using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Input;
using System.Windows.Media.Animation;

using TomsToolbox.Wpf;
using TomsToolbox.Wpf.Interactivity;

namespace LibScrollingOptimization
{
	/// <summary>
	/// 
	/// </summary>
	public class SmoothScrollingBehavior : FrameworkElementBehavior<Control>
	{
		private ScrollViewer? _scrollViewer;
		private ScrollContentPresenter? _scrollContentPresenter;

		private delegate bool GetBool(ScrollViewer scrollViewer);
		private static readonly GetBool _propertyHandlesMouseWheelScrollingGetter;
		private static readonly IEasingFunction _scrollingAnimationEase = new CubicEase() { EasingMode = EasingMode.EaseOut };
		private const long _millisecondsBetweenTouchpadScrolling = 100;

		private bool _animationRunning = false;
		private int _lastScrollDelta = 0;
		private int _lastVerticalScrollingDelta = 0;
		private int _lastHorizontalScrollingDelta = 0;
		private long _lastScrollingTick;

		static SmoothScrollingBehavior()
		{

#if NETCOREAPP
			_propertyHandlesMouseWheelScrollingGetter = typeof(ScrollViewer)
				.GetProperty("HandlesMouseWheelScrolling", BindingFlags.Instance | BindingFlags.NonPublic)!
				.GetGetMethod(true)!
				.CreateDelegate<GetBool>();
#else
			_propertyHandlesMouseWheelScrollingGetter = (GetBool)typeof(ScrollViewer)
				.GetProperty("HandlesMouseWheelScrolling", BindingFlags.Instance | BindingFlags.NonPublic)!
				.GetGetMethod(true)!
				.CreateDelegate(typeof(GetBool));
#endif
		}

		[UnsafeAccessor(UnsafeAccessorKind.Method, Name = "get_ScrollInfo")]
		static extern IScrollInfo GetScrollInfo(ScrollViewer scrollViewer);

		/// <inheritdoc />
		protected override void OnAssociatedObjectLoaded()
		{
			base.OnAssociatedObjectLoaded();

			_scrollViewer = AssociatedObject.VisualDescendantsAndSelf().OfType<ScrollViewer>().FirstOrDefault();

			if (_scrollViewer == null)
				return;

			_scrollViewer.PreviewMouseWheel += ScrollViewer_PreviewMouseWheel;
			_scrollContentPresenter = _scrollViewer.VisualDescendants().OfType<ScrollContentPresenter>().FirstOrDefault();
		}

		/// <inheritdoc />
		protected override void OnAssociatedObjectUnloaded()
		{
			base.OnAssociatedObjectUnloaded();

			if (_scrollViewer == null)
				return;

			_scrollViewer.PreviewMouseWheel -= ScrollViewer_PreviewMouseWheel;
		}


		private void ScrollViewer_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
		{
			if (!ScrollWithWheelDelta)
			{
				return;
			}
			else
			{
				Debug.WriteLine(e.Delta);

				CoreScrollWithWheelDelta(e);
			}
		}

		private void CoreScrollWithWheelDelta(MouseWheelEventArgs e)
		{
			if (_scrollViewer == null || _scrollContentPresenter == null)
				return;

			if (e.Handled)
			{
				return;
			}

			if (!AlwaysHandleMouseWheelScrolling &&
				!_propertyHandlesMouseWheelScrollingGetter.Invoke(_scrollViewer))
			{
				return;
			}

			bool vertical = _scrollViewer.ExtentHeight > 0;
			bool horizontal = _scrollViewer.ExtentWidth > 0;

			var tickCount = Environment.TickCount;
			var isTouchpadScrolling =
					e.Delta % Mouse.MouseWheelDeltaForOneLine != 0 ||
					(tickCount - _lastScrollingTick < _millisecondsBetweenTouchpadScrolling && _lastScrollDelta % Mouse.MouseWheelDeltaForOneLine != 0);

			double scrollDelta = e.Delta;

			if (isTouchpadScrolling)
			{
				// touchpad 应该滚动更慢一些, 所以这里预先除以一个合适的值
				scrollDelta /= 2;

