refactor(headlines-feed): implement HeadlinesFilterBloc for state management

- Replace local state management with HeadlinesFilterBloc
- Remove temporary filter selection variables and logic
- Add loading and failure states handling
- Update UI to reflect new state management approach
- Refactor filter tile building and selection logic

Author: fulleni

lib/headlines-feed/view/headlines_filter_page.dart

@@ -8,85 +8,62 @@ import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/models/ad_theme_style.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/app/bloc/app_bloc.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/bloc/headlines_feed_bloc.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/bloc/headlines_filter_bloc.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/models/headline_filter.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/l10n/l10n.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/router/routes.dart';
 import 'package:go_router/go_router.dart';
 import 'package:ui_kit/ui_kit.dart';
 
-// Keys for passing data to/from SourceFilterPage
-const String keySelectedSources = 'selectedSources';
-
 /// {@template headlines_filter_page}
 /// A full-screen dialog page for selecting headline filters.
 ///
 /// Allows users to navigate to specific pages for selecting categories,
 /// sources, and event countries. Manages the temporary state of these
 /// selections before applying them to the [HeadlinesFeedBloc].
 /// {@endtemplate}
-class HeadlinesFilterPage extends StatefulWidget {
+class HeadlinesFilterPage extends StatelessWidget {
   /// {@macro headlines_filter_page}
   const HeadlinesFilterPage({super.key});
 
   @override
-  State<HeadlinesFilterPage> createState() => _HeadlinesFilterPageState();
-}
-
-class _HeadlinesFilterPageState extends State<HeadlinesFilterPage> {
-  /// Temporary state for filter selections within this modal flow.
-  /// These hold the selections made by the user *while* this filter page
-  /// and its sub-pages (Category, Source, Country) are open.
-  /// They are initialized from the main [HeadlinesFeedBloc]'s current filter
-  /// and are only applied back to the BLoC when the user taps 'Apply'.
-  late List<Topic> _tempSelectedTopics;
-  late List<Source> _tempSelectedSources;
-  late List<Country> _tempSelectedEventCountries;
-
-  /// Flag to indicate if the "Apply my followed items" filter is active.
-  bool _useFollowedFilters = false;
-
-  @override
-  void initState() {
-    super.initState();
-    final headlinesFeedState = BlocProvider.of<HeadlinesFeedBloc>(
-      context,
-    ).state;
-
-    final currentFilter = headlinesFeedState.filter;
-    _tempSelectedTopics = List.from(currentFilter.topics ?? []);
-    _tempSelectedSources = List.from(currentFilter.sources ?? []);
-    _tempSelectedEventCountries = List.from(currentFilter.eventCountries ?? []);
+  Widget build(BuildContext context) {
+    // Access the HeadlinesFeedBloc to get the current filter state for initialization.
+    final headlinesFeedBloc = context.read<HeadlinesFeedBloc>();
+    final currentFilter = headlinesFeedBloc.state.filter;
 
-    _useFollowedFilters = currentFilter.isFromFollowedItems;
+    return BlocProvider(
+      create: (context) => HeadlinesFilterBloc(
+        topicsRepository: context.read<DataRepository<Topic>>(),
+        sourcesRepository: context.read<DataRepository<Source>>(),
+        countriesRepository: context.read<DataRepository<Country>>(),
+        appBloc: context.read<AppBloc>(),
+      )..add(
+          FilterDataLoaded(
+            initialSelectedTopics: currentFilter.topics ?? [],
+            initialSelectedSources: currentFilter.sources ?? [],
+            initialSelectedCountries: currentFilter.eventCountries ?? [],
+            isUsingFollowedItems: currentFilter.isFromFollowedItems,
+          ),
+        ),
+      child: const _HeadlinesFilterView(),
+    );
   }
+}
 
-  /// Clears all temporary filter selections.
-  void _clearTemporaryFilters() {
-    setState(() {
-      _tempSelectedTopics = [];
-      _tempSelectedSources = [];
-      _tempSelectedEventCountries = [];
-    });
-  }
+class _HeadlinesFilterView extends StatelessWidget {
+  const _HeadlinesFilterView();
 
