using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Diagnostics;



namespace LZ4Sharp

{

	#if LZ4_ARCH64

		#define CLASSNAME LZ4Decompressor64

	#else

		#define CLASSNAME LZ4Decompressor32

	#endif

    /// <summary>

    /// Class for decompressing an LZ4 compressed byte array.

    /// </summary>

     public unsafe class CLASSNAME : ILZ4Decompressor

    {

        #include "LZ4.h"



        readonly sbyte[] m_DecArray = new sbyte[8] { 0, 3, 2, 3,0,0,0,0 };

        #if LZ4_ARCH64

		readonly sbyte[] m_Dec2table= new sbyte[8]{0, 0, 0, -1, 0, 1, 2, 3};

        #endif



        // Note : The decoding functions LZ4_uncompress() and LZ4_uncompress_unknownOutputSize()

        //              are safe against "buffer overflow" attack type

        //              since they will *never* write outside of the provided output buffer :

        //              they both check this condition *before* writing anything.

        //              A corrupted packet however can make them *read* within the first 64K before the output buffer.



        /// <summary>

        /// Decompress.

        /// </summary>

        /// <param name="source">compressed array</param>

        /// <param name="dest">This must be the exact length of the decompressed item</param>

        public void DecompressKnownSize(byte[] compressed, byte[] decompressed)

        {

            int len = DecompressKnownSize(compressed, decompressed, decompressed.Length);

            Debug.Assert(len == decompressed.Length);

        }



        public int DecompressKnownSize(byte[] compressed, byte[] decompressedBuffer, int decompressedSize)

        {

            fixed (byte* src = compressed)

            fixed (byte* dst = decompressedBuffer)

                return DecompressKnownSize(src, dst, decompressedSize);

        }



        public int DecompressKnownSize(byte* compressed, byte* decompressedBuffer, int decompressedSize)

        {

            fixed (sbyte* dec = m_DecArray)

#if LZ4_ARCH64

            fixed(sbyte* dec2Ptr = m_Dec2table)

#endif

            {

                // Local Variables

                byte* ip = (byte*)compressed;

                byte* r;



                byte* op = (byte*)decompressedBuffer;

                byte* oend = op + decompressedSize;

                byte* cpy;



                byte token;

                int len, length;





                // Main Loop

                while (true)

                {

                    // get runLength

                    token = *ip++;

                    if ((length = (token >> LZ4Util.ML_BITS)) == LZ4Util.RUN_MASK) { for (; (len = *ip++) == 255; length += 255) { } length += len; }





                    cpy = op + length;

                    if (cpy > oend - LZ4Util.COPYLENGTH)

                    {

                        if (cpy > oend) goto _output_error;

                        LZ4Util.CopyMemory(op, ip, length);

                        ip += length;

                        break;

                    }



                    LZ4_WILDCOPY(ip, op, cpy); ip -= (op - cpy); op = cpy;





                    // get offset

                    LZ4_READ_LITTLEENDIAN_16(r,cpy,ip); ip+=2;

					if(r < decompressedBuffer) goto _output_error;



                    // get matchLength

                    if ((length = (int)(token & LZ4Util.ML_MASK)) == LZ4Util.ML_MASK) { for (; *ip == 255; length += 255) { ip++; } length += *ip++; }



                    // copy repeated sequence

                    if (op - r < STEPSIZE)

                    {

#if LZ4_ARCH64

                        var dec2 = dec2Ptr[(int)(op-r)];

#else

                        const int dec2 = 0;

#endif





                        *op++ = *r++;

                        *op++ = *r++;

                        *op++ = *r++;

                        *op++ = *r++;

                        r -= dec[op - r];

                        A32(op) = A32(r); op += STEPSIZE - 4;

                        r -= dec2;

                    }

                    else { LZ4_COPYSTEP(r, op);  }

                    cpy = op + length - (STEPSIZE - 4);

                    if (cpy > oend - LZ4Util.COPYLENGTH)

                    {

                        if (cpy > oend) goto _output_error;



                        LZ4_SECURECOPY(r, op, (oend - LZ4Util.COPYLENGTH));

                        while (op < cpy) *op++ = *r++;

                        op = cpy;

                        if (op == oend) break;

                        continue;

                    }

                    

                    LZ4_SECURECOPY(r, op, cpy);

                    op = cpy; // correction

                }



                // end of decoding

                return (int)(((byte*)ip) - compressed);



                // write overflow error detected

            _output_error:

                return (int)(-(((byte*)ip) - compressed));

            }

        }



        public byte[] Decompress(byte[] compressed)

