using System.IO;

namespace Syroot.Worms.Core
{
    /// <summary>
    /// Represents methods to decompress data which is compressed using Team17's internal compression algorithm for
    /// graphic file formats.
    /// S. http://worms2d.info/Team17_compression.
    /// </summary>
    internal static class Team17Compression
    {
        // ---- METHODS (INTERNAL) -------------------------------------------------------------------------------------

        /// <summary>
        /// Decompresses the data available in the given <paramref name="stream"/> into the provided
        /// <paramref name="buffer"/>.
        /// </summary>
        /// <param name="stream">The <see cref="Stream"/> to read the data from.</param>
        /// <param name="buffer">The byte array buffer to write the decompressed data to.</param>
        internal static void Decompress(Stream stream, ref byte[] buffer)
        {
            // TODO: This fails for compressed data in CD:\\Data\Mission\Training0-9.img.
            int output = 0; // Offset of next write.
            int cmd;
            while ((cmd = stream.ReadByte()) != -1)
            {
                // Read a byte.
                if ((cmd & 0x80) == 0)
                {
                    // Command: 1 byte (color)
                    buffer[output++] = (byte)cmd;
                }
                else
                {
                    // Arg1 = bits 2-5
                    int arg1 = (cmd >> 3) & 0xF;
                    int arg2 = stream.ReadByte();
                    if (arg2 == -1)
                    {
                        return;
                    }
                    // Arg2 = bits 6-16
                    arg2 = ((cmd << 8) | arg2) & 0x7FF;
                    if (arg1 == 0)
                    {
                        // Command: 0x80 0x00
                        if (arg2 == 0)
                        {
                            return;
                        }
                        int arg3 = stream.ReadByte();
                        if (arg3 == -1)
                        {
                            return;
                        }
                        // Command: 3 bytes
                        output = CopyData(output, arg2, arg3 + 18, ref buffer);
                    }
                    else
                    {
                        // Command: 2 bytes
                        output = CopyData(output, arg2 + 1, arg1 + 2, ref buffer);
                    }
                }
            }
        }

        // ---- METHODS (PRIVATE) --------------------------------------------------------------------------------------

        private static int CopyData(int offset, int compressedOffset, int count, ref byte[] buffer)
        {
            for (; count > 0; count--)
            {
                buffer[offset] = buffer[offset++ - compressedOffset];
            }
            return offset;
        }
    }
}