				// 
				scrollDelta *= TouchpadScrollDeltaFactor;
			}
			else
			{
				scrollDelta *= MouseScrollDeltaFactor;
			}

			if (vertical)
			{
				if (GetScrollInfo(_scrollViewer) is IScrollInfo scrollInfo)
				{
					// 考虑到 VirtualizingPanel 可能是虚拟的大小, 所以这里需要校正 Delta
					scrollDelta *= scrollInfo.ViewportHeight / (_scrollContentPresenter?.ActualHeight ?? _scrollViewer.ActualHeight);
				}

				var sameDirectionAsLast = Math.Sign(e.Delta) == Math.Sign(_lastVerticalScrollingDelta);
				var nowOffset = sameDirectionAsLast && _animationRunning ? VerticalOffsetTarget : _scrollViewer.VerticalOffset;
				var newOffset = nowOffset - scrollDelta;

				if (newOffset < 0)
					newOffset = 0;
				if (newOffset > _scrollViewer.ScrollableHeight)
					newOffset = _scrollViewer.ScrollableHeight;

				SetValue(VerticalOffsetTargetPropertyKey, newOffset);
				_scrollViewer.BeginAnimation(ScrollViewerUtils.VerticalOffsetProperty, null);

				if (!EnableScrollingAnimation || isTouchpadScrolling)
				{
					_scrollViewer.ScrollToVerticalOffset(newOffset);
				}
				else
				{
					var diff = newOffset - _scrollViewer.VerticalOffset;
					var absDiff = Math.Abs(diff);
					var duration = ScrollingAnimationDuration;
					if (absDiff < Mouse.MouseWheelDeltaForOneLine)
					{
						duration = new Duration(TimeSpan.FromTicks((long)(duration.TimeSpan.Ticks * absDiff / Mouse.MouseWheelDeltaForOneLine)));
					}

					DoubleAnimation doubleAnimation = new DoubleAnimation() {
						EasingFunction = _scrollingAnimationEase,
						Duration = duration,
						From = _scrollViewer.VerticalOffset,
						To = newOffset,
					};

					doubleAnimation.Completed += DoubleAnimation_Completed;

					_animationRunning = true;
					_scrollViewer.BeginAnimation(ScrollViewerUtils.VerticalOffsetProperty, doubleAnimation, HandoffBehavior.SnapshotAndReplace);
				}

				_lastVerticalScrollingDelta = e.Delta;
			}
			else if (horizontal)
			{
				if (GetScrollInfo(_scrollViewer) is IScrollInfo scrollInfo)
				{
					// 考虑到 VirtualizingPanel 可能是虚拟的大小, 所以这里需要校正 Delta
					scrollDelta *= scrollInfo.ViewportWidth / (_scrollContentPresenter?.ActualWidth ?? _scrollViewer.ActualWidth);
				}

				var sameDirectionAsLast = Math.Sign(e.Delta) == Math.Sign(_lastHorizontalScrollingDelta);
				var nowOffset = sameDirectionAsLast && _animationRunning ? HorizontalOffsetTarget : _scrollViewer.HorizontalOffset;
				var newOffset = nowOffset - scrollDelta;

				if (newOffset < 0)
					newOffset = 0;
				if (newOffset > _scrollViewer.ScrollableWidth)
					newOffset = _scrollViewer.ScrollableWidth;

				SetValue(HorizontalOffsetTargetPropertyKey, newOffset);
				_scrollViewer.BeginAnimation(ScrollViewerUtils.HorizontalOffsetProperty, null);

				if (!EnableScrollingAnimation || isTouchpadScrolling)
				{
					_scrollViewer.ScrollToHorizontalOffset(newOffset);
				}
				else
				{
					var diff = newOffset - _scrollViewer.HorizontalOffset;
					var absDiff = Math.Abs(diff);
					var duration = ScrollingAnimationDuration;
					if (absDiff < Mouse.MouseWheelDeltaForOneLine)
					{
						duration = new Duration(TimeSpan.FromTicks((long)(duration.TimeSpan.Ticks * absDiff / Mouse.MouseWheelDeltaForOneLine)));
					}

					DoubleAnimation doubleAnimation = new DoubleAnimation() {
						EasingFunction = _scrollingAnimationEase,
						Duration = duration,
						From = _scrollViewer.HorizontalOffset,
						To = newOffset,
					};

					doubleAnimation.Completed += DoubleAnimation_Completed;

					_animationRunning = true;
					_scrollViewer.BeginAnimation(ScrollViewerUtils.HorizontalOffsetProperty, doubleAnimation, HandoffBehavior.SnapshotAndReplace);
				}

				_lastHorizontalScrollingDelta = e.Delta;
			}

			_lastScrollingTick = tickCount;
			_lastScrollDelta = e.Delta;

			e.Handled = true;
		}

		private void DoubleAnimation_Completed(object? sender, EventArgs e)
		{
			_animationRunning = false;
		}

