feat: add resolve API with SongLink fallback, fix multi-artist tags (#288), and cleanup

Resolve API (api.zarz.moe):
- Refactor songlink.go: Spotify URLs use resolve API, non-Spotify uses SongLink API
- Add SongLink fallback when resolve API fails for Spotify (two-layer resilience)
- Remove dead code: page parser, XOR-obfuscated keys, legacy helpers

Multi-artist tag fix (#288):
- Add RewriteSplitArtistTags() in Go to rewrite ARTIST/ALBUMARTIST as split Vorbis comments
- Wire method channel handler in Android (MainActivity.kt) and iOS (AppDelegate.swift)
- Add PlatformBridge.rewriteSplitArtistTags() in Dart
- Call native FLAC rewriter after FFmpeg embed when split_vorbis mode is active
- Extract deezerTrackArtistDisplay() helper to use Contributors in album/playlist tracks

Code cleanup:
- Remove unused imports, dead code, and redundant comments across Go and Dart
- Fix build: remove stale getQobuzDebugKey() reference in deezer_download.go

lib/services/cover_cache_manager.dart

@@ -21,7 +21,6 @@ class CoverCacheManager {
 
   static CacheManager get instance {
     if (!_initialized || _instance == null) {
-      // Fallback to default cache manager if not initialized
       debugPrint('CoverCacheManager: Not initialized, using DefaultCacheManager');
       return DefaultCacheManager();
     }
@@ -36,13 +35,13 @@ class CoverCacheManager {
     try {
       final appDir = await getApplicationSupportDirectory();
       _cachePath = p.join(appDir.path, 'cover_cache');
-      
+
       await Directory(_cachePath!).create(recursive: true);
-      
+
       debugPrint('CoverCacheManager: Initializing at $_cachePath');
 
       _instance = _createManager(_cachePath!);
-      
+
       _initialized = true;
       debugPrint('CoverCacheManager: Initialized successfully');
     } catch (e) {
@@ -60,22 +59,18 @@ class CoverCacheManager {
 
     if (instance == null || cachePath == null) return;
 
-    // Ask cache manager to clear indexed entries first.
     try {
       await instance.emptyCache();
     } catch (e) {
       debugPrint('CoverCacheManager: emptyCache failed, fallback to wipe: $e');
     }
 
-    // Then wipe the directory to remove orphaned files/metadata leftovers.
     await _wipeDirectory(cachePath);
 
-    // Clear in-memory image cache so cleared covers are not retained in RAM.
     final imageCache = PaintingBinding.instance.imageCache;
     imageCache.clear();
     imageCache.clearLiveImages();
 
-    // Reset manager memory/index state after on-disk wipe.
     instance.store.emptyMemoryCache();
     _instance = _createManager(cachePath);
     _initialized = true;
@@ -124,7 +119,6 @@ class CoverCacheManager {
         _cacheKey,
         stalePeriod: _maxCacheAge,
         maxNrOfCacheObjects: _maxCacheObjects,
-        // Use path only (not databaseName) to store database in persistent directory
         repo: JsonCacheInfoRepository(path: cachePath),
         fileSystem: IOFileSystem(cachePath),
         fileService: HttpFileService(),

lib/services/ffmpeg_service.dart

@@ -1350,7 +1350,6 @@ class FFmpegService {
       return null;
     }
 
-    // Lossless targets: dedicated single-pass methods
     if (format == 'alac') {
       return _convertToAlac(
         inputPath: inputPath,
@@ -1369,7 +1368,6 @@ class FFmpegService {
       );
     }
 
-    // Lossy targets: MP3 / Opus
     final extension = format == 'opus' ? '.opus' : '.mp3';
     final outputPath = _buildOutputPath(inputPath, extension);
 
@@ -1966,7 +1964,6 @@ class FFmpegService {
   }
 }
 
-/// Track info for CUE splitting, passed from the CUE parser
 class CueSplitTrackInfo {
   final int number;
   final String title;

lib/services/history_database.dart

@@ -9,10 +9,8 @@ import 'package:spotiflac_android/utils/logger.dart';
 final _log = AppLogger('HistoryDatabase');
 final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
 
