perf: optimize widget rebuilds and reduce allocations

- Cache SharedPreferences instance in DownloadHistoryNotifier and DownloadQueueNotifier
- Precompile regex for folder sanitization and year extraction
- Use indexWhere instead of firstWhere with placeholder object
- Use selective watch for downloadQueueProvider (queuedCount, items)
- Pass Track directly to _buildTrackTile instead of index lookup
- Pass historyItems as parameter to _buildRecentAccess
- Add extended metadata (genre, label, copyright) support for MP3

CHANGELOG.md

@@ -1,18 +1,9 @@
 # Changelog
 
-## [Unreleased]
-
 ## [3.1.3] - 2026-01-19
 
 ### Added
 
-- **Persistent Cover Image Cache**: Album/track cover images now cached to persistent storage instead of temporary directory
-  - Cover images no longer disappear when app is closed or device restarts
-  - Cache stored in `app_flutter/cover_cache/` directory (not cleared by system)
-  - Maximum 1000 images cached for up to 365 days
-  - Covers are cached when displayed in History, Home, Album, Artist, or any other screen
-  - New `CoverCacheManager` service with `clearCache()` and `getStats()` methods for future cache management
-
 - **External LRC Lyrics File Support**: Option to save lyrics as separate .lrc files for compatibility with external music players
   - New "Lyrics Mode" setting in Settings > Download > Lyrics section
   - Three modes available:
@@ -28,6 +19,13 @@
   - Select between FLAC qualities (Lossless, Hi-Res, Hi-Res Max) or MP3
   - Respects "Ask quality before download" setting - uses default quality if disabled
 
+  - **Persistent Cover Image Cache**: Album/track cover images now cached to persistent storage instead of temporary directory
+  - Cover images no longer disappear when app is closed or device restarts
+  - Cache stored in `app_flutter/cover_cache/` directory (not cleared by system)
+  - Maximum 1000 images cached for up to 365 days
+  - Covers are cached when displayed in History, Home, Album, Artist, or any other screen
+  - New `CoverCacheManager` service with `clearCache()` and `getStats()` methods for future cache management
+
 - **Extended Metadata from Deezer Enrichment**: Track downloads now include label, copyright, and genre metadata from Deezer
   - New fields in `ExtTrackMetadata`: `label`, `copyright`, `genre`
   - Metadata fetched during `enrichTrack()` via Deezer album API

lib/providers/download_queue_provider.dart

@@ -26,6 +26,10 @@ String? _normalizeOptionalString(String? value) {
   return trimmed;
 }
 
+final _invalidFolderChars = RegExp(r'[<>:"/\\|?*]');
+final _trailingDotsRegex = RegExp(r'\.+$');
+final _yearRegex = RegExp(r'^(\d{4})');
+
 class DownloadHistoryItem {
   final String id;
   final String trackName;
@@ -143,6 +147,7 @@ class DownloadHistoryState {
 
 class DownloadHistoryNotifier extends Notifier<DownloadHistoryState> {
   static const _storageKey = 'download_history';
+  final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
   bool _isLoaded = false;
 
   @override
@@ -162,7 +167,7 @@ class DownloadHistoryNotifier extends Notifier<DownloadHistoryState> {
 
   Future<void> _loadFromStorage() async {
     try {
-      final prefs = await SharedPreferences.getInstance();
+      final prefs = await _prefs;
       final jsonStr = prefs.getString(_storageKey);
       if (jsonStr != null && jsonStr.isNotEmpty) {
         final List<dynamic> jsonList = jsonDecode(jsonStr);
@@ -223,7 +228,7 @@ class DownloadHistoryNotifier extends Notifier<DownloadHistoryState> {
 
   Future<void> _saveToStorage() async {
     try {
-      final prefs = await SharedPreferences.getInstance();
+      final prefs = await _prefs;
       final jsonList = state.items.map((e) => e.toJson()).toList();
       await prefs.setString(_storageKey, jsonEncode(jsonList));
       _historyLog.d('Saved ${state.items.length} items to storage');
@@ -385,6 +390,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
   static const _cleanupInterval = 50;
   static const _queueStorageKey = 'download_queue';
   final NotificationService _notificationService = NotificationService();
+  final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
   int _totalQueuedAtStart = 0;
   int _completedInSession = 0;
   int _failedInSession = 0;
@@ -410,7 +416,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
     _isLoaded = true;
 
     try {
-      final prefs = await SharedPreferences.getInstance();
+      final prefs = await _prefs;
       final jsonStr = prefs.getString(_queueStorageKey);
       if (jsonStr != null && jsonStr.isNotEmpty) {
         final List<dynamic> jsonList = jsonDecode(jsonStr);
@@ -448,7 +454,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
 
