// ==++==
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  zlib.h -- interface of the 'zlib' general purpose compression library
//  version 1.2.1, November 17th, 2003
//
//  Copyright (C) 1995-2003 Jean-loup Gailly and Mark Adler
//
//  This software is provided 'as-is', without any express or implied
//  warranty.  In no event will the authors be held liable for any damages
//  arising from the use of this software.
//
//  Permission is granted to anyone to use this software for any purpose,
//  including commercial applications, and to alter it and redistribute it
//  freely, subject to the following restrictions:
//
//  1. The origin of this software must not be misrepresented; you must not
//     claim that you wrote the original software. If you use this software
//     in a product, an acknowledgment in the product documentation would be
//     appreciated but is not required.
//  2. Altered source versions must be plainly marked as such, and must not be
//     misrepresented as being the original software.
//  3. This notice may not be removed or altered from any source distribution.
//
//
// ==--==

namespace System.IO.Compression
{
    using System;
    using System.Diagnostics;

    internal class Inflater {
        // const tables used in decoding:

        // Extra bits for length code 257 - 285.  
        private static readonly byte[] extraLengthBits = {
            0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0};

        // The base length for length code 257 - 285.
        // The formula to get the real length for a length code is lengthBase[code - 257] + (value stored in extraBits)
        private static readonly int[] lengthBase = {
            3,4,5,6,7,8,9,10,11,13,15,17,19,23,27,31,35,43,51,59,67,83,99,115,131,163,195,227,258};

        // The base distance for distance code 0 - 29    
        // The real distance for a distance code is  distanceBasePosition[code] + (value stored in extraBits)
        private static readonly int[] distanceBasePosition= {
            1,2,3,4,5,7,9,13,17,25,33,49,65,97,129,193,257,385,513,769,1025,1537,2049,3073,4097,6145,8193,12289,16385,24577,0,0};        

        // code lengths for code length alphabet is stored in following order
        private static readonly byte[] codeOrder = {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};

        private static readonly byte[] staticDistanceTreeTable = { 
            0x00,0x10,0x08,0x18,0x04,0x14,0x0c,0x1c,0x02,0x12,0x0a,0x1a,
            0x06,0x16,0x0e,0x1e,0x01,0x11,0x09,0x19,0x05,0x15,0x0d,0x1d,
            0x03,0x13,0x0b,0x1b,0x07,0x17,0x0f,0x1f,
        };

        private OutputWindow output;
        private InputBuffer  input;
        HuffmanTree literalLengthTree;
        HuffmanTree distanceTree;

        InflaterState state;
        bool hasFormatReader;
        int bfinal;
        BlockType blockType;
        
        // uncompressed block
        byte[] blockLengthBuffer = new byte[4];     
        int blockLength;

        // compressed block
        private int length;
        private int distanceCode;       
        private int extraBits;

        private int loopCounter;
        private int literalLengthCodeCount;
        private int distanceCodeCount;
        private int codeLengthCodeCount;        
        private int codeArraySize;
        private int lengthCode;

        private byte[] codeList;        // temporary array to store the code length for literal/Length and distance
        private byte[] codeLengthTreeCodeLength;
        HuffmanTree codeLengthTree;

        IFileFormatReader formatReader;  // class to decode header and footer (e.g. gzip)

        public Inflater() {           
            output = new OutputWindow();
            input  = new InputBuffer();

            codeList = new byte[HuffmanTree.MaxLiteralTreeElements + HuffmanTree.MaxDistTreeElements];
            codeLengthTreeCodeLength = new byte[HuffmanTree.NumberOfCodeLengthTreeElements];
            Reset();
        }

        internal void SetFileFormatReader(IFileFormatReader reader) {
            formatReader = reader;
            hasFormatReader = true;
            Reset();
        }

        private void Reset() {
            if ( hasFormatReader) {
                state   = InflaterState.ReadingHeader;     // start by reading Header info
            } 
            else {
                state   = InflaterState.ReadingBFinal;     // start by reading BFinal bit 
            }
        }
        
        public void SetInput(byte[] inputBytes, int offset, int length) {
            input.SetInput(inputBytes, offset, length);    // append the bytes
        }


        public bool Finished() {
            return (state == InflaterState.Done || state== InflaterState.VerifyingFooter);
        }

        public int AvailableOutput{
            get {
                return output.AvailableBytes;
            }
        }

