fix(navigation): open download queue from snackbar actions

lib/screens/artist_screen.dart

@@ -30,6 +30,7 @@ import 'package:spotiflac_android/utils/clickable_metadata.dart';
 import 'package:spotiflac_android/widgets/cached_cover_image.dart';
 import 'package:spotiflac_android/widgets/motion_header_banner.dart';
 import 'package:spotiflac_android/widgets/cross_extension_share_sheet.dart';
+import 'package:spotiflac_android/widgets/view_queue_snackbar_action.dart';
 
 class _ArtistCache {
   static final _cache = TtlCache<_CacheEntry>(const Duration(minutes: 10));
@@ -1055,10 +1056,7 @@ class _ArtistScreenState extends ConsumerState<ArtistScreen>
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(
           content: Text(message),
-          action: SnackBarAction(
-            label: context.l10n.snackbarViewQueue,
-            onPressed: () {},
-          ),
+          action: buildViewQueueSnackBarAction(context),
         ),
       );
     }

lib/screens/home_tab.dart

@@ -37,6 +37,7 @@ import 'package:spotiflac_android/widgets/error_card.dart';
 import 'package:spotiflac_android/widgets/in_library_badge.dart';
 import 'package:spotiflac_android/widgets/preview_button.dart';
 import 'package:spotiflac_android/widgets/settings_group.dart';
+import 'package:spotiflac_android/widgets/view_queue_snackbar_action.dart';
 
 part 'home_tab_helpers.dart';
 part 'home_tab_widgets.dart';
@@ -1077,10 +1078,7 @@ class _HomeTabState extends ConsumerState<HomeTab>
                 ScaffoldMessenger.of(this.context).showSnackBar(
                   SnackBar(
                     content: Text(queueSnackbarMessage),
-                    action: SnackBarAction(
-                      label: l10n.snackbarViewQueue,
-                      onPressed: () {},
-                    ),
+                    action: buildViewQueueSnackBarAction(this.context),
                   ),
                 );
               }
@@ -1109,10 +1107,7 @@ class _HomeTabState extends ConsumerState<HomeTab>
             ScaffoldMessenger.of(this.context).showSnackBar(
               SnackBar(
                 content: Text(queueSnackbarMessage),
-                action: SnackBarAction(
-                  label: l10n.snackbarViewQueue,
-                  onPressed: () {},
-                ),
+                action: buildViewQueueSnackBarAction(this.context),
               ),
             );
           }

lib/screens/main_shell.dart

@@ -105,6 +105,10 @@ class _MainShellState extends ConsumerState<MainShell>
       duration: const Duration(milliseconds: 180),
       value: 1,
     );
+    ShellNavigationService.registerTabSelectionHandler(
+      owner: this,
+      handler: _onShellTabRequested,
+    );
     ShellNavigationService.syncState(
       currentTabIndex: _currentIndex,
       showRepoTab: false,
@@ -433,6 +437,7 @@ class _MainShellState extends ConsumerState<MainShell>
   @override
   void dispose() {
     WidgetsBinding.instance.removeObserver(this);
+    ShellNavigationService.unregisterTabSelectionHandler(this);
     _shareSubscription?.cancel();
     _pageController.dispose();
     _tabJumpTransitionController.dispose();
@@ -452,6 +457,19 @@ class _MainShellState extends ConsumerState<MainShell>
     ref.read(trackProvider.notifier).clear();
   }
 
+  void _onShellTabRequested(ShellTab tab) {
+    final showStore = ref.read(
+      settingsProvider.select((s) => s.showExtensionStore),
+    );
+    final index = switch (tab) {
+      ShellTab.home => 0,
+      ShellTab.library => 1,
+      ShellTab.repository => showStore ? 2 : null,
+      ShellTab.settings => showStore ? 3 : 2,
+    };
+    if (index != null) _onNavTap(index);
+  }
+
   void _onNavTap(int index) {
     if (index == 0 && _currentIndex == 0) {
       _resetHomeToMain();

lib/services/shell_navigation_service.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/widgets.dart';
 
