @"MMM d, yyyy h:mm a";
static NSString *kNSDateHelperFormatFullDate            = @"MMM d, yyyy";
static NSString *kNSDateHelperFormatShortDateWithTime   = @"MMM d h:mm a";
static NSString *kNSDateHelperFormatShortDate           = @"MMM d";
static NSString *kNSDateHelperFormatWeekday             = @"EEEE";
static NSString *kNSDateHelperFormatWeekdayWithTime     = @"EEEE h:mm a";
static NSString *kNSDateHelperFormatTime                = @"h:mm a";
static NSString *kNSDateHelperFormatTimeWithPrefix      = @"'at' h:mm a";
static NSString *kNSDateHelperFormatSQLDate             = @"yyyy-MM-dd";
static NSString *kNSDateHelperFormatSQLTime             = @"HH:mm:ss";
static NSString *kNSDateHelperFormatSQLDateWithTime     = @"yyyy-MM-dd HH:mm:ss";

@implementation NSDate (Helper)

static NSCalendar *_calendar = nil;
static NSDateFormatter *_displayFormatter = nil;

+ (void)initializeStatics {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (_calendar == nil) {
            _calendar = [[NSCalendar currentCalendar] retain];
        }
        if (_displayFormatter == nil) {
            _displayFormatter = [[NSDateFormatter alloc] init];
        }
    });
}

/*
 * This guy can be a little unreliable and produce unexpected results,
 * you're better off using daysAgoAgainstMidnight
 */
- (NSUInteger)daysAgo {
    [[self class] initializeStatics];
    NSDateComponents *components = [_calendar components:(NSDayCalendarUnit)
                                                fromDate:self
                                                  toDate:[NSDate date]
                                                 options:0];
	return [components day];
}

- (NSUInteger)daysAgoAgainstMidnight {
    [[self class] initializeStatics];
	// get a midnight version of ourself:
	NSDateFormatter *mdf = _displayFormatter;
	[mdf setDateFormat:@"yyyy-MM-dd"];
	NSDate *midnight = [mdf dateFromString:[mdf stringFromDate:self]];
	return (int)[midnight timeIntervalSinceNow] / (60*60*24) *-1;
}

- (NSString *)stringDaysAgo {
    [[self class] initializeStatics];
	return [self stringDaysAgoAgainstMidnight:YES];
}

- (NSString *)stringDaysAgoAgainstMidnight:(BOOL)flag {
	NSUInteger daysAgo = (flag) ? [self daysAgoAgainstMidnight] : [self daysAgo];
	NSString *text = nil;
	switch (daysAgo) {
		case 0:
			text = @"Today";
			break;
		case 1:
			text = @"Yesterday";
			break;
		default:
			text = [NSString stringWithFormat:@"%d days ago", (int)daysAgo];
	}
	return text;
}

- (NSUInteger)weekday {
    [[self class] initializeStatics];
    NSDateComponents *weekdayComponents = [_calendar components:(NSWeekdayCalendarUnit) fromDate:self];
	return [weekdayComponents weekday];
}

+ (NSDate *)dateFromString:(NSString *)string {
    [self initializeStatics];
	return [NSDate dateFromString:string withFormat:[NSDate dbFormatString]];
}

+ (NSDate *)dateFromString:(NSString *)string withFormat:(NSString *)format {
    [self initializeStatics];
	[_displayFormatter setDateFormat:format];
	NSDate *date = [_displayFormatter dateFromString:string];
	return date;
}

+ (NSString *)stringFromDate:(NSDate *)date withFormat:(NSString *)format {
    [self initializeStatics];
	return [date stringWithFormat:format];
}

+ (NSString *)stringFromDate:(NSDate *)date {
    [self initializeStatics];
	return [date string];
}

+ (NSString *)stringForDisplayFromDate:(NSDate *)date prefixed:(BOOL)prefixed alwaysDisplayTime:(BOOL)displayTime {
    [self initializeStatics];
    /*
	 * if the date is in today, display 12-hour time with meridian,
	 * if it is within the last 7 days, display weekday name (Friday)
	 * if within the calendar year, display as Jan 23
	 * else display as Nov 11, 2008
	 */
	NSDate *today = [NSDate date];
    NSDateComponents *offsetComponents = [_calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
                                                      fromDate:today];
	
	NSDate *midnight = [_calendar dateFromComponents:offsetComponents];
	NSString *displayString = nil;
	
	// comparing against midnight
    NSComparisonResult midnight_result = [date compare:midnight];
	if (midnight_result == NSOrderedDescending) {
		if (prefixed) {
			[_displayFormatter setDateFormat:kNSDateHelperFormatTimeWithPrefix]; // at 11:30 am
		} else {
			[_displayFormatter setDateFormat:kNSDateHelperFormatTime]; // 11:30 am
		}
	} else {
		// check if date is within last 7 days
		NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init];
		[componentsToSubtract setDay:-7];
		NSDate *lastweek = [_calendar dateByAddingComponents:componentsToSubtract toDate:today options:0];
		[componentsToSubtract release];
        NSComparisonResult lastweek_result = [date compare:lastweek];
		if (lastweek_result == NSOrderedDescending) {
            if (displayTime) {
                [_displayFormatter setDateFormat:kNSDateHelperFormatWeekdayWithTime];
            } else {
                [_displayFormatter setDateFormat:kNSDateHelperFormatWeekday]; // Tuesday
            }
		} else {
			// check if same calendar year
			NSInteger thisYear = [offsetComponents year];
			
