using System.ComponentModel;
 
namespace Microsoft.Maui.Controls.Compatibility.Platform.iOS
{
	[System.Obsolete(Compatibility.Hosting.MauiAppBuilderExtensions.UseMapperInstead)]
	public class GroupableItemsViewRenderer<TItemsView, TViewController> : SelectableItemsViewRenderer<TItemsView, TViewController>
		where TItemsView : GroupableItemsView
		where TViewController : GroupableItemsViewController<TItemsView>
	{
		[Microsoft.Maui.Controls.Internals.Preserve(Conditional = true)]
		public GroupableItemsViewRenderer() { }
 
		protected override TViewController CreateController(TItemsView itemsView, ItemsViewLayout layout)
		{
			return new GroupableItemsViewController<TItemsView>(itemsView, layout) as TViewController;
		}
 
		protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs changedProperty)
		{
			base.OnElementPropertyChanged(sender, changedProperty);
 
			if (changedProperty.Is(GroupableItemsView.IsGroupedProperty))
			{
				Controller?.UpdateItemsSource();
			}
		}
 
		// This is awkward.
 
		// Under certain circumstances, scrolling to an item in a group does not scroll all the way to the item; the 
		// UICollectionView will stop short. This only happens when:
		// 1. The items are grouped
		// 2. The target scroll position is "End" or "MakeVisible"
		// 3. The ItemSizingStrategy is "MeasureAllItems" (i.e., we are using `estimatedItemSize` for the underlying
		//		UICollectionView, rather than setting `itemSize` or using `sizeForItemAtIndexPath`.)
		// 4. The item has never appeared on screen before
 
		// This may be an iOS bug.
 
		// To work around this, we check below for the right conditions and, it they are met, we simply call 
		// ScrollToItem twice. The first time gets us close to the correct offset, the second time gets us all the way
		// there. If the scroll is _not_ animated, we can simply call it twice in a row; if it's animated, then we 
		// have to wait for the first scroll to finish before calling the second one (`SetScrollAnimationEndedCallback`).
 
		protected override void ScrollToRequested(object sender, ScrollToRequestEventArgs args)
		{
			if (WillNeedScrollAdjustment(args))
			{
				if (args.IsAnimated)
				{
					Controller.SetScrollAnimationEndedCallback(() => base.ScrollToRequested(sender, args));
				}
				else
				{
					base.ScrollToRequested(sender, args);
				}
			}
 
			base.ScrollToRequested(sender, args);
		}
 
		bool WillNeedScrollAdjustment(ScrollToRequestEventArgs args)
		{
			return ItemsView.ItemSizingStrategy == ItemSizingStrategy.MeasureAllItems
				&& ItemsView.IsGrouped
				&& (args.ScrollToPosition == ScrollToPosition.End || args.ScrollToPosition == ScrollToPosition.MakeVisible);
		}
	}
}