using System;
using System.IO;
/*
 * Copyright 2001,2004-2005 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * This package is based on the work done by Keiron Liddle, Aftex Software
 * <keiron@aftexsw.com> to whom the Ant project is very grateful for his
 * great code.
 */

#nullable disable

namespace SharpCompress.Compressors.BZip2;

/**
  * An output stream that compresses into the BZip2 format (with the file
  * header chars) into another stream.
  *
  * @author <a href="mailto:keiron@aftexsw.com">Keiron Liddle</a>
  *
  * TODO:    Update to BZip2 1.0.1
  * <b>NB:</b> note this class has been modified to add a leading BZ to the
  * start of the BZIP2 stream to make it compatible with other PGP programs.
  */

internal sealed partial class CBZip2OutputStream : Stream
{
    private const int SETMASK = (1 << 21);
    private const int CLEARMASK = (~SETMASK);
    private const int GREATER_ICOST = 15;
    private const int LESSER_ICOST = 0;
    private const int SMALL_THRESH = 20;
    private const int DEPTH_THRESH = 10;

    /*
    If you are ever unlucky/improbable enough
    to get a stack overflow whilst sorting,
    increase the following constant and try
    again.  In practice I have never seen the
    stack go above 27 elems, so the following
    limit seems very generous.
    */
    private const int QSORT_STACK_SIZE = 1000;
    private bool finished;

    private static void Panic()
    {
        //System.out.Println("panic");
        //throw new CError();
    }

    private void MakeMaps()
    {
        int i;
        nInUse = 0;
        for (i = 0; i < 256; i++)
        {
            if (inUse[i])
            {
                seqToUnseq[nInUse] = (char)i;
                unseqToSeq[i] = (char)nInUse;
                nInUse++;
            }
        }
    }

    private static void HbMakeCodeLengths(char[] len, int[] freq, int alphaSize, int maxLen)
    {
        /*
        Nodes and heap entries run from 1.  Entry 0
        for both the heap and nodes is a sentinel.
        */
        int nNodes,
            nHeap,
            n1,
            n2,
            i,
            j,
            k;
        bool tooLong;

        Span<int> heap = stackalloc int[BZip2Constants.MAX_ALPHA_SIZE + 2]; // 1040 bytes
        Span<int> weight = stackalloc int[BZip2Constants.MAX_ALPHA_SIZE * 2]; // 1040 bytes
        Span<int> parent = stackalloc int[BZip2Constants.MAX_ALPHA_SIZE * 2]; // 1040 bytes

        for (i = 0; i < alphaSize; i++)
        {
            weight[i + 1] = (freq[i] == 0 ? 1 : freq[i]) << 8;
        }

        while (true)
        {
            nNodes = alphaSize;
            nHeap = 0;

            heap[0] = 0;
            weight[0] = 0;
            parent[0] = -2;

            for (i = 1; i <= alphaSize; i++)
            {
                parent[i] = -1;
                nHeap++;
                heap[nHeap] = i;
                {
                    int zz,
                        tmp;
                    zz = nHeap;
                    tmp = heap[zz];
                    while (weight[tmp] < weight[heap[zz >> 1]])
                    {
                        heap[zz] = heap[zz >> 1];
                        zz >>= 1;
                    }
                    heap[zz] = tmp;
                }
            }
            if (!(nHeap < (BZip2Constants.MAX_ALPHA_SIZE + 2)))
            {
                Panic();
            }

            while (nHeap > 1)
            {
                n1 = heap[1];
                heap[1] = heap[nHeap];
                nHeap--;
                {
                    int zz = 0,
                        yy = 0,
                        tmp = 0;
                    zz = 1;
                    tmp = heap[zz];
                    while (true)
                    {
                        yy = zz << 1;
                        if (yy > nHeap)
                        {
                            break;
                        }
                        if (yy < nHeap && weight[heap[yy + 1]] < weight[heap[yy]])
                        {
                            yy++;
                        }
                        if (weight[tmp] < weight[heap[yy]])
                        {
                            break;
                        }
                        heap[zz] = heap[yy];
                        zz = yy;
                    }
                    heap[zz] = tmp;
                }
                n2 = heap[1];
                heap[1] = heap[nHeap];
                nHeap--;
                {
                    int zz = 0,
                        yy = 0,
                        tmp = 0;
                    zz = 1;
                    tmp = heap[zz];
                    while (true)
                    {
                        yy = zz << 1;
                        if (yy > nHeap)
                        {
                            break;
                        }
                        if (yy < nHeap && weight[heap[yy + 1]] < weight[heap[yy]])
                        {
                            yy++;
                        }
                        if (weight[tmp] < weight[heap[yy]])
                        {
                            break;
                        }
                        heap[zz] = heap[yy];
                        zz = yy;
                    }
                    heap[zz] = tmp;
                }
                nNodes++;
                parent[n1] = parent[n2] = nNodes;

                weight[nNodes] = (int)(
                    (uint)((weight[n1] & 0xffffff00) + (weight[n2] & 0xffffff00))
                    | (uint)(
                        1
                        + (
                            ((weight[n1] & 0x000000ff) > (weight[n2] & 0x000000ff))
                                ? (weight[n1] & 0x000000ff)
                                : (weight[n2] & 0x000000ff)
                        )
                    )
                );

                parent[nNodes] = -1;
                nHeap++;
                heap[nHeap] = nNodes;
                {
                    int zz = 0,
                        tmp = 0;
                    zz = nHeap;
                    tmp = heap[zz];
                    while (weight[tmp] < weight[heap[zz >> 1]])
                    {
                        heap[zz] = heap[zz >> 1];
                        zz >>= 1;
                    }
                    heap[zz] = tmp;
                }
            }
            if (!(nNodes < (BZip2Constants.MAX_ALPHA_SIZE * 2)))
            {
                Panic();
            }

            tooLong = false;
            for (i = 1; i <= alphaSize; i++)
            {
                j = 0;
                k = i;
                while (parent[k] >= 0)
                {
                    k = parent[k];
                    j++;
                }
                len[i - 1] = (char)j;
                if (j > maxLen)
                {
                    tooLong = true;
                }
            }

            if (!tooLong)
            {
                break;
            }

            for (i = 1; i < alphaSize; i++)
            {
                j = weight[i] >> 8;
                j = 1 + (j / 2);
                weight[i] = j << 8;
            }
        }
    }

