Implement notifications for admin users (#700)

* First stab at notification settings

* Add "global" setting for notification levels

* Trigger notification task

* Get users with permission for event

* Actually send notification emails

* More notifications

* Allow to turn off notifications

* Link in email to pause all notifications

* Add NotificationType to wordlist

* Add notification tests

* Add documentation

* Rebase fixes

src/pretix/base/services/notifications.py

@@ -0,0 +1,104 @@
+from django.conf import settings
+from django.template.loader import get_template
+
+from pretix.base.i18n import language
+from pretix.base.models import LogEntry, NotificationSetting, User
+from pretix.base.notifications import Notification, get_all_notification_types
+from pretix.base.services.async import ProfiledTask, TransactionAwareTask
+from pretix.base.services.mail import mail_send_task
+from pretix.celery_app import app
+from pretix.helpers.urls import build_absolute_uri
+
+
+@app.task(base=TransactionAwareTask)
+def notify(logentry_id: int):
+    logentry = LogEntry.all.get(id=logentry_id)
+    if not logentry.event:
+        return  # Ignore, we only have event-related notifications right now
+    types = get_all_notification_types(logentry.event)
+    notification_type = types.get(logentry.action_type)
+    if not notification_type:
+        return  # Ignore, e.g. plugin not active for this event
+
+    # All users that have the permission to get the notification
+    users = logentry.event.get_users_with_permission(
+        notification_type.required_permission
+    ).filter(notifications_send=True)
+    if logentry.user:
+        users = users.exclude(pk=logentry.user.pk)
+
+    # Get all notification settings, both specific to this event as well as global
+    notify_specific = {
+        (ns.user, ns.method): ns.enabled
+        for ns in NotificationSetting.objects.filter(
+            event=logentry.event,
+            action_type=logentry.action_type,
+            user__pk__in=users.values_list('pk', flat=True)
+        )
+    }
+    notify_global = {
+        (ns.user, ns.method): ns.enabled
+        for ns in NotificationSetting.objects.filter(
+            action_type=logentry.action_type,
+            user__pk__in=users.values_list('pk', flat=True)
+        )
+    }
+
+    for um, enabled in notify_specific.items():
+        user, method = um
+        if enabled:
+            send_notification.apply_async(args=(logentry_id, user.pk, method))
+
+    for um, enabled in notify_global.items():
+        user, method = um
+        if enabled and um not in notify_specific:
+            send_notification.apply_async(args=(logentry_id, user.pk, method))
+
+
+@app.task(base=ProfiledTask)
+def send_notification(logentry_id: int, user_id: int, method: str):
+    logentry = LogEntry.all.get(id=logentry_id)
+    user = User.objects.get(id=user_id)
+    types = get_all_notification_types(logentry.event)
+    notification_type = types.get(logentry.action_type)
+    if not notification_type:
+        return  # Ignore, e.g. plugin not active for this event
+
+    with language(user.locale):
+        notification = notification_type.build_notification(logentry)
+
+        if method == "mail":
+            send_notification_mail(notification, user)
+
+
+def send_notification_mail(notification: Notification, user: User):
+    ctx = {
+        'site': settings.PRETIX_INSTANCE_NAME,
+        'site_url': settings.SITE_URL,
+        'color': '#8E44B3',
+        'notification': notification,
+        'settings_url': build_absolute_uri(
+            'control:user.settings.notifications',
+        ),
+        'disable_url': build_absolute_uri(
+            'control:user.settings.notifications.off',
+            kwargs={
+                'token': user.notifications_token,
+                'id': user.pk
+            }
+        )
+    }
+
+    tpl_html = get_template('pretixbase/email/notification.html')
+    body_html = tpl_html.render(ctx)
+    tpl_plain = get_template('pretixbase/email/notification.txt')
+    body_plain = tpl_plain.render(ctx)
+
+    mail_send_task.apply_async(kwargs={
+        'to': [user.email],
+        'subject': '[{}] {}'.format(settings.PRETIX_INSTANCE_NAME, notification.title),
+        'body': body_plain,
+        'html': body_html,
+        'sender': settings.MAIL_FROM,
+        'headers': {},
+    })