/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 *
 *   https://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.
 */
package org.apache.commons.compress.compressors.bzip2;

import java.io.IOException;
import java.io.OutputStream;
import java.util.Arrays;

import org.apache.commons.compress.compressors.CompressorOutputStream;

/**
 * An output stream that compresses into the BZip2 format into another stream.
 *
 * <p>
 * The compression requires large amounts of memory. Thus you should call the {@link #close() close()} method as soon as possible, to force
 * {@code BZip2CompressorOutputStream} to release the allocated memory.
 * </p>
 *
 * <p>
 * You can shrink the amount of allocated memory and maybe raise the compression speed by choosing a lower blocksize, which in turn may cause a lower
 * compression ratio. You can avoid unnecessary memory allocation by avoiding using a blocksize which is bigger than the size of the input.
 * </p>
 *
 * <p>
 * You can compute the memory usage for compressing by the following formula:
 * </p>
 *
 * <pre>
 * &lt;code&gt;400k + (9 * blocksize)&lt;/code&gt;.
 * </pre>
 *
 * <p>
 * To get the memory required for decompression by {@link BZip2CompressorInputStream} use
 * </p>
 *
 * <pre>
 * &lt;code&gt;65k + (5 * blocksize)&lt;/code&gt;.
 * </pre>
 *
 * <table style="width:100%" border="1">
 * <caption>Memory usage by blocksize</caption>
 * <tr>
 * <th colspan="3">Memory usage by blocksize</th>
 * </tr>
 * <tr>
 * <th style="text-align: right">Blocksize</th>
 * <th style="text-align: right">Compression<br>
 * memory usage</th>
 * <th style="text-align: right">Decompression<br>
 * memory usage</th>
 * </tr>
 * <tr>
 * <td style="text-align: right">100k</td>
 * <td style="text-align: right">1300k</td>
 * <td style="text-align: right">565k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">200k</td>
 * <td style="text-align: right">2200k</td>
 * <td style="text-align: right">1065k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">300k</td>
 * <td style="text-align: right">3100k</td>
 * <td style="text-align: right">1565k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">400k</td>
 * <td style="text-align: right">4000k</td>
 * <td style="text-align: right">2065k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">500k</td>
 * <td style="text-align: right">4900k</td>
 * <td style="text-align: right">2565k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">600k</td>
 * <td style="text-align: right">5800k</td>
 * <td style="text-align: right">3065k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">700k</td>
 * <td style="text-align: right">6700k</td>
 * <td style="text-align: right">3565k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">800k</td>
 * <td style="text-align: right">7600k</td>
 * <td style="text-align: right">4065k</td>
 * </tr>
 * <tr>
 * <td style="text-align: right">900k</td>
 * <td style="text-align: right">8500k</td>
 * <td style="text-align: right">4565k</td>
 * </tr>
 * </table>
 *
 * <p>
 * For decompression {@code BZip2CompressorInputStream} allocates less memory if the bzipped input is smaller than one block.
 * </p>
 *
 * <p>
 * Instances of this class are not threadsafe.
 * </p>
 *
 * <p>
 * TODO: Update to BZip2 1.0.1
 * </p>
 *
 * @NotThreadSafe
 */
public class BZip2CompressorOutputStream extends CompressorOutputStream<OutputStream> implements BZip2Constants {

    static final class Data {

        // with blockSize 900k
        /* maps unsigned byte => "does it occur in block" */
        final boolean[] inUse = new boolean[256]; // 256 byte
        final byte[] unseqToSeq = new byte[256]; // 256 byte
        final int[] mtfFreq = new int[MAX_ALPHA_SIZE]; // 1032 byte
        final byte[] selector = new byte[MAX_SELECTORS]; // 18002 byte
        final byte[] selectorMtf = new byte[MAX_SELECTORS]; // 18002 byte

        final byte[] generateMTFValues_yy = new byte[256]; // 256 byte
        final byte[][] sendMTFValues_len = new byte[N_GROUPS][MAX_ALPHA_SIZE]; // 1548
        // byte
        final int[][] sendMTFValues_rfreq = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192
        // byte
        final int[] sendMTFValues_fave = new int[N_GROUPS]; // 24 byte
        final short[] sendMTFValues_cost = new short[N_GROUPS]; // 12 byte
        final int[][] sendMTFValues_code = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192
        // byte
        final byte[] sendMTFValues2_pos = new byte[N_GROUPS]; // 6 byte
        final boolean[] sentMTFValues4_inUse16 = new boolean[16]; // 16 byte