        public bool NeedsInput(){
            return input.NeedsInput();
        }

        public int Inflate(byte[] bytes, int offset, int length) {
            // copy bytes from output to outputbytes if we have aviable bytes 
            // if buffer is not filled up. keep decoding until no input are available
            // if decodeBlock returns false. Throw an exception.
            int count = 0;
            do 
            {
                int copied = output.CopyTo(bytes, offset, length);
                if( copied > 0) {
                    if( hasFormatReader) {
                        formatReader.UpdateWithBytesRead(bytes, offset, copied);
                    }

                    offset += copied;
                    count += copied;
                    length -= copied;
                }

                if (length == 0) {   // filled in the bytes array
                    break;
                }
                // Decode will return false when more input is needed
            } while ( !Finished() && Decode());

            if( state == InflaterState.VerifyingFooter) {  // finished reading CRC
                // In this case finished is true and output window has all the data.
                // But some data in output window might not be copied out.
                if( output.AvailableBytes == 0) {
                    formatReader.Validate();
                }
            }

            return count;
        }

        //Each block of compressed data begins with 3 header bits
        // containing the following data:
        //    first bit       BFINAL
        //    next 2 bits     BTYPE
        // Note that the header bits do not necessarily begin on a byte
        // boundary, since a block does not necessarily occupy an integral
        // number of bytes.
        // BFINAL is set if and only if this is the last block of the data
        // set.
        // BTYPE specifies how the data are compressed, as follows:
        //    00 - no compression
        //    01 - compressed with fixed Huffman codes
        //    10 - compressed with dynamic Huffman codes
        //    11 - reserved (error)
        // The only difference between the two compressed cases is how the
        // Huffman codes for the literal/length and distance alphabets are
        // defined.
        //
        // This function returns true for success (end of block or output window is full,) 
        // false if we are short of input
        //
        private bool Decode() {
            bool eob = false;
            bool result = false;

            if( Finished()) {
                return true;
            }

            if (hasFormatReader) {
                if (state == InflaterState.ReadingHeader) {
                    if (!formatReader.ReadHeader(input)) {
                        return false;
                    }
                    state = InflaterState.ReadingBFinal;              
                }
                else if (state == InflaterState.StartReadingFooter || state == InflaterState.ReadingFooter) {
                    if (!formatReader.ReadFooter(input))
                        return false;

                    state = InflaterState.VerifyingFooter;
                    return true;
                }
            }

            if( state == InflaterState.ReadingBFinal) {   // reading bfinal bit
                // Need 1 bit
                if (!input.EnsureBitsAvailable(1))
                    return false;

                bfinal = input.GetBits(1);
                state = InflaterState.ReadingBType;
            }
            
            if( state == InflaterState.ReadingBType) {
                // Need 2 bits
                if (!input.EnsureBitsAvailable(2)) {
                    state = InflaterState.ReadingBType;
                    return false;
                }

                blockType = (BlockType)input.GetBits(2);
                if (blockType == BlockType.Dynamic) {
                    Debug.WriteLineIf(CompressionTracingSwitch.Informational, "Decoding Dynamic Block", "Compression");
                    state = InflaterState.ReadingNumLitCodes;
                } 
                else if (blockType == BlockType.Static) {
                    Debug.WriteLineIf(CompressionTracingSwitch.Informational, "Decoding Static Block", "Compression");
                    literalLengthTree = HuffmanTree.StaticLiteralLengthTree;
                    distanceTree = HuffmanTree.StaticDistanceTree;
                    state = InflaterState.DecodeTop;
                } 
                else if (blockType == BlockType.Uncompressed) {
                    Debug.WriteLineIf(CompressionTracingSwitch.Informational, "Decoding UnCompressed Block", "Compression");
                    state = InflaterState.UncompressedAligning;
                } 
                else {
                    throw new InvalidDataException(SR.GetString(SR.UnknownBlockType));
                }
            }

            if (blockType == BlockType.Dynamic) {
                if (state < InflaterState.DecodeTop) {   // we are reading the header
                    result = DecodeDynamicBlockHeader();
                }
                else {                    
                    result = DecodeBlock(out eob);  // this can returns true when output is full
                }
            } 
            else if (blockType == BlockType.Static) {
                result = DecodeBlock(out eob);
            } 
            else if (blockType == BlockType.Uncompressed) {
                result = DecodeUncompressedBlock(out eob);
            } 
            else {
                throw new InvalidDataException(SR.GetString(SR.UnknownBlockType));
            }

