using System;
using System.ComponentModel;
using System.Threading;
using Xamarin.Forms;
using Xamarin.Forms.Internals;

namespace Ooui.Forms
{
	public class VisualElementTracker
	{
		readonly EventHandler<EventArg<VisualElement>> _batchCommittedHandler;

		readonly PropertyChangedEventHandler _propertyChangedHandler;
		readonly EventHandler _sizeChangedEventHandler;
		bool _disposed;
		VisualElement _element;

		// Track these by hand because the calls down into iOS are too expensive
		bool _isInteractive;
		Rectangle _lastBounds;
#if !__MOBILE__
		Rectangle _lastParentBounds;
#endif
		int _updateCount;

		public VisualElementTracker (IVisualElementRenderer renderer)
		{
			if (renderer == null)
				throw new ArgumentNullException (nameof (renderer));

			_propertyChangedHandler = HandlePropertyChanged;
			_sizeChangedEventHandler = HandleSizeChanged;
			_batchCommittedHandler = HandleRedrawNeeded;

			Renderer = renderer;
			renderer.ElementChanged += OnRendererElementChanged;
			SetElement (null, renderer.Element);
		}

		IVisualElementRenderer Renderer { get; set; }

		public void Dispose ()
		{
			Dispose (true);
		}

		public event EventHandler NativeControlUpdated;

		protected virtual void Dispose (bool disposing)
		{
			if (_disposed)
				return;

			_disposed = true;

			if (disposing) {
				SetElement (_element, null);

				Renderer.ElementChanged -= OnRendererElementChanged;
				Renderer = null;
			}
		}

		void HandlePropertyChanged (object sender, PropertyChangedEventArgs e)
		{
			if (e.PropertyName == VisualElement.XProperty.PropertyName || e.PropertyName == VisualElement.YProperty.PropertyName || e.PropertyName == VisualElement.WidthProperty.PropertyName ||
				e.PropertyName == VisualElement.HeightProperty.PropertyName || e.PropertyName == VisualElement.AnchorXProperty.PropertyName || e.PropertyName == VisualElement.AnchorYProperty.PropertyName ||
				e.PropertyName == VisualElement.TranslationXProperty.PropertyName || e.PropertyName == VisualElement.TranslationYProperty.PropertyName || e.PropertyName == VisualElement.ScaleProperty.PropertyName ||
				e.PropertyName == VisualElement.RotationProperty.PropertyName || e.PropertyName == VisualElement.RotationXProperty.PropertyName || e.PropertyName == VisualElement.RotationYProperty.PropertyName ||
				e.PropertyName == VisualElement.IsVisibleProperty.PropertyName || e.PropertyName == VisualElement.IsEnabledProperty.PropertyName ||
				e.PropertyName == VisualElement.InputTransparentProperty.PropertyName || e.PropertyName == VisualElement.OpacityProperty.PropertyName)
				UpdateNativeControl (); // poorly optimized
		}

		void HandleRedrawNeeded (object sender, EventArgs e)
		{
			UpdateNativeControl ();
		}

		void HandleSizeChanged (object sender, EventArgs e)
		{
			UpdateNativeControl ();
		}

		void OnRendererElementChanged (object s, VisualElementChangedEventArgs e)
		{
			if (_element == e.NewElement)
				return;

			SetElement (_element, e.NewElement);
		}

		void OnUpdateNativeControl ()
		{
			var view = Renderer.Element;
			var uiview = Renderer.NativeView;

			if (view == null || view.Batched)
				return;

			var shouldInteract = !view.InputTransparent && view.IsEnabled;
			if (_isInteractive != shouldInteract) {
				_isInteractive = shouldInteract;
			}

			var boundsChanged = _lastBounds != view.Bounds;
			var viewParent = view.RealParent as VisualElement;
			var parentBoundsChanged = _lastParentBounds != (viewParent == null ? Rectangle.Zero : viewParent.Bounds);
			var thread = !boundsChanged;

