using System;
using System.Collections;
using System.Collections.Generic;
using System.Windows.Media;

namespace ScreenToGif.ImageUtil.Gif.Encoder.Quantization
{
    public class GrayscaleQuantizer : PaletteQuantizer
    {
        /// <summary>
        /// Grayscale palette quantizer.
        /// </summary>
        /// <remarks>
        /// Palette quantization only requires a single quantization step, because there's no need to build the palette.
        /// </remarks>
        public GrayscaleQuantizer(Color? transparent = null, int maxColors = 256) : base(new ArrayList())
        {
            Colors = new List<Color>(maxColors);

            MaxColorsWithTransparency = transparent.HasValue ? maxColors - 1 : maxColors;

            //Initialize a new color table with entries that are determined by some optimal palette-finding algorithm.
            for (var i = 0; i < MaxColorsWithTransparency; i++)
            {
                //Even distribution of grayscale colors. 
                var intensity = Convert.ToUInt32(i * 0xFF / (MaxColorsWithTransparency - 1));

                Colors.Add(Color.FromArgb(0xFF, (byte)intensity, (byte)intensity, (byte)intensity));
            }

            if (transparent.HasValue)
                Colors.Add(transparent.Value);
        }

        /// <summary>
        /// Override this to process the pixel in the second pass of the algorithm
        /// </summary>
        /// <param name="pixel">The pixel to quantize</param>
        /// <returns>The quantized value</returns>
        protected override byte QuantizePixel(Color pixel)
        {
            var luminance = pixel.R * 0.299 + pixel.G * 0.587 + pixel.B * 0.114;

            //Gray scale is an intensity map from black to white.
            //Compute the index to the grayscale entry that approximates the luminance, and then round the index.
            //Also, constrain the index choices by the number of colors to do, and then set that pixel's index to the byte value.

            //return (byte)((int)((luminance + 0.5) * Colors.Length) >> 8); //Without transparency.
            //return (byte)(luminance + 0.5); //Without configurable color count.

            return (byte)((int)((luminance + 0.5) * MaxColorsWithTransparency) >> 8); //Returns the color index.
        }
    }
}