// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

//
//  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.
//
//

#nullable disable

using System;
using System.Diagnostics;
using SharpCompress.Compressors.Deflate;

namespace SharpCompress.Compressors.Deflate64;

internal sealed class InflaterManaged
{
    // const tables used in decoding:

    // Extra bits for length code 257 - 285.
    private static ReadOnlySpan<byte> S_EXTRA_LENGTH_BITS =>
        new byte[]
        {
            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,
            16,
        };

    // 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[] S_LENGTH_BASE =
    {
        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,
        3,
    };

    // The base distance for distance code 0 - 31
    // The real distance for a distance code is  distanceBasePosition[code] + (value stored in extraBits)
    private static readonly int[] S_DISTANCE_BASE_POSITION =
    {
        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,
        32769,
        49153,
    };

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

    private static ReadOnlySpan<byte> S_STATIC_DISTANCE_TREE_TABLE =>
        new byte[]
        {
            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 readonly OutputWindow _output;
    private readonly InputBuffer _input;
    private HuffmanTree _literalLengthTree;
    private HuffmanTree _distanceTree;

    private InflaterState _state;

    //private bool _hasFormatReader;
    private int _bfinal;
    private BlockType _blockType;

    // uncompressed block
    private readonly byte[] _blockLengthBuffer = new byte[4];
    private 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 readonly byte[] _codeList; // temporary array to store the code length for literal/Length and distance
    private readonly byte[] _codeLengthTreeCodeLength;
    private readonly bool _deflate64;
    private HuffmanTree _codeLengthTree;

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

    internal InflaterManaged( /*IFileFormatReader reader, */
        bool deflate64
    )
    {
        _output = new OutputWindow();
        _input = new InputBuffer();

        _codeList = new byte[
            HuffmanTree.MAX_LITERAL_TREE_ELEMENTS + HuffmanTree.MAX_DIST_TREE_ELEMENTS
        ];
        _codeLengthTreeCodeLength = new byte[HuffmanTree.NUMBER_OF_CODE_LENGTH_TREE_ELEMENTS];
        _deflate64 = deflate64;
        //if (reader != null)
        //{
        //    _formatReader = reader;
        //    _hasFormatReader = true;
        //}
        Reset();
    }

    private void Reset() =>
        _state = //_hasFormatReader ?
            //InflaterState.ReadingHeader :   // start by reading Header info
            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() =>
        _state == InflaterState.Done || _state == InflaterState.VerifyingFooter;

    public int AvailableOutput => _output.AvailableBytes;

    public int Inflate(byte[] bytes, int offset, int length)
    {
        // copy bytes from output to outputbytes if we have available bytes
        // if buffer is not filled up. keep decoding until no input are available
        // if decodeBlock returns false. Throw an exception.
        var count = 0;
        do
        {
            var 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()
    {
        var eob = false;
        var 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)
            {
                _state = InflaterState.ReadingNumLitCodes;
            }
            else if (_blockType == BlockType.Static)
            {
                _literalLengthTree = HuffmanTree.StaticLiteralLengthTree;
                _distanceTree = HuffmanTree.StaticDistanceTree;
                _state = InflaterState.DecodeTop;
            }
            else if (_blockType == BlockType.Uncompressed)
            {
                _state = InflaterState.UncompressedAligning;
            }
            else
            {
                throw new ZlibException("Deflate64: unknown block type");
            }
        }

        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 ZlibException("Deflate64: unknown block type");
        }

        //
        // 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.
    private bool DecodeUncompressedBlock(out bool endOfBlock)
    {
        endOfBlock = false;
        while (true)
        {
            switch (_state)
            {
                case InflaterState.UncompressedAligning: // initial 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:
                    var bits = _input.GetBits(8);
                    if (bits < 0)
                    {
                        return false;
                    }

                    _blockLengthBuffer[_state - InflaterState.UncompressedByte1] = (byte)bits;
                    if (_state == InflaterState.UncompressedByte4)
                    {
                        _blockLength = _blockLengthBuffer[0] + (_blockLengthBuffer[1] * 256);
                        var blockLengthComplement =
                            _blockLengthBuffer[2] + (_blockLengthBuffer[3] * 256);

                        // make sure complement matches
                        if ((ushort)_blockLength != (ushort)(~blockLengthComplement))
                        {
                            throw new ZlibException("Deflate64: invalid block length");
                        }
                    }

                    _state += 1;
                    break;

                case InflaterState.DecodingUncompressed: // copying block data

                    // Directly copy bytes from input to output.
                    var 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;
                        endOfBlock = true;
                        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. /*Fail*/
                    Assert(false, "check why we are here!");
                    throw new ZlibException("Deflate64: unknown state");
            }
        }
    }

    private bool DecodeBlock(out bool endOfBlockCodeSeen)
    {
        endOfBlockCodeSeen = false;

        var freeBytes = _output.FreeBytes; // it is a little bit faster than frequently accessing the property
        while (freeBytes > 65536)
        {
            // With Deflate64 we can have up to a 64kb length, so we ensure at least that much space is available
            // in the OutputWindow to avoid overwriting previous unflushed output data.