        final int[] heap = new int[MAX_ALPHA_SIZE + 2]; // 1040 byte
        final int[] weight = new int[MAX_ALPHA_SIZE * 2]; // 2064 byte
        final int[] parent = new int[MAX_ALPHA_SIZE * 2]; // 2064 byte

        // ------------
        // 333408 byte

        /*
         * holds the RLEd block of original data starting at index 1. After sorting the last byte added to the buffer is at index 0.
         */
        final byte[] block; // 900021 byte
        /*
         * maps index in Burrows-Wheeler transformed block => index of byte in original block
         */
        final int[] fmap; // 3600000 byte
        final char[] sfmap; // 3600000 byte
        // ------------
        // 8433529 byte
        // ============

        /**
         * Index of original line in Burrows-Wheeler table.
         *
         * <p>
         * This is the index in fmap that points to the last byte of the original data.
         * </p>
         */
        int origPtr;

        Data(final int blockSize100k) {
            final int n = blockSize100k * BASEBLOCKSIZE;
            this.block = new byte[n + 1 + NUM_OVERSHOOT_BYTES];
            this.fmap = new int[n];
            this.sfmap = new char[2 * n];
        }

    }

    /**
     * The minimum supported blocksize {@code  == 1}.
     */
    public static final int MIN_BLOCKSIZE = 1;

    /**
     * The maximum supported blocksize {@code  == 9}.
     */
    public static final int MAX_BLOCKSIZE = 9;
    private static final int GREATER_ICOST = 15;

    private static final int LESSER_ICOST = 0;

    /**
     * Chooses a blocksize based on the given length of the data to compress.
     *
     * @return The blocksize, between {@link #MIN_BLOCKSIZE} and {@link #MAX_BLOCKSIZE} both inclusive. For a negative {@code inputLength} this method returns
     *         {@code MAX_BLOCKSIZE} always.
     *
     * @param inputLength The length of the data which will be compressed by {@code BZip2CompressorOutputStream}.
     */
    public static int chooseBlockSize(final long inputLength) {
        return inputLength > 0 ? (int) Math.min(inputLength / 132000 + 1, 9) : MAX_BLOCKSIZE;
    }

    private static void hbAssignCodes(final int[] code, final byte[] length, final int minLen, final int maxLen, final int alphaSize) {
        int vec = 0;
        for (int n = minLen; n <= maxLen; n++) {
            for (int i = 0; i < alphaSize; i++) {
                if ((length[i] & 0xff) == n) {
                    code[i] = vec;
                    vec++;
                }
            }
            vec <<= 1;
        }
    }

    private static void hbMakeCodeLengths(final byte[] len, final int[] freq, final Data dat, final int alphaSize, final int maxLen) {
        /*
         * Nodes and heap entries run from 1. Entry 0 for both the heap and nodes is a sentinel.
         */
        final int[] heap = dat.heap;
        final int[] weight = dat.weight;
        final int[] parent = dat.parent;

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

        for (boolean tooLong = true; tooLong;) {
            tooLong = false;

            int nNodes = alphaSize;
            int nHeap = 0;
            heap[0] = 0;
            weight[0] = 0;
            parent[0] = -2;

            for (int i = 1; i <= alphaSize; i++) {
                parent[i] = -1;
                nHeap++;
                heap[nHeap] = i;

                int zz = nHeap;
                final int tmp = heap[zz];
                while (weight[tmp] < weight[heap[zz >> 1]]) {
                    heap[zz] = heap[zz >> 1];
                    zz >>= 1;
                }
                heap[zz] = tmp;
            }

            while (nHeap > 1) {
                final int n1 = heap[1];
                heap[1] = heap[nHeap];
                nHeap--;

                int yy = 0;
                int zz = 1;
                int tmp = heap[1];

