refactor(ads): improve AdNavigatorObserver testability and modularity

- Replace direct AppBloc dependency with AppStateProvider function
- Implement page transition counting logic internally
- Enhance interstitial ad showing logic with detailed frequency checks
- Update method names and access modifiers for clarity

Author: fulleni

lib/ads/ad_navigator_observer.dart

@@ -6,8 +6,15 @@ import 'package:flutter_news_app_mobile_client_full_source_code/ads/ad_service.d
 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/ads/models/interstitial_ad.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/app/bloc/app_bloc.dart';
-import 'package:logging/logging.dart';
 import 'package:google_mobile_ads/google_mobile_ads.dart' as admob;
+import 'package:logging/logging.dart';
+
+/// A function that provides the current [AppState].
+///
+/// This is used for dependency injection to decouple the [AdNavigatorObserver]
+/// from a direct dependency on the [AppBloc] instance, making it more
+/// testable and reusable.
+typedef AppStateProvider = AppState Function();
 
 /// {@template ad_navigator_observer}
 /// A [NavigatorObserver] that listens to route changes and triggers
@@ -18,54 +25,112 @@ import 'package:google_mobile_ads/google_mobile_ads.dart' as admob;
 /// 2. Requesting an interstitial ad from the [AdService] when the criteria are met.
 /// 3. Showing the interstitial ad to the user.
 ///
-/// It interacts with the [AppBloc] to get the current [RemoteConfig] and
-/// user's ad frequency settings, and to dispatch events for page transitions.
+/// It retrieves the current [AppState] via the [appStateProvider] to get the
+/// latest [RemoteConfig] and user's ad frequency settings.
 /// {@endtemplate}
 class AdNavigatorObserver extends NavigatorObserver {
   /// {@macro ad_navigator_observer}
   AdNavigatorObserver({
-    required this.appBloc,
+    required this.appStateProvider,
     required this.adService,
     required AdThemeStyle adThemeStyle,
     Logger? logger,
-  })  : _logger = logger ?? Logger('AdNavigatorObserver'),
-        _adThemeStyle = adThemeStyle;
+  }) : _logger = logger ?? Logger('AdNavigatorObserver'),
+       _adThemeStyle = adThemeStyle;
+
+  /// A function that provides the current [AppState].
+  final AppStateProvider appStateProvider;
 
-  final AppBloc appBloc;
+  /// The service responsible for fetching and loading ads.
   final AdService adService;
+
   final Logger _logger;
   final AdThemeStyle _adThemeStyle;
 
+  /// Tracks the number of page transitions since the last interstitial ad.
+  int _pageTransitionCount = 0;
+
   @override
   void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
     super.didPush(route, previousRoute);
     _logger.info('Route pushed: ${route.settings.name}');
-    _handlePageTransition(route);
+    if (route is PageRoute && route.settings.name != null) {
+      _handlePageTransition();
+    }
   }
 
   @override
   void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) {
     super.didPop(route, previousRoute);
     _logger.info('Route popped: ${route.settings.name}');
-    _handlePageTransition(route);
+    if (route is PageRoute && route.settings.name != null) {
+      _handlePageTransition();
+    }
   }
 
