using System;

namespace Oni.Imaging
{
    internal static class TgaReader
	{
		public static Surface Read(string filePath)
		{
            using (var reader = new BinaryReader(filePath))
			{
				var header = TgaHeader.Read(reader);

				Surface surface;

				switch (header.ImageType)
				{
					case TgaImageType.TrueColor:
						surface = LoadTrueColor(header, reader);
						break;

					case TgaImageType.RleTrueColor:
						surface = LoadRleTrueColor(header, reader);
						break;

					default:
						throw new NotSupportedException(string.Format("Invalid or unsupported TGA image type {0}", header.ImageType));
				}

				if (header.XFlip)
					surface.FlipHorizontal();

				if (!header.YFlip)
					surface.FlipVertical();

                return surface;
			}
		}

		private static Surface LoadTrueColor(TgaHeader header, BinaryReader reader)
		{
			int pixelSize = header.PixelSize;
			var format = header.GetSurfaceFormat();

			var dst = new Surface(header.Width, header.Height, format);
			var src = reader.ReadBytes(header.Width * header.Height * pixelSize);
			int srcOffset = 0;

			for (int y = 0; y < header.Height; y++)
			{
				for (int x = 0; x < header.Width; x++)
				{
					dst[x, y] = header.GetPixel(src, srcOffset);
					srcOffset += pixelSize;
				}
			}

			return dst;
		}

		private static Surface LoadRleTrueColor(TgaHeader header, BinaryReader reader)
		{
			int pixelSize = header.PixelSize;
			var format = header.GetSurfaceFormat();

            var dst = new Surface(header.Width, header.Height, format);

			var src = reader.ReadBytes(reader.Length - reader.Position);
			int srcOffset = 0;

			int y = 0;
			int x = 0;

			var color = Color.Black;

			while (y < header.Height)
			{
				int packetType = src[srcOffset++];

				int packetPixelCount = (packetType & 127) + 1;
				bool isRle = ((packetType & 128) != 0);

				for (int i = 0; i < packetPixelCount && y < header.Height; i++)
				{
					if (i == 0 || !isRle)
					{
						color = header.GetPixel(src, srcOffset);
						srcOffset += pixelSize;
					}

					dst[x, y] = color;
					x++;

					if (x == header.Width)
					{
						x = 0;
						y++;
					}
				}
			}

			return dst;
		}
	}
}