using System;
using System.Diagnostics.CodeAnalysis;
using CoreGraphics;
using Microsoft.Maui.Graphics;
using ObjCRuntime;
using UIKit;
 
namespace Microsoft.Maui.Platform
{
	public abstract class MauiView : UIView, ICrossPlatformLayoutBacking, IVisualTreeElementProvidable, IUIViewLifeCycleEvents
	{
		bool _fireSetNeedsLayoutOnParentWhenWindowAttached;
		static bool? _respondsToSafeArea;
 
		double _lastMeasureHeight = double.NaN;
		double _lastMeasureWidth = double.NaN;
 
		WeakReference<IView>? _reference;
		WeakReference<ICrossPlatformLayout>? _crossPlatformLayoutReference;
 
		public IView? View
		{
			get => _reference != null && _reference.TryGetTarget(out var v) ? v : null;
			set => _reference = value == null ? null : new(value);
		}
 
		bool RespondsToSafeArea()
		{
			if (_respondsToSafeArea.HasValue)
				return _respondsToSafeArea.Value;
			return (bool)(_respondsToSafeArea = RespondsToSelector(new Selector("safeAreaInsets")));
		}
 
		protected CGRect AdjustForSafeArea(CGRect bounds)
		{
			if (KeyboardAutoManagerScroll.ShouldIgnoreSafeAreaAdjustment)
			{
				KeyboardAutoManagerScroll.ShouldScrollAgain = true;
			}
 
			if (View is not ISafeAreaView sav || sav.IgnoreSafeArea || !RespondsToSafeArea())
			{
				return bounds;
			}
 
#pragma warning disable CA1416 // TODO 'UIView.SafeAreaInsets' is only supported on: 'ios' 11.0 and later, 'maccatalyst' 11.0 and later, 'tvos' 11.0 and later.
			return SafeAreaInsets.InsetRect(bounds);
#pragma warning restore CA1416
		}
 
		protected bool IsMeasureValid(double widthConstraint, double heightConstraint)
		{
			// Check the last constraints this View was measured with; if they're the same,
			// then the current measure info is already correct and we don't need to repeat it
			return heightConstraint == _lastMeasureHeight && widthConstraint == _lastMeasureWidth;
		}
 
		protected void InvalidateConstraintsCache()
		{
			_lastMeasureWidth = double.NaN;
			_lastMeasureHeight = double.NaN;
		}
 
		protected void CacheMeasureConstraints(double widthConstraint, double heightConstraint)
		{
			_lastMeasureWidth = widthConstraint;
			_lastMeasureHeight = heightConstraint;
		}
 
		public override void SafeAreaInsetsDidChange()
		{
			base.SafeAreaInsetsDidChange();
 
			if (View is ISafeAreaView2 isav2)
				isav2.SafeAreaInsets = this.SafeAreaInsets.ToThickness();
		}
 
		public ICrossPlatformLayout? CrossPlatformLayout
		{
			get => _crossPlatformLayoutReference != null && _crossPlatformLayoutReference.TryGetTarget(out var v) ? v : null;
			set => _crossPlatformLayoutReference = value == null ? null : new WeakReference<ICrossPlatformLayout>(value);
		}
 
		Size CrossPlatformMeasure(double widthConstraint, double heightConstraint)
		{
			return CrossPlatformLayout?.CrossPlatformMeasure(widthConstraint, heightConstraint) ?? Size.Zero;
		}
 
		Size CrossPlatformArrange(Rect bounds)
		{
			return CrossPlatformLayout?.CrossPlatformArrange(bounds) ?? Size.Zero;
		}
 
		public override CGSize SizeThatFits(CGSize size)
		{
			if (_crossPlatformLayoutReference == null)
			{
				return base.SizeThatFits(size);
			}
 
			var widthConstraint = size.Width;
			var heightConstraint = size.Height;
 
			var crossPlatformSize = CrossPlatformMeasure(widthConstraint, heightConstraint);
 
			CacheMeasureConstraints(widthConstraint, heightConstraint);
 
			return crossPlatformSize.ToCGSize();
		}
 
		// TODO: Possibly reconcile this code with ViewHandlerExtensions.LayoutVirtualView
		// If you make changes here please review if those changes should also
		// apply to ViewHandlerExtensions.LayoutVirtualView
		public override void LayoutSubviews()
		{
			base.LayoutSubviews();
 
			if (_crossPlatformLayoutReference == null)
			{
				return;
			}
 
			var bounds = AdjustForSafeArea(Bounds).ToRectangle();
 
			var widthConstraint = bounds.Width;
			var heightConstraint = bounds.Height;
 
			// If the SuperView is a MauiView (backing a cross-platform ContentView or Layout), then measurement
			// has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews. But we
			// _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
			// the window); there's no guarantee that SizeThatFits has been called in that case.
 
			if (!IsMeasureValid(widthConstraint, heightConstraint) && Superview is not MauiView)
			{
				CrossPlatformMeasure(widthConstraint, heightConstraint);
				CacheMeasureConstraints(widthConstraint, heightConstraint);
			}
 
			CrossPlatformArrange(bounds);
			OnLayoutChanged();
		}
 
		public override void SetNeedsLayout()
		{
			InvalidateConstraintsCache();
			base.SetNeedsLayout();
			TryToInvalidateSuperView(false);
		}
 
		private protected void TryToInvalidateSuperView(bool shouldOnlyInvalidateIfPending)
		{
			if (shouldOnlyInvalidateIfPending && !_fireSetNeedsLayoutOnParentWhenWindowAttached)
			{
				return;
			}
 
			// We check for Window to avoid scenarios where an invalidate might propagate up the tree
			// To a SuperView that's been disposed which will cause a crash when trying to access it
			if (Window is not null)
			{
				this.Superview?.SetNeedsLayout();
				_fireSetNeedsLayoutOnParentWhenWindowAttached = false;
			}
			else
			{
				_fireSetNeedsLayoutOnParentWhenWindowAttached = true;
			}
		}
 
		IVisualTreeElement? IVisualTreeElementProvidable.GetElement()
		{
 
			if (View is IVisualTreeElement viewElement &&
				viewElement.IsThisMyPlatformView(this))
			{
				return viewElement;
			}
 
			if (CrossPlatformLayout is IVisualTreeElement layoutElement &&
				layoutElement.IsThisMyPlatformView(this))
			{
				return layoutElement;
			}
 
			return null;
		}
 
		[UnconditionalSuppressMessage("Memory", "MEM0002", Justification = IUIViewLifeCycleEvents.UnconditionalSuppressMessage)]
		EventHandler? _movedToWindow;
		event EventHandler? IUIViewLifeCycleEvents.MovedToWindow
		{
			add => _movedToWindow += value;
			remove => _movedToWindow -= value;
		}
 
		public override void MovedToWindow()
		{
			base.MovedToWindow();
			_movedToWindow?.Invoke(this, EventArgs.Empty);
			TryToInvalidateSuperView(true);
		}
 
		[UnconditionalSuppressMessage("Memory", "MEM0001", Justification = IUIViewLifeCycleEvents.UnconditionalSuppressMessage)]
		internal event EventHandler? LayoutChanged;
 
		private void OnLayoutChanged()
		{
			LayoutChanged?.Invoke(this, EventArgs.Empty);
		}
	}
}