refactor(player): centralize chapter traversal

lib/media/media_source_info.dart

@@ -238,6 +238,30 @@ class MediaChapter {
     }
     return null;
   }
+
+  /// Find the chapter targeted by next/previous traversal. Previous traversal
+  /// restarts the current chapter only after [previousRestartThreshold]; before
+  /// that it selects an earlier chapter.
+  static int? seekTargetIndex(
+    Duration position,
+    List<MediaChapter> chapters, {
+    required bool forward,
+    Duration previousRestartThreshold = const Duration(seconds: 3),
+  }) {
+    final positionMs = position.inMilliseconds;
+    if (forward) {
+      for (int i = 0; i < chapters.length; i++) {
+        if ((chapters[i].startTimeOffset ?? 0) > positionMs) return i;
+      }
+      return null;
+    }
+
+    final thresholdMs = previousRestartThreshold.inMilliseconds;
+    for (int i = chapters.length - 1; i >= 0; i--) {
+      if (positionMs > (chapters[i].startTimeOffset ?? 0) + thresholdMs) return i;
+    }
+    return null;
+  }
 }
 
 class MediaMarker {

lib/widgets/video_controls/desktop_video_controls.dart

@@ -1054,28 +1054,14 @@ class DesktopVideoControlsState extends State<DesktopVideoControls> {
 
   /// Returns the label of the next chapter the user would seek to, or null.
   String? _getNextChapterLabel(Duration position) {
-    if (widget.chapters.isEmpty) return null;
+    final index = MediaChapter.seekTargetIndex(position, widget.chapters, forward: true);
-    final currentPositionMs = position.inMilliseconds;
+    return index == null ? null : widget.chapters[index].label;
-    for (final chapter in widget.chapters) {
-      final chapterStart = chapter.startTimeOffset ?? 0;
-      if (chapterStart > currentPositionMs) {
-        return chapter.label;
-      }
-    }
-    return null;
   }
 
   /// Returns the label of the previous chapter the user would seek to, or null.
   String? _getPreviousChapterLabel(Duration position) {
-    if (widget.chapters.isEmpty) return null;
+    final index = MediaChapter.seekTargetIndex(position, widget.chapters, forward: false);
-    final currentPositionMs = position.inMilliseconds;
+    return index == null ? null : widget.chapters[index].label;
-    for (int i = widget.chapters.length - 1; i >= 0; i--) {
-      final chapterStart = widget.chapters[i].startTimeOffset ?? 0;
-      if (currentPositionMs > chapterStart + 3000) {
-        return widget.chapters[i].label;
-      }
-    }
-    return null;
   }
 
   Widget _buildFocusableButton({

lib/widgets/video_controls/parts/playback_input.dart

@@ -31,25 +31,10 @@ extension _PlexVideoControlsPlaybackInputMethods on _PlexVideoControlsState {
       return;
     }
 
-    final currentPositionMs = widget.player.state.position.inMilliseconds;
+    final targetIndex = MediaChapter.seekTargetIndex(widget.player.state.position, _chapters, forward: forward);
-
+    if (targetIndex != null) {
-    if (forward) {
+      await _seekToPosition(_chapters[targetIndex].startTime);
-      for (final chapter in _chapters) {
+    } else if (!forward) {
-        final chapterStart = chapter.startTimeOffset ?? 0;
-        if (chapterStart > currentPositionMs) {
-          await _seekToPosition(Duration(milliseconds: chapterStart));
-          return;
-        }
-      }
-    } else {
-      for (int i = _chapters.length - 1; i >= 0; i--) {
-        final chapterStart = _chapters[i].startTimeOffset ?? 0;
-        if (currentPositionMs > chapterStart + 3000) {
-          // If more than 3 seconds into chapter, go to start of current chapter
-          await _seekToPosition(Duration(milliseconds: chapterStart));
-          return;
-        }
-      }
       await _seekToPosition(Duration.zero);
     }
   }

lib/widgets/video_controls/widgets/content_strip.dart

@@ -110,7 +110,7 @@ class ContentStripState extends State<ContentStrip> {
   /// Request focus on the current chapter or queue item (called by parent when strip appears).
   void requestInitialFocus() {
     if (_activeTab == _StripTab.chapters && _chapterFocusNodes.isNotEmpty) {
-      final currentIndex = _getCurrentChapterIndex();
+      final currentIndex = MediaChapter.indexAtPosition(widget.player.state.position, widget.chapters);
       final idx = (currentIndex ?? 0).clamp(0, _chapterFocusNodes.length - 1);
       _chapterFocusNodes[idx].requestFocus();
       _scrollToFocusedNode(_chapterFocusNodes[idx]);
@@ -122,21 +122,6 @@ class ContentStripState extends State<ContentStrip> {
     }
   }
 