            //
            // If we reached the end of the block and the block we were decoding had
            // bfinal=1 (final block)
            //
            if (eob && (bfinal != 0)) {
                if (hasFormatReader)
                    state = InflaterState.StartReadingFooter;
                else
                    state = InflaterState.Done;
            }
            return result;
        }


         // Format of Non-compressed blocks (BTYPE=00):
         //
         // Any bits of input up to the next byte boundary are ignored.
         // The rest of the block consists of the following information:
         //
         //     0   1   2   3   4...
         //   +---+---+---+---+================================+
         //   |  LEN  | NLEN  |... LEN bytes of literal data...|
         //   +---+---+---+---+================================+
         // 
         // LEN is the number of data bytes in the block.  NLEN is the
         // one's complement of LEN.

        bool DecodeUncompressedBlock(out bool end_of_block) {
            end_of_block = false;
            while(true) {
                switch( state) {

                case InflaterState.UncompressedAligning: // intial state when calling this function
                    // we must skip to a byte boundary
                    input.SkipToByteBoundary();
                    state = InflaterState.UncompressedByte1;
                    goto case InflaterState.UncompressedByte1;

                case InflaterState.UncompressedByte1:   // decoding block length 
                case InflaterState.UncompressedByte2:
                case InflaterState.UncompressedByte3:
                case InflaterState.UncompressedByte4:
                    int bits = input.GetBits(8);
                    if( bits < 0) {
                        return false;
                    }

                    blockLengthBuffer[state - InflaterState.UncompressedByte1] = (byte)bits;                             
                    if( state == InflaterState.UncompressedByte4) {

                        blockLength = blockLengthBuffer[0] + ((int)blockLengthBuffer[1]) * 256;
                        int blockLengthComplement= blockLengthBuffer[2] + ((int)blockLengthBuffer[3]) * 256;

                        // make sure complement matches
                        if ((ushort) blockLength != (ushort)(~blockLengthComplement)) {
                            throw new InvalidDataException(SR.GetString(SR.InvalidBlockLength));
                        }
                    }

                    state += 1;
                    break;

                case InflaterState.DecodingUncompressed: // copying block data 

                    // Directly copy bytes from input to output. 
                    int bytesCopied = output.CopyFrom(input, blockLength);
                    blockLength -= bytesCopied;

                    if (blockLength == 0) {             
                        // Done with this block, need to re-init bit buffer for next block
                        state = InflaterState.ReadingBFinal;
                        end_of_block = true;
                        Debug.WriteLineIf(CompressionTracingSwitch.Informational, "End of Block", "Compression");
                        return true;
                    }
                    
                    // We can fail to copy all bytes for two reasons:
                    //    Running out of Input 
                    //    running out of free space in output window
                    if(output.FreeBytes == 0) {
                        return true;
                    }

                    return false;

                default:
                    Debug.Assert(false, "check why we are here!");
                    throw new InvalidDataException(SR.GetString(SR.UnknownState));
                }
            }
        }

        bool DecodeBlock(out bool end_of_block_code_seen) {
            end_of_block_code_seen = false;

            int freeBytes = output.FreeBytes;   // it is a little bit faster than frequently accessing the property 
            while(freeBytes > 258) { 
                // 258 means we can safely do decoding since maximum repeat length is 258

                int symbol;
                switch (state) {
                case InflaterState.DecodeTop:
                    // decode an element from the literal tree

                    // 
                    symbol = literalLengthTree.GetNextSymbol(input);
                    if( symbol < 0) {          // running out of input
                        return false;
                    }

                    if (symbol < 256) {        // literal
                        output.Write((byte)symbol);
                        --freeBytes;
                    } 
                    else if( symbol == 256) { // end of block
                        end_of_block_code_seen = true;
                        Debug.WriteLineIf(CompressionTracingSwitch.Informational, "End of Block", "Compression");
                        // Reset state
                        state = InflaterState.ReadingBFinal;                                      
                        return true;           // ***********
                    }
                    else {                 // length/distance pair
                        symbol -= 257;     // length code started at 257
                        if( symbol < 8) {
                            symbol += 3;   // match length = 3,4,5,6,7,8,9,10
                            extraBits = 0;
                        }
                        else if( symbol == 28) { // extra bits for code 285 is 0 
                            symbol = 258;             // code 285 means length 258    
                            extraBits = 0;                            
                        }
                        else {
                            if( symbol < 0 || symbol >= extraLengthBits.Length ) {
                                throw new InvalidDataException(SR.GetString(SR.GenericInvalidData));
                            }
                            extraBits = extraLengthBits[symbol];
                            Debug.Assert(extraBits != 0, "We handle other cases seperately!"); 
                        }
                        length = symbol;
                        goto case InflaterState.HaveInitialLength;
                    }
                    break;

                case InflaterState.HaveInitialLength:
                    if( extraBits > 0) {
                        state = InflaterState.HaveInitialLength;
                        int bits = input.GetBits(extraBits);
                        if( bits < 0) {
                            return false;
                        }