                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;

                final int n2 = heap[1];
                heap[1] = heap[nHeap];
                nHeap--;

                yy = 0;
                zz = 1;
                tmp = heap[1];

                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;

                final int weight_n1 = weight[n1];
                final int weight_n2 = weight[n2];
                weight[nNodes] = (weight_n1 & 0xffffff00) + (weight_n2 & 0xffffff00) | 1 + Math.max(weight_n1 & 0x000000ff, weight_n2 & 0x000000ff);

                parent[nNodes] = -1;
                nHeap++;
                heap[nHeap] = nNodes;

                tmp = 0;
                zz = nHeap;
                tmp = heap[zz];
                final int weight_tmp = weight[tmp];
                while (weight_tmp < weight[heap[zz >> 1]]) {
                    heap[zz] = heap[zz >> 1];
                    zz >>= 1;
                }
                heap[zz] = tmp;

            }

            for (int i = 1; i <= alphaSize; i++) {
                int j = 0;
                int k = i;

                for (int parent_k; (parent_k = parent[k]) >= 0;) {
                    k = parent_k;
                    j++;
                }

                len[i - 1] = (byte) j;
                if (j > maxLen) {
                    tooLong = true;
                }
            }

            if (tooLong) {
                for (int i = 1; i < alphaSize; i++) {
                    int j = weight[i] >> 8;
                    j = 1 + (j >> 1);
                    weight[i] = j << 8;
                }
            }
        }
    }

    /**
     * Index of the last char in the block, so the block size == last + 1.
     */
    private int last;
    /**
     * Always: in the range 0 .. 9. The current block size is 100000 * this number.
     */
    private final int blockSize100k;

    private int bsBuff;

    private int bsLive;

    private final CRC crc = new CRC();
    private int nInUse;

    private int nMTF;
    private int currentChar = -1;
    private int runLength;

    private int combinedCRC;

    private final int allowableBlockSize;
    /**
     * All memory intensive stuff.
     */
    private Data data;

    private BlockSort blockSorter;

    /**
     * Constructs a new {@code BZip2CompressorOutputStream} with a blocksize of 900k.
     *
     * @param out the destination stream.
     * @throws IOException          if an I/O error occurs in the specified stream.
     * @throws NullPointerException if {@code out == null}.
     */
    public BZip2CompressorOutputStream(final OutputStream out) throws IOException {
        this(out, MAX_BLOCKSIZE);
    }

    /**
     * Constructs a new {@code BZip2CompressorOutputStream} with specified blocksize.
     *
     * @param out       the destination stream.
     * @param blockSize the blockSize as 100k units.
     * @throws IOException              if an I/O error occurs in the specified stream.
     * @throws IllegalArgumentException if {@code (blockSize &lt; 1) || (blockSize &gt; 9)}.
     * @throws NullPointerException     if {@code out == null}.
     * @see #MIN_BLOCKSIZE
     * @see #MAX_BLOCKSIZE
     */
    public BZip2CompressorOutputStream(final OutputStream out, final int blockSize) throws IOException {
        super(out);
        if (blockSize < 1) {
            throw new IllegalArgumentException("blockSize(" + blockSize + ") < 1");
        }
        if (blockSize > 9) {
            throw new IllegalArgumentException("blockSize(" + blockSize + ") > 9");
        }
        this.blockSize100k = blockSize;
        /* 20 is just a paranoia constant */
        this.allowableBlockSize = this.blockSize100k * BASEBLOCKSIZE - 20;
        init();
    }

    private void blockSort() {
        blockSorter.blockSort(data, last);
    }

    private void bsFinishedWithStream() throws IOException {
        while (this.bsLive > 0) {
            final int ch = this.bsBuff >> 24;
            this.out.write(ch); // write 8-bit
            this.bsBuff <<= 8;
            this.bsLive -= 8;
        }
    }

    private void bsPutInt(final int u) throws IOException {
        bsW(8, u >> 24 & 0xff);
        bsW(8, u >> 16 & 0xff);
        bsW(8, u >> 8 & 0xff);
        bsW(8, u & 0xff);
    }

    private void bsPutUByte(final int c) throws IOException {
        bsW(8, c);
    }

    private void bsW(final int n, final int v) throws IOException {
        final OutputStream outShadow = this.out;
        int bsLiveShadow = this.bsLive;
        int bsBuffShadow = this.bsBuff;

        while (bsLiveShadow >= 8) {
            outShadow.write(bsBuffShadow >> 24); // write 8-bit
            bsBuffShadow <<= 8;
            bsLiveShadow -= 8;
        }

        this.bsBuff = bsBuffShadow | v << 32 - bsLiveShadow - n;
        this.bsLive = bsLiveShadow + n;
    }