			NSDateComponents *dateComponents = [_calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
                                                            fromDate:date];
			NSInteger thatYear = [dateComponents year];
			if (thatYear >= thisYear) {
                if (displayTime) {
                    [_displayFormatter setDateFormat:kNSDateHelperFormatShortDateWithTime];
                }
                else {
                    [_displayFormatter setDateFormat:kNSDateHelperFormatShortDate];
                }
			} else {
                if (displayTime) {
                    [_displayFormatter setDateFormat:kNSDateHelperFormatFullDateWithTime];
                }
                else {
                    [_displayFormatter setDateFormat:kNSDateHelperFormatFullDate];
                }
			}
		}
		if (prefixed) {
			NSString *dateFormat = [_displayFormatter dateFormat];
			NSString *prefix = @"'on' ";
			[_displayFormatter setDateFormat:[prefix stringByAppendingString:dateFormat]];
		}
	}
	
	// use display formatter to return formatted date string
	displayString = [_displayFormatter stringFromDate:date];
	return displayString;
}

+ (NSString *)stringForDisplayFromDate:(NSDate *)date prefixed:(BOOL)prefixed {
	return [[self class] stringForDisplayFromDate:date prefixed:prefixed alwaysDisplayTime:NO];
}

+ (NSString *)stringForDisplayFromDate:(NSDate *)date {
	return [self stringForDisplayFromDate:date prefixed:NO];
}

- (NSString *)stringWithFormat:(NSString *)format {
	[_displayFormatter setDateFormat:format];
	NSString *timestamp_str = [_displayFormatter stringFromDate:self];
	return timestamp_str;
}

- (NSString *)string {
	return [self stringWithFormat:[NSDate dbFormatString]];
}

- (NSString *)stringWithDateStyle:(NSDateFormatterStyle)dateStyle timeStyle:(NSDateFormatterStyle)timeStyle {
	[_displayFormatter setDateStyle:dateStyle];
	[_displayFormatter setTimeStyle:timeStyle];
	NSString *outputString = [_displayFormatter stringFromDate:self];
	return outputString;
}

- (NSDate *)beginningOfWeek {
	// largely borrowed from "Date and Time Programming Guide for Cocoa"
	// we'll use the default calendar and hope for the best
	NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDate *beginningOfWeek = nil;
	BOOL ok = [calendar rangeOfUnit:NSWeekCalendarUnit startDate:&beginningOfWeek
						   interval:NULL forDate:self];
	if (ok) {
		return beginningOfWeek;
	}
	
	// couldn't calc via range, so try to grab Sunday, assuming gregorian style
	// Get the weekday component of the current date
	NSDateComponents *weekdayComponents = [calendar components:NSWeekdayCalendarUnit fromDate:self];
	
	/*
	 Create a date components to represent the number of days to subtract from the current date.
	 The weekday value for Sunday in the Gregorian calendar is 1, so subtract 1 from the number of days to subtract from the date in question.  (If today's Sunday, subtract 0 days.)
	 */
	NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init];
	[componentsToSubtract setDay: 0 - ([weekdayComponents weekday] - 1)];
	beginningOfWeek = nil;
	beginningOfWeek = [calendar dateByAddingComponents:componentsToSubtract toDate:self options:0];
	[componentsToSubtract release];
	
	//normalize to midnight, extract the year, month, and day components and create a new date from those components.
	NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
											   fromDate:beginningOfWeek];
	return [calendar dateFromComponents:components];
}

- (NSDate *)beginningOfDay {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // Get the weekday component of the current date
	NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
											   fromDate:self];
	return [calendar dateFromComponents:components];
}

- (NSDate *)endOfWeek {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // Get the weekday component of the current date
	NSDateComponents *weekdayComponents = [calendar components:NSWeekdayCalendarUnit fromDate:self];
	NSDateComponents *componentsToAdd = [[NSDateComponents alloc] init];
	// to get the end of week for a particular date, add (7 - weekday) days
	[componentsToAdd setDay:(7 - [weekdayComponents weekday])];
	NSDate *endOfWeek = [calendar dateByAddingComponents:componentsToAdd toDate:self options:0];
	[componentsToAdd release];
	
	return endOfWeek;
}

+ (NSString *)dateFormatString {
	return kNSDateHelperFormatSQLDate;
}

+ (NSString *)timeFormatString {
	return kNSDateHelperFormatSQLTime;
}

+ (NSString *)timestampFormatString {
	return kNSDateHelperFormatSQLDateWithTime;
}

// preserving for compatibility
+ (NSString *)dbFormatString {
	return [NSDate timestampFormatString];
}

@end