chore(): final fixes before deadline

- added images of notification feature working
- added seed data script
- race condition fix for notifications worker
- small improvements

src/backend/apps/notifications/services.py

@@ -5,7 +5,7 @@ from typing import Any
 import requests
 from django.core.exceptions import ValidationError
 from django.core.mail import EmailMessage, get_connection
-from django.db import transaction
+from django.db import connection, transaction
 from django.db.models import Q, QuerySet
 from django.utils import timezone
 
@@ -334,15 +334,64 @@ def _send_smtp(config: dict[str, Any], payload: dict[str, Any]) -> None:
     email.send(fail_silently=False)
 
 
-def flush_pending_notifications() -> dict[str, int]:
+def _pending_notifications_for_flush() -> QuerySet[NotificationLog]:
     pending = (
         NotificationLog.objects.filter(
             status=NotificationStatus.PENDING,
         )
-        .select_related("channel")
         .order_by("created_at")
     )
+    if not connection.features.has_select_for_update:
+        return pending
+    if connection.features.has_select_for_update_skip_locked:
+        return pending.select_for_update(skip_locked=True)
+    return pending.select_for_update()
 
+
+def _flush_notification_log(
+    *,
+    log: NotificationLog,
+    senders: dict[str, Any],
+    results: dict[str, int],
+) -> None:
+    channel = log.channel
+    if not channel or not channel.is_active:
+        log.status = NotificationStatus.FAILED
+        log.error = "Channel is inactive or missing."
+        log.save(update_fields=["status", "error"])
+        results["failed"] += 1
+        return
+
+    sender = senders.get(channel.channel_type)
+    if not sender:
+        log.status = NotificationStatus.FAILED
+        log.error = f"No sender for channel type '{channel.channel_type}'."
+        log.save(update_fields=["status", "error"])
+        results["failed"] += 1
+        return
+
+    try:
+        sender(channel.config, log.payload)
+        log.status = NotificationStatus.SENT
+        log.sent_at = timezone.now()
+        log.save(update_fields=["status", "sent_at"])
+        results["sent"] += 1
+    except Exception as exc:
+        logger.exception(
+            "notification_send_failed",
+            extra={
+                "log_id": str(log.pk),
+                "channel": channel.name,
+                "error": str(exc),
+            },
+        )
+        log.status = NotificationStatus.FAILED
+        log.error = str(exc)[:1000]
+        log.save(update_fields=["status", "error"])
+        results["failed"] += 1
+
+
+def flush_pending_notifications() -> dict[str, int]:
     senders = {
         ChannelType.TELEGRAM: _send_telegram,
         ChannelType.SMTP: _send_smtp,
@@ -350,42 +399,15 @@ def flush_pending_notifications() -> dict[str, int]:
 
     results = {"sent": 0, "failed": 0}
 
-    for log in pending:
-        if not log.channel or not log.channel.is_active:
-            log.status = NotificationStatus.FAILED
-            log.error = "Channel is inactive or missing."
-            log.save(update_fields=["status", "error"])
-            results["failed"] += 1
-            continue
-
-        sender = senders.get(log.channel.channel_type)
-        if not sender:
-            log.status = NotificationStatus.FAILED
-            log.error = (
-                f"No sender for channel type '{log.channel.channel_type}'."
+    while True:
+        with transaction.atomic():
+            log = _pending_notifications_for_flush().first()
+            if log is None:
+                break
+            _flush_notification_log(
+                log=log,
+                senders=senders,
+                results=results,
             )
-            log.save(update_fields=["status", "error"])
-            results["failed"] += 1
-            continue
-
-        try:
-            sender(log.channel.config, log.payload)
-            log.status = NotificationStatus.SENT
-            log.sent_at = timezone.now()
-            log.save(update_fields=["status", "sent_at"])
-            results["sent"] += 1
-        except Exception as exc:
-            logger.exception(
-                "notification_send_failed",
-                extra={
-                    "log_id": str(log.pk),
-                    "channel": log.channel.name,
-                    "error": str(exc),
-                },
-            )
-            log.status = NotificationStatus.FAILED
-            log.error = str(exc)[:1000]
-            log.save(update_fields=["status", "error"])
-            results["failed"] += 1
 
     return results