    @Override
    public void close() throws IOException {
        if (!isClosed()) {
            try {
                finish();
            } finally {
                super.close();
            }
        }
    }

    private void endBlock() throws IOException {
        final int blockCRC = this.crc.getValue();
        this.combinedCRC = this.combinedCRC << 1 | this.combinedCRC >>> 31;
        this.combinedCRC ^= blockCRC;

        // empty block at end of file
        if (this.last == -1) {
            return;
        }

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

        /*
         * 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 data stream. 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 doesn't rely on these statistical properties. They are only important when trying to recover blocks from damaged files.
         */
        bsPutUByte(0x31);
        bsPutUByte(0x41);
        bsPutUByte(0x59);
        bsPutUByte(0x26);
        bsPutUByte(0x53);
        bsPutUByte(0x59);

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

        /* Now a single bit indicating no randomization. */
        bsW(1, 0);

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

    private void endCompression() throws IOException {
        /*
         * 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.)
         */
        bsPutUByte(0x17);
        bsPutUByte(0x72);
        bsPutUByte(0x45);
        bsPutUByte(0x38);
        bsPutUByte(0x50);
        bsPutUByte(0x90);

        bsPutInt(this.combinedCRC);
        bsFinishedWithStream();
    }

    @Override
    public void finish() throws IOException {
        if (!isClosed()) {
            try {
                if (this.runLength > 0) {
                    writeRun();
                }
                this.currentChar = -1;
                endBlock();
                endCompression();
            } finally {
                this.blockSorter = null;
                this.data = null;
            }
        }
    }

    @Override
    public void flush() throws IOException {
        if (out != null) {
            super.flush();
        }
    }

    /*
     * Performs Move-To-Front on the Burrows-Wheeler transformed buffer, storing the MTFed data in data.sfmap in RUNA/RUNB run-length-encoded form.
     *
     * <p>Keeps track of byte frequencies in data.mtfFreq at the same time.</p>
     */
    private void generateMTFValues() {
        final int lastShadow = this.last;
        final Data dataShadow = this.data;
        final boolean[] inUse = dataShadow.inUse;
        final byte[] block = dataShadow.block;
        final int[] fmap = dataShadow.fmap;
        final char[] sfmap = dataShadow.sfmap;
        final int[] mtfFreq = dataShadow.mtfFreq;
        final byte[] unseqToSeq = dataShadow.unseqToSeq;
        final byte[] yy = dataShadow.generateMTFValues_yy;

        // make maps
        int nInUseShadow = 0;
        for (int i = 0; i < 256; i++) {
            if (inUse[i]) {
                unseqToSeq[i] = (byte) nInUseShadow;
                nInUseShadow++;
            }
        }
        this.nInUse = nInUseShadow;

        final int eob = nInUseShadow + 1;

        Arrays.fill(mtfFreq, 0, eob + 1, 0);

        for (int i = nInUseShadow; --i >= 0;) {
            yy[i] = (byte) i;
        }

        int wr = 0;
        int zPend = 0;

        for (int i = 0; i <= lastShadow; i++) {
            final byte ll_i = unseqToSeq[block[fmap[i]] & 0xff];
            byte tmp = yy[0];
            int j = 0;

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

            if (j == 0) {
                zPend++;
            } else {
                if (zPend > 0) {
                    zPend--;
                    while (true) {
                        if ((zPend & 1) == 0) {
                            sfmap[wr] = RUNA;
                            wr++;
                            mtfFreq[RUNA]++;
                        } else {
                            sfmap[wr] = RUNB;
                            wr++;
                            mtfFreq[RUNB]++;
                        }