+enum ShellTab { home, library, repository, settings }
+
 class ShellNavigationService {
   static final GlobalKey<NavigatorState> homeTabNavigatorKey =
       GlobalKey<NavigatorState>();
@@ -10,6 +12,29 @@ class ShellNavigationService {
 
   static int _currentTabIndex = 0;
   static bool _showRepoTab = false;
+  static Object? _tabSelectionOwner;
+  static ValueChanged<ShellTab>? _tabSelectionHandler;
+
+  static void registerTabSelectionHandler({
+    required Object owner,
+    required ValueChanged<ShellTab> handler,
+  }) {
+    _tabSelectionOwner = owner;
+    _tabSelectionHandler = handler;
+  }
+
+  static void unregisterTabSelectionHandler(Object owner) {
+    if (!identical(_tabSelectionOwner, owner)) return;
+    _tabSelectionOwner = null;
+    _tabSelectionHandler = null;
+  }
+
+  static bool requestTab(ShellTab tab) {
+    final handler = _tabSelectionHandler;
+    if (handler == null) return false;
+    handler(tab);
+    return true;
+  }
 
   static void syncState({
     required int currentTabIndex,

lib/widgets/view_queue_snackbar_action.dart

@@ -0,0 +1,12 @@
+import 'package:flutter/material.dart';
+import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/services/shell_navigation_service.dart';
+
+SnackBarAction buildViewQueueSnackBarAction(BuildContext context) {
+  return SnackBarAction(
+    label: context.l10n.snackbarViewQueue,
+    onPressed: () {
+      ShellNavigationService.requestTab(ShellTab.library);
+    },
+  );
+}

test/shell_navigation_service_test.dart

@@ -0,0 +1,90 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/l10n/app_localizations.dart';
+import 'package:spotiflac_android/services/shell_navigation_service.dart';
+import 'package:spotiflac_android/widgets/view_queue_snackbar_action.dart';
+
+void main() {
+  group('ShellNavigationService tab requests', () {
+    test('forwards a named tab request to the registered shell', () {
+      final owner = Object();
+      ShellTab? requestedTab;
+      addTearDown(
+        () => ShellNavigationService.unregisterTabSelectionHandler(owner),
+      );
+
+      ShellNavigationService.registerTabSelectionHandler(
+        owner: owner,
+        handler: (tab) => requestedTab = tab,
+      );
+
+      expect(ShellNavigationService.requestTab(ShellTab.library), isTrue);
+      expect(requestedTab, ShellTab.library);
+    });
+
+    test('does not remove a newer shell handler', () {
+      final oldOwner = Object();
+      final currentOwner = Object();
+      ShellTab? requestedTab;
+      addTearDown(
+        () =>
+            ShellNavigationService.unregisterTabSelectionHandler(currentOwner),
+      );
+
+      ShellNavigationService.registerTabSelectionHandler(
+        owner: oldOwner,
+        handler: (_) {},
+      );
+      ShellNavigationService.registerTabSelectionHandler(
+        owner: currentOwner,
+        handler: (tab) => requestedTab = tab,
+      );
+
+      ShellNavigationService.unregisterTabSelectionHandler(oldOwner);
+
+      expect(ShellNavigationService.requestTab(ShellTab.settings), isTrue);
+      expect(requestedTab, ShellTab.settings);
+    });
+
+    test('reports when no shell can handle the request', () {
+      final owner = Object();
+      ShellNavigationService.registerTabSelectionHandler(
+        owner: owner,
+        handler: (_) {},
+      );
+      ShellNavigationService.unregisterTabSelectionHandler(owner);
+
+      expect(ShellNavigationService.requestTab(ShellTab.library), isFalse);
+    });
+
+    testWidgets('View Queue snackbar action requests the Library tab', (
+      tester,
+    ) async {
+      final owner = Object();
+      ShellTab? requestedTab;
+      addTearDown(
+        () => ShellNavigationService.unregisterTabSelectionHandler(owner),
+      );
+      ShellNavigationService.registerTabSelectionHandler(
+        owner: owner,
+        handler: (tab) => requestedTab = tab,
+      );
+
+      await tester.pumpWidget(
+        MaterialApp(
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          home: Scaffold(
+            body: Builder(
+              builder: (context) => buildViewQueueSnackBarAction(context),
+            ),
+          ),
+        ),
+      );
+
+      await tester.tap(find.text('View Queue'));
+
+      expect(requestedTab, ShellTab.library);
+    });
+  });
+}