[feature] Batch email notifications

README.rst

@@ -1013,6 +1013,19 @@ The default configuration is as follows:
         'max_allowed_backoff': 15,
     }
 
+``OPENWISP_NOTIFICATIONS_EMAIL_BATCH_INTERVAL``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
++---------+-----------------------------------+
+| type    | ``int``                           |
++---------+-----------------------------------+
+| default | ``1800`` `(30 mins, in seconds)`  |
++---------+-----------------------------------+
+
+This setting defines the interval at which the email notifications are sent in batches to users within the specified interval.
+
+If you want to send email notifications immediately, then set it to ``0``.
+
 Exceptions
 ----------
 

openwisp_notifications/base/models.py

@@ -139,7 +139,7 @@ def message(self):
     @cached_property
     def rendered_description(self):
         if not self.description:
-            return
+            return ''
         with notification_render_attributes(self):
             data = self.data or {}
             desc = self.description.format(notification=self, **data)

openwisp_notifications/handlers.py

@@ -10,7 +10,6 @@
 from django.db.models.signals import post_delete, post_save
 from django.dispatch import receiver
 from django.utils import timezone
-from django.utils.translation import gettext as _
 
 from openwisp_notifications import settings as app_settings
 from openwisp_notifications import tasks
@@ -20,12 +19,13 @@
     NOTIFICATION_ASSOCIATED_MODELS,
     get_notification_configuration,
 )
+from openwisp_notifications.utils import send_notification_email
 from openwisp_notifications.websockets import handlers as ws_handlers
-from openwisp_utils.admin_theme.email import send_email
 
 logger = logging.getLogger(__name__)
 
 EXTRA_DATA = app_settings.get_config()['USE_JSONFIELD']
+EMAIL_BATCH_INTERVAL = app_settings.OPENWISP_NOTIFICATIONS_EMAIL_BATCH_INTERVAL
 
 User = get_user_model()
 
@@ -192,35 +192,43 @@ def send_email_notification(sender, instance, created, **kwargs):
     if not (email_preference and instance.recipient.email and email_verified):
         return
 
-    try:
-        subject = instance.email_subject
-    except NotificationRenderException:
-        # Do not send email if notification is malformed.
-        return
-    url = instance.data.get('url', '') if instance.data else None
-    body_text = instance.email_message
-    if url:
-        target_url = url
-    elif instance.target:
-        target_url = instance.redirect_view_url
-    else:
-        target_url = None
-    if target_url:
-        body_text += _('\n\nFor more information see %(target_url)s.') % {
-            'target_url': target_url
-        }
-
-    send_email(
-        subject=subject,
-        body_text=body_text,
-        body_html=instance.email_message,
-        recipients=[instance.recipient.email],
-        extra_context={
-            'call_to_action_url': target_url,
-            'call_to_action_text': _('Find out more'),
+    recipient_id = instance.recipient.id
+    cache_key = f'email_batch_{recipient_id}'
+
+    cache_data = cache.get(
+        cache_key,
+        {
+            'last_email_sent_time': None,
+            'batch_scheduled': False,
+            'pks': [],
+            'email_id': instance.recipient.email,
         },
     )
 
+    if cache_data['last_email_sent_time'] and EMAIL_BATCH_INTERVAL > 0:
+        # Case 1: Batch email sending logic
+        if not cache_data['batch_scheduled']:
+            # Schedule batch email notification task if not already scheduled
+            tasks.batch_email_notification.apply_async(
+                (instance.recipient.id,), countdown=EMAIL_BATCH_INTERVAL
+            )
+            # Mark batch as scheduled to prevent duplicate scheduling
+            cache_data['batch_scheduled'] = True
+            cache_data['pks'] = [instance.id]
+            cache.set(cache_key, cache_data)
+        else:
+            # Add current instance ID to the list of IDs for batch
+            cache_data['pks'].append(instance.id)
+            cache.set(cache_key, cache_data)
+        return
+
+    # Case 2: Single email sending logic
+    # Update the last email sent time and cache the data
+    cache_data['last_email_sent_time'] = timezone.now()
+    cache.set(cache_key, cache_data, timeout=EMAIL_BATCH_INTERVAL)
+
+    send_notification_email(instance)
+
     # flag as emailed
     instance.emailed = True
     # bulk_update is used to prevent emitting post_save signal

openwisp_notifications/settings.py

@@ -37,6 +37,10 @@
     'openwisp-notifications/audio/notification_bell.mp3',
 )
 
+OPENWISP_NOTIFICATIONS_EMAIL_BATCH_INTERVAL = getattr(
+    settings, 'OPENWISP_NOTIFICATIONS_EMAIL_BATCH_INTERVAL', 30 * 60  # 30 minutes
+)
+
 # Remove the leading "/static/" here as it will
 # conflict with the "static()" call in context_processors.py.
 # This is done for backward compatibility.

openwisp_notifications/tasks.py

@@ -3,14 +3,22 @@
 from celery import shared_task
 from django.contrib.auth import get_user_model
 from django.contrib.contenttypes.models import ContentType
+from django.contrib.sites.models import Site
+from django.core.cache import cache
 from django.db.models import Q
 from django.db.utils import OperationalError
+from django.template.loader import render_to_string
 from django.utils import timezone
 
+from openwisp_notifications import settings as app_settings
 from openwisp_notifications import types
 from openwisp_notifications.swapper import load_model, swapper_load_model
+from openwisp_notifications.utils import send_notification_email
+from openwisp_utils.admin_theme.email import send_email
 from openwisp_utils.tasks import OpenwispCeleryTask
 
+EMAIL_BATCH_INTERVAL = app_settings.OPENWISP_NOTIFICATIONS_EMAIL_BATCH_INTERVAL
+
 User = get_user_model()
 