   Future<void> _saveQueueToStorage() async {
     try {
-      final prefs = await SharedPreferences.getInstance();
+      final prefs = await _prefs;
 
       final pendingItems = state.items
           .where(
@@ -783,15 +789,15 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
 
   String _sanitizeFolderName(String name) {
     return name
-        .replaceAll(RegExp(r'[<>:"/\\|?*]'), '_')
-        .replaceAll(RegExp(r'\.+$'), '') // Remove trailing dots
+        .replaceAll(_invalidFolderChars, '_')
+        .replaceAll(_trailingDotsRegex, '') // Remove trailing dots
         .trim();
   }
 
   /// Extract year from release date (format: "2005-06-13" or "2005")
   String? _extractYear(String? releaseDate) {
     if (releaseDate == null || releaseDate.isEmpty) return null;
-    final match = RegExp(r'^(\d{4})').firstMatch(releaseDate);
+    final match = _yearRegex.firstMatch(releaseDate);
     return match?.group(1);
   }
 
@@ -1216,7 +1222,13 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
     }
   }
 
-  Future<void> _embedMetadataToMp3(String mp3Path, Track track) async {
+  Future<void> _embedMetadataToMp3(
+    String mp3Path, 
+    Track track, {
+    String? genre,
+    String? label,
+    String? copyright,
+  }) async {
     final settings = ref.read(settingsProvider);
     
     String? coverPath;
@@ -1283,6 +1295,19 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
         metadata['ISRC'] = track.isrc!;
       }
 
+      if (genre != null && genre.isNotEmpty) {
+        metadata['GENRE'] = genre;
+        _log.d('Adding GENRE to MP3: $genre');
+      }
+      if (label != null && label.isNotEmpty) {
+        metadata['ORGANIZATION'] = label;
+        _log.d('Adding ORGANIZATION (label) to MP3: $label');
+      }
+      if (copyright != null && copyright.isNotEmpty) {
+        metadata['COPYRIGHT'] = copyright;
+        _log.d('Adding COPYRIGHT to MP3: $copyright');
+      }
+
       _log.d('MP3 Metadata map content: $metadata');
 
       if (settings.embedLyrics) {
@@ -1447,29 +1472,17 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
       }
 
       final currentItems = state.items;
-      final nextItem = currentItems.firstWhere(
+      final nextIndex = currentItems.indexWhere(
         (item) => item.status == DownloadStatus.queued,
-        orElse: () => DownloadItem(
-          id: '',
-          track: const Track(
-            id: '',
-            name: '',
-            artistName: '',
-            albumName: '',
-            duration: 0,
-          ),
-          service: '',
-          createdAt: DateTime.now(),
-        ),
       );
-
-      if (nextItem.id.isEmpty) {
+      if (nextIndex == -1) {
         _log.d(
           'No more items to process (checked ${currentItems.length} items)',
         );
         break;
       }
 
+      final nextItem = currentItems[nextIndex];
       _log.d(
         'Processing next item: ${nextItem.track.name} (id: ${nextItem.id})',
       );
@@ -1956,7 +1969,18 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
                   DownloadStatus.downloading,
                   progress: 0.99,
                 );
-                await _embedMetadataToMp3(mp3Path, trackToDownload);
+                
+                final mp3BackendGenre = result['genre'] as String?;
+                final mp3BackendLabel = result['label'] as String?;
+                final mp3BackendCopyright = result['copyright'] as String?;
+                
+                await _embedMetadataToMp3(
+                  mp3Path, 
+                  trackToDownload,
+                  genre: mp3BackendGenre ?? genre,
+                  label: mp3BackendLabel ?? label,
+                  copyright: mp3BackendCopyright,
+                );
               } else {
                 _log.w('MP3 conversion failed, keeping FLAC file');
               }

lib/screens/home_screen.dart

@@ -46,16 +46,15 @@ class _HomeScreenState extends ConsumerState<HomeScreen> {
     }
   }
 
