fix(theme): listen to platformDispatcher.onPlatformBrightnessChanged for ThemeMode.system

lib/core/theme/theme_controller.dart

@@ -24,7 +24,7 @@ import 'theme_remote_install_service.dart';
 import '../extensions/extension_paths.dart';
 
 /// Active theme state: preset, optional imported colors, user overrides.
-class ThemeController extends ChangeNotifier {
+class ThemeController extends ChangeNotifier with WidgetsBindingObserver {
   static const String builtinQueryaDarkId = 'querya-dark';
   static const String builtinQueryaLightId = 'querya-light';
 
@@ -79,6 +79,8 @@ class ThemeController extends ChangeNotifier {
   ThemeFolderWatcher? _themeFolderWatcher;
   bool _editorPreviewActive = false;
   String? _editorPreviewRestoreThemeId;
+  Brightness? _lastPlatformBrightness;
+  bool _isObservingBrightness = false;
 
   QueryaTheme? _cachedLightTheme;
   QueryaTheme? _cachedDarkTheme;
@@ -90,6 +92,9 @@ class ThemeController extends ChangeNotifier {
 
   ThemeMode get themeMode => _themeMode;
 
+  @visibleForTesting
+  bool get isObservingPlatformBrightness => _isObservingBrightness;
+
   /// Preference toggle for theme cross-fades.
   ///
   /// [QueryaApp] still gates animation with [QueryaThemeMotion] (motion level /
@@ -238,8 +243,21 @@ class ThemeController extends ChangeNotifier {
     await _themeFolderWatcher?.stop();
   }
 
+  WidgetsBinding? get _binding {
+    try {
+      return WidgetsBinding.instance;
+    } catch (_) {
+      return null;
+    }
+  }
+
   @override
   void dispose() {
+    if (_isObservingBrightness) {
+      _binding?.removeObserver(this);
+      _isObservingBrightness = false;
+      _lastPlatformBrightness = null;
+    }
     unawaited(stopThemeFolderWatcher());
     super.dispose();
   }
@@ -254,7 +272,35 @@ class ThemeController extends ChangeNotifier {
     _cachedMaterialThemeScheme = null;
   }
 
+  void _updateBrightnessObserver() {
+    final binding = _binding;
+    if (binding == null) return;
+    final shouldObserve = _themeMode == ThemeMode.system;
+    if (shouldObserve && !_isObservingBrightness) {
+      _lastPlatformBrightness = binding.platformDispatcher.platformBrightness;
+      binding.addObserver(this);
+      _isObservingBrightness = true;
+    } else if (!shouldObserve && _isObservingBrightness) {
+      binding.removeObserver(this);
+      _isObservingBrightness = false;
+      _lastPlatformBrightness = null;
+    }
+  }
+
+  @override
+  void didChangePlatformBrightness() {
+    if (_themeMode != ThemeMode.system) return;
+    final binding = _binding;
+    if (binding == null) return;
+    final current = binding.platformDispatcher.platformBrightness;
+    if (_lastPlatformBrightness != current) {
+      _lastPlatformBrightness = current;
+      _notifyThemeChanged();
+    }
+  }
+
   void _notifyThemeChanged() {
+    _updateBrightnessObserver();
     _invalidateThemeCache();
     notifyListeners();
   }
@@ -660,8 +706,11 @@ class ThemeController extends ChangeNotifier {
 
   Brightness _effectiveBrightness() {
     if (_themeMode == ThemeMode.system) {
-      final b = WidgetsBinding.instance.platformDispatcher.platformBrightness;
-      return b;
+      final binding = _binding;
+      if (binding != null) {
+        return binding.platformDispatcher.platformBrightness;
+      }
+      return Brightness.dark;
     }
     return _themeMode == ThemeMode.light ? Brightness.light : Brightness.dark;
   }

test/core/theme/theme_controller_test.dart

@@ -68,6 +68,7 @@ void main() {
   late ThemeRegistryService registry;
 
   setUpAll(() async {
+    TestWidgetsFlutterBinding.ensureInitialized();
     tempDir =
         await Directory.systemTemp.createTemp('querya_theme_controller_test_');
     PathProviderPlatform.instance = _FakePathProvider(tempDir.path);
@@ -498,4 +499,70 @@ void main() {
           c.activeTheme.colorScheme.primary, parseQueryaThemeColor('#38BDF8'));
     });
   });
+
+  group('ThemeMode.system platform brightness listener (#899)', () {
+    test(
+        'listens to platform brightness when ThemeMode.system and updates activeTheme',
+        () async {
+      final c = ThemeController.instance;
+      await c.load();
+
+      // Initially not system, so should not observe
+      await c.setThemeMode(ThemeMode.dark);
+      expect(c.isObservingPlatformBrightness, isFalse);
+
+      // Set to system mode with dark platform brightness
+      TestWidgetsFlutterBinding.instance.platformDispatcher
+          .platformBrightnessTestValue = Brightness.dark;
+      await c.setThemeMode(ThemeMode.system);
+      expect(c.themeMode, ThemeMode.system);
+      expect(c.isObservingPlatformBrightness, isTrue);
+      expect(c.activeTheme.brightness, Brightness.dark);
+
+      // Track listener notifications
+      var notifyCount = 0;
+      void listener() => notifyCount++;
+      c.addListener(listener);
+
+      try {
+        // Change platform brightness to light
+        TestWidgetsFlutterBinding.instance.platformDispatcher
+            .platformBrightnessTestValue = Brightness.light;
+        c.didChangePlatformBrightness();
+
+        expect(notifyCount, 1);
+        expect(c.activeTheme.brightness, Brightness.light);
+
+        // Repeating same brightness does not fire redundant notification
+        c.didChangePlatformBrightness();
+        expect(notifyCount, 1);
+
+        // Change back to dark
+        TestWidgetsFlutterBinding.instance.platformDispatcher
+            .platformBrightnessTestValue = Brightness.dark;
+        c.didChangePlatformBrightness();
+        expect(notifyCount, 2);
+        expect(c.activeTheme.brightness, Brightness.dark);
+
+        // Switching away from system unregisters observer
+        await c.setThemeMode(ThemeMode.light);
+        expect(c.isObservingPlatformBrightness, isFalse);
+      } finally {
+        c.removeListener(listener);
+        TestWidgetsFlutterBinding.instance.platformDispatcher
+            .clearPlatformBrightnessTestValue();
+      }
+    });
+
+    test('cleans up brightness observer on resetToDefaults', () async {
+      final c = ThemeController.instance;
+      await c.load();
+      await c.setThemeMode(ThemeMode.system);
+      expect(c.isObservingPlatformBrightness, isTrue);
+
+      await c.resetToDefaults();
+      expect(c.themeMode, ThemeMode.dark);
+      expect(c.isObservingPlatformBrightness, isFalse);
+    });
+  });
 }