-  /// Handles a page transition event.
-  ///
-  /// Dispatches an [AppPageTransitioned] event to the [AppBloc] to update
-  /// the transition count and potentially trigger an interstitial ad.
-  void _handlePageTransition(Route<dynamic> route) {
-    if (route is PageRoute && route.settings.name != null) {
-      appBloc.add(const AppPageTransitioned());
+  /// Handles a page transition event, checks ad frequency, and shows an ad if needed.
+  void _handlePageTransition() {
+    _pageTransitionCount++;
+    _logger.info('Page transitioned. Current count: $_pageTransitionCount');
+
+    final appState = appStateProvider();
+    final remoteConfig = appState.remoteConfig;
+    final user = appState.user;
+
+    // Only proceed if remote config is available, ads are globally enabled,
+    // and interstitial ads are enabled in the config.
+    if (remoteConfig == null ||
+        !remoteConfig.adConfig.enabled ||
+        !remoteConfig.adConfig.interstitialAdConfiguration.enabled) {
+      _logger.info('Interstitial ads are not enabled or config not ready.');
+      return;
+    }
+
+    final interstitialConfig =
+        remoteConfig.adConfig.interstitialAdConfiguration;
+    final frequencyConfig =
+        interstitialConfig.feedInterstitialAdFrequencyConfig;
+
+    // Determine the required transitions based on user role.
+    final int requiredTransitions;
+    switch (user?.appRole) {
+      case AppUserRole.guestUser:
+        requiredTransitions =
+            frequencyConfig.guestTransitionsBeforeShowingInterstitialAds;
+        break;
+      case AppUserRole.standardUser:
+        requiredTransitions =
+            frequencyConfig.standardUserTransitionsBeforeShowingInterstitialAds;
+        break;
+      case AppUserRole.premiumUser:
+        requiredTransitions =
+            frequencyConfig.premiumUserTransitionsBeforeShowingInterstitialAds;
+        break;
+      case null:
+        // If user is null, default to guest user settings.
+        requiredTransitions =
+            frequencyConfig.guestTransitionsBeforeShowingInterstitialAds;
+        break;
+    }
+
+    _logger.info(
+      'Required transitions for user role ${user?.appRole}: $requiredTransitions',
+    );
+
+    // Check if it's time to show an interstitial ad.
+    if (requiredTransitions > 0 &&
+        _pageTransitionCount >= requiredTransitions) {
+      _logger.info('Interstitial ad due. Requesting ad.');
+      _showInterstitialAd();
+      _pageTransitionCount = 0; // Reset count after showing
     }
   }
 
   /// Requests and shows an interstitial ad if conditions are met.
-  ///
-  /// This method is called by the [AppBloc] when it determines an ad is due.
-  Future<void> showInterstitialAd() async {
-    final remoteConfig = appBloc.state.remoteConfig;
+  Future<void> _showInterstitialAd() async {
+    final remoteConfig = appStateProvider().remoteConfig;
 
+    // This is a secondary check. The primary check is in _handlePageTransition.
     if (remoteConfig == null || !remoteConfig.adConfig.enabled) {
       _logger.info('Interstitial ads disabled or remote config not available.');
       return;
@@ -91,21 +156,20 @@ class AdNavigatorObserver extends NavigatorObserver {
       if (interstitialAd.provider == AdPlatformType.admob &&
           interstitialAd.adObject is admob.InterstitialAd) {
         final admobInterstitialAd =
-            interstitialAd.adObject as admob.InterstitialAd;
-        admobInterstitialAd.fullScreenContentCallback =
-            admob.FullScreenContentCallback(
-          onAdDismissedFullScreenContent: (ad) {
-            _logger.info('Interstitial Ad dismissed.');
-            ad.dispose();
-          },
-          onAdFailedToShowFullScreenContent: (ad, error) {
-            _logger.severe('Interstitial Ad failed to show: $error');
-            ad.dispose();
-          },
-          onAdShowedFullScreenContent: (ad) {
-            _logger.info('Interstitial Ad showed.');
-          },
-        );
+            interstitialAd.adObject as admob.InterstitialAd
+              ..fullScreenContentCallback = admob.FullScreenContentCallback(
+                onAdDismissedFullScreenContent: (ad) {
+                  _logger.info('Interstitial Ad dismissed.');
+                  ad.dispose();
+                },
+                onAdFailedToShowFullScreenContent: (ad, error) {
+                  _logger.severe('Interstitial Ad failed to show: $error');
+                  ad.dispose();
+                },
+                onAdShowedFullScreenContent: (ad) {
+                  _logger.info('Interstitial Ad showed.');
+                },
+              );
         await admobInterstitialAd.show();
       } else if (interstitialAd.provider == AdPlatformType.local &&
           interstitialAd.adObject is LocalInterstitialAd) {