perf: reduce queue and extension runtime overhead

lib/providers/download_queue_provider.dart

@@ -1861,27 +1861,37 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
         continue;
       }
 
+      final maxConcurrent = ref
+          .read(settingsProvider)
+          .concurrentDownloads
+          .clamp(1, 3);
+      if (activeDownloads.length >= maxConcurrent) {
+        // Keep pause/settings changes responsive without rescanning the full
+        // queue while every worker slot is already occupied.
+        await Future.any([
+          Future.any(activeDownloads.values),
+          Future<void>.delayed(_queueSchedulingInterval),
+        ]);
+        continue;
+      }
+
+      final availableSlots = maxConcurrent - activeDownloads.length;
       final queuedItems = state.items
           .where(
             (item) =>
                 item.status == DownloadStatus.queued &&
                 !_pausePendingItemIds.contains(item.id),
           )
-          .toList();
+          .take(availableSlots)
+          .toList(growable: false);
 
       if (queuedItems.isEmpty && activeDownloads.isEmpty) {
         _log.d('No more items to process');
         break;
       }
 
-      final maxConcurrent = ref
-          .read(settingsProvider)
-          .concurrentDownloads
-          .clamp(1, 3);
-      while (activeDownloads.length < maxConcurrent &&
-          queuedItems.isNotEmpty &&
-          !state.isPaused) {
-        final item = queuedItems.removeAt(0);
+      for (final item in queuedItems) {
+        if (state.isPaused) break;
 
         updateItemStatus(item.id, DownloadStatus.downloading);
 

lib/providers/download_queue_state.dart

@@ -80,6 +80,7 @@ class DownloadQueueLookup {
   final Map<String, DownloadItem> byItemId;
   final Map<String, int> indexByItemId;
   final List<String> itemIds;
+  final List<String> notCompletedItemIds;
   final int queuedCount;
   final int completedCount;
   final int failedCount;
@@ -91,6 +92,7 @@ class DownloadQueueLookup {
       byItemId = const {},
       indexByItemId = const {},
       itemIds = const [],
+      notCompletedItemIds = const [],
       queuedCount = 0,
       completedCount = 0,
       failedCount = 0,
@@ -102,6 +104,7 @@ class DownloadQueueLookup {
     required this.byItemId,
     required this.indexByItemId,
     required this.itemIds,
+    required this.notCompletedItemIds,
     required this.queuedCount,
     required this.completedCount,
     required this.failedCount,
@@ -114,6 +117,7 @@ class DownloadQueueLookup {
     final byItemId = <String, DownloadItem>{};
     final indexByItemId = <String, int>{};
     final itemIds = <String>[];
+    final notCompletedItemIds = <String>[];
     var queuedCount = 0;
     var completedCount = 0;
     var failedCount = 0;
@@ -125,6 +129,9 @@ class DownloadQueueLookup {
       byItemId[item.id] = item;
       indexByItemId[item.id] = index;
       itemIds.add(item.id);
+      if (item.status != DownloadStatus.completed) {
+        notCompletedItemIds.add(item.id);
+      }
       if (_countsAsQueued(item.status)) queuedCount++;
       if (item.status == DownloadStatus.completed) completedCount++;
       if (item.status == DownloadStatus.failed) failedCount++;
@@ -136,6 +143,7 @@ class DownloadQueueLookup {
       byItemId: Map.unmodifiable(byItemId),
       indexByItemId: Map.unmodifiable(indexByItemId),
       itemIds: List.unmodifiable(itemIds),
+      notCompletedItemIds: List.unmodifiable(notCompletedItemIds),
       queuedCount: queuedCount,
       completedCount: completedCount,
       failedCount: failedCount,
@@ -185,6 +193,7 @@ class DownloadQueueLookup {
     var nextFailedCount = failedCount;
     var nextActiveDownloadsCount = activeDownloadsCount;
     var nextFinalizingCount = finalizingCount;
+    var notCompletedMembershipChanged = false;
     Map<String, DownloadItem>? nextByItemId;
     Map<String, DownloadItem>? nextByTrackId;
 
@@ -195,6 +204,11 @@ class DownloadQueueLookup {
         return DownloadQueueLookup.fromItems(nextItems);
       }
 