 Notification = load_model('Notification')
@@ -202,3 +210,67 @@ def delete_ignore_object_notification(instance_id):
     Deletes IgnoreObjectNotification object post it's expiration.
     """
     IgnoreObjectNotification.objects.filter(id=instance_id).delete()
+
+
+@shared_task(base=OpenwispCeleryTask)
+def batch_email_notification(instance_id):
+    """
+    Sends a summary of notifications to the specified email address.
+    """
+    if not instance_id:
+        return
+
+    cache_key = f'email_batch_{instance_id}'
+    cache_data = cache.get(cache_key, {'pks': []})
+
+    if not cache_data['pks']:
+        return
+
+    unsent_notifications = Notification.objects.filter(id__in=cache_data['pks'])
+    notifications_count = unsent_notifications.count()
+    current_site = Site.objects.get_current()
+    email_id = cache_data.get('email_id')
+
+    # Send individual email if there is only one notification
+    if notifications_count == 1:
+        notification = unsent_notifications.first()
+        send_notification_email(notification)
+    else:
+        # Show notification description upto 5 notifications
+        show_notification_description = notifications_count <= 5
+        for notification in unsent_notifications:
+            url = notification.data.get('url', '') if notification.data else None
+            if url:
+                notification.url = url
+            elif notification.target:
+                notification.url = notification.redirect_view_url
+            else:
+                notification.url = None
+
+        context = {
+            'notifications': unsent_notifications,
+            'notifications_count': notifications_count,
+            'show_notification_description': show_notification_description,
+            'site_name': current_site.name,
+        }
+        html_content = render_to_string('emails/batch_email.html', context)
+        plain_text_content = render_to_string('emails/batch_email.txt', context)
+
+        extra_context = {}
+        if notifications_count > 5:
+            extra_context = {
+                'call_to_action_url': f"https://{current_site.domain}/admin",
+                'call_to_action_text': 'View all Notifications',
+            }
+
+        send_email(
+            subject=f'Summary of {notifications_count} Notifications from {current_site.name}',
+            body_text=plain_text_content,
+            body_html=html_content,
+            recipients=[email_id],
+            extra_context=extra_context,
+        )
+
+    unsent_notifications.update(emailed=True)
+    Notification.objects.bulk_update(unsent_notifications, ['emailed'])
+    cache.delete(cache_key)

openwisp_notifications/templates/emails/batch_email.html

@@ -0,0 +1,107 @@
+{% block styles %}
+    <style type="text/css">
+        .alert {
+            border: 1px solid #e0e0e0;
+            border-radius: 5px;
+            margin-bottom: 10px;
+            padding: 10px;
+        }
+        .alert.error {
+            background-color: #ffefef;
+        }
+        .alert.info {
+            background-color: #f0f0f0;
+        }
+        .alert.success {
+            background-color: #e6f9e8;
+        }
+        .alert h2 {
+            margin: 0 0 5px 0;
+            font-size: 16px;
+        }
+        .alert h2 .title {
+            display: inline-block;
+            max-width: 80%;
+            white-space: nowrap;
+            overflow: hidden;
+            text-overflow: ellipsis;
+            vertical-align: middle;
+        }
+        .alert.error h2 {
+            color: #d9534f;
+        }
+        .alert.info h2 {
+            color: #333333;
+        }
+        .alert.success h2 {
+            color: #1c8828;
+        }
+        .alert p {
+            margin: 0;
+            font-size: 14px;
+            color: #666;
+        }
+        .alert .title p {
+            display: inline;
+            overflow: hidden;
+            text-overflow: ellipsis;
+        }
+        .badge {
+            display: inline-block;
+            padding: 2px 8px;
+            border-radius: 3px;
+            font-size: 12px;
+            font-weight: bold;
+            text-transform: uppercase;
+            margin-right: 5px;
+            color: white;
+        }
+        .badge.error {
+            background-color: #d9534f;
+        }
+        .badge.info {
+            background-color: #333333;
+        }
+        .badge.success {
+            background-color: #1c8828;
+        }
+        .alert a {
+            text-decoration: none;
+        }
+        .alert.error a {
+            color: #d9534f;
+        }
+        .alert.info a {
+            color: #333333;
+        }
+        .alert.success a {
+            color: #1c8828;
+        }
+        .alert a:hover {
+            text-decoration: underline;
+        }
+    </style>
+{% endblock styles %}
+
+{% block mail_body %}
+    <div>
+        {% for notification in notifications %}
+            <div class="alert {{ notification.level }}">
+                <h2>
+                    <span class="badge {{ notification.level }}">{{ notification.level|upper }}</span>
+                    <span class="title">
+                        {% if notification.url %}
+                            <a href="{{ notification.url }}" target="_blank">{{ notification.message }}</a>
+                        {% else %}
+                            {{ notification.message }}
+                        {% endif %}
+                    </span>
+                </h2>
+                <p>{{ notification.timestamp|date:"F j, Y, g:i a" }}</p>
+                {% if show_notification_description %}
+                    <p>{{ notification.rendered_description|safe }}</p>
+                {% endif %}
+            </div>
+        {% endfor %}
+    </div>
+{% endblock mail_body %}

openwisp_notifications/templates/emails/batch_email.txt

@@ -0,0 +1,15 @@
+Summary of {{ notifications_count }} Notifications from {{ site_name }}
+
+{% for notification in notifications %}
+- {{ notification.message }}
+  URL: {{ notification.url }}
+  Timestamp: {{ notification.timestamp|date:"F j, Y, g:i a" }}
+  {% if show_notification_description %}
+      Description: {{ notification.rendered_description }}
+  {% endif %}
+{% endfor %}
+
+{% if notifications_count > 5 %}
+View all Notifications: {{ call_to_action_url }}
+{% endif %}
+