using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Diagnostics;

namespace Microsoft.Research.DynamicDataDisplay.ViewportConstraints
{
	/// <summary>
	/// Represents a restriction in which actual visible rect's proportions depends on 
	/// actual output rect's proportions.
	/// </summary>
	public sealed class PhysicalProportionsConstraint : ViewportConstraint
	{
		/// <summary>
		/// Initializes a new instance of the <see cref="PhysicalProportionsConstraint"/> class.
		/// </summary>
		public PhysicalProportionsConstraint() { }

		/// <summary>
		/// Initializes a new instance of the <see cref="PhysicalProportionsConstraint"/> class with the given proportion ratio.
		/// </summary>
		/// <param name="proportionRatio">The proportion ratio.</param>
		public PhysicalProportionsConstraint(double proportionRatio)
		{
			ProportionRatio = proportionRatio;
		}

		private double proportionRatio = 1.0;
		/// <summary>Gets or sets the proportion ratio (width / height). Default value is 1.0.</summary>
		/// <value>The proportion ratio.</value>
		public double ProportionRatio
		{
			get { return proportionRatio; }
			set
			{
				if (proportionRatio != value)
				{
					proportionRatio = value;
					RaiseChanged();
				}
			}
		}

		/// <summary>
		/// Applies the restriction.
		/// </summary>
		/// <param name="previousDataRect">Previous data rectangle.</param>
		/// <param name="proposedDataRect">Proposed data rectangle.</param>
		/// <param name="viewport">The viewport, to which current restriction is being applied.</param>
		/// <returns>New changed visible rectangle.</returns>
		public override DataRect Apply(DataRect previousDataRect, DataRect proposedDataRect, Viewport2D viewport)
		{
			Rect output = viewport.Output;
			if (output.Height == 0 || output.Width == 0)
				return proposedDataRect;

            double newRatio = proposedDataRect.Width * output.Height / 
                (proposedDataRect.Height * output.Width);

            // Don't modify rect if new ratio differs only slightly 
            if (Math.Abs(newRatio - proportionRatio) < 1e-3)
                return proposedDataRect;

            // Try to keep visible rect's square constant
            double width = proposedDataRect.Width, height = proposedDataRect.Height;
            double square = proposedDataRect.Width * proposedDataRect.Height;
            if (square > 0)
            {
                width = Math.Sqrt(proportionRatio * output.Width * square / output.Height);
                height = Math.Sqrt(output.Height * square / (proportionRatio * output.Width));
            }

            // Finally ensure we have correct aspect ratio
            double delta = (proportionRatio * height * output.Width - width * output.Height) /
                (output.Height + proportionRatio * output.Width);
            width += delta;
            height -= delta;

            double x0 = (proposedDataRect.XMax + proposedDataRect.XMin) / 2;
            double y0 = (proposedDataRect.YMax + proposedDataRect.YMin) / 2;

            return new DataRect
            {
                XMin = x0 - width / 2,
                Width = width,
                YMin = y0 - height / 2,
                Height = height
            };
		}
	}
}