+      if ((previous.status == DownloadStatus.completed) !=
+          (next.status == DownloadStatus.completed)) {
+        notCompletedMembershipChanged = true;
+      }
+
       nextByItemId ??= Map<String, DownloadItem>.from(byItemId);
       nextByItemId[next.id] = next;
       if (byTrackId[next.track.id]?.id == previous.id) {
@@ -237,6 +251,12 @@ class DownloadQueueLookup {
           : Map.unmodifiable(nextByItemId),
       indexByItemId: indexByItemId,
       itemIds: itemIds,
+      notCompletedItemIds: notCompletedMembershipChanged
+          ? List.unmodifiable([
+              for (final item in nextItems)
+                if (item.status != DownloadStatus.completed) item.id,
+            ])
+          : notCompletedItemIds,
       queuedCount: nextQueuedCount,
       completedCount: nextCompletedCount,
       failedCount: nextFailedCount,

lib/screens/now_playing_screen.dart

@@ -1314,6 +1314,7 @@ class _SyncedLyricsViewState extends ConsumerState<_SyncedLyricsView> {
   ProviderSubscription<bool>? _playingSubscription;
   ProviderSubscription<bool>? _loadingSubscription;
   Timer? _lineBoundaryTimer;
+  Timer? _userScrollIdleTimer;
   late List<GlobalKey> _lineKeys;
   int _active = -1;
   Duration _activeTransitionPosition = Duration.zero;
@@ -1432,6 +1433,7 @@ class _SyncedLyricsViewState extends ConsumerState<_SyncedLyricsView> {
     _playingSubscription?.close();
     _loadingSubscription?.close();
     _lineBoundaryTimer?.cancel();
+    _userScrollIdleTimer?.cancel();
     _scroll.dispose();
     super.dispose();
   }
@@ -1488,7 +1490,8 @@ class _SyncedLyricsViewState extends ConsumerState<_SyncedLyricsView> {
       onNotification: (notification) {
         if (notification.direction != ScrollDirection.idle) {
           _userScrolling = true;
-          Future.delayed(const Duration(seconds: 4), () {
+          _userScrollIdleTimer?.cancel();
+          _userScrollIdleTimer = Timer(const Duration(seconds: 4), () {
             if (mounted) _userScrolling = false;
           });
         }
@@ -1883,13 +1886,27 @@ class _SweepingTimedLyricTextState extends State<_SweepingTimedLyricText> {
             ? constraints.maxWidth
             : pendingPainter.width;
         final height = pendingPainter.height;
+        final segmentBoxes = <List<TextBox>>[];
+        var segmentOffset = 0;
+        for (final segment in widget.segments) {
+          final segmentEnd = segmentOffset + segment.length;
+          segmentBoxes.add(
+            highlightedPainter.getBoxesForSelection(
+              TextSelection(
+                baseOffset: segmentOffset,
+                extentOffset: segmentEnd,
+              ),
+            ),
+          );
+          segmentOffset = segmentEnd;
+        }
 
         return Semantics(
           label: widget.semanticsLabel,
           child: CustomPaint(
             size: Size(width, height),
             painter: _TimedLyricSweepPainter(
-              segments: widget.segments,
+              segmentBoxes: segmentBoxes,
               starts: widget.starts,
               ends: widget.ends,
               currentPosition: widget.currentPosition,
@@ -1905,7 +1922,7 @@ class _SweepingTimedLyricTextState extends State<_SweepingTimedLyricText> {
 }
 
 class _TimedLyricSweepPainter extends CustomPainter {
-  final List<String> segments;
+  final List<List<TextBox>> segmentBoxes;
   final List<Duration> starts;
   final List<Duration> ends;
   final Duration Function() currentPosition;
@@ -1913,7 +1930,7 @@ class _TimedLyricSweepPainter extends CustomPainter {
   final TextPainter highlightedPainter;
 
   _TimedLyricSweepPainter({
-    required this.segments,
+    required this.segmentBoxes,
     required this.starts,
     required this.ends,
     required this.currentPosition,
@@ -1929,9 +1946,7 @@ class _TimedLyricSweepPainter extends CustomPainter {
     final completedPath = Path();
     final partialBoxes = <(Rect, double)>[];
     final position = currentPosition();
-    var offset = 0;
-    for (var index = 0; index < segments.length; index++) {
-      final end = offset + segments[index].length;
+    for (var index = 0; index < segmentBoxes.length; index++) {
       final value = index < starts.length && index < ends.length
           ? syncedLyricSegmentProgress(
               position: position,
@@ -1939,11 +1954,8 @@ class _TimedLyricSweepPainter extends CustomPainter {
               end: ends[index],
             )
           : 0.0;
-      if (value > 0 && end > offset) {
-        final boxes = highlightedPainter.getBoxesForSelection(
-          TextSelection(baseOffset: offset, extentOffset: end),
-        );
-        for (final box in boxes) {
+      if (value > 0) {
+        for (final box in segmentBoxes[index]) {
           final rect = box.toRect();
           if (value >= 1) {
             completedPath.addRect(rect);
@@ -1952,7 +1964,6 @@ class _TimedLyricSweepPainter extends CustomPainter {
           }
         }
       }
-      offset = end;
     }
 
     if (!completedPath.getBounds().isEmpty) {
@@ -1998,7 +2009,7 @@ class _TimedLyricSweepPainter extends CustomPainter {
 