   /// Builds a [ListTile] representing a filter criterion (e.g., Categories).
   ///
   /// Displays the criterion [title], the number of currently selected items
   /// ([selectedCount]), and navigates to the corresponding selection page
   /// specified by [routeName] when tapped.
-  ///
-  /// Uses [currentSelection] to pass the current temporary selection state
-  /// (e.g., `_tempSelectedSources`) to the corresponding criterion selection page
-  /// (e.g., `SourceFilterPage`) via the `extra` parameter of `context.pushNamed`.
-  /// Updates the temporary state via the [onResult] callback when the
-  /// criterion page pops with a result (the user tapped 'Apply' on that page).
-  Widget _buildFilterTile<T>({
+  Widget _buildFilterTile({
     required BuildContext context,
     required String title,
     required int selectedCount,
     required String routeName,
-    required List<T> currentSelectionData,
-    required void Function(List<T>)? onResult,
     bool enabled = true,
   }) {
     final l10n = AppLocalizationsX(context).l10n;
@@ -103,14 +80,10 @@ class _HeadlinesFilterPageState extends State<HeadlinesFilterPage> {
       trailing: const Icon(Icons.chevron_right),
       enabled: enabled,
       onTap: enabled
-          ? () async {
-              final result = await context.pushNamed<List<T>>(
-                routeName,
-                extra: currentSelectionData,
-              );
-              if (result != null && onResult != null) {
-                onResult(result);
-              }
+          ? () {
+              // Navigate to the child filter page. The child page will read
+              // the current selections from HeadlinesFilterBloc directly.
+              context.pushNamed(routeName);
             }
           : null,
     );
@@ -121,10 +94,6 @@ class _HeadlinesFilterPageState extends State<HeadlinesFilterPage> {
     final l10n = AppLocalizationsX(context).l10n;
     final theme = Theme.of(context);
 
-    // Determine if the "Apply my followed items" feature is active.
-    // This will disable the individual filter tiles.
-    final isFollowedFilterActive = _useFollowedFilters;
-
     return Scaffold(
       appBar: AppBar(
         leading: IconButton(
@@ -139,22 +108,15 @@ class _HeadlinesFilterPageState extends State<HeadlinesFilterPage> {
             icon: const Icon(Icons.refresh),
             tooltip: l10n.headlinesFeedFilterResetButton,
             onPressed: () {
-              context.read<HeadlinesFeedBloc>().add(
-                HeadlinesFeedFiltersCleared(
-                  adThemeStyle: AdThemeStyle.fromTheme(Theme.of(context)),
-                ),
-              );
-              // Also reset local state for the "Apply my followed items"
-              setState(() {
-                _useFollowedFilters = false;
-                _clearTemporaryFilters();
-              });
-              context.pop();
+              context.read<HeadlinesFilterBloc>().add(
+                    const FilterSelectionsCleared(),
+                  );
             },
           ),
           // Apply My Followed Items Button
-          BlocBuilder<AppBloc, AppState>(
-            builder: (context, appState) {
+          BlocBuilder<HeadlinesFilterBloc, HeadlinesFilterState>(
+            builder: (context, filterState) {
+              final appState = context.watch<AppBloc>().state;
               final followedTopics =
                   appState.userContentPreferences?.followedTopics ?? [];
               final followedSources =
@@ -167,24 +129,21 @@ class _HeadlinesFilterPageState extends State<HeadlinesFilterPage> {
                   followedCountries.isNotEmpty;
 
