refactor: use audio_conversion_utils in downloaded_album_screen

- Replace inline format detection with convertibleAudioSourceFormat()
- Replace inline conversion rules with canConvertAudioFormat()
- Add unit tests for Dolby format detection and conversion rules

lib/screens/downloaded_album_screen.dart

@@ -945,35 +945,24 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
     for (final id in _selectedIds) {
       final item = tracksById[id];
       if (item == null) continue;
-      final nameToCheck =
-          (item.safFileName != null && item.safFileName!.isNotEmpty)
-          ? item.safFileName!.toLowerCase()
-          : item.filePath.toLowerCase();
-      final ext = nameToCheck.endsWith('.flac')
-          ? 'FLAC'
-          : nameToCheck.endsWith('.alac')
-          ? 'ALAC'
-          : nameToCheck.endsWith('.m4a')
-          ? 'M4A'
-          : (nameToCheck.endsWith('.aac') || nameToCheck.endsWith('.mp4a'))
-          ? 'AAC'
-          : nameToCheck.endsWith('.mp3')
-          ? 'MP3'
-          : (nameToCheck.endsWith('.opus') || nameToCheck.endsWith('.ogg'))
-          ? 'Opus'
-          : null;
-      if (ext != null) sourceFormats.add(ext);
+      final sourceFormat = convertibleAudioSourceFormat(
+        storedFormat: item.format,
+        filePath: item.filePath,
+        fileName: item.safFileName,
+      );
+      if (sourceFormat != null) sourceFormats.add(sourceFormat);
     }
 
-    final formats = ['ALAC', 'FLAC', 'AAC', 'MP3', 'Opus'].where((target) {
-      return sourceFormats.any((src) {
-        if (src == target) return false;
-        final isLosslessTarget = target == 'ALAC' || target == 'FLAC';
-        final isLosslessSource = src == 'FLAC' || src == 'ALAC' || src == 'M4A';
-        if (isLosslessTarget && !isLosslessSource) return false;
-        return true;
-      });
-    }).toList();
+    final formats = audioConversionTargetFormats
+        .where(
+          (target) => sourceFormats.any(
+            (source) => canConvertAudioFormat(
+              sourceFormat: source,
+              targetFormat: target,
+            ),
+          ),
+        )
+        .toList();
 
     if (formats.isEmpty) return;
 
@@ -1148,23 +1137,18 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
     for (final id in _selectedIds) {
       final item = tracksById[id];
       if (item == null) continue;
-      final nameToCheck =
-          (item.safFileName != null && item.safFileName!.isNotEmpty)
-          ? item.safFileName!.toLowerCase()
-          : item.filePath.toLowerCase();
-      final ext = nameToCheck.endsWith('.flac')
-          ? 'FLAC'
-          : nameToCheck.endsWith('.m4a')
-          ? 'M4A'
-          : nameToCheck.endsWith('.mp3')
-          ? 'MP3'
-          : (nameToCheck.endsWith('.opus') || nameToCheck.endsWith('.ogg'))
-          ? 'Opus'
-          : null;
-      if (ext == null || ext == targetFormat) continue;
-      final isLosslessTarget = targetFormat == 'ALAC' || targetFormat == 'FLAC';
-      final isLosslessSource = ext == 'FLAC' || ext == 'M4A';
-      if (isLosslessTarget && !isLosslessSource) continue;
+      final sourceFormat = convertibleAudioSourceFormat(
+        storedFormat: item.format,
+        filePath: item.filePath,
+        fileName: item.safFileName,
+      );
+      if (sourceFormat == null ||
+          !canConvertAudioFormat(
+            sourceFormat: sourceFormat,
+            targetFormat: targetFormat,
+          )) {
+        continue;
+      }
       selected.add(item);
     }
 

test/models_and_utils_test.dart

@@ -7,6 +7,7 @@ import 'package:spotiflac_android/models/track.dart';
 import 'package:spotiflac_android/services/app_remote_config_service.dart';
 import 'package:spotiflac_android/services/download_request_payload.dart';
 import 'package:spotiflac_android/utils/artist_utils.dart';
+import 'package:spotiflac_android/utils/audio_conversion_utils.dart';
 import 'package:spotiflac_android/utils/mime_utils.dart';
 import 'package:spotiflac_android/utils/path_match_keys.dart';
 import 'package:spotiflac_android/utils/string_utils.dart';
@@ -426,6 +427,49 @@ void main() {
     });
   });
 
+  group('audio conversion utils', () {
+    test('detects Dolby formats from stored scan format before file extension', () {
+      expect(
+        convertibleAudioSourceFormat(
+          storedFormat: 'eac3',
+          filePath: 'content://media/song.m4a',
+        ),
+        'EAC3',
+      );
+      expect(
+        convertibleAudioSourceFormat(fileName: 'Song.ac-3'),
+        'AC3',
+      );
+      expect(
+        convertibleAudioSourceFormat(storedFormat: 'ac4'),
+        'AC4',
+      );
+    });
+
+    test('allows Dolby sources only for lossy batch conversion targets', () {
+      expect(
+        canConvertAudioFormat(sourceFormat: 'EAC3', targetFormat: 'MP3'),
+        isTrue,
+      );
+      expect(
+        canConvertAudioFormat(sourceFormat: 'EAC3', targetFormat: 'Opus'),
+        isTrue,
+      );
+      expect(
+        canConvertAudioFormat(sourceFormat: 'EAC3', targetFormat: 'AAC'),
+        isTrue,
+      );
+      expect(
+        canConvertAudioFormat(sourceFormat: 'EAC3', targetFormat: 'FLAC'),
+        isFalse,
+      );
+      expect(
+        canConvertAudioFormat(sourceFormat: 'EAC3', targetFormat: 'ALAC'),
+        isFalse,
+      );
+    });
+  });
+
   group('string utils', () {
     test('normalizes optional strings and cover references', () {
       expect(normalizeOptionalString(null), isNull);