refactor(headlines-feed): migrate CountryFilterPage to HeadlinesFilterBloc

- Replace CountriesFilterBloc with HeadlinesFilterBloc for centralized state management
- Convert CountryFilterPage from StatefulWidget to StatelessWidget
- Remove local selection state and rely on HeadlinesFilterBloc for country selections
- Update UI to reflect changes in state management logic
- Simplify page navigation and data handling by integrating with HeadlinesFilterBloc

Author: fulleni

lib/headlines-feed/view/country_filter_page.dart

@@ -2,80 +2,23 @@ import 'package:core/core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.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/countries_filter_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/l10n/l10n.dart';
-import 'package:go_router/go_router.dart';
 import 'package:ui_kit/ui_kit.dart';
 
-enum CountryFilterUsage {
-  // countries with active sources
-  hasActiveSources,
-
-  // countries with active headlines
-  hasActiveHeadlines,
-}
-
 /// {@template country_filter_page}
 /// A page dedicated to selecting event countries for filtering headlines.
 ///
-/// Uses [CountriesFilterBloc] to fetch countries paginatively, allows multiple
-/// selections, and returns the selected list via `context.pop` when the user
-/// applies the changes.
+/// This page now interacts with the centralized [HeadlinesFilterBloc]
+/// to manage the list of available countries and the user's selections.
 /// {@endtemplate}
-class CountryFilterPage extends StatefulWidget {
+class CountryFilterPage extends StatelessWidget {
   /// {@macro country_filter_page}
-  const CountryFilterPage({required this.title, this.filter, super.key});
+  const CountryFilterPage({required this.title, super.key});
 
   /// The title to display in the app bar for this filter page.
   final String title;
 
-  /// The usage context for filtering countries (e.g., 'hasActiveSources', 'hasActiveHeadlines').
-  /// If null, fetches all countries (though this is not the primary use case for this page).
-  final CountryFilterUsage? filter;
-
-  @override
-  State<CountryFilterPage> createState() => _CountryFilterPageState();
-}
-
-/// State for the [CountryFilterPage].
-///
-/// Manages the local selection state ([_pageSelectedCountries]) and interacts
-/// with [CountriesFilterBloc] for data fetching.
-class _CountryFilterPageState extends State<CountryFilterPage> {
-  /// Stores the countries selected by the user *on this specific page*.
-  /// This state is local to the `CountryFilterPage` lifecycle.
-  /// It's initialized in `initState` using the list of previously selected
-  /// countries passed via the `extra` parameter during navigation from
-  /// `HeadlinesFilterPage`. This ensures the checkboxes reflect the state
-  /// from the main filter page when this page loads.
-  late Set<Country> _pageSelectedCountries;
-
-  @override
-  void initState() {
-    super.initState();
-
-    // Initialization needs to happen after the first frame to safely access
-    // GoRouterState.of(context).
-    WidgetsBinding.instance.addPostFrameCallback((_) {
-      // 1. Retrieve the list of countries that were already selected on the
-      //    previous page (HeadlinesFilterPage). This list is passed dynamically
-      //    via the `extra` parameter in the `context.pushNamed` call.
-      final initialSelection =
-          GoRouterState.of(context).extra as List<Country>?;
-
-      // 2. Initialize the local selection state (`_pageSelectedCountries`) for this
-      //    page. Use a Set for efficient add/remove/contains operations.
-      //    This ensures the checkboxes on this page are initially checked
-      //    correctly based on the selections made previously.
-      _pageSelectedCountries = Set.from(initialSelection ?? []);
-    });
-  }
-
-  @override
-  void dispose() {
-    super.dispose();
-  }
-
   @override
   Widget build(BuildContext context) {
     final l10n = AppLocalizationsX(context).l10n;
@@ -85,19 +28,22 @@ class _CountryFilterPageState extends State<CountryFilterPage> {
     return Scaffold(
       appBar: AppBar(
         title: Text(
-          widget.title, // Use the dynamic title
+          title, // Use the dynamic title
           style: textTheme.titleLarge,
         ),
         actions: [
           // Apply My Followed Countries Button
-          BlocBuilder<AppBloc, AppState>(
-            builder: (context, appState) {
+          BlocBuilder<HeadlinesFilterBloc, HeadlinesFilterState>(
+            builder: (context, filterState) {
+              final appState = context.watch<AppBloc>().state;
               final followedCountries =
                   appState.userContentPreferences?.followedCountries ?? [];
-              final isFollowedFilterActive =
-                  followedCountries.isNotEmpty &&
-                  _pageSelectedCountries.length == followedCountries.length &&
-                  _pageSelectedCountries.containsAll(followedCountries);
+
+              // Determine if the current selection matches the followed countries
+              final isFollowedFilterActive = followedCountries.isNotEmpty &&
+                  filterState.selectedCountries.length ==
+                      followedCountries.length &&
+                  filterState.selectedCountries.containsAll(followedCountries);
 
