Add Notification Type

Web push notifications are the default method for delivering notifications.

To implement a new notification type, the send_notification(subscription, message) method in notification.py is triggered on these events:

1. Alert initialization
2. Successful alert evaluation condition
3. Alert expiration

Simply add a new method handler in notifications/YOUR_NOTIFICATION_TYPE.py and call it from notification.py. You can see an example in notifications/web_push.py.