refactor(database): improve admin user seeding and override process

- Rename `_seedInitialAdminUser` to `_seedOverrideAdminUser`
- Update logic to handle admin user override based on OVERRIDE_ADMIN_EMAIL
- Add functionality to delete existing admin user and their data if overridden
- Separate user sub-document creation into a reusable method
- Update method names and variables to reflect new functionality

Author: fulleni

lib/src/services/database_seeding_service.dart

@@ -26,7 +26,7 @@ class DatabaseSeedingService {
     _log.info('Starting database seeding process...');
 
     await _ensureIndexes();
-    await _seedInitialAdminUser();
+    await _seedOverrideAdminUser();
 
     await _seedCollection<Country>(
       collectionName: 'countries',
@@ -75,31 +75,54 @@ class DatabaseSeedingService {
     _log.info('Database seeding process completed.');
   }
 
-  /// Seeds the initial administrator user from the environment variable.
-  Future<void> _seedInitialAdminUser() async {
-    _log.info('Checking for initial admin user...');
-    final adminEmail = EnvironmentConfig.initialAdminEmail;
+  /// Ensures the single administrator account is correctly configured based on
+  /// the `OVERRIDE_ADMIN_EMAIL` environment variable.
+  Future<void> _seedOverrideAdminUser() async {
+    _log.info('Checking for admin user override...');
+    final overrideEmail = EnvironmentConfig.overrideAdminEmail;
 
-    if (adminEmail == null || adminEmail.isEmpty) {
-      _log.info('INITIAL_ADMIN_EMAIL not set. Skipping admin user seeding.');
+    if (overrideEmail == null || overrideEmail.isEmpty) {
+      _log.info(
+        'OVERRIDE_ADMIN_EMAIL not set. Skipping admin user override.',
+      );
       return;
     }
 
     final usersCollection = _db.collection('users');
-    final existingAdmin = await usersCollection.findOne({'email': adminEmail});
+    final existingAdmin = await usersCollection.findOne(
+      where.eq('dashboardRole', DashboardUserRole.admin.name),
+    );
 
+    // Case 1: An admin exists.
     if (existingAdmin != null) {
-      _log.info('Admin user with email $adminEmail already exists.');
-      return;
+      final existingAdminEmail = existingAdmin['email'] as String;
+      // If the existing admin's email is the same as the override, do nothing.
+      if (existingAdminEmail == overrideEmail) {
+        _log.info(
+          'Admin user with email $overrideEmail already exists and matches '
+          'override. No action needed.',
+        );
+        return;
+      }
+
+      // If emails differ, delete the old admin and their data.
+      _log.warning(
+        'Found existing admin with email "$existingAdminEmail". It will be '
+        'replaced by the override email "$overrideEmail".',
+      );
+      final oldAdminId = existingAdmin['_id'] as ObjectId;
+      await _deleteUserAndData(oldAdminId);
     }
 
-    _log.info('Creating initial admin user for email: $adminEmail');
-    final adminId = ObjectId();
-    final adminUser = User(
-      id: adminId.oid,
-      email: adminEmail,
-      appRole: AppUserRole.standardUser, // Admins are standard app users
-      dashboardRole: DashboardUserRole.admin, // With admin dashboard role
+    // Case 2: No admin exists, or the old one was just deleted.
+    // Create the new admin.
+    _log.info('Creating admin user for email: $overrideEmail');
+    final newAdminId = ObjectId();
+    final newAdminUser = User(
+      id: newAdminId.oid,
+      email: overrideEmail,
+      appRole: AppUserRole.standardUser,
+      dashboardRole: DashboardUserRole.admin,
       createdAt: DateTime.now(),
       feedActionStatus: Map.fromEntries(
         FeedActionType.values.map(
@@ -110,12 +133,31 @@ class DatabaseSeedingService {
     );
 
     await usersCollection.insertOne(
-      {'_id': adminId, ...adminUser.toJson()..remove('id')},
+      {'_id': newAdminId, ...newAdminUser.toJson()..remove('id')},
     );
 
-    // Also create their default settings and preferences documents
+    // Create default settings and preferences for the new admin.
+    await _createUserSubDocuments(newAdminId);
+
+    _log.info('Successfully created admin user for $overrideEmail.');
+  }
+
+  /// Deletes a user and their associated sub-documents.
+  Future<void> _deleteUserAndData(ObjectId userId) async {
+    await _db.collection('users').deleteOne(where.eq('_id', userId));
+    await _db
+        .collection('user_app_settings')
+        .deleteOne(where.eq('_id', userId));
+    await _db
+        .collection('user_content_preferences')
+        .deleteOne(where.eq('_id', userId));
+    _log.info('Deleted user and associated data for ID: ${userId.oid}');
+  }
+
+  /// Creates the default sub-documents (settings, preferences) for a new user.
+  Future<void> _createUserSubDocuments(ObjectId userId) async {
     final defaultAppSettings = UserAppSettings(
-      id: adminId.oid,
+      id: userId.oid,
       displaySettings: const DisplaySettings(
         baseTheme: AppBaseTheme.system,
         accentTheme: AppAccentTheme.defaultBlue,
@@ -131,24 +173,20 @@ class DatabaseSeedingService {
         showPublishDateInHeadlineFeed: true,
       ),
     );
-
     await _db.collection('user_app_settings').insertOne(
-      {'_id': adminId, ...defaultAppSettings.toJson()..remove('id')},
+      {'_id': userId, ...defaultAppSettings.toJson()..remove('id')},
     );
 
     final defaultUserPreferences = UserContentPreferences(
-      id: adminId.oid,
+      id: userId.oid,
       followedCountries: const [],
       followedSources: const [],
       followedTopics: const [],
       savedHeadlines: const [],
     );
-
     await _db.collection('user_content_preferences').insertOne(
-      {'_id': adminId, ...defaultUserPreferences.toJson()..remove('id')},
+      {'_id': userId, ...defaultUserPreferences.toJson()..remove('id')},
     );
-
-    _log.info('Successfully created initial admin user for $adminEmail.');
   }
 
   /// Seeds a specific collection from a given list of fixture data.