using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

namespace DSDecmp.Formats.Nitro
{
    /// <summary>
    /// Decompressor for the LZ-0x10 format used in many of the games for the
    /// newer Nintendo consoles and handhelds.
    /// </summary>
    public class LZ10 : NitroCFormat
    {
        public LZ10() : base(0x10) { }

        public override void Decompress(Stream instream, long inLength,
                                            Stream outstream)
        {
            #region format definition form GBATEK/NDSTEK
            /*  Data header (32bit)
                  Bit 0-3   Reserved
                  Bit 4-7   Compressed type (must be 1 for LZ77)
                  Bit 8-31  Size of decompressed data
                Repeat below. Each Flag Byte followed by eight Blocks.
                Flag data (8bit)
                  Bit 0-7   Type Flags for next 8 Blocks, MSB first
                Block Type 0 - Uncompressed - Copy 1 Byte from Source to Dest
                  Bit 0-7   One data byte to be copied to dest
                Block Type 1 - Compressed - Copy N+3 Bytes from Dest-Disp-1 to Dest
                  Bit 0-3   Disp MSBs
                  Bit 4-7   Number of bytes to copy (minus 3)
                  Bit 8-15  Disp LSBs
             */
            #endregion

            long readBytes = 0;

            byte type = (byte)instream.ReadByte();
            if (type != base.magicByte)
                throw new InvalidDataException("The provided stream is not a valid LZ-0x10 "
                            + "compressed stream (invalid type 0x" + type.ToString("X") + ")");
            byte[] sizeBytes = new byte[3];
            instream.Read(sizeBytes, 0, 3);
            int decompressedSize = base.Bytes2Size(sizeBytes);
            readBytes += 4;
            if (decompressedSize == 0)
            {
                sizeBytes = new byte[4];
                instream.Read(sizeBytes, 0, 4);
                decompressedSize = base.Bytes2Size(sizeBytes);
                readBytes += 4;
            }

            // the maximum 'DISP-1' is 0xFFF.
            int bufferLength = 0x1000;
            byte[] buffer = new byte[bufferLength];
            int bufferOffset = 0;
            

            int currentOutSize = 0;
            int flags = 0, mask = 0;
            while (currentOutSize < decompressedSize)
            {
                // (throws when requested new flags byte is not available)
                #region Update the mask. If all flag bits have been read, get a new set.
                // the current mask is the mask used in the previous run. So if it masks the
                // last flag bit, get a new flags byte.
                if (mask == 1)
                {
                    if (readBytes >= inLength)
                        throw new NotEnoughDataException(currentOutSize, decompressedSize);
                    flags = instream.ReadByte(); readBytes++;
                    if (flags < 0)
                        throw new StreamTooShortException();
                    mask = 0x80;
                }
                else
                {
                    mask >>= 1;
                }
                #endregion

                // bit = 1 <=> compressed.
                if ((flags & mask) > 0)
                {
                    // (throws when < 2 bytes are available)
                    #region Get length and displacement('disp') values from next 2 bytes
                    // there are < 2 bytes available when the end is at most 1 byte away
                    if (readBytes + 1 >= inLength)
                    {
                        // make sure the stream is at the end
                        if (readBytes < inLength)
                        {
                            instream.ReadByte(); readBytes++;
                        }
                        throw new NotEnoughDataException(currentOutSize, decompressedSize);
                    }
                    int byte1 = instream.ReadByte(); readBytes++;
                    int byte2 = instream.ReadByte(); readBytes++;
                    if (byte2 < 0)
                        throw new StreamTooShortException();

                    // the number of bytes to copy
                    int length = byte1 >> 4;
                    length += 3;

                    // from where the bytes should be copied (relatively)
                    int disp = ((byte1 & 0x0F) << 8) | byte2;
                    disp += 1;

                    if (disp > currentOutSize)
                        throw new InvalidDataException("Cannot go back more than already written. "
                                + "DISP = " + disp + ", #written bytes = 0x" + currentOutSize.ToString("X")
                                + " at 0x" + instream.Position.ToString("X"));
                    #endregion

                    int bufIdx = bufferOffset + bufferLength - disp;
                    for (int i = 0; i < length; i++)
                    {
                        byte next = buffer[bufIdx % bufferLength];
                        bufIdx++;
                        outstream.WriteByte(next);
                        buffer[bufferOffset] = next;
                        bufferOffset = (bufferOffset + 1) % bufferLength;
                    }

                }
                else
                {
                    if (readBytes >= inLength)
                        throw new NotEnoughDataException(currentOutSize, decompressedSize);
                    int next = instream.ReadByte(); readBytes++;
                    if (next < 0)
                        throw new StreamTooShortException();
                        
                    currentOutSize++;
                    outstream.WriteByte((byte)next);
                    buffer[bufferOffset] = (byte)next;
                    bufferOffset = (bufferOffset + 1) % bufferLength;
                }
            }

        }

        public override void Compress(Stream instream, long inLength, Stream outstream)
        {
            throw new NotImplementedException();
        }
    }
}