-  void _downloadTrack(int index) {
-    final trackState = ref.read(trackProvider);
-    if (index >= 0 && index < trackState.tracks.length) {
-      final track = trackState.tracks[index];
-      final settings = ref.read(settingsProvider);
-      ref.read(downloadQueueProvider.notifier).addToQueue(track, settings.defaultService);
-      ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text('Added "${track.name}" to queue')),
-      );
-    }
+  void _downloadTrack(Track track) {
+    final settings = ref.read(settingsProvider);
+    ref.read(downloadQueueProvider.notifier).addToQueue(
+      track,
+      settings.defaultService,
+    );
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(content: Text('Added "${track.name}" to queue')),
+    );
   }
 
   void _downloadAll() {
@@ -89,8 +88,10 @@ class _HomeScreenState extends ConsumerState<HomeScreen> {
   @override
   Widget build(BuildContext context) {
     final trackState = ref.watch(trackProvider);
-    final queueState = ref.watch(downloadQueueProvider);
+    final queuedCount =
+        ref.watch(downloadQueueProvider.select((s) => s.queuedCount));
     final colorScheme = Theme.of(context).colorScheme;
+    final tracks = trackState.tracks;
 
     return Scaffold(
       appBar: AppBar(
@@ -146,13 +147,13 @@ class _HomeScreenState extends ConsumerState<HomeScreen> {
           if (trackState.albumName != null || trackState.playlistName != null)
             _buildHeader(trackState, colorScheme),
 
-          if (trackState.tracks.length > 1)
+          if (tracks.length > 1)
             Padding(
               padding: const EdgeInsets.symmetric(horizontal: 16.0, vertical: 8.0),
               child: FilledButton.icon(
                 onPressed: _downloadAll,
                 icon: const Icon(Icons.download),
-                label: Text('Download All (${trackState.tracks.length})'),
+                label: Text('Download All (${tracks.length})'),
                 style: FilledButton.styleFrom(
                   minimumSize: const Size.fromHeight(48),
                 ),
@@ -160,11 +161,12 @@ class _HomeScreenState extends ConsumerState<HomeScreen> {
             ),
 
           Expanded(
-            child: trackState.tracks.isEmpty
+            child: tracks.isEmpty
                 ? _buildEmptyState(colorScheme)
                 : ListView.builder(
-                    itemCount: trackState.tracks.length,
-                    itemBuilder: (context, index) => _buildTrackTile(index, colorScheme),
+                    itemCount: tracks.length,
+                    itemBuilder: (context, index) =>
+                        _buildTrackTile(tracks[index], colorScheme),
                   ),
           ),
         ],
@@ -180,13 +182,13 @@ class _HomeScreenState extends ConsumerState<HomeScreen> {
           ),
           NavigationDestination(
             icon: Badge(
-              isLabelVisible: queueState.queuedCount > 0,
-              label: Text('${queueState.queuedCount}'),
+              isLabelVisible: queuedCount > 0,
+              label: Text('$queuedCount'),
               child: const Icon(Icons.queue_music_outlined),
             ),
             selectedIcon: Badge(
-              isLabelVisible: queueState.queuedCount > 0,
-              label: Text('${queueState.queuedCount}'),
+              isLabelVisible: queuedCount > 0,
+              label: Text('$queuedCount'),
               child: const Icon(Icons.queue_music),
             ),
             label: 'Queue',
@@ -261,8 +263,7 @@ child: CachedNetworkImage(
     );
   }
 
-  Widget _buildTrackTile(int index, ColorScheme colorScheme) {
-    final track = ref.watch(trackProvider).tracks[index];
+  Widget _buildTrackTile(Track track, ColorScheme colorScheme) {
     final isCollection = track.isCollection;
     
     String subtitleText;
@@ -318,7 +319,7 @@ child: CachedNetworkImage(
                 color: colorScheme.onSurfaceVariant,
               ),
             ),
-      onTap: () => isCollection ? _openCollection(track) : _downloadTrack(index),
+      onTap: () => isCollection ? _openCollection(track) : _downloadTrack(track),
     );
   }
   

lib/screens/home_tab.dart

@@ -548,7 +548,11 @@ class _HomeTabState extends ConsumerState<HomeTab> with AutomaticKeepAliveClient
           
           if (showRecentAccess)
             SliverToBoxAdapter(
-              child: _buildRecentAccess(recentAccessItems, colorScheme),
+              child: _buildRecentAccess(
+                recentAccessItems,
+                historyItems,
+                colorScheme,
+              ),
             ),
           
           SliverToBoxAdapter(
@@ -666,9 +670,11 @@ class _HomeTabState extends ConsumerState<HomeTab> with AutomaticKeepAliveClient
     );
   }
 