    /*
    index of the last char in the block, so
    the block size == last + 1.
    */
    private int last;

    /*
    index in zptr[] of original string after sorting.
    */
    private int origPtr;

    /*
    always: in the range 0 .. 9.
    The current block size is 100000 * this number.
    */
    private readonly int blockSize100k;

    private bool blockRandomised;

    private int bytesOut;
    private int bsBuff;
    private int bsLive;
    private readonly CRC mCrc = new();

    private readonly bool[] inUse = new bool[256];
    private int nInUse;

    private readonly char[] seqToUnseq = new char[256];
    private readonly char[] unseqToSeq = new char[256];

    private readonly char[] selector = new char[BZip2Constants.MAX_SELECTORS];
    private readonly char[] selectorMtf = new char[BZip2Constants.MAX_SELECTORS];

    private char[] block;
    private int[] quadrant;
    private int[] zptr;
    private short[] szptr;
    private int[] ftab;

    private int nMTF;

    private readonly int[] mtfFreq = new int[BZip2Constants.MAX_ALPHA_SIZE];

    /*
    * Used when sorting.  If too many long comparisons
    * happen, we stop sorting, randomise the block
    * slightly, and try again.
    */
    private readonly int workFactor;
    private int workDone;
    private int workLimit;
    private bool firstAttempt;
    private int nBlocksRandomised;

    private int currentChar = -1;
    private int runLength;
    private readonly bool leaveOpen;

    public CBZip2OutputStream(Stream inStream, bool leaveOpen = false)
        : this(inStream, 9, leaveOpen) { }

    public CBZip2OutputStream(Stream inStream, int inBlockSize, bool leaveOpen = false)
    {
        this.leaveOpen = leaveOpen;
        block = null;
        quadrant = null;
        zptr = null;
        ftab = null;

        BsSetStream(inStream);

        workFactor = 50;
        if (inBlockSize > 9)
        {
            inBlockSize = 9;
        }
        if (inBlockSize < 1)
        {
            inBlockSize = 1;
        }
        blockSize100k = inBlockSize;
        AllocateCompressStructures();
        // Defer Initialize() and InitBlock() to EnsureStreamHeaderWritten/Async:
        // they write to the underlying stream which may be async-only.
    }

    private bool _streamHeaderWritten;

    /**
    *
    * modified by Oliver Merkel, 010128
    *
    */

    /// <summary>
    /// Ensures the BZip2 stream header ('B', 'Z', 'h', blocksize) has been written
    /// synchronously before the first compressed byte is written.
    /// </summary>
    private void EnsureStreamHeaderWritten()
    {
        if (!_streamHeaderWritten)
        {
            _streamHeaderWritten = true;
            bsStream.WriteByte((byte)'B');
            bsStream.WriteByte((byte)'Z');
            Initialize();
            InitBlock();
        }
    }

    public override void WriteByte(byte bv)
    {
        EnsureStreamHeaderWritten();
        var b = (256 + bv) % 256;
        if (currentChar != -1)
        {
            if (currentChar == b)
            {
                runLength++;
                if (runLength > 254)
                {
                    WriteRun();
                    currentChar = -1;
                    runLength = 0;
                }
            }
            else
            {
                WriteRun();
                runLength = 1;
                currentChar = b;
            }
        }
        else
        {
            currentChar = b;
            runLength++;
        }
    }

    private void WriteRun()
    {
        if (last < allowableBlockSize)
        {
            inUse[currentChar] = true;
            for (var i = 0; i < runLength; i++)
            {
                mCrc.UpdateCRC((char)currentChar);
            }
            switch (runLength)
            {
                case 1:
                    last++;
                    block[last + 1] = (char)currentChar;
                    break;
                case 2:
                    last++;
                    block[last + 1] = (char)currentChar;
                    last++;
                    block[last + 1] = (char)currentChar;
                    break;
                case 3:
                    last++;
                    block[last + 1] = (char)currentChar;
                    last++;
                    block[last + 1] = (char)currentChar;
                    last++;
                    block[last + 1] = (char)currentChar;
                    break;
                default:
                    inUse[runLength - 4] = true;
                    last++;
                    block[last + 1] = (char)currentChar;
                    last++;
                    block[last + 1] = (char)currentChar;
                    last++;
                    block[last + 1] = (char)currentChar;
                    last++;
                    block[last + 1] = (char)currentChar;
                    last++;
                    block[last + 1] = (char)(runLength - 4);
                    break;
            }
        }
        else
        {
            EndBlock();
            InitBlock();
            WriteRun();
        }
    }

    private bool disposed;

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            if (disposed)
            {
                base.Dispose(disposing);
                return;
            }

            Finish();

            disposed = true;
            Dispose();
            if (!leaveOpen)
            {
                bsStream?.Dispose();
            }
            bsStream = null;
        }
        base.Dispose(disposing);
    }

    public void Finish()
    {
        if (finished)
        {
            return;
        }

        EnsureStreamHeaderWritten();
        if (runLength > 0)
        {
            WriteRun();
        }
        currentChar = -1;
        EndBlock();
        EndCompression();
        finished = true;
        Flush();
    }

    public override void Flush() => bsStream.Flush();

    private int blockCRC,
        combinedCRC;

    private void Initialize()
    {
        bytesOut = 0;
        nBlocksRandomised = 0;