               return IconButton(
-                icon: _useFollowedFilters
+                icon: filterState.isUsingFollowedItems
                     ? const Icon(Icons.favorite)
                     : const Icon(Icons.favorite_border),
-                color: _useFollowedFilters ? theme.colorScheme.primary : null,
+                color: filterState.isUsingFollowedItems
+                    ? theme.colorScheme.primary
+                    : null,
                 tooltip: l10n.headlinesFeedFilterApplyFollowedLabel,
                 onPressed: hasFollowedItems
                     ? () {
-                        setState(() {
-                          _useFollowedFilters = !_useFollowedFilters;
-                          if (_useFollowedFilters) {
-                            _tempSelectedTopics = List.from(followedTopics);
-                            _tempSelectedSources = List.from(followedSources);
-                            _tempSelectedEventCountries =
-                                List.from(followedCountries);
-                          } else {
-                            _clearTemporaryFilters();
-                          }
-                        });
+                        context.read<HeadlinesFilterBloc>().add(
+                              FollowedItemsFilterToggled(
+                                isUsingFollowedItems:
+                                    !filterState.isUsingFollowedItems,
+                              ),
+                            );
                       }
                     : () {
                         ScaffoldMessenger.of(context)
@@ -206,67 +165,92 @@ class _HeadlinesFilterPageState extends State<HeadlinesFilterPage> {
             icon: const Icon(Icons.check),
             tooltip: l10n.headlinesFeedFilterApplyButton,
             onPressed: () {
+              final filterState = context.read<HeadlinesFilterBloc>().state;
               final newFilter = HeadlineFilter(
-                topics: _tempSelectedTopics.isNotEmpty
-                    ? _tempSelectedTopics
+                topics: filterState.selectedTopics.isNotEmpty
+                    ? filterState.selectedTopics.toList()
                     : null,
-                sources: _tempSelectedSources.isNotEmpty
-                    ? _tempSelectedSources
+                sources: filterState.selectedSources.isNotEmpty
+                    ? filterState.selectedSources.toList()
                     : null,
-                eventCountries: _tempSelectedEventCountries.isNotEmpty
-                    ? _tempSelectedEventCountries
+                eventCountries: filterState.selectedCountries.isNotEmpty
+                    ? filterState.selectedCountries.toList()
                     : null,
-                isFromFollowedItems: _useFollowedFilters,
+                isFromFollowedItems: filterState.isUsingFollowedItems,
               );
               context.read<HeadlinesFeedBloc>().add(
-                HeadlinesFeedFiltersApplied(
-                  filter: newFilter,
-                  adThemeStyle: AdThemeStyle.fromTheme(Theme.of(context)),
-                ),
-              );
+                    HeadlinesFeedFiltersApplied(
+                      filter: newFilter,
+                      adThemeStyle: AdThemeStyle.fromTheme(Theme.of(context)),
+                    ),
+                  );
               context.pop();
             },
           ),
         ],
       ),
-      body: ListView(
-        padding: const EdgeInsets.symmetric(vertical: AppSpacing.md),
-        children: [
-          const Divider(),
-          _buildFilterTile<Topic>(
-            context: context,
-            title: l10n.headlinesFeedFilterTopicLabel,
-            enabled: !isFollowedFilterActive,
-            selectedCount: _tempSelectedTopics.length,
-            routeName: Routes.feedFilterTopicsName,
-            currentSelectionData: _tempSelectedTopics,
-            onResult: (result) {
-              setState(() => _tempSelectedTopics = result);
-            },
-          ),
-          _buildFilterTile<Source>(
-            context: context,
-            title: l10n.headlinesFeedFilterSourceLabel,
-            enabled: !isFollowedFilterActive,
-            selectedCount: _tempSelectedSources.length,
-            routeName: Routes.feedFilterSourcesName,
-            currentSelectionData: _tempSelectedSources,
-            onResult: (result) {
-              setState(() => _tempSelectedSources = result);
-            },
-          ),
-          _buildFilterTile<Country>(
-            context: context,
-            title: l10n.headlinesFeedFilterEventCountryLabel,
-            enabled: !isFollowedFilterActive,
-            selectedCount: _tempSelectedEventCountries.length,
-            routeName: Routes.feedFilterEventCountriesName,
-            currentSelectionData: _tempSelectedEventCountries,
-            onResult: (result) {
-              setState(() => _tempSelectedEventCountries = result);
-            },
-          ),
-        ],
+      body: BlocBuilder<HeadlinesFilterBloc, HeadlinesFilterState>(
+        builder: (context, filterState) {
+          // Determine if the "Apply my followed items" feature is active.
+          // This will disable the individual filter tiles.
+          final isFollowedFilterActive = filterState.isUsingFollowedItems;
+
+          if (filterState.status == HeadlinesFilterStatus.loading) {
+            return LoadingStateWidget(
+              icon: Icons.filter_list,
+              headline: l10n.headlinesFeedFilterLoadingHeadline,
+              subheadline: l10n.pleaseWait,
+            );
+          }
+
+          if (filterState.status == HeadlinesFilterStatus.failure) {
+            return FailureStateWidget(
+              exception: filterState.error ??
+                  const UnknownException('Failed to load filter data.'),
+              onRetry: () {
+                final headlinesFeedBloc = context.read<HeadlinesFeedBloc>();
+                final currentFilter = headlinesFeedBloc.state.filter;
+                context.read<HeadlinesFilterBloc>().add(
+                      FilterDataLoaded(
+                        initialSelectedTopics: currentFilter.topics ?? [],
+                        initialSelectedSources: currentFilter.sources ?? [],
+                        initialSelectedCountries:
+                            currentFilter.eventCountries ?? [],
+                        isUsingFollowedItems: currentFilter.isFromFollowedItems,
+                      ),
+                    );
+              },
+            );
+          }
+
+          return ListView(
+            padding: const EdgeInsets.symmetric(vertical: AppSpacing.md),
+            children: [
+              const Divider(),
+              _buildFilterTile(
+                context: context,
+                title: l10n.headlinesFeedFilterTopicLabel,
+                enabled: !isFollowedFilterActive,
+                selectedCount: filterState.selectedTopics.length,
+                routeName: Routes.feedFilterTopicsName,
+              ),
+              _buildFilterTile(
+                context: context,
+                title: l10n.headlinesFeedFilterSourceLabel,
+                enabled: !isFollowedFilterActive,
+                selectedCount: filterState.selectedSources.length,
+                routeName: Routes.feedFilterSourcesName,
+              ),
+              _buildFilterTile(
+                context: context,
+                title: l10n.headlinesFeedFilterEventCountryLabel,
+                enabled: !isFollowedFilterActive,
+                selectedCount: filterState.selectedCountries.length,
+                routeName: Routes.feedFilterEventCountriesName,
+              ),
+            ],
+          );
+        },
       ),
     );
   }