		/// <summary>
		/// The horizontal offset of scrolling target 
		/// </summary>
		public double HorizontalOffsetTarget {
			get { return (double)GetValue(HorizontalOffsetTargetProperty); }
		}

		/// <summary>
		/// The vertical offset of scrolling target 
		/// </summary>
		public double VerticalOffsetTarget {
			get { return (double)GetValue(VerticalOffsetTargetProperty); }
		}

		/// <summary>
		/// Scroll with wheel delta instead of scrolling fixed number of lines
		/// </summary>
		public bool ScrollWithWheelDelta {
			get { return (bool)GetValue(ScrollWithWheelDeltaProperty); }
			set { SetValue(ScrollWithWheelDeltaProperty, value); }
		}

		/// <summary>
		/// Enable scrolling animation while using mouse <br/>
		/// You need to set ScrollWithWheelDelta to true to use this
		/// </summary>
		public bool EnableScrollingAnimation {
			get { return (bool)GetValue(EnableScrollingAnimationProperty); }
			set { SetValue(EnableScrollingAnimationProperty, value); }
		}

		/// <summary>
		/// Scrolling animation duration
		/// </summary>
		public Duration ScrollingAnimationDuration {
			get { return (Duration)GetValue(ScrollingAnimationDurationProperty); }
			set { SetValue(ScrollingAnimationDurationProperty, value); }
		}

		/// <summary>
		/// Delta value factor while mouse scrolling
		/// </summary>
		public double MouseScrollDeltaFactor {
			get { return (double)GetValue(MouseScrollDeltaFactorProperty); }
			set { SetValue(MouseScrollDeltaFactorProperty, value); }
		}

		/// <summary>
		/// Delta value factor while touchpad scrolling
		/// </summary>
		public double TouchpadScrollDeltaFactor {
			get { return (double)GetValue(TouchpadScrollDeltaFactorProperty); }
			set { SetValue(TouchpadScrollDeltaFactorProperty, value); }
		}

		/// <summary>
		/// Always handle mouse wheel scrolling. <br />
		/// (Especially in "TextBox")
		/// </summary>
		public bool AlwaysHandleMouseWheelScrolling {
			get { return (bool)GetValue(AlwaysHandleMouseWheelScrollingProperty); }
			set { SetValue(AlwaysHandleMouseWheelScrollingProperty, value); }
		}








		/// <summary>
		/// The key needed set a read-only property
		/// </summary>
		public static readonly DependencyPropertyKey HorizontalOffsetTargetPropertyKey =
			DependencyProperty.RegisterReadOnly(nameof(HorizontalOffsetTarget), typeof(double), typeof(SmoothScrollingBehavior), new PropertyMetadata(0.0));

		/// <summary>
		/// The key needed set a read-only property
		/// </summary>
		public static readonly DependencyPropertyKey VerticalOffsetTargetPropertyKey =
			DependencyProperty.RegisterReadOnly(nameof(VerticalOffsetTarget), typeof(double), typeof(SmoothScrollingBehavior), new PropertyMetadata(0.0));

		/// <summary>
		/// The key needed set a read-only property
		/// </summary>
		public static readonly DependencyProperty HorizontalOffsetTargetProperty =
			HorizontalOffsetTargetPropertyKey.DependencyProperty;

		/// <summary>
		/// The key needed set a read-only property
		/// </summary>
		public static readonly DependencyProperty VerticalOffsetTargetProperty =
			VerticalOffsetTargetPropertyKey.DependencyProperty;



		/// <summary>
		/// Get value of ScrollWithWheelDelta property
		/// </summary>
		/// <param name="obj"></param>
		/// <returns></returns>
		public static bool GetScrollWithWheelDelta(DependencyObject obj)
		{
			return (bool)obj.GetValue(ScrollWithWheelDeltaProperty);
		}

		/// <summary>
		/// Set value of ScrollWithWheelDelta property
		/// </summary>
		/// <param name="obj"></param>
		/// <param name="value"></param>
		public static void SetScrollWithWheelDelta(DependencyObject obj, bool value)
		{
			obj.SetValue(ScrollWithWheelDeltaProperty, value);
		}

		/// <summary>
		/// Get value of EnableScrollingAnimation property
		/// </summary>
		/// <param name="obj"></param>
		/// <returns></returns>
		public static bool GetEnableScrollingAnimation(DependencyObject obj)
		{
			return (bool)obj.GetValue(EnableScrollingAnimationProperty);
		}