        /* Write `magic' bytes h indicating file-format == huffmanised,
        followed by a digit indicating blockSize100k.
        */
        BsPutUChar('h');
        BsPutUChar('0' + blockSize100k);

        combinedCRC = 0;
    }

    private int allowableBlockSize;

    private void InitBlock()
    {
        //        blockNo++;
        mCrc.InitialiseCRC();
        last = -1;

        //        ch = 0;

        for (var i = 0; i < 256; i++)
        {
            inUse[i] = false;
        }

        /* 20 is just a paranoia constant */
        allowableBlockSize = (BZip2Constants.baseBlockSize * blockSize100k) - 20;
    }

    private void EndBlock()
    {
        // Skip block processing for empty input (no data written)
        if (last < 0)
        {
            return;
        }

        blockCRC = mCrc.GetFinalCRC();
        combinedCRC = (combinedCRC << 1) | (int)(((uint)combinedCRC) >> 31);
        combinedCRC ^= blockCRC;

        /* sort the block and establish posn of original string */
        DoReversibleTransformation();

        /*
        A 6-byte block header, the value chosen arbitrarily
        as 0x314159265359 :-).  A 32 bit value does not really
        give a strong enough guarantee that the value will not
        appear by chance in the compressed datastream.  Worst-case
        probability of this event, for a 900k block, is about
        2.0e-3 for 32 bits, 1.0e-5 for 40 bits and 4.0e-8 for 48 bits.
        For a compressed file of size 100Gb -- about 100000 blocks --
        only a 48-bit marker will do.  NB: normal compression/
        decompression do *not* rely on these statistical properties.
        They are only important when trying to recover blocks from
        damaged files.
        */
        BsPutUChar(0x31);
        BsPutUChar(0x41);
        BsPutUChar(0x59);
        BsPutUChar(0x26);
        BsPutUChar(0x53);
        BsPutUChar(0x59);

        /* Now the block's CRC, so it is in a known place. */
        BsPutint(blockCRC);

        /* Now a single bit indicating randomisation. */
        if (blockRandomised)
        {
            BsW(1, 1);
            nBlocksRandomised++;
        }
        else
        {
            BsW(1, 0);
        }

        /* Finally, block's contents proper. */
        MoveToFrontCodeAndSend();
    }

    private void EndCompression()
    {
        /*
        Now another magic 48-bit number, 0x177245385090, to
        indicate the end of the last block.  (Sqrt(pi), if
        you want to know.  I did want to use e, but it contains
        too much repetition -- 27 18 28 18 28 46 -- for me
        to feel statistically comfortable.  Call me paranoid.)
        */
        BsPutUChar(0x17);
        BsPutUChar(0x72);
        BsPutUChar(0x45);
        BsPutUChar(0x38);
        BsPutUChar(0x50);
        BsPutUChar(0x90);

        BsPutint(combinedCRC);

        BsFinishedWithStream();
    }

    private void HbAssignCodes(int[] code, char[] length, int minLen, int maxLen, int alphaSize)
    {
        int n,
            vec,
            i;

        vec = 0;
        for (n = minLen; n <= maxLen; n++)
        {
            for (i = 0; i < alphaSize; i++)
            {
                if (length[i] == n)
                {
                    code[i] = vec;
                    vec++;
                }
            }
            ;
            vec <<= 1;
        }
    }

    private void BsSetStream(Stream f)
    {
        bsStream = f;
        bsLive = 0;
        bsBuff = 0;
        bytesOut = 0;
    }

    private void BsFinishedWithStream()
    {
        while (bsLive > 0)
        {
            var ch = (bsBuff >> 24);
            bsStream.WriteByte((byte)ch); // write 8-bit
            bsBuff <<= 8;
            bsLive -= 8;
            bytesOut++;
        }
    }

    private void BsW(int n, int v)
    {
        while (bsLive >= 8)
        {
            var ch = (bsBuff >> 24);
            bsStream.WriteByte((byte)ch); // write 8-bit
            bsBuff <<= 8;
            bsLive -= 8;
            bytesOut++;
        }
        bsBuff |= (v << (32 - bsLive - n));
        bsLive += n;
    }

    private void BsPutUChar(int c) => BsW(8, c);

    private void BsPutint(int u)
    {
        BsW(8, (u >> 24) & 0xff);
        BsW(8, (u >> 16) & 0xff);
        BsW(8, (u >> 8) & 0xff);
        BsW(8, u & 0xff);
    }

    private void BsPutIntVS(int numBits, int c) => BsW(numBits, c);

    private void SendMTFValues()
    {
        var len = CBZip2InputStream.InitCharArray(
            BZip2Constants.N_GROUPS,
            BZip2Constants.MAX_ALPHA_SIZE
        );

        int v,
            t,
            i,
            j,
            gs,
            ge,
            totc,
            bt,
            bc,
            iter;
        int nSelectors = 0,
            alphaSize,
            minLen,
            maxLen,
            selCtr;
        int nGroups; //, nBytes;

        alphaSize = nInUse + 2;
        for (t = 0; t < BZip2Constants.N_GROUPS; t++)
        {
            for (v = 0; v < alphaSize; v++)
            {
                len[t][v] = (char)GREATER_ICOST;
            }
        }

        /* Decide how many coding tables to use */
        if (nMTF <= 0)
        {
            Panic();
        }

        if (nMTF < 200)
        {
            nGroups = 2;
        }
        else if (nMTF < 600)
        {
            nGroups = 3;
        }
        else if (nMTF < 1200)
        {
            nGroups = 4;
        }
        else if (nMTF < 2400)
        {
            nGroups = 5;
        }
        else
        {
            nGroups = 6;
        }