                        if( length < 0 || length >= lengthBase.Length ) {
                            throw new InvalidDataException(SR.GetString(SR.GenericInvalidData));
                        }
                        length = lengthBase[length] + bits;
                    }
                    state = InflaterState.HaveFullLength;                
                    goto case InflaterState.HaveFullLength;

                case InflaterState.HaveFullLength:
                    if( blockType == BlockType.Dynamic) {
                        distanceCode = distanceTree.GetNextSymbol(input);   
                    }
                    else {   // get distance code directly for static block
                        distanceCode = input.GetBits(5);   
                        if( distanceCode >= 0 ) {
                            distanceCode = staticDistanceTreeTable[distanceCode];
                        }                        
                    }

                    if( distanceCode < 0) { // running out input                    
                        return false;
                    }

                    state = InflaterState.HaveDistCode;
                    goto case InflaterState.HaveDistCode;

                case InflaterState.HaveDistCode:
                    // To avoid a table lookup we note that for distanceCode >= 2,
                    // extra_bits = (distanceCode-2) >> 1
                    int offset;
                    if( distanceCode > 3) {
                        extraBits = (distanceCode-2) >> 1;
                        int bits = input.GetBits(extraBits);
                        if( bits < 0 ) {
                            return false;
                        }
                        offset = distanceBasePosition[distanceCode] + bits;
                    }
                    else {
                        offset = distanceCode + 1;
                    }

                    Debug.Assert(freeBytes>= 258, "following operation is not safe!");
                    output.WriteLengthDistance(length, offset);
                    freeBytes -= length;
                    state = InflaterState.DecodeTop;
                    break;

                default:
                    Debug.Assert(false, "check why we are here!");
                    throw new InvalidDataException(SR.GetString(SR.UnknownState));
                }
            }

            return true;
        }


        // Format of the dynamic block header:
        //      5 Bits: HLIT, # of Literal/Length codes - 257 (257 - 286)
        //      5 Bits: HDIST, # of Distance codes - 1        (1 - 32)
        //      4 Bits: HCLEN, # of Code Length codes - 4     (4 - 19)
        //
        //      (HCLEN + 4) x 3 bits: code lengths for the code length
        //          alphabet given just above, in the order: 16, 17, 18,
        //          0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
        //
        //          These code lengths are interpreted as 3-bit integers
        //          (0-7); as above, a code length of 0 means the
        //          corresponding symbol (literal/length or distance code
        //          length) is not used.
        //
        //      HLIT + 257 code lengths for the literal/length alphabet,
        //          encoded using the code length Huffman code
        //
        //       HDIST + 1 code lengths for the distance alphabet,
        //          encoded using the code length Huffman code
        //
        // The code length repeat codes can cross from HLIT + 257 to the
        // HDIST + 1 code lengths.  In other words, all code lengths form
        // a single sequence of HLIT + HDIST + 258 values.
        bool DecodeDynamicBlockHeader() {
            switch (state) {
            case InflaterState.ReadingNumLitCodes:               
                literalLengthCodeCount = input.GetBits(5);
                if( literalLengthCodeCount < 0) {
                    return false;
                }
                literalLengthCodeCount += 257;
                state = InflaterState.ReadingNumDistCodes;
                goto case InflaterState.ReadingNumDistCodes;

            case InflaterState.ReadingNumDistCodes:
                distanceCodeCount = input.GetBits(5);
                if( distanceCodeCount < 0) {
                    return false;
                }
                distanceCodeCount += 1;
                state = InflaterState.ReadingNumCodeLengthCodes;
                goto case InflaterState.ReadingNumCodeLengthCodes;

            case InflaterState.ReadingNumCodeLengthCodes:
                codeLengthCodeCount = input.GetBits(4);
                if( codeLengthCodeCount < 0) {
                    return false;
                }
                codeLengthCodeCount += 4;
                loopCounter = 0;
                state = InflaterState.ReadingCodeLengthCodes;
                goto case InflaterState.ReadingCodeLengthCodes;

            case InflaterState.ReadingCodeLengthCodes:
                while(loopCounter < codeLengthCodeCount) {
                    int bits = input.GetBits(3);
                    if( bits < 0) {
                        return false;
                    }
                    codeLengthTreeCodeLength[codeOrder[loopCounter]] = (byte)bits;
                    ++loopCounter;
                }
                
                for (int i = codeLengthCodeCount; i < codeOrder.Length; i++) {
                    codeLengthTreeCodeLength[ codeOrder[i] ] = 0;
                }

