[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/handlers.py

@@ -26,6 +26,7 @@
 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()
 
@@ -164,6 +165,36 @@ def notify_handler(**kwargs):
     return notification_list
 
 
+def send_single_email(instance):
+    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
+    description = instance.message
+    if url:
+        target_url = url
+    elif instance.target:
+        target_url = instance.redirect_view_url
+    else:
+        target_url = None
+    if target_url:
+        description += _('\n\nFor more information see %(target_url)s.') % {
+            'target_url': target_url
+        }
+    send_email(
+        subject,
+        description,
+        instance.message,
+        recipients=[instance.recipient.email],
+        extra_context={
+            'call_to_action_url': target_url,
+            'call_to_action_text': _('Find out more'),
+        },
+    )
+
+
 @receiver(post_save, sender=Notification, dispatch_uid='send_email_notification')
 def send_email_notification(sender, instance, created, **kwargs):
     # Abort if a new notification is not created
@@ -192,34 +223,32 @@ 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.
+    recipient_id = instance.recipient.id
+    cache_key = f'email_batch_{recipient_id}'
+    cache_key_pks = f'{instance.recipient.email}_pks'
+    cache_data = cache.get(
+        cache_key, {'last_email_sent_time': None, 'batch_scheduled': False}
+    )
+
+    if cache_data['last_email_sent_time'] and EMAIL_BATCH_INTERVAL > 0:
+        if not cache_data['batch_scheduled']:
+            # Schedule batch email notification task
+            tasks.batch_email_notification.apply_async(
+                (instance.recipient.email,), countdown=EMAIL_BATCH_INTERVAL
+            )
+            cache_data['batch_scheduled'] = True
+            cache.set(cache_key_pks, [instance.id], timeout=EMAIL_BATCH_INTERVAL * 2)
+            cache.set(cache_key, cache_data, timeout=EMAIL_BATCH_INTERVAL)
+        else:
+            ids = cache.get(cache_key_pks, [])
+            ids.append(instance.id)
+            cache.set(cache_key_pks, ids, timeout=EMAIL_BATCH_INTERVAL * 2)
         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'),
-        },
-    )
+    cache_data['last_email_sent_time'] = timezone.now()
+    cache.set(cache_key, cache_data, timeout=EMAIL_BATCH_INTERVAL)
+
+    send_single_email(instance)
 
     # flag as emailed
     instance.emailed = True

openwisp_notifications/settings.py

@@ -37,6 +37,10 @@
     'openwisp-notifications/audio/notification_bell.mp3',
 )
 
+OPENWISP_NOTIFICATIONS_EMAIL_BATCH_INTERVAL = getattr(
+    settings, '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 +3,23 @@
 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 django.utils.html import strip_tags
 
+from openwisp_notifications import handlers
+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_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 +211,69 @@ 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(email_id):
+    """
+    Sends a summary of notifications to the specified email address.
+    """
+    ids = cache.get(f'{email_id}_pks', [])
+
+    if not ids:
+        return
+
+    unsent_notifications = Notification.objects.filter(id__in=ids)
+    notifications_count = unsent_notifications.count()
+    current_site = Site.objects.get_current()
+
+    if notifications_count == 1:
+        instance = unsent_notifications.first()
+        handlers.send_single_email(instance)
+    else:
+        alerts = []
+        for notification in unsent_notifications:
+            url = notification.data.get('url', '') if notification.data else None
+            if url:
+                target_url = url
+            elif notification.target:
+                target_url = notification.redirect_view_url
+            else:
+                target_url = None
+
+            description = notification.message if notifications_count <= 5 else None
+            alerts.append(
+                {
+                    'level': notification.level,
+                    'message': notification.message,
+                    'description': description,
+                    'timestamp': notification.timestamp,
+                    'url': target_url,
+                }
+            )
+
+        context = {
+            'alerts': alerts,
+            'notifications_count': notifications_count,
+            'site_name': current_site.name,
+            'site_domain': current_site.domain,
+        }
+        html_content = render_to_string('emails/batch_email.html', context)
+        plain_text_content = strip_tags(html_content)
+
+        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',
+            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'])

openwisp_notifications/templates/emails/batch_email.html

@@ -0,0 +1,133 @@
+{% block styles %}
+    <style type="text/css">
+        .container-alerts {
+            margin: 0 auto;
+            background-color: #fff;
+            padding: 20px;
+            border: 1px solid #ddd;
+            box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
+        }
+        .header {
+            text-align: center;
+            padding: 10px 0;
+            border-bottom: 1px solid #ddd;
+            margin-bottom: 20px;
+        }
+        .header h1 {
+            margin: 0;
+            font-size: 24px;
+        }
+        .header p {
+            margin: 5px 0 0 0;
+            font-size: 14px;
+            color: #666;
+        }
+        .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 class="container-alerts">
+        <div class="header">
+            <h1>Summary of {{ notifications_count }} Notifications</h1>
+            <p>From <a href="https://{{ site_domain }}" target="_blank">{{ site_name }}</a></p>
+        </div>
+        {% for alert in alerts %}
+        <div class="alert {{ alert.level }}">
+            <h2>
+                <span class="badge {{ alert.level }}">{{ alert.level|upper }}</span>
+                <span class="title">
+                    {% if alert.url %}
+                        <a href="{{ alert.url }}" target="_blank">{{ alert.message }}</a>
+                    {% else %}
+                        {{ alert.message }}
+                    {% endif %}
+                </span>
+            </h2>
+            <p>{{ alert.timestamp|date:"F j, Y, g:i a" }}</p>
+            {% if alert.description %}
+                <p>{{ alert.description }}</p>
+            {% endif %}
+        </div>
+        {% endfor %}
+    </div>
+{% endblock mail_body %}

openwisp_notifications/tests/test_notifications.py

@@ -944,6 +944,22 @@ def test_notification_for_unverified_email(self):
         # we don't send emails to unverified email addresses
         self.assertEqual(len(mail.outbox), 0)
 
+    @patch('openwisp_notifications.tasks.batch_email_notification.apply_async')
+    def test_batch_email_notification(self, mock_send_email):
+        notify.send(**self.notification_options)
+        notify.send(**self.notification_options)
+        notify.send(**self.notification_options)
+
+        # Check if only one mail is sent
+        self.assertEqual(len(mail.outbox), 1)
+
+        # Call the task
+        tasks.batch_email_notification(self.admin.email)
+
+        # Check if the rest of the notifications are sent in a batch
+        self.assertEqual(len(mail.outbox), 2)
+        self.assertEqual(mail.outbox[1].subject, "Summary of 2 Notifications")
+
     def test_that_the_notification_is_only_sent_once_to_the_user(self):
         first_org = self._create_org()
         first_org.organization_id = first_org.id