-/// Cached current iOS container path for path normalization
 String? _currentContainerPath;
 
-/// Provides O(1) lookups by spotify_id and isrc with proper indexing
 class HistoryDatabase {
   static final HistoryDatabase instance = HistoryDatabase._init();
   static Database? _database;
@@ -102,21 +100,16 @@ class HistoryDatabase {
     }
   }
 
-  /// Pattern to match iOS container paths
-  /// Example: /var/mobile/Containers/Data/Application/UUID-HERE/Documents/...
   static final _iosContainerPattern = RegExp(
     r'/var/mobile/Containers/Data/Application/[A-F0-9\-]+/',
     caseSensitive: false,
   );
 
-  /// Initialize and cache the current iOS container path
   Future<void> _initContainerPath() async {
     if (!Platform.isIOS || _currentContainerPath != null) return;
 
     try {
       final docDir = await getApplicationDocumentsDirectory();
-      // Extract container path up to and including the UUID folder
-      // e.g., /var/mobile/Containers/Data/Application/UUID/
       final match = _iosContainerPattern.firstMatch(docDir.path);
       if (match != null) {
         _currentContainerPath = match.group(0);
@@ -127,13 +120,10 @@ class HistoryDatabase {
     }
   }
 
-  /// Normalize iOS file path by replacing old container UUID with current one
-  /// This fixes the issue where iOS changes container UUID after app updates
   String _normalizeIosPath(String? filePath) {
     if (filePath == null || filePath.isEmpty) return filePath ?? '';
     if (!Platform.isIOS || _currentContainerPath == null) return filePath;
 
-    // Check if path contains an iOS container path
     if (_iosContainerPattern.hasMatch(filePath)) {
       final normalized = filePath.replaceFirst(
         _iosContainerPattern,
@@ -148,8 +138,6 @@ class HistoryDatabase {
     return filePath;
   }
 
-  /// Migrate iOS paths in database to use current container UUID
-  /// This is called once after app update if container changed
   Future<bool> migrateIosContainerPaths() async {
     if (!Platform.isIOS) return false;
 
@@ -205,8 +193,6 @@ class HistoryDatabase {
     }
   }
 
-  /// Migrate data from SharedPreferences to SQLite
-  /// Returns true if migration was performed, false if already migrated
   Future<bool> migrateFromSharedPreferences() async {
     final prefs = await _prefs;
     final migrationKey = 'history_migrated_to_sqlite';
@@ -243,7 +229,6 @@ class HistoryDatabase {
 
       await batch.commit(noResult: true);
 
-      // Mark as migrated but keep old data for safety
       await prefs.setBool(migrationKey, true);
       _log.i('Migration complete: ${jsonList.length} items');
 
@@ -254,7 +239,6 @@ class HistoryDatabase {
     }
   }
 
-  /// Convert JSON format (camelCase) to DB row (snake_case)
   Map<String, dynamic> _jsonToDbRow(Map<String, dynamic> json) {
     return {
       'id': json['id'],
@@ -286,8 +270,6 @@ class HistoryDatabase {
     };
   }
 
-  /// Convert DB row (snake_case) to JSON format (camelCase)
-  /// Also normalizes iOS paths if container UUID changed
   Map<String, dynamic> _dbRowToJson(Map<String, dynamic> row) {
     return {
       'id': row['id'],
@@ -342,7 +324,6 @@ class HistoryDatabase {
     await batch.commit(noResult: true);
   }
 
-  /// Get all history items ordered by download date (newest first)
   Future<List<Map<String, dynamic>>> getAll({int? limit, int? offset}) async {
     final db = await database;
     final rows = await db.query(
@@ -366,7 +347,6 @@ class HistoryDatabase {
     return _dbRowToJson(rows.first);
   }
 
-  /// Get item by Spotify ID - O(1) with index
   Future<Map<String, dynamic>?> getBySpotifyId(String spotifyId) async {
     final db = await database;
     final rows = await db.query(
@@ -379,7 +359,6 @@ class HistoryDatabase {
     return _dbRowToJson(rows.first);
   }
 
