#nullable disable
using System;
using System.Collections;
using System.Collections.Specialized;
using Foundation;
using ObjCRuntime;
using UIKit;
 
namespace Microsoft.Maui.Controls.Handlers.Items
{
	public class ReorderableItemsViewController<TItemsView> : GroupableItemsViewController<TItemsView>
		where TItemsView : ReorderableItemsView
	{
		bool _disposed;
		UILongPressGestureRecognizer _longPressGestureRecognizer;
 
		public ReorderableItemsViewController(TItemsView reorderableItemsView, ItemsViewLayout layout)
			: base(reorderableItemsView, layout)
		{
			// The UICollectionViewController has built-in recognizer for reorder that can be installed by setting "InstallsStandardGestureForInteractiveMovement".
			// For some reason it only seemed to work when the CollectionView was inside the Flyout section of a FlyoutPage.
			// The UILongPressGestureRecognizer is simple enough to set up so let's just add our own.
			InstallsStandardGestureForInteractiveMovement = false;
		}
 
		public override bool CanMoveItem(UICollectionView collectionView, NSIndexPath indexPath)
		{
			return ItemsView?.CanReorderItems == true;
		}
 
		protected override UICollectionViewDelegateFlowLayout CreateDelegator()
		{
			return new ReorderableItemsViewDelegator<TItemsView, ReorderableItemsViewController<TItemsView>>(ItemsViewLayout, this);
		}
 
		protected override IItemsViewSource CreateItemsViewSource()
		{
			if (ItemsSource != null)
			{
				// There's a bug in the current Maui Controls library.
				// It will call "CreateItemsViewSource" 2x in a row when opening a page.
				// It's invoked from both ViewDidLoad & UpdateItemsSource
				// For the time being, until the issue is fixed, we need to dispose of the current source if one already exist.
				ItemsSource.Dispose();
			}
			return base.CreateItemsViewSource();
		}
 
		protected override void Dispose(bool disposing)
		{
			if (disposing && !_disposed)
			{
				if (_longPressGestureRecognizer != null)
				{
					CollectionView.RemoveGestureRecognizer(_longPressGestureRecognizer);
					_longPressGestureRecognizer.Dispose();
					_longPressGestureRecognizer = null;
				}
 
				_disposed = true;
			}
 
			base.Dispose(disposing);
		}
 
		void HandleLongPress(UILongPressGestureRecognizer gestureRecognizer)
		{
			var collectionView = CollectionView;
			if (collectionView == null)
				return;
 
			var location = gestureRecognizer.LocationInView(collectionView);
 
			// We are updating "CancelsTouchesInView" so views can still receive touch events when this gesture runs.
			// Those events shouldn't be aborted until they've actually moved the position of the CollectionView item.
			switch (gestureRecognizer.State)
			{
				case UIGestureRecognizerState.Began:
					var indexPath = collectionView?.IndexPathForItemAtPoint(location);
					if (indexPath == null)
					{
						return;
					}
					gestureRecognizer.CancelsTouchesInView = false;
					collectionView.BeginInteractiveMovementForItem(indexPath);
					break;
				case UIGestureRecognizerState.Changed:
					gestureRecognizer.CancelsTouchesInView = true;
					collectionView.UpdateInteractiveMovement(location);
					break;
				case UIGestureRecognizerState.Ended:
					collectionView.EndInteractiveMovement();
					break;
				default:
					collectionView.CancelInteractiveMovement();
					break;
			}
		}
 
		public override void MoveItem(UICollectionView collectionView, NSIndexPath sourceIndexPath, NSIndexPath destinationIndexPath)
		{
			var itemsSource = ItemsSource;
			var itemsView = ItemsView;
 
			if (itemsSource == null || itemsView == null)
			{
				return;
			}
 
			if (itemsView.IsGrouped)
			{
				var fromList = itemsSource.Group(sourceIndexPath) as IList;
				var fromItemsSource = fromList is INotifyCollectionChanged ? itemsSource.GroupItemsViewSource(sourceIndexPath) : null;
				var fromItemIndex = sourceIndexPath.Row;
 
				var toList = itemsSource.Group(destinationIndexPath) as IList;
				var toItemsSource = toList is INotifyCollectionChanged ? itemsSource.GroupItemsViewSource(destinationIndexPath) : null;
				var toItemIndex = destinationIndexPath.Row;
 
				if (fromList != null && toList != null)
				{
					var fromItem = fromList[fromItemIndex];
					SetObserveChanges(fromItemsSource, false);
					SetObserveChanges(toItemsSource, false);
					fromList.RemoveAt(fromItemIndex);
					toList.Insert(toItemIndex, fromItem);
					SetObserveChanges(fromItemsSource, true);
					SetObserveChanges(toItemsSource, true);
					itemsView.SendReorderCompleted();
				}
			}
			else if (itemsView.ItemsSource is IList list)
			{
				var fromPosition = sourceIndexPath.Row;
				var toPosition = destinationIndexPath.Row;
				var fromItem = list[fromPosition];
				SetObserveChanges(itemsSource, false);
				list.RemoveAt(fromPosition);
				list.Insert(toPosition, fromItem);
				SetObserveChanges(itemsSource, true);
				itemsView.SendReorderCompleted();
			}
		}
 
		void SetObserveChanges(IItemsViewSource itemsSource, bool enable)
		{
			if (itemsSource is IObservableItemsViewSource observableSource)
			{
				observableSource.ObserveChanges = enable;
			}
		}
 
		public void UpdateCanReorderItems()
		{
			if (ItemsView.CanReorderItems)
			{
				if (_longPressGestureRecognizer == null)
				{
					_longPressGestureRecognizer = new UILongPressGestureRecognizer(HandleLongPress);
					CollectionView.AddGestureRecognizer(_longPressGestureRecognizer);
				}
			}
			else
			{
				if (_longPressGestureRecognizer != null)
				{
					CollectionView.RemoveGestureRecognizer(_longPressGestureRecognizer);
					_longPressGestureRecognizer.Dispose();
					_longPressGestureRecognizer = null;
				}
			}
		}
	}
}