-  int? _getCurrentChapterIndex() {
-    final currentPositionMs = widget.player.state.position.inMilliseconds;
-    for (int i = 0; i < widget.chapters.length; i++) {
-      final chapter = widget.chapters[i];
-      final startMs = chapter.startTimeOffset ?? 0;
-      final endMs =
-          chapter.endTimeOffset ??
-          (i < widget.chapters.length - 1 ? widget.chapters[i + 1].startTimeOffset ?? 0 : double.maxFinite.toInt());
-      if (currentPositionMs >= startMs && currentPositionMs < endMs) {
-        return i;
-      }
-    }
-    return null;
-  }
-
   Future<void> _handleChapterTap(Duration position) async {
     final clamped = clampSeekPosition(widget.player, position);
     await (widget.onSeekRequested ?? widget.player.seek)(clamped);
@@ -226,7 +211,8 @@ class ContentStripState extends State<ContentStrip> {
         });
         WidgetsBinding.instance.addPostFrameCallback((_) {
           if (mounted && _chapterFocusNodes.isNotEmpty) {
-            final idx = (_getCurrentChapterIndex() ?? 0).clamp(0, _chapterFocusNodes.length - 1);
+            final currentIndex = MediaChapter.indexAtPosition(widget.player.state.position, widget.chapters);
+            final idx = (currentIndex ?? 0).clamp(0, _chapterFocusNodes.length - 1);
             _chapterFocusNodes[idx].requestFocus();
             _scrollToFocusedNode(_chapterFocusNodes[idx]);
           }

test/media/media_source_info_test.dart

@@ -3,6 +3,40 @@ import 'package:plezy/media/media_source_info.dart';
 import 'package:plezy/utils/track_label_builder.dart';
 
 void main() {
+  group('MediaChapter traversal', () {
+    final chapters = [
+      MediaChapter(id: 1, startTimeOffset: 0, title: 'One'),
+      MediaChapter(id: 2, startTimeOffset: 10000, title: 'Two'),
+      MediaChapter(id: 3, startTimeOffset: 20000, title: 'Three'),
+    ];
+
+    test('forward traversal uses the first strictly later chapter', () {
+      expect(MediaChapter.seekTargetIndex(const Duration(milliseconds: 9999), chapters, forward: true), 1);
+      expect(MediaChapter.seekTargetIndex(const Duration(milliseconds: 10000), chapters, forward: true), 2);
+      expect(MediaChapter.seekTargetIndex(const Duration(milliseconds: 20000), chapters, forward: true), isNull);
+    });
+
+    test('previous traversal preserves the strict three-second restart threshold', () {
+      expect(MediaChapter.seekTargetIndex(const Duration(milliseconds: 13000), chapters, forward: false), 0);
+      expect(MediaChapter.seekTargetIndex(const Duration(milliseconds: 13001), chapters, forward: false), 1);
+      expect(MediaChapter.seekTargetIndex(const Duration(milliseconds: 3000), chapters, forward: false), isNull);
+    });
+
+    test('handles empty chapters and null starts', () {
+      expect(MediaChapter.seekTargetIndex(Duration.zero, const [], forward: true), isNull);
+      final missingStart = [MediaChapter(id: 1), MediaChapter(id: 2, startTimeOffset: 5000)];
+      expect(MediaChapter.seekTargetIndex(Duration.zero, missingStart, forward: true), 1);
+      expect(MediaChapter.seekTargetIndex(const Duration(milliseconds: 3001), missingStart, forward: false), 0);
+    });
+
+    test('indexAtPosition uses start-inclusive and end-exclusive ranges', () {
+      expect(MediaChapter.indexAtPosition(Duration.zero, chapters), 0);
+      expect(MediaChapter.indexAtPosition(const Duration(milliseconds: 9999), chapters), 0);
+      expect(MediaChapter.indexAtPosition(const Duration(milliseconds: 10000), chapters), 1);
+      expect(MediaChapter.indexAtPosition(const Duration(hours: 1), chapters), 2);
+    });
+  });
+
   group('MediaSubtitleTrack label', () {
     test('language leads; a bare "Forced" title folds into the suffix', () {
       final track = MediaSubtitleTrack(