refactor(push-notification): update breaking news subscription query

- Replace interest-based query with user preferences-based query
- Improve efficiency by directly targeting embedded interests array
- Simplify user ID collection process
- Update logging to reflect new query approach

Author: fulleni

lib/src/services/push_notification_service.dart

@@ -32,21 +32,23 @@ class DefaultPushNotificationService implements IPushNotificationService {
   DefaultPushNotificationService({
     required DataRepository<PushNotificationDevice>
     pushNotificationDeviceRepository,
-    required DataRepository<Interest> interestRepository,
+    required DataRepository<UserContentPreferences>
+    userContentPreferencesRepository,
     required DataRepository<RemoteConfig> remoteConfigRepository,
     required IPushNotificationClient? firebaseClient,
     required IPushNotificationClient? oneSignalClient,
     required Logger log,
   }) : _pushNotificationDeviceRepository = pushNotificationDeviceRepository,
-       _interestRepository = interestRepository,
+       _userContentPreferencesRepository = userContentPreferencesRepository,
        _remoteConfigRepository = remoteConfigRepository,
        _firebaseClient = firebaseClient,
        _oneSignalClient = oneSignalClient,
        _log = log;
 
   final DataRepository<PushNotificationDevice>
   _pushNotificationDeviceRepository;
-  final DataRepository<Interest> _interestRepository;
+  final DataRepository<UserContentPreferences>
+  _userContentPreferencesRepository;
   final DataRepository<RemoteConfig> _remoteConfigRepository;
   final IPushNotificationClient? _firebaseClient;
   final IPushNotificationClient? _oneSignalClient;
@@ -115,33 +117,34 @@ class DefaultPushNotificationService implements IPushNotificationService {
         return;
       }
 
-      // 2. Find all interests subscribed to breaking news.
-      // The query now correctly finds interests where the 'deliveryTypes'
-      // set *contains* the 'breakingOnly' value.
-      final breakingNewsInterests = await _interestRepository.readAll(
-        filter: {
-          'deliveryTypes': {
-            r'$in': [
-              PushNotificationSubscriptionDeliveryType.breakingOnly.name,
-            ],
-          },
-        },
-      );
+      // 2. Find all user preferences that contain an interest subscribed to
+      //    breaking news. This query targets the embedded 'interests' array.
+      final subscribedUserPreferences = await _userContentPreferencesRepository
+          .readAll(
+            filter: {
+              'interests.deliveryTypes': {
+                r'$in': [
+                  PushNotificationSubscriptionDeliveryType.breakingOnly.name,
+                ],
+              },
+            },
+          );
 
-      if (breakingNewsInterests.items.isEmpty) {
+      if (subscribedUserPreferences.items.isEmpty) {
         _log.info('No users subscribed to breaking news. Aborting.');
         return;
       }
 
-      // 3. Collect all unique user IDs from the subscriptions.
+      // 3. Collect all unique user IDs from the preference documents.
       // Using a Set automatically handles deduplication.
-      final userIds = breakingNewsInterests.items
-          .map((interest) => interest.userId)
+      // The ID of the UserContentPreferences document is the user's ID.
+      final userIds = subscribedUserPreferences.items
+          .map((preference) => preference.id)
           .toSet();
 
       _log.info(
-        'Found ${breakingNewsInterests.items.length} interests subscribed to '
-        'breaking news, corresponding to ${userIds.length} unique users.',
+        'Found ${subscribedUserPreferences.items.length} users with '
+        'subscriptions to breaking news.',
       );
 
       // 4. Fetch all devices for all subscribed users in a single bulk query.