feat: disable snapping when a timeline has less than 12 months (#21649)

* feat: disable snapping when a timeline has less than 12 months

* fix: disable placeholders when not snapping

also moved month constant to constants.dart

---------

Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/lib/constants/constants.dart

@@ -45,3 +45,5 @@ const List<(String, String)> kWidgetNames = [
 
 const double kUploadStatusFailed = -1.0;
 const double kUploadStatusCanceled = -2.0;
+
+const int kMinMonthsToEnableScrubberSnap = 12;

mobile/lib/presentation/widgets/timeline/scrubber.widget.dart

@@ -3,14 +3,15 @@ import 'dart:async';
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:immich_mobile/constants/constants.dart';
 import 'package:immich_mobile/domain/models/timeline.model.dart';
 import 'package:immich_mobile/extensions/build_context_extensions.dart';
 import 'package:immich_mobile/extensions/theme_extensions.dart';
 import 'package:immich_mobile/presentation/widgets/timeline/constants.dart';
 import 'package:immich_mobile/presentation/widgets/timeline/segment.model.dart';
 import 'package:immich_mobile/presentation/widgets/timeline/timeline.state.dart';
-import 'package:intl/intl.dart' hide TextDirection;
 import 'package:immich_mobile/providers/haptic_feedback.provider.dart';
+import 'package:intl/intl.dart' hide TextDirection;
 
 /// A widget that will display a BoxScrollView with a ScrollThumb that can be dragged
 /// for quick navigation of the BoxScrollView.
@@ -79,6 +80,7 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
   double _thumbTopOffset = 0.0;
   bool _isDragging = false;
   List<_Segment> _segments = [];
+  int _monthCount = 0;
 
   late AnimationController _thumbAnimationController;
   Timer? _fadeOutTimer;
@@ -105,6 +107,7 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
     _thumbAnimationController = AnimationController(vsync: this, duration: kTimelineScrubberFadeInDuration);
     _thumbAnimation = CurvedAnimation(parent: _thumbAnimationController, curve: Curves.fastEaseInToSlowEaseOut);
     _labelAnimationController = AnimationController(vsync: this, duration: kTimelineScrubberFadeInDuration);
+    _monthCount = getMonthCount();
 
     _labelAnimation = CurvedAnimation(parent: _labelAnimationController, curve: Curves.fastOutSlowIn);
   }
@@ -121,6 +124,7 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
 
     if (oldWidget.layoutSegments.lastOrNull?.endOffset != widget.layoutSegments.lastOrNull?.endOffset) {
       _segments = _buildSegments(layoutSegments: widget.layoutSegments, timelineHeight: _scrubberHeight);
+      _monthCount = getMonthCount();
     }
   }
 
@@ -140,6 +144,10 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
     });
   }
 
+  int getMonthCount() {
+    return _segments.map((e) => "${e.date.month}_${e.date.year}").toSet().length;
+  }
+
   bool _onScrollNotification(ScrollNotification notification) {
     if (_isDragging) {
       // If the user is dragging the thumb, we don't want to update the position
@@ -169,7 +177,10 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
   }
 
   void _onDragStart(DragStartDetails _) {
-    ref.read(timelineStateProvider.notifier).setScrubbing(true);
+    if (_monthCount >= kMinMonthsToEnableScrubberSnap) {
+      ref.read(timelineStateProvider.notifier).setScrubbing(true);
+    }
+
     setState(() {
       _isDragging = true;
       _labelAnimationController.forward();
@@ -191,13 +202,22 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
     final nearestMonthSegment = _findNearestMonthSegment(dragPosition);
 
     if (nearestMonthSegment != null) {
-      _snapToSegment(nearestMonthSegment);
       final label = nearestMonthSegment.scrollLabel;
       if (_lastLabel != label) {
         ref.read(hapticFeedbackProvider.notifier).selectionClick();
         _lastLabel = label;
       }
     }
+
+    if (_monthCount < kMinMonthsToEnableScrubberSnap) {
+      // If there are less than kMinMonthsToEnableScrubberSnap months, we don't need to snap to segments
+      setState(() {
+        _thumbTopOffset = dragPosition;
+        _scrollController.jumpTo((dragPosition / _scrubberHeight) * _scrollController.position.maxScrollExtent);
+      });
+    } else if (nearestMonthSegment != null) {
+      _snapToSegment(nearestMonthSegment);
+    }
   }
 
   /// Calculate the drag position relative to the scrubber area