			var anchorX = (float)view.AnchorX;
			var anchorY = (float)view.AnchorY;
			var translationX = (float)view.TranslationX;
			var translationY = (float)view.TranslationY;
			var rotationX = (float)view.RotationX;
			var rotationY = (float)view.RotationY;
			var rotation = (float)view.Rotation;
			var scale = (float)view.Scale;
			var width = (float)view.Width;
			var height = (float)view.Height;
			var x = (float)view.X;
			var y = (float)view.Y;
			var opacity = (float)view.Opacity;
			var isVisible = view.IsVisible;

			var updateTarget = Interlocked.Increment (ref _updateCount);

			if (updateTarget != _updateCount)
				return;
			var parent = view.RealParent;

			if (isVisible && uiview.IsHidden) {
				uiview.IsHidden = false;
			}

			if (!isVisible && !uiview.IsHidden) {
				uiview.IsHidden = true;
			}

			parentBoundsChanged = true;
			bool shouldUpdate = width > 0 && height > 0 && parent != null && (boundsChanged || parentBoundsChanged);
			if (shouldUpdate) {
				var visualParent = parent as VisualElement;
				float newY = visualParent == null ? y : Math.Max (0, (float)(visualParent.Height - y - view.Height));
				var target = new Rectangle (x, newY, width, height);

				uiview.Style.Left = x;
				uiview.Style.Top = newY;
				uiview.Style.Width = width;
				uiview.Style.Height = height;
			}
			else if (width <= 0 || height <= 0) {
				return;
			}
			uiview.Style.Opacity = opacity;

			//var transform = 0;
			//const double epsilon = 0.001;
			//caLayer.AnchorPoint = new PointF (anchorX - 0.5f, anchorY - 0.5f);

			//// position is relative to anchor point
			//if (Math.Abs (anchorX - .5) > epsilon)
			//	transform = transform.Translate ((anchorX - .5f) * width, 0, 0);
			//if (Math.Abs (anchorY - .5) > epsilon)
			//	transform = transform.Translate (0, (anchorY - .5f) * height, 0);

			//if (Math.Abs (translationX) > epsilon || Math.Abs (translationY) > epsilon)
			//	transform = transform.Translate (translationX, translationY, 0);

			//if (Math.Abs (scale - 1) > epsilon)
			//	transform = transform.Scale (scale);

			//// not just an optimization, iOS will not "pixel align" a view which has m34 set
			//if (Math.Abs (rotationY % 180) > epsilon || Math.Abs (rotationX % 180) > epsilon)
			//	transform.m34 = 1.0f / -400f;

			//if (Math.Abs (rotationX % 360) > epsilon)
			//	transform = transform.Rotate (rotationX * (float)Math.PI / 180.0f, 1.0f, 0.0f, 0.0f);
			//if (Math.Abs (rotationY % 360) > epsilon)
			//	transform = transform.Rotate (rotationY * (float)Math.PI / 180.0f, 0.0f, 1.0f, 0.0f);

			//transform = transform.Rotate (rotation * (float)Math.PI / 180.0f, 0.0f, 0.0f, 1.0f);
			//caLayer.Transform = transform;

			_lastBounds = view.Bounds;
			_lastParentBounds = viewParent?.Bounds ?? Rectangle.Zero;
		}

		void SetElement (VisualElement oldElement, VisualElement newElement)
		{
			if (oldElement != null) {
				oldElement.PropertyChanged -= _propertyChangedHandler;
				oldElement.SizeChanged -= _sizeChangedEventHandler;
				oldElement.BatchCommitted -= _batchCommittedHandler;
			}

			_element = newElement;

			if (newElement != null) {
				newElement.BatchCommitted += _batchCommittedHandler;
				newElement.SizeChanged += _sizeChangedEventHandler;
				newElement.PropertyChanged += _propertyChangedHandler;

				UpdateNativeControl ();
			}
		}

		void UpdateNativeControl ()
		{
			if (_disposed)
				return;

			OnUpdateNativeControl ();

			NativeControlUpdated?.Invoke (this, EventArgs.Empty);
		}
	}
}