-  /// Get item by ISRC - O(1) with index
   Future<Map<String, dynamic>?> getByIsrc(String isrc) async {
     final db = await database;
     final rows = await db.query(
@@ -392,7 +371,6 @@ class HistoryDatabase {
     return _dbRowToJson(rows.first);
   }
 
-  /// Check if spotify_id exists - O(1) with index
   Future<bool> existsBySpotifyId(String spotifyId) async {
     final db = await database;
     final result = await db.rawQuery(
@@ -402,7 +380,6 @@ class HistoryDatabase {
     return result.isNotEmpty;
   }
 
-  /// Get all spotify_ids as Set for fast in-memory lookup
   Future<Set<String>> getAllSpotifyIds() async {
     final db = await database;
     final rows = await db.rawQuery(
@@ -433,7 +410,6 @@ class HistoryDatabase {
     return Sqflite.firstIntValue(result) ?? 0;
   }
 
-  /// Find existing item by spotify_id or isrc (for deduplication)
   Future<Map<String, dynamic>?> findExisting({
     String? spotifyId,
     String? isrc,
@@ -442,7 +418,6 @@ class HistoryDatabase {
       final bySpotify = await getBySpotifyId(spotifyId);
       if (bySpotify != null) return bySpotify;
 
-      // Check for deezer: prefix matching
       if (spotifyId.startsWith('deezer:')) {
         final deezerId = spotifyId.substring(7);
         final db = await database;
@@ -469,7 +444,6 @@ class HistoryDatabase {
     _database = null;
   }
 
-  /// Update file path for a history entry (e.g. after format conversion)
   Future<void> updateFilePath(
     String id,
     String newFilePath, {
@@ -524,8 +498,6 @@ class HistoryDatabase {
     await db.update('history', values, where: 'id = ?', whereArgs: [id]);
   }
 
-  /// Get all file paths from download history
-  /// Used to exclude downloaded files from local library scan
   Future<Set<String>> getAllFilePaths() async {
     final db = await database;
     final rows = await db.rawQuery(
@@ -534,8 +506,6 @@ class HistoryDatabase {
     return rows.map((r) => r['file_path'] as String).toSet();
   }
 
-  /// Get all entries with file paths for orphan detection
-  /// Returns list of (id, file_path, storage_mode, download_tree_uri, saf_relative_dir, saf_file_name)
   Future<List<Map<String, dynamic>>> getAllEntriesWithPaths() async {
     final db = await database;
     final rows = await db.rawQuery('''
@@ -569,7 +539,6 @@ class HistoryDatabase {
     return rows.map((r) => Map<String, dynamic>.from(r)).toList();
   }
 
-  /// Delete multiple entries by IDs
   Future<int> deleteByIds(List<String> ids) async {
     if (ids.isEmpty) return 0;
 

lib/services/library_database.dart

@@ -96,7 +96,6 @@ class LocalLibraryItem {
         format: json['format'] as String?,
       );
 
-  /// Create a unique key for matching tracks
   String get matchKey =>
       '${trackName.toLowerCase()}|${artistName.toLowerCase()}';
   String get albumKey =>
@@ -183,13 +182,11 @@ class LibraryDatabase {
     }
 
     if (oldVersion < 3) {
-      // Add file_mod_time column for incremental scanning
       await db.execute('ALTER TABLE library ADD COLUMN file_mod_time INTEGER');
       _log.i('Added file_mod_time column for incremental scanning');
     }
 
     if (oldVersion < 4) {
-      // Add bitrate column for lossy format quality info
       await db.execute('ALTER TABLE library ADD COLUMN bitrate INTEGER');
       _log.i('Added bitrate column for lossy format quality');
     }
@@ -475,8 +472,6 @@ class LibraryDatabase {
     _database = null;
   }
 
-  /// Get all file paths with their modification times for incremental scanning
-  /// Returns a map of filePath -> fileModTime (unix timestamp in milliseconds)
   Future<Map<String, int>> getFileModTimes() async {
     final db = await database;
     final rows = await db.rawQuery(
@@ -491,8 +486,6 @@ class LibraryDatabase {
     return result;
   }
 
