using Avalonia;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Markup.Xaml;
using Avalonia.Media;
using System;

namespace Avalar.Views.Image
{
    public class ImageControl : UserControl
    {
        private const double ZoomTick = 0.1;
        private double CurrentZoom { get; set; } = 1.0;

        private double InvCurrentZoom => 1 / CurrentZoom;

        private ImageBrush Image { get; }

        private Canvas ImageCanvas { get; }
        public ImageControl()
        {
            InitializeComponent();

            Image = this.FindResource("ImageBrush") as ImageBrush ?? throw new System.ArgumentException("ImageBrush");
            ImageCanvas = this.FindControl<Canvas>("ImageCanvas");
        }

        private void InitializeComponent()
        {
            AvaloniaXamlLoader.Load(this);
        }

        private Point MousePointerInImageSpace(Point mouseCoordinates)
        {
            var imageSize = Image.Source.Size;
            var canvasSize = new Size(ImageCanvas.Bounds.Width, ImageCanvas.Bounds.Height);

            double focalPointX;
            double focalPointY;

            if (canvasSize.AspectRatio > imageSize.AspectRatio)
            {
                focalPointY = mouseCoordinates.Y / canvasSize.Height;

                var halfUnusedX = (canvasSize.AspectRatio - imageSize.AspectRatio) * canvasSize.Width / 2;
                var clampedX = Math.Clamp(mouseCoordinates.X - halfUnusedX, 0, imageSize.Width);

                focalPointX = clampedX / imageSize.Width;
            }
            else
            {
                focalPointX = mouseCoordinates.X / canvasSize.Width;

                var halfUnusedY = 1 / (canvasSize.AspectRatio - imageSize.AspectRatio) * canvasSize.Height / 2;
                var clampedY = Math.Clamp(mouseCoordinates.Y - halfUnusedY, 0, imageSize.Height);

                focalPointY = clampedY / imageSize.Height;
            }

            return new Point(focalPointX, focalPointY);
        }

        private Point TransformToSourceRectSpace(Point from)
        {
            var sourceRectPosition = Image.SourceRect.Rect.Position;
            var sourceRectSize = Image.SourceRect.Rect.Size;
            return new Point(
                from.X * sourceRectSize.Width + sourceRectPosition.X,
                from.Y * sourceRectSize.Height + sourceRectPosition.Y
            );
        }

        public void OnPointerWheelChanged(object sender, PointerWheelEventArgs e)
        {
            var invOldZoom = InvCurrentZoom;
            var zoomFactor = e.Delta.Y * ZoomTick + 1.0;
            CurrentZoom = Math.Clamp(CurrentZoom * zoomFactor, 1, double.PositiveInfinity);

            var sourceRect = Image.SourceRect.Rect;

            var canvasMouseCoordinates = e.GetPosition(ImageCanvas);
            
            var currentCenter = sourceRect.Center;
            var desiredCenterInImageCoords = MousePointerInImageSpace(canvasMouseCoordinates);
            if(e.Delta.Y < 0)
            {
                desiredCenterInImageCoords = new Point(1 - desiredCenterInImageCoords.X, 1 - desiredCenterInImageCoords.Y);
            }
            var desiredCenter = TransformToSourceRectSpace(desiredCenterInImageCoords);

            var maxTravelDistance = Math.Abs(invOldZoom - InvCurrentZoom);

            var newCenterX = Math.Clamp(desiredCenter.X, currentCenter.X - maxTravelDistance, currentCenter.X + maxTravelDistance);
            var newCenterY = Math.Clamp(desiredCenter.Y, currentCenter.Y - maxTravelDistance, currentCenter.Y + maxTravelDistance);

            var sourceRectNewTopLeft = new Point(newCenterX - InvCurrentZoom / 2, newCenterY - InvCurrentZoom / 2);
            Image.SourceRect = new RelativeRect(sourceRectNewTopLeft, new Size(InvCurrentZoom, InvCurrentZoom), RelativeUnit.Relative);
        }
    }
}