		/// <summary>
		/// Set value of EnableScrollingAnimation property
		/// </summary>
		/// <param name="obj"></param>
		/// <param name="value"></param>
		public static void SetEnableScrollingAnimation(DependencyObject obj, bool value)
		{
			obj.SetValue(EnableScrollingAnimationProperty, value);
		}

		/// <summary>
		/// Get value of ScrollingAnimationDuration property
		/// </summary>
		/// <param name="obj"></param>
		/// <returns></returns>
		public static Duration GetScrollingAnimationDuration(DependencyObject obj)
		{
			return (Duration)obj.GetValue(ScrollingAnimationDurationProperty);
		}

		/// <summary>
		/// Set value of ScrollingAnimationDuration property
		/// </summary>
		/// <param name="obj"></param>
		/// <param name="value"></param>
		public static void SetScrollingAnimationDuration(DependencyObject obj, Duration value)
		{
			obj.SetValue(ScrollingAnimationDurationProperty, value);
		}


		/// <summary>
		/// Set value of AlwaysHandleMouseWheelScrolling property
		/// </summary>
		/// <param name="obj"></param>
		/// <returns></returns>
		public static bool GetAlwaysHandleMouseWheelScrolling(DependencyObject obj)
		{
			return (bool)obj.GetValue(AlwaysHandleMouseWheelScrollingProperty);
		}

		/// <summary>
		/// Get value of AlwaysHandleMouseWheelScrolling property
		/// </summary>
		/// <param name="obj"></param>
		/// <param name="value"></param>
		public static void SetAlwaysHandleMouseWheelScrolling(DependencyObject obj, bool value)
		{
			obj.SetValue(AlwaysHandleMouseWheelScrollingProperty, value);
		}


		/// <summary>
		/// The DependencyProperty of <see cref="ScrollWithWheelDelta"/> property.
		/// </summary>
		public static readonly DependencyProperty ScrollWithWheelDeltaProperty =
			DependencyProperty.RegisterAttached(nameof(ScrollWithWheelDelta), typeof(bool), typeof(SmoothScrollingBehavior),
				new FrameworkPropertyMetadata(true));

		/// <summary>
		/// The DependencyProperty of <see cref="EnableScrollingAnimation"/> property.
		/// </summary>
		public static readonly DependencyProperty EnableScrollingAnimationProperty =
			DependencyProperty.RegisterAttached(nameof(EnableScrollingAnimation), typeof(bool), typeof(SmoothScrollingBehavior),
				new FrameworkPropertyMetadata(true));

		/// <summary>
		/// The DependencyProperty of <see cref="ScrollingAnimationDuration"/> property.
		/// </summary>
		public static readonly DependencyProperty ScrollingAnimationDurationProperty =
			DependencyProperty.RegisterAttached(nameof(ScrollingAnimationDuration), typeof(Duration), typeof(SmoothScrollingBehavior),
				new FrameworkPropertyMetadata(new Duration(TimeSpan.FromMilliseconds(250))), ValidateScrollingAnimationDuration);

		/// <summary>
		/// The DependencyProperty of <see cref="AlwaysHandleMouseWheelScrolling"/> property
		/// </summary>
		public static readonly DependencyProperty AlwaysHandleMouseWheelScrollingProperty =
			DependencyProperty.RegisterAttached(nameof(AlwaysHandleMouseWheelScrolling), typeof(bool), typeof(SmoothScrollingBehavior), new FrameworkPropertyMetadata(true));

		/// <summary>
		/// The DependencyProperty of <see cref="MouseScrollDeltaFactor"/> property
		/// </summary>
		public static readonly DependencyProperty MouseScrollDeltaFactorProperty =
			DependencyProperty.Register(nameof(MouseScrollDeltaFactor), typeof(double), typeof(SmoothScrollingBehavior), new PropertyMetadata(1.0));

		/// <summary>
		/// The DependencyProperty of <see cref="TouchpadScrollDeltaFactor"/> property
		/// </summary>
		public static readonly DependencyProperty TouchpadScrollDeltaFactorProperty =
			DependencyProperty.Register(nameof(TouchpadScrollDeltaFactor), typeof(double), typeof(SmoothScrollingBehavior), new PropertyMetadata(1.0));

		private static bool ValidateScrollingAnimationDuration(object value)
			=> value is Duration duration && duration.HasTimeSpan;
	}
}