                // create huffman tree for code length
                codeLengthTree = new HuffmanTree(codeLengthTreeCodeLength);
                codeArraySize = literalLengthCodeCount + distanceCodeCount;
                loopCounter = 0;     // reset loop count

                state = InflaterState.ReadingTreeCodesBefore;
                goto case InflaterState.ReadingTreeCodesBefore;

            case InflaterState.ReadingTreeCodesBefore:
            case InflaterState.ReadingTreeCodesAfter:                
                while (loopCounter < codeArraySize) {
                    if( state == InflaterState.ReadingTreeCodesBefore) {
                        if( (lengthCode = codeLengthTree.GetNextSymbol(input)) < 0) {
                            return false;
                        }
                    }

                    // The alphabet for code lengths is as follows:
                    //  0 - 15: Represent code lengths of 0 - 15
                    //  16: Copy the previous code length 3 - 6 times.
                    //  The next 2 bits indicate repeat length
                    //         (0 = 3, ... , 3 = 6)
                    //      Example:  Codes 8, 16 (+2 bits 11),
                    //                16 (+2 bits 10) will expand to
                    //                12 code lengths of 8 (1 + 6 + 5)
                    //  17: Repeat a code length of 0 for 3 - 10 times.
                    //    (3 bits of length)
                    //  18: Repeat a code length of 0 for 11 - 138 times
                    //    (7 bits of length)
                    if (lengthCode <= 15) {  
                        codeList[loopCounter++] = (byte)lengthCode;
                    }
                    else {
                        if( !input.EnsureBitsAvailable(7)) { // it doesn't matter if we require more bits here
                            state = InflaterState.ReadingTreeCodesAfter;
                            return false;
                        }

                        int repeatCount;
                        if (lengthCode == 16) {
                            if (loopCounter == 0) {          // can't have "prev code" on first code
                                throw new InvalidDataException();
                            }

                            byte previousCode = codeList[loopCounter-1];
                            repeatCount = input.GetBits(2) + 3;

                            if (loopCounter + repeatCount > codeArraySize) {
                                throw new InvalidDataException();
                            }

                            for (int j = 0; j < repeatCount; j++) {
                                codeList[loopCounter++] = previousCode;
                            }
                        } 
                        else if (lengthCode == 17) {
                            repeatCount = input.GetBits(3) + 3;

                            if (loopCounter + repeatCount > codeArraySize) {
                                throw new InvalidDataException();
                            }

                            for (int j = 0; j < repeatCount; j++) {
                                codeList[loopCounter++] = 0;
                            }
                        } 
                        else { // code == 18
                            repeatCount = input.GetBits(7) + 11;

                            if (loopCounter + repeatCount > codeArraySize) {
                                throw new InvalidDataException();
                            }

                            for (int j = 0; j < repeatCount; j++) {
                                codeList[loopCounter++] = 0;
                            }
                        }
                    }
                    state = InflaterState.ReadingTreeCodesBefore; // we want to read the next code.
                }
                break;

            default:
                Debug.Assert(false, "check why we are here!");
                throw new InvalidDataException(SR.GetString(SR.UnknownState));
            }

            byte[]  literalTreeCodeLength  = new byte[HuffmanTree.MaxLiteralTreeElements];
            byte[]  distanceTreeCodeLength = new byte[HuffmanTree.MaxDistTreeElements];

            // Create literal and distance tables
            Array.Copy(codeList, literalTreeCodeLength, literalLengthCodeCount);
            Array.Copy(codeList, literalLengthCodeCount, distanceTreeCodeLength, 0, distanceCodeCount);

            // Make sure there is an end-of-block code, otherwise how could we ever end?
            if (literalTreeCodeLength[HuffmanTree.EndOfBlockCode] == 0) {
                throw new InvalidDataException();
            }                

            literalLengthTree = new HuffmanTree(literalTreeCodeLength);
            distanceTree = new HuffmanTree(distanceTreeCodeLength);
            state = InflaterState.DecodeTop;
            return true;
        }
    }
}