        /* Generate an initial set of coding tables */
        {
            int nPart,
                remF,
                tFreq,
                aFreq;

            nPart = nGroups;
            remF = nMTF;
            gs = 0;
            while (nPart > 0)
            {
                tFreq = remF / nPart;
                ge = gs - 1;
                aFreq = 0;
                while (aFreq < tFreq && ge < alphaSize - 1)
                {
                    ge++;
                    aFreq += mtfFreq[ge];
                }

                if (ge > gs && nPart != nGroups && nPart != 1 && ((nGroups - nPart) % 2 == 1))
                {
                    aFreq -= mtfFreq[ge];
                    ge--;
                }

                for (v = 0; v < alphaSize; v++)
                {
                    if (v >= gs && v <= ge)
                    {
                        len[nPart - 1][v] = (char)LESSER_ICOST;
                    }
                    else
                    {
                        len[nPart - 1][v] = (char)GREATER_ICOST;
                    }
                }

                nPart--;
                gs = ge + 1;
                remF -= aFreq;
            }
        }

        var rfreq = CBZip2InputStream.InitIntArray(
            BZip2Constants.N_GROUPS,
            BZip2Constants.MAX_ALPHA_SIZE
        );
        var fave = new int[BZip2Constants.N_GROUPS];
        var cost = new short[BZip2Constants.N_GROUPS];
        /*
        Iterate up to N_ITERS times to improve the tables.
        */
        for (iter = 0; iter < BZip2Constants.N_ITERS; iter++)
        {
            for (t = 0; t < nGroups; t++)
            {
                fave[t] = 0;
            }

            for (t = 0; t < nGroups; t++)
            {
                for (v = 0; v < alphaSize; v++)
                {
                    rfreq[t][v] = 0;
                }
            }

            nSelectors = 0;
            totc = 0;
            gs = 0;
            while (true)
            {
                /* Set group start & end marks. */
                if (gs >= nMTF)
                {
                    break;
                }
                ge = gs + BZip2Constants.G_SIZE - 1;
                if (ge >= nMTF)
                {
                    ge = nMTF - 1;
                }

                /*
                Calculate the cost of this group as coded
                by each of the coding tables.
                */
                for (t = 0; t < nGroups; t++)
                {
                    cost[t] = 0;
                }

                if (nGroups == 6)
                {
                    short cost0,
                        cost1,
                        cost2,
                        cost3,
                        cost4,
                        cost5;
                    cost0 = cost1 = cost2 = cost3 = cost4 = cost5 = 0;
                    for (i = gs; i <= ge; i++)
                    {
                        var icv = szptr[i];
                        cost0 += (short)len[0][icv];
                        cost1 += (short)len[1][icv];
                        cost2 += (short)len[2][icv];
                        cost3 += (short)len[3][icv];
                        cost4 += (short)len[4][icv];
                        cost5 += (short)len[5][icv];
                    }
                    cost[0] = cost0;
                    cost[1] = cost1;
                    cost[2] = cost2;
                    cost[3] = cost3;
                    cost[4] = cost4;
                    cost[5] = cost5;
                }
                else
                {
                    for (i = gs; i <= ge; i++)
                    {
                        var icv = szptr[i];
                        for (t = 0; t < nGroups; t++)
                        {
                            cost[t] += (short)len[t][icv];
                        }
                    }
                }

                /*
                Find the coding table which is best for this group,
                and record its identity in the selector table.
                */
                bc = 999999999;
                bt = -1;
                for (t = 0; t < nGroups; t++)
                {
                    if (cost[t] < bc)
                    {
                        bc = cost[t];
                        bt = t;
                    }
                }
                ;
                totc += bc;
                fave[bt]++;
                selector[nSelectors] = (char)bt;
                nSelectors++;

                /*
                Increment the symbol frequencies for the selected table.
                */
                for (i = gs; i <= ge; i++)
                {
                    rfreq[bt][szptr[i]]++;
                }

                gs = ge + 1;
            }

            /*
            Recompute the tables based on the accumulated frequencies.
            */
            for (t = 0; t < nGroups; t++)
            {
                HbMakeCodeLengths(len[t], rfreq[t], alphaSize, 20);
            }
        }

        rfreq = null;
        fave = null;
        cost = null;

        if (!(nGroups < 8))
        {
            Panic();
        }
        if (!(nSelectors < 32768 && nSelectors <= (2 + (900000 / BZip2Constants.G_SIZE))))
        {
            Panic();
        }

        /* Compute MTF values for the selectors. */
        {
            var pos = new char[BZip2Constants.N_GROUPS];
            char ll_i,
                tmp2,
                tmp;
            for (i = 0; i < nGroups; i++)
            {
                pos[i] = (char)i;
            }
            for (i = 0; i < nSelectors; i++)
            {
                ll_i = selector[i];
                j = 0;
                tmp = pos[j];
                while (ll_i != tmp)
                {
                    j++;
                    tmp2 = tmp;
                    tmp = pos[j];
                    pos[j] = tmp2;
                }
                pos[0] = tmp;
                selectorMtf[i] = (char)j;
            }
        }

        var code = CBZip2InputStream.InitIntArray(
            BZip2Constants.N_GROUPS,
            BZip2Constants.MAX_ALPHA_SIZE
        );

        /* Assign actual codes for the tables. */
        for (t = 0; t < nGroups; t++)
        {
            minLen = 32;
            maxLen = 0;
            for (i = 0; i < alphaSize; i++)
            {
                if (len[t][i] > maxLen)
                {
                    maxLen = len[t][i];
                }
                if (len[t][i] < minLen)
                {
                    minLen = len[t][i];
                }
            }
            if (maxLen > 20)
            {
                Panic();
            }
            if (minLen < 1)
            {
                Panic();
            }
            HbAssignCodes(code[t], len[t], minLen, maxLen, alphaSize);
        }

