feat(headlines-feed): implement apply followed countries filter

- Add new event handler for applying followed countries filter
- Inject UserContentPreferencesRepository and AppBloc into CountriesFilterBloc
- Implement logic to fetch user's followed countries from preferences
- Handle unauthorized and empty followed countries scenarios
- Update state based on success or failure of the operation

Author: fulleni

lib/headlines-feed/bloc/countries_filter_bloc.dart

@@ -5,6 +5,7 @@ import 'package:bloc_concurrency/bloc_concurrency.dart';
 import 'package:core/core.dart';
 import 'package:data_repository/data_repository.dart';
 import 'package:equatable/equatable.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/app/bloc/app_bloc.dart'; // Import AppBloc
 
 part 'countries_filter_event.dart';
 part 'countries_filter_state.dart';
@@ -20,16 +21,28 @@ class CountriesFilterBloc
   /// {@macro countries_filter_bloc}
   ///
   /// Requires a [DataRepository<Country>] to interact with the data layer.
-  CountriesFilterBloc({required DataRepository<Country> countriesRepository})
-    : _countriesRepository = countriesRepository,
-      super(const CountriesFilterState()) {
+  CountriesFilterBloc({
+    required DataRepository<Country> countriesRepository,
+    required DataRepository<UserContentPreferences>
+        userContentPreferencesRepository, // Inject UserContentPreferencesRepository
+    required AppBloc appBloc, // Inject AppBloc
+  })  : _countriesRepository = countriesRepository,
+        _userContentPreferencesRepository = userContentPreferencesRepository,
+        _appBloc = appBloc,
+        super(const CountriesFilterState()) {
     on<CountriesFilterRequested>(
       _onCountriesFilterRequested,
       transformer: restartable(),
     );
+    on<CountriesFilterApplyFollowedRequested>(
+      _onCountriesFilterApplyFollowedRequested,
+      transformer: restartable(),
+    ); // Register new event handler
   }
 
   final DataRepository<Country> _countriesRepository;
+  final DataRepository<UserContentPreferences> _userContentPreferencesRepository;
+  final AppBloc _appBloc;
 
   /// Handles the request to fetch countries based on a specific usage.
   ///
@@ -74,4 +87,62 @@ class CountriesFilterBloc
       emit(state.copyWith(status: CountriesFilterStatus.failure, error: e));
     }
   }
+
+  /// Handles the request to apply the user's followed countries as filters.
+  Future<void> _onCountriesFilterApplyFollowedRequested(
+    CountriesFilterApplyFollowedRequested event,
+    Emitter<CountriesFilterState> emit,
+  ) async {
+    emit(state.copyWith(followedCountriesStatus: CountriesFilterStatus.loading));
+
+    final currentUser = _appBloc.state.user;
+
+    if (currentUser == null) {
+      emit(
+        state.copyWith(
+          followedCountriesStatus: CountriesFilterStatus.failure,
+          error: const UnauthorizedException(
+            'User must be logged in to apply followed countries.',
+          ),
+        ),
+      );
+      return;
+    }
+
+    try {
+      final preferences = await _userContentPreferencesRepository.read(
+        id: currentUser.id,
+        userId: currentUser.id,
+      );
+
+      if (preferences.followedCountries.isEmpty) {
+        emit(
+          state.copyWith(
+            followedCountriesStatus: CountriesFilterStatus.success,
+            followedCountries: const [],
+            error: const OperationFailedException('No followed countries found.'),
+            clearFollowedCountriesError: true,
+          ),
+        );
+        return;
+      }
+
+      emit(
+        state.copyWith(
+          followedCountriesStatus: CountriesFilterStatus.success,
+          followedCountries: preferences.followedCountries,
+          clearFollowedCountriesError: true,
+        ),
+      );
+    } on HttpException catch (e) {
+      emit(state.copyWith(followedCountriesStatus: CountriesFilterStatus.failure, error: e));
+    } catch (e) {
+      emit(
+        state.copyWith(
+          followedCountriesStatus: CountriesFilterStatus.failure,
+          error: UnknownException(e.toString()),
+        ),
+      );
+    }
+  }
 }