        {

			int length = compressed.Length;

            int len;

            byte[] dest;

			const int Multiplier = 4; // Just a number. Determines how fast length should increase.

            do

            {

                length *= Multiplier;

                dest = new byte[length];

                len = Decompress(compressed, dest, compressed.Length);

            }

            while (len < 0 || dest.Length < len);



            byte[] d = new byte[len];

            Buffer.BlockCopy(dest, 0, d, 0, d.Length);

            return d;

        }



        public int Decompress(byte[] compressed, byte[] decompressedBuffer)

        {

            return Decompress(compressed, decompressedBuffer, compressed.Length);

        }



        public int Decompress(byte[] compressedBuffer, byte[] decompressedBuffer, int compressedSize)

        {

            fixed (byte* src = compressedBuffer)

            fixed (byte* dst = decompressedBuffer)

                return Decompress(src, dst, compressedSize, decompressedBuffer.Length);

        }



        public int Decompress(byte[] compressedBuffer, int compressedPosition, byte[] decompressedBuffer, int decompressedPosition, int compressedSize)

        {

            fixed (byte* src = &compressedBuffer[compressedPosition])

            fixed (byte* dst = &decompressedBuffer[decompressedPosition])

                return Decompress(src, dst, compressedSize, decompressedBuffer.Length);

        }



        public int Decompress(

            byte* compressedBuffer,

            byte* decompressedBuffer,

            int compressedSize,

            int maxDecompressedSize)

        {

            fixed (sbyte* dec = m_DecArray)

#if LZ4_ARCH64

            fixed(sbyte* dec2Ptr = m_Dec2table)

#endif

            {

                // Local Variables

                byte* ip = (byte*)compressedBuffer;

                byte* iend = ip + compressedSize;

                byte* r;



                byte* op = (byte*)decompressedBuffer;

                byte* oend = op + maxDecompressedSize;

                byte* cpy;



                byte token;

                int len, length;





                // Main Loop

                while (ip < iend)

                {

                    // get runLength

                    token = *ip++;

					if ((length=(token>>LZ4Util.ML_BITS)) == LZ4Util.RUN_MASK) { int s=255; while ((ip<iend) && (s==255)) { s=*ip++; length += s; } }



                    // copy literals

                    cpy = op + length;

					if ((cpy>oend-LZ4Util.COPYLENGTH) || (ip+length>iend-LZ4Util.COPYLENGTH))

                    {

						if (cpy > oend) goto _output_error;          // Error : request to write beyond destination buffer

						if (ip+length > iend) goto _output_error;    // Error : request to read beyond source buffer

                        LZ4Util.CopyMemory(op, ip, length);

                        op += length;

						ip += length;

						if (ip<iend) goto _output_error;             // Error : LZ4 format violation

                        break; //Necessarily EOF

                    }



                    LZ4_WILDCOPY(ip, op, cpy); ip -= (op - cpy); op = cpy;



                    // get offset

                    LZ4_READ_LITTLEENDIAN_16(r,cpy,ip); ip+=2;

                    if (r < decompressedBuffer) goto _output_error;



                    // get matchlength

					if ((length=(int)(token&LZ4Util.ML_MASK)) == LZ4Util.ML_MASK) { while (ip<iend) { int s = *ip++; length +=s; if (s==255) continue; break; } }



                    // copy repeated sequence

                    if (op - r < STEPSIZE)

                    {

#if LZ4_ARCH64

                        var dec2 = dec2Ptr[op-ref];

#else

			            const int dec2 = 0;

#endif



                        *op++ = *r++;

                        *op++ = *r++;

                        *op++ = *r++;

                        *op++ = *r++;

                        r -= dec[op - r];

                        A32(op) = A32(r); op += STEPSIZE - 4;

                        r -= dec2;

                    }

                    else { LZ4_COPYSTEP(r, op); }

                    cpy = op + length - (STEPSIZE - 4);

                    if (cpy > oend - LZ4Util.COPYLENGTH)

                    {

                        if (cpy > oend) goto _output_error;



                        LZ4_SECURECOPY(r, op, (oend - LZ4Util.COPYLENGTH));

                        while (op < cpy) *op++ = *r++;

                        op = cpy;

                        if (op == oend) goto _output_error; // Check EOF (should never happen, since last 5 bytes are supposed to be literals)

                        continue;

                    }

                    LZ4_SECURECOPY(r, op, cpy);

                    op = cpy; // correction

                }





                return (int)(((byte*)op) - decompressedBuffer);





            _output_error:

                return (int)(-(((byte*)ip) - compressedBuffer));

            }

        }

    }

}