-  Widget _buildRecentAccess(List<RecentAccessItem> items, ColorScheme colorScheme) {
-    final historyItems = ref.read(downloadHistoryProvider).items;
-    
+  Widget _buildRecentAccess(
+    List<RecentAccessItem> items,
+    List<DownloadHistoryItem> historyItems,
+    ColorScheme colorScheme,
+  ) {
     // Group download history by album
     final albumGroups = <String, List<DownloadHistoryItem>>{};
     for (final h in historyItems) {

lib/screens/queue_screen.dart

@@ -11,20 +11,20 @@ class QueueScreen extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final queueState = ref.watch(downloadQueueProvider);
+    final items = ref.watch(downloadQueueProvider.select((s) => s.items));
     final colorScheme = Theme.of(context).colorScheme;
 
     return Scaffold(
       appBar: AppBar(
         title: Text(context.l10n.queueTitle),
         actions: [
-          if (queueState.items.isNotEmpty)
+          if (items.isNotEmpty)
             IconButton(
               icon: const Icon(Icons.delete_sweep),
               onPressed: () => ref.read(downloadQueueProvider.notifier).clearCompleted(),
               tooltip: context.l10n.queueClearCompleted,
             ),
-          if (queueState.items.isNotEmpty)
+          if (items.isNotEmpty)
             IconButton(
               icon: const Icon(Icons.clear_all),
               onPressed: () => _showClearAllDialog(context, ref),
@@ -32,11 +32,12 @@ class QueueScreen extends ConsumerWidget {
             ),
         ],
       ),
-      body: queueState.items.isEmpty
+      body: items.isEmpty
           ? _buildEmptyState(context, colorScheme)
           : ListView.builder(
-              itemCount: queueState.items.length,
-              itemBuilder: (context, index) => _buildQueueItem(context, ref, queueState.items[index], colorScheme),
+              itemCount: items.length,
+              itemBuilder: (context, index) =>
+                  _buildQueueItem(context, ref, items[index], colorScheme),
             ),
     );
   }

lib/screens/search_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:cached_network_image/cached_network_image.dart';
 import 'package:spotiflac_android/services/cover_cache_manager.dart';
+import 'package:spotiflac_android/models/track.dart';
 import 'package:spotiflac_android/providers/track_provider.dart';
 import 'package:spotiflac_android/providers/download_queue_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
@@ -44,22 +45,22 @@ class _SearchScreenState extends ConsumerState<SearchScreen> {
     }
   }
 
-  void _downloadTrack(int index) {
-    final trackState = ref.read(trackProvider);
-    if (index >= 0 && index < trackState.tracks.length) {
-      final track = trackState.tracks[index];
-      final settings = ref.read(settingsProvider);
-      ref.read(downloadQueueProvider.notifier).addToQueue(track, settings.defaultService);
-      ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text('Added "${track.name}" to queue')),
-      );
-    }
+  void _downloadTrack(Track track) {
+    final settings = ref.read(settingsProvider);
+    ref.read(downloadQueueProvider.notifier).addToQueue(
+      track,
+      settings.defaultService,
+    );
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(content: Text('Added "${track.name}" to queue')),
+    );
   }
 
   @override
   Widget build(BuildContext context) {
     final trackState = ref.watch(trackProvider);
     final colorScheme = Theme.of(context).colorScheme;
+    final tracks = trackState.tracks;
 
     return Scaffold(
       appBar: AppBar(
@@ -96,11 +97,12 @@ class _SearchScreenState extends ConsumerState<SearchScreen> {
               ),
             ),
           Expanded(
-            child: trackState.tracks.isEmpty
+            child: tracks.isEmpty
                 ? _buildEmptyState(colorScheme)
                 : ListView.builder(
-                    itemCount: trackState.tracks.length,
-                    itemBuilder: (context, index) => _buildTrackTile(index, colorScheme),
+                    itemCount: tracks.length,
+                    itemBuilder: (context, index) =>
+                        _buildTrackTile(tracks[index], colorScheme),
                   ),
           ),
         ],
@@ -130,8 +132,7 @@ class _SearchScreenState extends ConsumerState<SearchScreen> {
     );
   }
 
-  Widget _buildTrackTile(int index, ColorScheme colorScheme) {
-    final track = ref.watch(trackProvider).tracks[index];
+  Widget _buildTrackTile(Track track, ColorScheme colorScheme) {
     return ListTile(
       leading: track.coverUrl != null
           ? ClipRRect(
@@ -175,9 +176,9 @@ child: CachedNetworkImage(
       ),
       trailing: IconButton(
         icon: Icon(Icons.download, color: colorScheme.primary),
-        onPressed: () => _downloadTrack(index),
+        onPressed: () => _downloadTrack(track),
       ),
-      onTap: () => _downloadTrack(index),
+      onTap: () => _downloadTrack(track),
     );
   }
 }