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using System;
using System.Collections;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Linq;

// Reading and writing 18-bit RGB VGA Palette (pal) files with C#
// http://www.cyotek.com/blog/reading-and-writing-18-bit-rgb-vga-palette-pal-files-with-csharp

namespace Cyotek.Demonstrations.Rgb18BitPalette
{
  internal sealed class WestwoodPalette : IEnumerable<Color>
  {
    #region Fields

    private Color[] _palette;

    #endregion

    #region Constructors

    public WestwoodPalette()
    {
      _palette = new Color[0];
    }

    public WestwoodPalette(IEnumerable<Color> colors)
    {
      if (colors == null)
      {
        throw new ArgumentNullException(nameof(colors));
      }

      _palette = colors.ToArray();
    }

    #endregion

    #region Static Methods

    public static WestwoodPalette LoadFrom(string fileName)
    {
      WestwoodPalette palette;

      palette = new WestwoodPalette();
      palette.Load(fileName);

      return palette;
    }

    public static WestwoodPalette LoadFrom(Stream stream)
    {
      WestwoodPalette palette;

      palette = new WestwoodPalette();
      palette.Load(stream);

      return palette;
    }

    #endregion

    #region Properties

    public int Count
    {
      get { return _palette.Length; }
    }

    public Color this[int index]
    {
      get { return _palette[index]; }
    }

    #endregion

    #region Methods

    public void Load(string fileName)
    {
      using (Stream stream = File.OpenRead(fileName))
      {
        this.Load(stream);
      }
    }

    public void Load(Stream stream)
    {
      int length;

      length = (int)(stream.Length / 3);

      _palette = new Color[length];

      for (int i = 0; i < length; i++)
      {
        int r;
        int g;
        int b;

        r = stream.ReadByte() << 2;
        g = stream.ReadByte() << 2;
        b = stream.ReadByte() << 2;

        //_palette[i] = Color.FromArgb(r, g, b); // NOTE: Will crash if used with 24-bit palettes
        _palette[i] = Color.FromArgb((255 << 24) | (r << 16) | (g << 8) | b);
      }
    }

    public void Save(string fileName)
    {
      using (Stream stream = File.Create(fileName))
      {
        this.Save(stream);
      }
    }

    public void Save(Stream stream)
    {
      for (int i = 0; i < _palette.Length; i++)
      {
        Color color;
        byte r;
        byte g;
        byte b;

        color = _palette[i];

        r = (byte)(color.R >> 2);
        g = (byte)(color.G >> 2);
        b = (byte)(color.B >> 2);

        stream.WriteByte(r);
        stream.WriteByte(g);
        stream.WriteByte(b);
      }
    }

    public Color[] ToArray()
    {
      return (Color[])_palette.Clone();
    }

    #endregion

    #region IEnumerable<Color> Interface

    public IEnumerator<Color> GetEnumerator()
    {
      return ((IEnumerable<Color>)_palette).GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
      return this.GetEnumerator();
    }

    #endregion
  }
}