                        if (zPend < 2) {
                            break;
                        }
                        zPend = zPend - 2 >> 1;
                    }
                    zPend = 0;
                }
                sfmap[wr] = (char) (j + 1);
                wr++;
                mtfFreq[j + 1]++;
            }
        }

        if (zPend > 0) {
            zPend--;
            while (true) {
                if ((zPend & 1) == 0) {
                    sfmap[wr] = RUNA;
                    wr++;
                    mtfFreq[RUNA]++;
                } else {
                    sfmap[wr] = RUNB;
                    wr++;
                    mtfFreq[RUNB]++;
                }

                if (zPend < 2) {
                    break;
                }
                zPend = zPend - 2 >> 1;
            }
        }

        sfmap[wr] = (char) eob;
        mtfFreq[eob]++;
        this.nMTF = wr + 1;
    }

    /**
     * Returns the blocksize parameter specified at construction time.
     *
     * @return the blocksize parameter specified at construction time
     */
    public final int getBlockSize() {
        return this.blockSize100k;
    }

    /**
     * Writes magic bytes like BZ on the first position of the stream and bytes indicating the file-format, which is huffmanized, followed by a digit indicating
     * blockSize100k.
     *
     * @throws IOException if the magic bytes could not been written
     */
    private void init() throws IOException {
        bsPutUByte('B');
        bsPutUByte('Z');

        this.data = new Data(this.blockSize100k);
        this.blockSorter = new BlockSort(this.data);

        // huffmanized magic bytes
        bsPutUByte('h');
        bsPutUByte('0' + this.blockSize100k);

        this.combinedCRC = 0;
        initBlock();
    }

    private void initBlock() {
        // blockNo++;
        this.crc.reset();
        this.last = -1;
        // ch = 0;

        final boolean[] inUse = this.data.inUse;
        for (int i = 256; --i >= 0;) {
            inUse[i] = false;
        }

    }

    private void moveToFrontCodeAndSend() throws IOException {
        bsW(24, this.data.origPtr);
        generateMTFValues();
        sendMTFValues();
    }

    private void sendMTFValues() throws IOException {
        final byte[][] len = this.data.sendMTFValues_len;
        final int alphaSize = this.nInUse + 2;

        for (int t = N_GROUPS; --t >= 0;) {
            final byte[] len_t = len[t];
            for (int v = alphaSize; --v >= 0;) {
                len_t[v] = GREATER_ICOST;
            }
        }

        /* Decide how many coding tables to use */
        // assert (this.nMTF > 0) : this.nMTF;
        final int nGroups = this.nMTF < 200 ? 2 : this.nMTF < 600 ? 3 : this.nMTF < 1200 ? 4 : this.nMTF < 2400 ? 5 : 6;

        /* Generate an initial set of coding tables */
        sendMTFValues0(nGroups, alphaSize);

        /*
         * Iterate up to N_ITERS times to improve the tables.
         */
        final int nSelectors = sendMTFValues1(nGroups, alphaSize);

        /* Compute MTF values for the selectors. */
        sendMTFValues2(nGroups, nSelectors);

        /* Assign actual codes for the tables. */
        sendMTFValues3(nGroups, alphaSize);

        /* Transmit the mapping table. */
        sendMTFValues4();

        /* Now the selectors. */
        sendMTFValues5(nGroups, nSelectors);

        /* Now the coding tables. */
        sendMTFValues6(nGroups, alphaSize);

        /* And finally, the block data proper */
        sendMTFValues7();
    }

    private void sendMTFValues0(final int nGroups, final int alphaSize) {
        final byte[][] len = this.data.sendMTFValues_len;
        final int[] mtfFreq = this.data.mtfFreq;

        int remF = this.nMTF;
        int gs = 0;

        for (int nPart = nGroups; nPart > 0; nPart--) {
            final int tFreq = remF / nPart;
            int ge = gs - 1;
            int aFreq = 0;

            for (final int a = alphaSize - 1; aFreq < tFreq && ge < a;) {
                aFreq += mtfFreq[++ge];
            }

            if (ge > gs && nPart != nGroups && nPart != 1 && (nGroups - nPart & 1) != 0) {
                aFreq -= mtfFreq[ge--];
            }