-  /// Export file modification times to a compact line-based snapshot that
-  /// native code can read without receiving a large method-channel payload.
   Future<String> writeFileModTimesSnapshot() async {
     final db = await database;
     final rows = await db.rawQuery(
@@ -519,7 +512,6 @@ class LibraryDatabase {
     return file.path;
   }
 
-  /// Update file_mod_time for existing rows using file_path as key.
   Future<void> updateFileModTimes(Map<String, int> fileModTimes) async {
     if (fileModTimes.isEmpty) return;
     final db = await database;
@@ -535,7 +527,6 @@ class LibraryDatabase {
     await batch.commit(noResult: true);
   }
 
-  /// Get all file paths in the library (for detecting deleted files)
   Future<Set<String>> getAllFilePaths() async {
     final db = await database;
     final rows = await db.rawQuery('SELECT file_path FROM library');

lib/services/platform_bridge.dart

@@ -422,6 +422,21 @@ class PlatformBridge {
     return jsonDecode(result as String) as Map<String, dynamic>;
   }
 
+  /// Rewrites ARTIST/ALBUMARTIST Vorbis comments as multiple split entries
+  /// using the native Go FLAC writer, fixing FFmpeg's tag deduplication.
+  static Future<Map<String, dynamic>> rewriteSplitArtistTags(
+    String filePath,
+    String artist,
+    String albumArtist,
+  ) async {
+    final result = await _channel.invokeMethod('rewriteSplitArtistTags', {
+      'file_path': filePath,
+      'artist': artist,
+      'album_artist': albumArtist,
+    });
+    return jsonDecode(result as String) as Map<String, dynamic>;
+  }
+
   static Future<bool> writeTempToSaf(String tempPath, String safUri) async {
     final result = await _channel.invokeMethod('writeTempToSaf', {
       'temp_path': tempPath,

lib/services/share_intent_service.dart

@@ -10,7 +10,6 @@ class ShareIntentService {
   factory ShareIntentService() => _instance;
   ShareIntentService._internal();
 
-  // Spotify patterns
   static final RegExp _spotifyUriPattern = RegExp(
     r'spotify:(track|album|playlist|artist):[a-zA-Z0-9]+',
   );
@@ -18,7 +17,6 @@ class ShareIntentService {
     r'https?://open\.spotify\.com/(track|album|playlist|artist)/[a-zA-Z0-9]+(\?[^\s]*)?',
   );
 
-  // Deezer patterns
   static final RegExp _deezerUrlPattern = RegExp(
     r'https?://(www\.)?deezer\.com/(track|album|playlist|artist)/\d+(\?[^\s]*)?',
   );
@@ -26,17 +24,14 @@ class ShareIntentService {
     r'https?://deezer\.page\.link/[a-zA-Z0-9]+',
   );
 
-  // Tidal patterns
   static final RegExp _tidalUrlPattern = RegExp(
     r'https?://(listen\.)?tidal\.com/(track|album|playlist|artist)/[a-zA-Z0-9-]+(\?[^\s]*)?',
   );
 
-  // YouTube Music patterns
   static final RegExp _ytMusicUrlPattern = RegExp(
     r'https?://music\.youtube\.com/(watch\?v=|playlist\?list=|channel/|browse/)[a-zA-Z0-9_-]+([?&][^\s]*)?',
   );
 
-  // Standard YouTube patterns (youtu.be short links and www.youtube.com/watch)
   static final RegExp _youtubeUrlPattern = RegExp(
     r'https?://(youtu\.be/[a-zA-Z0-9_-]+|www\.youtube\.com/watch\?v=[a-zA-Z0-9_-]+)([?&][^\s]*)?',
   );
@@ -117,7 +112,6 @@ class ShareIntentService {
       final match = pattern.firstMatch(text);
       if (match != null) {
         final fullUrl = match.group(0)!;
-        // Keep query params for YouTube URLs (needed for ?v=, ?list=, etc.)
         if (pattern == _ytMusicUrlPattern || pattern == _youtubeUrlPattern) {
           return fullUrl;
         }