using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace Vectorform
{
    public class CanvasViewport
    {
        #region Private Data

        /// <summary>
        /// Provides easy access to the Canvas' Translation
        /// </summary>
        private TranslateTransform _Translation;

        /// <summary>
        /// Provides easy access to the Canvas' Scale
        /// </summary>
        private ScaleTransform _Scale;

        /// <summary>
        /// Provides easy access to the canvas.
        /// </summary>
        private Canvas _TheCanvas;
        #endregion

        #region Properties
        /// <summary>
        /// Get or set the size of the viewport (in logical units).
        /// </summary>
        public Size Size
        {
            get
            {
                return new Size(_TheCanvas.Width / _Scale.ScaleX, _TheCanvas.Height / _Scale.ScaleY);
            }
            set
            {
                _Scale.ScaleX = _TheCanvas.Width / value.Width;
                _Scale.ScaleY = _TheCanvas.Height / value.Height;
            }
        }

        /// <summary>
        /// Get or set the center of the view (in logical units).
        /// </summary>
        public Point Center
        {
            get
            {
                return new Point(_Translation.X + Size.Width * 0.5, _Translation.Y + Size.Height * 0.5);
            }
            set
            {
                _Translation.X = -(value.X - Size.Width * 0.5) * _Scale.ScaleX;
                _Translation.Y = -(value.Y - Size.Height * 0.5) * _Scale.ScaleY;
            }
        }
        #endregion

        #region Methods
        /// <summary>
        /// Construct the viewport on a canvas.
        /// </summary>
        /// <param name="thePage"></param>
        public CanvasViewport(Canvas thePage)
        {
            _TheCanvas = thePage;

            // Find the transformations.
            TransformGroup xforms = thePage.RenderTransform as TransformGroup;
            if (xforms != null)
            {
                foreach (Transform x in xforms.Children)
                {
                    if (x is TranslateTransform)
                    {
                        _Translation = x as TranslateTransform;
                    }
                    else if (x is ScaleTransform)
                    {
                        _Scale = x as ScaleTransform;
                    }
                }
            }
        }

        /// <summary>
        /// Convert from a screen point to a logical point.
        /// </summary>
        /// <param name="devicePoint"></param>
        /// <returns></returns>
        public Point ToLogical(Point devicePoint)
        {
            return new Point((devicePoint.X - _Translation.X) / _Scale.ScaleX, (devicePoint.Y - _Translation.Y) / _Scale.ScaleY);
        }

        #endregion

    }
}