        /* Transmit the mapping table. */
        {
            var inUse16 = new bool[16];
            for (i = 0; i < 16; i++)
            {
                inUse16[i] = false;
                for (j = 0; j < 16; j++)
                {
                    if (inUse[(i * 16) + j])
                    {
                        inUse16[i] = true;
                    }
                }
            }

            //nBytes = bytesOut;
            for (i = 0; i < 16; i++)
            {
                if (inUse16[i])
                {
                    BsW(1, 1);
                }
                else
                {
                    BsW(1, 0);
                }
            }

            for (i = 0; i < 16; i++)
            {
                if (inUse16[i])
                {
                    for (j = 0; j < 16; j++)
                    {
                        if (inUse[(i * 16) + j])
                        {
                            BsW(1, 1);
                        }
                        else
                        {
                            BsW(1, 0);
                        }
                    }
                }
            }
        }

        /* Now the selectors. */
        //nBytes = bytesOut;
        BsW(3, nGroups);
        BsW(15, nSelectors);
        for (i = 0; i < nSelectors; i++)
        {
            for (j = 0; j < selectorMtf[i]; j++)
            {
                BsW(1, 1);
            }
            BsW(1, 0);
        }

        /* Now the coding tables. */
        //nBytes = bytesOut;

        for (t = 0; t < nGroups; t++)
        {
            int curr = len[t][0];
            BsW(5, curr);
            for (i = 0; i < alphaSize; i++)
            {
                while (curr < len[t][i])
                {
                    BsW(2, 2);
                    curr++; /* 10 */
                }
                while (curr > len[t][i])
                {
                    BsW(2, 3);
                    curr--; /* 11 */
                }
                BsW(1, 0);
            }
        }

        /* And finally, the block data proper */
        //nBytes = bytesOut;
        selCtr = 0;
        gs = 0;
        while (true)
        {
            if (gs >= nMTF)
            {
                break;
            }
            ge = gs + BZip2Constants.G_SIZE - 1;
            if (ge >= nMTF)
            {
                ge = nMTF - 1;
            }
            for (i = gs; i <= ge; i++)
            {
                BsW(len[selector[selCtr]][szptr[i]], code[selector[selCtr]][szptr[i]]);
            }

            gs = ge + 1;
            selCtr++;
        }
        if (!(selCtr == nSelectors))
        {
            Panic();
        }
    }

    private void MoveToFrontCodeAndSend()
    {
        BsPutIntVS(24, origPtr);
        GenerateMTFValues();
        SendMTFValues();
    }

    private Stream bsStream;

    private void SimpleSort(int lo, int hi, int d)
    {
        int i,
            j,
            h,
            bigN,
            hp;
        int v;

        bigN = hi - lo + 1;
        if (bigN < 2)
        {
            return;
        }

        hp = 0;
        while (incs[hp] < bigN)
        {
            hp++;
        }
        hp--;

        for (; hp >= 0; hp--)
        {
            h = incs[hp];

            i = lo + h;
            while (true)
            {
                /* copy 1 */
                if (i > hi)
                {
                    break;
                }
                v = zptr[i];
                j = i;
                while (FullGtU(zptr[j - h] + d, v + d))
                {
                    zptr[j] = zptr[j - h];
                    j -= h;
                    if (j <= (lo + h - 1))
                    {
                        break;
                    }
                }
                zptr[j] = v;
                i++;

                /* copy 2 */
                if (i > hi)
                {
                    break;
                }
                v = zptr[i];
                j = i;
                while (FullGtU(zptr[j - h] + d, v + d))
                {
                    zptr[j] = zptr[j - h];
                    j -= h;
                    if (j <= (lo + h - 1))
                    {
                        break;
                    }
                }
                zptr[j] = v;
                i++;

                /* copy 3 */
                if (i > hi)
                {
                    break;
                }
                v = zptr[i];
                j = i;
                while (FullGtU(zptr[j - h] + d, v + d))
                {
                    zptr[j] = zptr[j - h];
                    j -= h;
                    if (j <= (lo + h - 1))
                    {
                        break;
                    }
                }
                zptr[j] = v;
                i++;

                if (workDone > workLimit && firstAttempt)
                {
                    return;
                }
            }
        }
    }

    private void Vswap(int p1, int p2, int n)
    {
        var temp = 0;
        while (n > 0)
        {
            temp = zptr[p1];
            zptr[p1] = zptr[p2];
            zptr[p2] = temp;
            p1++;
            p2++;
            n--;
        }
    }

    private char Med3(char a, char b, char c)
    {
        char t;
        if (a > b)
        {
            t = a;
            a = b;
            b = t;
        }
        if (b > c)
        {
            t = b;
            b = c;
            c = t;
        }
        if (a > b)
        {
            b = a;
        }
        return b;
    }

    internal class StackElem
    {
        internal int ll;
        internal int hh;
        internal int dd;
    }

    private void QSort3(int loSt, int hiSt, int dSt)
    {
        int unLo,
            unHi,
            ltLo,
            gtHi,
            med,
            n,
            m;
        int sp,
            lo,
            hi,
            d;
        var stack = new StackElem[QSORT_STACK_SIZE];
        for (var count = 0; count < QSORT_STACK_SIZE; count++)
        {
            stack[count] = new StackElem();
        }

        sp = 0;

        stack[sp].ll = loSt;
        stack[sp].hh = hiSt;
        stack[sp].dd = dSt;
        sp++;

        while (sp > 0)
        {
            if (sp >= QSORT_STACK_SIZE)
            {
                Panic();
            }

            sp--;
            lo = stack[sp].ll;
            hi = stack[sp].hh;
            d = stack[sp].dd;

