feat: add notification field for vault letters and helper tasks

backend/letters/tasks.py

@@ -0,0 +1,38 @@
+import logging
+from datetime import UTC, datetime
+
+from django.core.mail import send_mail
+
+from config import settings
+from letters.models import Letter
+
+logger = logging.getLogger(__name__)
+
+
+def get_vault_letters_to_notify():
+    """
+    Identifies the vault letters that have been recently unlocked and not notified
+    """
+    letters = Letter.objects.filter(unlock_at__lt=datetime.now(UTC), notified_at=None)
+    return letters
+
+
+def notify_unlocked_letter(letter):
+    """
+    Notifies the author of the letter via email and if successful, updates the notified_at field for the letter.
+    """
+    author = letter.user.get_username()
+    try:
+        send_mail(subject="", message="", from_email=settings.FROM_EMAIL, recipient_list=[author], fail_silently=False)
+        letter.notified_at = datetime.now(UTC)
+        letter.save()
+    except Exception:
+        logger.exception(f"Failed to notify {author} of unlocked letter")
+
+
+def vault_unlock_notification_polling_scheduler():
+    logger.info("Starting vault_unlock_notification_polling_scheduler")
+    letters_to_notify = get_vault_letters_to_notify()
+    print("letters_to_notify", letters_to_notify)
+    for letter in letters_to_notify:
+        notify_unlocked_letter(letter)