   @override
   bool shouldRepaint(covariant _TimedLyricSweepPainter oldDelegate) {
-    return oldDelegate.segments != segments ||
+    return oldDelegate.segmentBoxes != segmentBoxes ||
         oldDelegate.starts != starts ||
         oldDelegate.ends != ends ||
         oldDelegate.currentPosition != currentPosition ||

lib/screens/queue_tab.dart

@@ -1,6 +1,6 @@
 import 'dart:async';
 import 'dart:io';
-import 'package:flutter/foundation.dart';
+import 'package:flutter/foundation.dart' show ValueListenable;
 import 'package:flutter/material.dart';
 import 'package:spotiflac_android/services/shell_navigation_service.dart';
 import 'package:spotiflac_android/widgets/error_card.dart';
@@ -1223,7 +1223,10 @@ class _QueueTabState extends ConsumerState<QueueTab> {
 
     ref.listen(downloadQueueLookupProvider, (previous, next) {
       if (previous == null) return;
-      for (final id in previous.itemIds) {
+      if (identical(previous.notCompletedItemIds, next.notCompletedItemIds)) {
+        return;
+      }
+      for (final id in previous.notCompletedItemIds) {
         final prevItem = previous.byItemId[id];
         final nextItem = next.byItemId[id];
         if (prevItem == null) continue;
@@ -1656,16 +1659,9 @@ class _QueueTabState extends ConsumerState<QueueTab> {
     return Consumer(
       builder: (context, ref, child) {
         final queueCount = ref.watch(
-          downloadQueueLookupProvider.select((lookup) {
-            var count = 0;
-            for (final id in lookup.itemIds) {
-              final entry = lookup.byItemId[id];
-              if (entry != null && entry.status != DownloadStatus.completed) {
-                count++;
-              }
-            }
-            return count;
-          }),
+          downloadQueueLookupProvider.select(
+            (lookup) => lookup.notCompletedItemIds.length,
+          ),
         );
         final failedCount = ref.watch(
           downloadQueueProvider.select((state) => state.failedCount),

lib/screens/queue_tab_filter_widgets.dart

@@ -57,19 +57,10 @@ extension _QueueTabFilterWidgets on _QueueTabState {
         ? const <String>[]
         : ref
               .watch(
-                downloadQueueLookupProvider.select((lookup) {
-                  final ids = <String>[];
-                  for (final id in lookup.itemIds) {
-                    final entry = lookup.byItemId[id];
-                    if (entry != null &&
-                        entry.status != DownloadStatus.completed) {
-                      ids.add(id);
-                    }
-                  }
-                  return _QueueItemIdsSnapshot(ids);
-                }),
+                downloadQueueLookupProvider.select(
+                  (lookup) => lookup.notCompletedItemIds,
+                ),
               )
-              .ids
               .reversed
               .toList(growable: false);
 

lib/screens/queue_tab_helpers.dart

@@ -495,17 +495,3 @@ final _queueLibraryCountsProvider = FutureProvider.autoDispose
       );
       return LibraryDatabase.instance.getQueueCounts(request.toDbQuery());
     });
-
-class _QueueItemIdsSnapshot {
-  final List<String> ids;
-
-  const _QueueItemIdsSnapshot(this.ids);
-
-  @override
-  bool operator ==(Object other) =>
-      identical(this, other) ||
-      other is _QueueItemIdsSnapshot && listEquals(ids, other.ids);
-
-  @override
-  int get hashCode => Object.hashAll(ids);
-}

lib/services/music_player_service.dart

@@ -36,6 +36,24 @@ void setPlaybackNormalizationEnabled(bool enabled) {
   _activeMusicPlayerHandler?.reapplyNormalization();
 }
 
+List<int> buildShuffleCandidatePool({
+  required int mediaCount,
+  required int currentIndex,
+  required Iterable<int> recentIndices,
+}) {
+  final recent = recentIndices.toSet();
+  final pool = <int>[];
+  for (var index = 0; index < mediaCount; index++) {
+    if (index != currentIndex && !recent.contains(index)) pool.add(index);
+  }
+  if (pool.isEmpty) {
+    for (var index = 0; index < mediaCount; index++) {
+      if (index != currentIndex) pool.add(index);
+    }
+  }
+  return pool;
+}
+
 final AudioContext _musicAudioContext = AudioContext(
   android: const AudioContextAndroid(
     audioFocus: AndroidAudioFocus.none,
@@ -967,15 +985,11 @@ class MusicPlayerHandler extends BaseAudioHandler
 
   int _pickNextShuffle() {
     if (_media.length <= 1) return _index;
-    final pool = <int>[];
-    for (var i = 0; i < _media.length; i++) {
-      if (i != _index && !_recent.contains(i)) pool.add(i);
-    }
-    if (pool.isEmpty) {
-      for (var i = 0; i < _media.length; i++) {
-        if (i != _index) pool.add(i);
-      }
-    }
+    final pool = buildShuffleCandidatePool(
+      mediaCount: _media.length,
+      currentIndex: _index,
+      recentIndices: _recent,
+    );
     return pool[_random.nextInt(pool.length)];
   }