            if (hi - lo < SMALL_THRESH || d > DEPTH_THRESH)
            {
                SimpleSort(lo, hi, d);
                if (workDone > workLimit && firstAttempt)
                {
                    return;
                }
                continue;
            }

            med = Med3(
                block[zptr[lo] + d + 1],
                block[zptr[hi] + d + 1],
                block[zptr[(lo + hi) >> 1] + d + 1]
            );

            unLo = ltLo = lo;
            unHi = gtHi = hi;

            while (true)
            {
                while (true)
                {
                    if (unLo > unHi)
                    {
                        break;
                    }
                    n = block[zptr[unLo] + d + 1] - med;
                    if (n == 0)
                    {
                        var temp = 0;
                        temp = zptr[unLo];
                        zptr[unLo] = zptr[ltLo];
                        zptr[ltLo] = temp;
                        ltLo++;
                        unLo++;
                        continue;
                    }
                    ;
                    if (n > 0)
                    {
                        break;
                    }
                    unLo++;
                }
                while (true)
                {
                    if (unLo > unHi)
                    {
                        break;
                    }
                    n = block[zptr[unHi] + d + 1] - med;
                    if (n == 0)
                    {
                        var temp = 0;
                        temp = zptr[unHi];
                        zptr[unHi] = zptr[gtHi];
                        zptr[gtHi] = temp;
                        gtHi--;
                        unHi--;
                        continue;
                    }
                    ;
                    if (n < 0)
                    {
                        break;
                    }
                    unHi--;
                }
                if (unLo > unHi)
                {
                    break;
                }
                var tempx = zptr[unLo];
                zptr[unLo] = zptr[unHi];
                zptr[unHi] = tempx;
                unLo++;
                unHi--;
            }

            if (gtHi < ltLo)
            {
                stack[sp].ll = lo;
                stack[sp].hh = hi;
                stack[sp].dd = d + 1;
                sp++;
                continue;
            }

            n = ((ltLo - lo) < (unLo - ltLo)) ? (ltLo - lo) : (unLo - ltLo);
            Vswap(lo, unLo - n, n);
            m = ((hi - gtHi) < (gtHi - unHi)) ? (hi - gtHi) : (gtHi - unHi);
            Vswap(unLo, hi - m + 1, m);

            n = lo + unLo - ltLo - 1;
            m = hi - (gtHi - unHi) + 1;

            stack[sp].ll = lo;
            stack[sp].hh = n;
            stack[sp].dd = d;
            sp++;

            stack[sp].ll = n + 1;
            stack[sp].hh = m - 1;
            stack[sp].dd = d + 1;
            sp++;

            stack[sp].ll = m;
            stack[sp].hh = hi;
            stack[sp].dd = d;
            sp++;
        }
    }

    private void MainSort()
    {
        int i,
            j,
            ss,
            sb;
        Span<int> runningOrder = stackalloc int[256];
        Span<int> copy = stackalloc int[256];
        var bigDone = new bool[256];
        int c1,
            c2;
        int numQSorted;

        /*
        In the various block-sized structures, live data runs
        from 0 to last+NUM_OVERSHOOT_BYTES inclusive.  First,
        set up the overshoot area for block.
        */

        //   if (verbosity >= 4) fprintf ( stderr, "   sort initialise ...\n" );
        for (i = 0; i < BZip2Constants.NUM_OVERSHOOT_BYTES; i++)
        {
            block[last + i + 2] = block[(i % (last + 1)) + 1];
        }
        for (i = 0; i <= last + BZip2Constants.NUM_OVERSHOOT_BYTES; i++)
        {
            quadrant[i] = 0;
        }

        block[0] = block[last + 1];

        if (last < 4000)
        {
            /*
            Use SimpleSort(), since the full sorting mechanism
            has quite a large constant overhead.
            */
            for (i = 0; i <= last; i++)
            {
                zptr[i] = i;
            }
            firstAttempt = false;
            workDone = workLimit = 0;
            SimpleSort(0, last, 0);
        }
        else
        {
            numQSorted = 0;
            for (i = 0; i <= 255; i++)
            {
                bigDone[i] = false;
            }

            for (i = 0; i <= 65536; i++)
            {
                ftab[i] = 0;
            }

            c1 = block[0];
            for (i = 0; i <= last; i++)
            {
                c2 = block[i + 1];
                ftab[(c1 << 8) + c2]++;
                c1 = c2;
            }

            for (i = 1; i <= 65536; i++)
            {
                ftab[i] += ftab[i - 1];
            }

            c1 = block[1];
            for (i = 0; i < last; i++)
            {
                c2 = block[i + 2];
                j = (c1 << 8) + c2;
                c1 = c2;
                ftab[j]--;
                zptr[ftab[j]] = i;
            }

            j = ((block[last + 1]) << 8) + (block[1]);
            ftab[j]--;
            zptr[ftab[j]] = last;

            /*
            Now ftab contains the first loc of every small bucket.
            Calculate the running order, from smallest to largest
            big bucket.
            */

            for (i = 0; i <= 255; i++)
            {
                runningOrder[i] = i;
            }

            {
                int vv;
                var h = 1;
                do
                {
                    h = (3 * h) + 1;
                } while (h <= 256);
                do
                {
                    h /= 3;
                    for (i = h; i <= 255; i++)
                    {
                        vv = runningOrder[i];
                        j = i;
                        while (
                            (
                                ftab[((runningOrder[j - h]) + 1) << 8]
                                - ftab[(runningOrder[j - h]) << 8]
                            ) > (ftab[((vv) + 1) << 8] - ftab[(vv) << 8])
                        )
                        {
                            runningOrder[j] = runningOrder[j - h];
                            j -= h;
                            if (j <= (h - 1))
                            {
                                break;
                            }
                        }
                        runningOrder[j] = vv;
                    }
                } while (h != 1);
            }