               return IconButton(
                 icon: isFollowedFilterActive
@@ -108,9 +54,6 @@ class _CountryFilterPageState extends State<CountryFilterPage> {
                     : null,
                 tooltip: l10n.headlinesFeedFilterApplyFollowedLabel,
                 onPressed: () {
-                  setState(() {
-                    _pageSelectedCountries = Set.from(followedCountries);
-                  });
                   if (followedCountries.isEmpty) {
                     ScaffoldMessenger.of(context)
                       ..hideCurrentSnackBar()
@@ -120,29 +63,35 @@ class _CountryFilterPageState extends State<CountryFilterPage> {
                           duration: const Duration(seconds: 3),
                         ),
                       );
+                  } else {
+                    // Toggle the followed items filter in the HeadlinesFilterBloc
+                    context.read<HeadlinesFilterBloc>().add(
+                          FollowedItemsFilterToggled(
+                            isUsingFollowedItems: !isFollowedFilterActive,
+                          ),
+                        );
                   }
                 },
               );
             },
           ),
+          // Apply Filters Button (now just pops, as state is managed centrally)
           IconButton(
             icon: const Icon(Icons.check),
             tooltip: l10n.headlinesFeedFilterApplyButton,
             onPressed: () {
-              // When the user taps 'Apply' (checkmark), pop the current route
-              // and return the final list of selected countries (`_pageSelectedCountries`)
-              // from this page back to the previous page (`HeadlinesFilterPage`).
-              // `HeadlinesFilterPage` receives this list in its `onResult` callback.
-              context.pop(_pageSelectedCountries.toList());
+              // The selections are already managed by HeadlinesFilterBloc.
+              // Just pop the page.
+              Navigator.of(context).pop();
             },
           ),
         ],
       ),
-      body: BlocBuilder<CountriesFilterBloc, CountriesFilterState>(
-        builder: (context, state) {
+      body: BlocBuilder<HeadlinesFilterBloc, HeadlinesFilterState>(
+        builder: (context, filterState) {
           // Determine overall loading status for the main list
           final isLoadingMainList =
-              state.status == CountriesFilterStatus.loading;
+              filterState.status == HeadlinesFilterStatus.loading;
 
           // Handle initial loading state
           if (isLoadingMainList) {
@@ -154,19 +103,24 @@ class _CountryFilterPageState extends State<CountryFilterPage> {
           }
 
           // Handle failure state (show error and retry button)
-          if (state.status == CountriesFilterStatus.failure &&
-              state.countries.isEmpty) {
+          if (filterState.status == HeadlinesFilterStatus.failure &&
+              filterState.allCountries.isEmpty) {
             return FailureStateWidget(
-              exception: state.error ?? const UnknownException('Unknown error'),
-              onRetry: () => context.read<CountriesFilterBloc>().add(
-                CountriesFilterRequested(usage: widget.filter),
-              ),
+              exception:
+                  filterState.error ?? const UnknownException('Unknown error'),
+              onRetry: () => context.read<HeadlinesFilterBloc>().add(
+                    FilterDataLoaded(
+                      initialSelectedTopics: filterState.selectedTopics.toList(),
+                      initialSelectedSources: filterState.selectedSources.toList(),
+                      initialSelectedCountries: filterState.selectedCountries.toList(),
+                      isUsingFollowedItems: filterState.isUsingFollowedItems,
+                    ),
+                  ),
             );
           }
 
           // Handle empty state (after successful load but no countries found)
-          if (state.status == CountriesFilterStatus.success &&
-              state.countries.isEmpty) {
+          if (filterState.allCountries.isEmpty) {
             return InitialStateWidget(
               icon: Icons.flag_circle_outlined,
               headline: l10n.countryFilterEmptyHeadline,
@@ -179,10 +133,10 @@ class _CountryFilterPageState extends State<CountryFilterPage> {
             padding: const EdgeInsets.symmetric(
               vertical: AppSpacing.paddingSmall,
             ).copyWith(bottom: AppSpacing.xxl),
-            itemCount: state.countries.length,
+            itemCount: filterState.allCountries.length,
             itemBuilder: (context, index) {
-              final country = state.countries[index];
-              final isSelected = _pageSelectedCountries.contains(country);
+              final country = filterState.allCountries[index];
+              final isSelected = filterState.selectedCountries.contains(country);
 
               return CheckboxListTile(
                 title: Text(country.name, style: textTheme.titleMedium),
@@ -217,13 +171,14 @@ class _CountryFilterPageState extends State<CountryFilterPage> {
                 ),
                 value: isSelected,
                 onChanged: (bool? value) {
-                  setState(() {
-                    if (value == true) {
-                      _pageSelectedCountries.add(country);
-                    } else {
-                      _pageSelectedCountries.remove(country);
-                    }
-                  });
+                  if (value != null) {
+                    context.read<HeadlinesFilterBloc>().add(
+                          FilterCountryToggled(
+                            country: country,
+                            isSelected: value,
+                          ),
+                        );
+                  }
                 },
                 controlAffinity: ListTileControlAffinity.leading,
                 contentPadding: const EdgeInsets.symmetric(