Batch flip-view range updates for programmatic calendar navigation (#805)

* Batch calendar range updates during programmatic navigation

* Refine programmatic calendar navigation batching state

Wino.Mail.WinUI/Controls/Calendar/WinoCalendarControl.cs

@@ -142,7 +142,14 @@ public partial class WinoCalendarControl : Control
     }
 
     private void ManageHighlightedDateRange()
-        => SelectedFlipViewDayRange = InternalFlipView.SelectedItem as DayRangeRenderModel;
+    {
+        if (InternalFlipView?.IsProgrammaticNavigationInProgress == true)
+        {
+            return;
+        }
+
+        SelectedFlipViewDayRange = InternalFlipView?.SelectedItem as DayRangeRenderModel;
+    }
 
     private void DeregisterCanvas(WinoDayTimelineCanvas canvas)
     {
@@ -190,14 +197,29 @@ public partial class WinoCalendarControl : Control
     {
         base.OnApplyTemplate();
 
+        if (InternalFlipView != null)
+        {
+            InternalFlipView.ProgrammaticNavigationCompleted -= InternalFlipViewProgrammaticNavigationCompleted;
+        }
+
         InternalFlipView = GetTemplateChild(PART_WinoFlipView) as WinoCalendarFlipView;
         IdleGrid = GetTemplateChild(PART_IdleGrid) as Grid;
 
+        if (InternalFlipView != null)
+        {
+            InternalFlipView.ProgrammaticNavigationCompleted += InternalFlipViewProgrammaticNavigationCompleted;
+        }
+
         UpdateIdleState();
         ManageCalendarOrientation();
         ManageDisplayType();
     }
 
+    private void InternalFlipViewProgrammaticNavigationCompleted(object? sender, ProgrammaticNavigationCompletedEventArgs e)
+    {
+        SelectedFlipViewDayRange = e.DayRange;
+    }
+
     private void UpdateIdleState()
     {
         InternalFlipView.Opacity = IsFlipIdle ? 0 : 1;

Wino.Mail.WinUI/Controls/Calendar/WinoCalendarFlipView.cs

@@ -43,6 +43,12 @@ public partial class WinoCalendarFlipView : CustomCalendarFlipView
         set { SetValue(IsIdleProperty, value); }
     }
 
+    internal bool IsProgrammaticNavigationInProgress { get; private set; }
+
+    internal int? PendingTargetIndex { get; private set; }
+
+    internal event EventHandler<ProgrammaticNavigationCompletedEventArgs>? ProgrammaticNavigationCompleted;
+
     public WinoCalendarFlipView()
     {
         RegisterPropertyChangedCallback(ItemsSourceProperty, new DependencyPropertyChangedCallback(OnItemsSourceChanged));
@@ -123,37 +129,61 @@ public partial class WinoCalendarFlipView : CustomCalendarFlipView
         await DispatcherQueue.EnqueueAsync(() =>
         {
             // Find the day range that contains the date.
-            var dayRange = GetItemsSource()?.FirstOrDefault(a => a.CalendarDays.Any(b => b.RepresentingDate.Date == dateTime.Date));
+            var dayRanges = GetItemsSource();
+            var dayRange = dayRanges?.FirstOrDefault(a => a.CalendarDays.Any(b => b.RepresentingDate.Date == dateTime.Date));
 
-            if (dayRange != null)
+            if (dayRange != null && dayRanges != null)
             {
-                var navigationItemIndex = GetItemsSource().IndexOf(dayRange);
+                var navigationItemIndex = dayRanges.IndexOf(dayRange);
+                var hasNavigationWork = navigationItemIndex != SelectedIndex;
 
-                if (Math.Abs(navigationItemIndex - SelectedIndex) > 4)
+                IsProgrammaticNavigationInProgress = hasNavigationWork;
+                PendingTargetIndex = navigationItemIndex;
+
+                if (!hasNavigationWork)
                 {
-                    // Difference between dates are high.
+                    PendingTargetIndex = null;
-                    // No need to animate this much, just go without animating.
+                    return;
-
-                    SelectedIndex = navigationItemIndex;
                 }
-                else
-                {
-                    // Until we reach the day in the flip, simulate next-prev button clicks.
-                    // This will make sure the FlipView animations are triggered.
-                    // Setting SelectedIndex directly doesn't trigger the animations.
 
-                    while (SelectedIndex != navigationItemIndex)
+                try
+                {
+                    if (Math.Abs(navigationItemIndex - SelectedIndex) > 4)
                     {
-                        if (SelectedIndex > navigationItemIndex)
+                        // Difference between dates are high.
+                        // No need to animate this much, just go without animating.
+
+                        SelectedIndex = navigationItemIndex;
+                    }
+                    else
+                    {
+                        // Until we reach the day in the flip, simulate next-prev button clicks.
+                        // This will make sure the FlipView animations are triggered.
+                        // Setting SelectedIndex directly doesn't trigger the animations.
+
+                        while (SelectedIndex != navigationItemIndex)
                         {
-                            GoPreviousFlip();
+                            if (SelectedIndex > navigationItemIndex)
-                        }
+                            {
-                        else
+                                GoPreviousFlip();
-                        {
+                            }
-                            GoNextFlip();
+                            else
+                            {
+                                GoNextFlip();
+                            }
                         }
                     }
                 }
+                finally
+                {
+                    if (SelectedIndex == PendingTargetIndex)
+                    {
+                        ProgrammaticNavigationCompleted?.Invoke(this, new ProgrammaticNavigationCompletedEventArgs(SelectedItem as DayRangeRenderModel ?? dayRange));
+                    }
+
+                    IsProgrammaticNavigationInProgress = false;
+                    PendingTargetIndex = null;
+                }
             }
         });
     }
@@ -161,3 +191,13 @@ public partial class WinoCalendarFlipView : CustomCalendarFlipView
     private ObservableRangeCollection<DayRangeRenderModel> GetItemsSource()
         => ItemsSource as ObservableRangeCollection<DayRangeRenderModel>;
 }
+
+internal sealed class ProgrammaticNavigationCompletedEventArgs : EventArgs
+{
+    public ProgrammaticNavigationCompletedEventArgs(DayRangeRenderModel dayRange)
+    {
+        DayRange = dayRange;
+    }
+
+    public DayRangeRenderModel DayRange { get; }
+}