            /*
            The main sorting loop.
            */
            for (i = 0; i <= 255; i++)
            {
                /*
                Process big buckets, starting with the least full.
                */
                ss = runningOrder[i];

                /*
                Complete the big bucket [ss] by quicksorting
                any unsorted small buckets [ss, j].  Hopefully
                previous pointer-scanning phases have already
                completed many of the small buckets [ss, j], so
                we don't have to sort them at all.
                */
                for (j = 0; j <= 255; j++)
                {
                    sb = (ss << 8) + j;
                    if (!((ftab[sb] & SETMASK) == SETMASK))
                    {
                        var lo = ftab[sb] & CLEARMASK;
                        var hi = (ftab[sb + 1] & CLEARMASK) - 1;
                        if (hi > lo)
                        {
                            QSort3(lo, hi, 2);
                            numQSorted += (hi - lo + 1);
                            if (workDone > workLimit && firstAttempt)
                            {
                                return;
                            }
                        }
                        ftab[sb] |= SETMASK;
                    }
                }

                /*
                The ss big bucket is now done.  Record this fact,
                and update the quadrant descriptors.  Remember to
                update quadrants in the overshoot area too, if
                necessary.  The "if (i < 255)" test merely skips
                this updating for the last bucket processed, since
                updating for the last bucket is pointless.
                */
                bigDone[ss] = true;

                if (i < 255)
                {
                    var bbStart = ftab[ss << 8] & CLEARMASK;
                    var bbSize = (ftab[(ss + 1) << 8] & CLEARMASK) - bbStart;
                    var shifts = 0;

                    while ((bbSize >> shifts) > 65534)
                    {
                        shifts++;
                    }

                    for (j = 0; j < bbSize; j++)
                    {
                        var a2update = zptr[bbStart + j];
                        var qVal = (j >> shifts);
                        quadrant[a2update] = qVal;
                        if (a2update < BZip2Constants.NUM_OVERSHOOT_BYTES)
                        {
                            quadrant[a2update + last + 1] = qVal;
                        }
                    }

                    if (!(((bbSize - 1) >> shifts) <= 65535))
                    {
                        Panic();
                    }
                }

                /*
                Now scan this big bucket so as to synthesise the
                sorted order for small buckets [t, ss] for all t != ss.
                */
                for (j = 0; j <= 255; j++)
                {
                    copy[j] = ftab[(j << 8) + ss] & CLEARMASK;
                }

                for (j = ftab[ss << 8] & CLEARMASK; j < (ftab[(ss + 1) << 8] & CLEARMASK); j++)
                {
                    c1 = block[zptr[j]];
                    if (!bigDone[c1])
                    {
                        zptr[copy[c1]] = zptr[j] == 0 ? last : zptr[j] - 1;
                        copy[c1]++;
                    }
                }

                for (j = 0; j <= 255; j++)
                {
                    ftab[(j << 8) + ss] |= SETMASK;
                }
            }
        }
    }

    private void RandomiseBlock()
    {
        int i;
        var rNToGo = 0;
        var rTPos = 0;
        for (i = 0; i < 256; i++)
        {
            inUse[i] = false;
        }

        for (i = 0; i <= last; i++)
        {
            if (rNToGo == 0)
            {
                rNToGo = (char)BZip2Constants.rNums[rTPos];
                rTPos++;
                if (rTPos == 512)
                {
                    rTPos = 0;
                }
            }
            rNToGo--;
            block[i + 1] ^= (char)((rNToGo == 1) ? 1 : 0);

            // handle 16 bit signed numbers
            block[i + 1] &= (char)0xFF;

            inUse[block[i + 1]] = true;
        }
    }

    private void DoReversibleTransformation()
    {
        int i;

        workLimit = workFactor * last;
        workDone = 0;
        blockRandomised = false;
        firstAttempt = true;

        MainSort();

        if (workDone > workLimit && firstAttempt)
        {
            RandomiseBlock();
            workLimit = workDone = 0;
            blockRandomised = true;
            firstAttempt = false;
            MainSort();
        }

        origPtr = -1;
        for (i = 0; i <= last; i++)
        {
            if (zptr[i] == 0)
            {
                origPtr = i;
                break;
            }
        }
        ;

        if (origPtr == -1)
        {
            Panic();
        }
    }

    private bool FullGtU(int i1, int i2)
    {
        int k;
        char c1,
            c2;
        int s1,
            s2;

        c1 = block[i1 + 1];
        c2 = block[i2 + 1];
        if (c1 != c2)
        {
            return (c1 > c2);
        }
        i1++;
        i2++;

        c1 = block[i1 + 1];
        c2 = block[i2 + 1];
        if (c1 != c2)
        {
            return (c1 > c2);
        }
        i1++;
        i2++;

        c1 = block[i1 + 1];
        c2 = block[i2 + 1];
        if (c1 != c2)
        {
            return (c1 > c2);
        }
        i1++;
        i2++;

        c1 = block[i1 + 1];
        c2 = block[i2 + 1];
        if (c1 != c2)
        {
            return (c1 > c2);
        }
        i1++;
        i2++;

        c1 = block[i1 + 1];
        c2 = block[i2 + 1];
        if (c1 != c2)
        {
            return (c1 > c2);
        }
        i1++;
        i2++;

        c1 = block[i1 + 1];
        c2 = block[i2 + 1];
        if (c1 != c2)
        {
            return (c1 > c2);
        }
        i1++;
        i2++;

        k = last + 1;

        do
        {
            c1 = block[i1 + 1];
            c2 = block[i2 + 1];
            if (c1 != c2)
            {
                return (c1 > c2);
            }
            s1 = quadrant[i1];
            s2 = quadrant[i2];
            if (s1 != s2)
            {
                return (s1 > s2);
            }
            i1++;
            i2++;

