From a582d3a03ed7dccbe5a928de1088e1b6045acf81 Mon Sep 17 00:00:00 2001
From: shenlong <139912620+shenlong-tanwen@users.noreply.github.com>
Date: Mon, 22 Sep 2025 01:12:30 +0530
Subject: [PATCH] fix: retain scroll position on scale update (#22237)

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
---
 .../widgets/timeline/timeline.widget.dart     | 45 ++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/mobile/lib/presentation/widgets/timeline/timeline.widget.dart b/mobile/lib/presentation/widgets/timeline/timeline.widget.dart
index 98831403f6..c38116c64e 100644
--- a/mobile/lib/presentation/widgets/timeline/timeline.widget.dart
+++ b/mobile/lib/presentation/widgets/timeline/timeline.widget.dart
@@ -107,7 +107,7 @@ class _SliverTimeline extends ConsumerStatefulWidget {
 }
 
 class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
-  final _scrollController = ScrollController();
+  late final ScrollController _scrollController;
   StreamSubscription? _eventSubscription;
 
   // Drag selection state
@@ -119,10 +119,12 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
   int _perRow = 4;
   double _scaleFactor = 3.0;
   double _baseScaleFactor = 3.0;
+  int? _scaleRestoreAssetIndex;
 
   @override
   void initState() {
     super.initState();
+    _scrollController = ScrollController(onAttach: _restoreScalePosition);
     _eventSubscription = EventStream.shared.listen(_onEvent);
 
     final currentTilesPerRow = ref.read(settingsProvider).get(Setting.tilesPerRow);
@@ -154,6 +156,28 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
     EventStream.shared.emit(MultiSelectToggleEvent(isEnabled));
   }
 
+  void _restoreScalePosition(_) {
+    if (_scaleRestoreAssetIndex == null) return;
+
+    final asyncSegments = ref.read(timelineSegmentProvider);
+    asyncSegments.whenData((segments) {
+      final targetSegment = segments.lastWhereOrNull((segment) => segment.firstAssetIndex <= _scaleRestoreAssetIndex!);
+      if (targetSegment != null) {
+        final assetIndexInSegment = _scaleRestoreAssetIndex! - targetSegment.firstAssetIndex;
+        final newColumnCount = ref.read(timelineArgsProvider).columnCount;
+        final rowIndexInSegment = (assetIndexInSegment / newColumnCount).floor();
+        final targetRowIndex = targetSegment.firstIndex + 1 + rowIndexInSegment;
+        final targetOffset = targetSegment.indexToLayoutOffset(targetRowIndex);
+        WidgetsBinding.instance.addPostFrameCallback((_) {
+          if (mounted) {
+            _scrollController.jumpTo(targetOffset.clamp(0.0, _scrollController.position.maxScrollExtent));
+          }
+        });
+      }
+    });
+    _scaleRestoreAssetIndex = null;
+  }
+
   @override
   void dispose() {
     _scrollController.dispose();
@@ -345,9 +369,28 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
                       final newPerRow = 7 - newScaleFactor.toInt();
 
                       if (newPerRow != _perRow) {
+                        final currentOffset = _scrollController.offset.clamp(
+                          0.0,
+                          _scrollController.position.maxScrollExtent,
+                        );
+                        final segment = segments.findByOffset(currentOffset) ?? segments.lastOrNull;
+                        int? targetAssetIndex;
+                        if (segment != null) {
+                          final rowIndex = segment.getMinChildIndexForScrollOffset(currentOffset);
+                          if (rowIndex > segment.firstIndex) {
+                            final rowIndexInSegment = rowIndex - (segment.firstIndex + 1);
+                            final assetsPerRow = ref.read(timelineArgsProvider).columnCount;
+                            final assetIndexInSegment = rowIndexInSegment * assetsPerRow;
+                            targetAssetIndex = segment.firstAssetIndex + assetIndexInSegment;
+                          } else {
+                            targetAssetIndex = segment.firstAssetIndex;
+                          }
+                        }
+
                         setState(() {
                           _scaleFactor = newScaleFactor;
                           _perRow = newPerRow;
+                          _scaleRestoreAssetIndex = targetAssetIndex;
                         });
 
                         ref.read(settingsProvider.notifier).set(Setting.tilesPerRow, _perRow);