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

                    // TODO: optimize this!!!
                    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
                        endOfBlockCodeSeen = true;
                        // 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 (!_deflate64 && symbol == 28)
                        {
                            // extra bits for code 285 is 0
                            symbol = 258; // code 285 means length 258
                            _extraBits = 0;
                        }
                        else
                        {
                            if (symbol < 0 || symbol >= S_EXTRA_LENGTH_BITS.Length)
                            {
                                throw new ZlibException("Deflate64: invalid data");
                            }
                            _extraBits = S_EXTRA_LENGTH_BITS[symbol];
                        }
                        _length = symbol;
                        goto case InflaterState.HaveInitialLength;
                    }
                    break;

                case InflaterState.HaveInitialLength:
                    if (_extraBits > 0)
                    {
                        _state = InflaterState.HaveInitialLength;
                        var bits = _input.GetBits(_extraBits);
                        if (bits < 0)
                        {
                            return false;
                        }

                        if (_length < 0 || _length >= S_LENGTH_BASE.Length)
                        {
                            throw new ZlibException("Deflate64: invalid data");
                        }
                        _length = S_LENGTH_BASE[_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 = S_STATIC_DISTANCE_TREE_TABLE[_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 > 3,
                    // extra_bits = (distanceCode-2) >> 1
                    int offset;
                    if (_distanceCode > 3)
                    {
                        _extraBits = (_distanceCode - 2) >> 1;
                        var bits = _input.GetBits(_extraBits);
                        if (bits < 0)
                        {
                            return false;
                        }
                        offset = S_DISTANCE_BASE_POSITION[_distanceCode] + bits;
                    }
                    else
                    {
                        offset = _distanceCode + 1;
                    }

                    _output.WriteLengthDistance(_length, offset);
                    freeBytes -= _length;
                    _state = InflaterState.DecodeTop;
                    break;

                default:
                    Debug. /*Fail*/
                    Assert(false, "check why we are here!");
                    throw new ZlibException("Deflate64: unknown state");
            }
        }

        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.
    private 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)
                {
                    var bits = _input.GetBits(3);
                    if (bits < 0)
                    {
                        return false;
                    }
                    _codeLengthTreeCodeLength[S_CODE_ORDER[_loopCounter]] = (byte)bits;
                    ++_loopCounter;
                }

                for (var i = _codeLengthCodeCount; i < S_CODE_ORDER.Length; i++)
                {
                    _codeLengthTreeCodeLength[S_CODE_ORDER[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
                    {
                        int repeatCount;
                        if (_lengthCode == 16)
                        {
                            if (!_input.EnsureBitsAvailable(2))
                            {
                                _state = InflaterState.ReadingTreeCodesAfter;
                                return false;
                            }

                            if (_loopCounter == 0)
                            {
                                // can't have "prev code" on first code
                                throw new ZlibException();
                            }

                            var previousCode = _codeList[_loopCounter - 1];
                            repeatCount = _input.GetBits(2) + 3;

                            if (_loopCounter + repeatCount > _codeArraySize)
                            {
                                throw new ZlibException();
                            }

                            for (var j = 0; j < repeatCount; j++)
                            {
                                _codeList[_loopCounter++] = previousCode;
                            }
                        }
                        else if (_lengthCode == 17)
                        {
                            if (!_input.EnsureBitsAvailable(3))
                            {
                                _state = InflaterState.ReadingTreeCodesAfter;
                                return false;
                            }

                            repeatCount = _input.GetBits(3) + 3;

                            if (_loopCounter + repeatCount > _codeArraySize)
                            {
                                throw new ZlibException();
                            }

                            for (var j = 0; j < repeatCount; j++)
                            {
                                _codeList[_loopCounter++] = 0;
                            }
                        }
                        else
                        {
                            // code == 18
                            if (!_input.EnsureBitsAvailable(7))
                            {
                                _state = InflaterState.ReadingTreeCodesAfter;
                                return false;
                            }

                            repeatCount = _input.GetBits(7) + 11;

                            if (_loopCounter + repeatCount > _codeArraySize)
                            {
                                throw new ZlibException();
                            }

                            for (var j = 0; j < repeatCount; j++)
                            {
                                _codeList[_loopCounter++] = 0;
                            }
                        }
                    }
                    _state = InflaterState.ReadingTreeCodesBefore; // we want to read the next code.
                }
                break;

            default:
                Debug. /*Fail*/
                Assert(false, "check why we are here!");
                throw new ZlibException("Deflate64: unknown state");
        }

        var literalTreeCodeLength = new byte[HuffmanTree.MAX_LITERAL_TREE_ELEMENTS];
        var distanceTreeCodeLength = new byte[HuffmanTree.MAX_DIST_TREE_ELEMENTS];

        // 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.END_OF_BLOCK_CODE] == 0)
        {
            throw new ZlibException();
        }

        _literalLengthTree = new HuffmanTree(literalTreeCodeLength);
        _distanceTree = new HuffmanTree(distanceTreeCodeLength);
        _state = InflaterState.DecodeTop;
        return true;
    }

    public void Dispose() { }
}