            c1 = block[i1 + 1];
            c2 = block[i2 + 1];
            if (c1 != c2)
            {
                return (c1 > c2);
            }
            s1 = quadrant[i1];
            s2 = quadrant[i2];
            if (s1 != s2)
            {
                return (s1 > s2);
            }
            i1++;
            i2++;

            c1 = block[i1 + 1];
            c2 = block[i2 + 1];
            if (c1 != c2)
            {
                return (c1 > c2);
            }
            s1 = quadrant[i1];
            s2 = quadrant[i2];
            if (s1 != s2)
            {
                return (s1 > s2);
            }
            i1++;
            i2++;

            c1 = block[i1 + 1];
            c2 = block[i2 + 1];
            if (c1 != c2)
            {
                return (c1 > c2);
            }
            s1 = quadrant[i1];
            s2 = quadrant[i2];
            if (s1 != s2)
            {
                return (s1 > s2);
            }
            i1++;
            i2++;

            if (i1 > last)
            {
                i1 -= last;
                i1--;
            }
            ;
            if (i2 > last)
            {
                i2 -= last;
                i2--;
            }
            ;

            k -= 4;
            workDone++;
        } while (k >= 0);

        return false;
    }

    /*
    Knuth's increments seem to work better
    than Incerpi-Sedgewick here.  Possibly
    because the number of elems to sort is
    usually small, typically <= 20.
    */

    private readonly int[] incs =
    {
        1,
        4,
        13,
        40,
        121,
        364,
        1093,
        3280,
        9841,
        29524,
        88573,
        265720,
        797161,
        2391484,
    };

    private void AllocateCompressStructures()
    {
        var n = BZip2Constants.baseBlockSize * blockSize100k;
        block = new char[(n + 1 + BZip2Constants.NUM_OVERSHOOT_BYTES)];
        quadrant = new int[(n + BZip2Constants.NUM_OVERSHOOT_BYTES)];
        zptr = new int[n];
        ftab = new int[65537];

        if (block is null || quadrant is null || zptr is null || ftab is null)
        {
            //int totalDraw = (n + 1 + NUM_OVERSHOOT_BYTES) + (n + NUM_OVERSHOOT_BYTES) + n + 65537;
            //compressOutOfMemory ( totalDraw, n );
        }

        /*
        The back end needs a place to store the MTF values
        whilst it calculates the coding tables.  We could
        put them in the zptr array.  However, these values
        will fit in a short, so we overlay szptr at the
        start of zptr, in the hope of reducing the number
        of cache misses induced by the multiple traversals
        of the MTF values when calculating coding tables.
        Seems to improve compression speed by about 1%.
        */
        //    szptr = zptr;

        szptr = new short[2 * n];
    }

    private void GenerateMTFValues()
    {
        var yy = new char[256];
        int i,
            j;
        char tmp;
        char tmp2;
        int zPend;
        int wr;
        int EOB;

        MakeMaps();
        EOB = nInUse + 1;

        for (i = 0; i <= EOB; i++)
        {
            mtfFreq[i] = 0;
        }

        wr = 0;
        zPend = 0;
        for (i = 0; i < nInUse; i++)
        {
            yy[i] = (char)i;
        }

        for (i = 0; i <= last; i++)
        {
            char ll_i;

            ll_i = unseqToSeq[block[zptr[i]]];

            j = 0;
            tmp = yy[j];
            while (ll_i != tmp)
            {
                j++;
                tmp2 = tmp;
                tmp = yy[j];
                yy[j] = tmp2;
            }
            ;
            yy[0] = tmp;

            if (j == 0)
            {
                zPend++;
            }
            else
            {
                if (zPend > 0)
                {
                    zPend--;
                    while (true)
                    {
                        switch (zPend % 2)
                        {
                            case 0:
                                szptr[wr] = BZip2Constants.RUNA;
                                wr++;
                                mtfFreq[BZip2Constants.RUNA]++;
                                break;
                            case 1:
                                szptr[wr] = BZip2Constants.RUNB;
                                wr++;
                                mtfFreq[BZip2Constants.RUNB]++;
                                break;
                        }
                        ;
                        if (zPend < 2)
                        {
                            break;
                        }
                        zPend = (zPend - 2) / 2;
                    }
                    ;
                    zPend = 0;
                }
                szptr[wr] = (short)(j + 1);
                wr++;
                mtfFreq[j + 1]++;
            }
        }

        if (zPend > 0)
        {
            zPend--;
            while (true)
            {
                switch (zPend % 2)
                {
                    case 0:
                        szptr[wr] = BZip2Constants.RUNA;
                        wr++;
                        mtfFreq[BZip2Constants.RUNA]++;
                        break;
                    case 1:
                        szptr[wr] = BZip2Constants.RUNB;
                        wr++;
                        mtfFreq[BZip2Constants.RUNB]++;
                        break;
                }
                if (zPend < 2)
                {
                    break;
                }
                zPend = (zPend - 2) / 2;
            }
        }

        szptr[wr] = (short)EOB;
        wr++;
        mtfFreq[EOB]++;

        nMTF = wr;
    }

    public override int Read(byte[] buffer, int offset, int count) => 0;

    public override int ReadByte() => -1;

    public override long Seek(long offset, SeekOrigin origin) => 0;

    public override void SetLength(long value) { }

    public override void Write(byte[] buffer, int offset, int count)
    {
        EnsureStreamHeaderWritten();
        for (var k = 0; k < count; ++k)
        {
            WriteByte(buffer[k + offset]);
        }
    }

    public override bool CanRead => false;

    public override bool CanSeek => false;

    public override bool CanWrite => true;

    public override long Length => 0;

    public override long Position
    {
        get => 0;
        set { }
    }
}