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

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

    private int sendMTFValues1(final int nGroups, final int alphaSize) {
        final Data dataShadow = this.data;
        final int[][] rfreq = dataShadow.sendMTFValues_rfreq;
        final int[] fave = dataShadow.sendMTFValues_fave;
        final short[] cost = dataShadow.sendMTFValues_cost;
        final char[] sfmap = dataShadow.sfmap;
        final byte[] selector = dataShadow.selector;
        final byte[][] len = dataShadow.sendMTFValues_len;
        final byte[] len_0 = len[0];
        final byte[] len_1 = len[1];
        final byte[] len_2 = len[2];
        final byte[] len_3 = len[3];
        final byte[] len_4 = len[4];
        final byte[] len_5 = len[5];
        final int nMTFShadow = this.nMTF;

        int nSelectors = 0;

        for (int iter = 0; iter < N_ITERS; iter++) {
            for (int t = nGroups; --t >= 0;) {
                fave[t] = 0;
                final int[] rfreqt = rfreq[t];
                for (int i = alphaSize; --i >= 0;) {
                    rfreqt[i] = 0;
                }
            }

            nSelectors = 0;

            for (int gs = 0; gs < this.nMTF;) {
                // Set group start & end marks.

                // Calculate the cost of this group as coded by each of the
                // coding tables.

                final int ge = Math.min(gs + G_SIZE - 1, nMTFShadow - 1);

                final byte mask = (byte) 0xff;
                if (nGroups == N_GROUPS) {
                    // unrolled version of the else-block

                    short cost0 = 0;
                    short cost1 = 0;
                    short cost2 = 0;
                    short cost3 = 0;
                    short cost4 = 0;
                    short cost5 = 0;

                    for (int i = gs; i <= ge; i++) {
                        final int icv = sfmap[i];
                        cost0 += (short) (len_0[icv] & mask);
                        cost1 += (short) (len_1[icv] & mask);
                        cost2 += (short) (len_2[icv] & mask);
                        cost3 += (short) (len_3[icv] & mask);
                        cost4 += (short) (len_4[icv] & mask);
                        cost5 += (short) (len_5[icv] & mask);
                    }

                    cost[0] = cost0;
                    cost[1] = cost1;
                    cost[2] = cost2;
                    cost[3] = cost3;
                    cost[4] = cost4;
                    cost[5] = cost5;

                } else {
                    for (int t = nGroups; --t >= 0;) {
                        cost[t] = 0;
                    }

                    for (int i = gs; i <= ge; i++) {
                        final int icv = sfmap[i];
                        for (int t = nGroups; --t >= 0;) {
                            cost[t] += (short) (len[t][icv] & mask);
                        }
                    }
                }

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

                fave[bt]++;
                selector[nSelectors] = (byte) bt;
                nSelectors++;

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

                gs = ge + 1;
            }

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

        return nSelectors;
    }

    private void sendMTFValues2(final int nGroups, final int nSelectors) {
        // assert (nGroups < 8) : nGroups;

        final Data dataShadow = this.data;
        final byte[] pos = dataShadow.sendMTFValues2_pos;

        for (int i = nGroups; --i >= 0;) {
            pos[i] = (byte) i;
        }

        for (int i = 0; i < nSelectors; i++) {
            final byte ll_i = dataShadow.selector[i];
            byte tmp = pos[0];
            int j = 0;

            while (ll_i != tmp) {
                j++;
                final byte tmp2 = tmp;
                tmp = pos[j];
                pos[j] = tmp2;
            }

            pos[0] = tmp;
            dataShadow.selectorMtf[i] = (byte) j;
        }
    }

    private void sendMTFValues3(final int nGroups, final int alphaSize) {
        final int[][] code = this.data.sendMTFValues_code;
        final byte[][] len = this.data.sendMTFValues_len;

        for (int t = 0; t < nGroups; t++) {
            int minLen = 32;
            int maxLen = 0;
            final byte[] len_t = len[t];
            for (int i = alphaSize; --i >= 0;) {
                final int l = len_t[i] & 0xff;
                if (l > maxLen) {
                    maxLen = l;
                }
                if (l < minLen) {
                    minLen = l;
                }
            }

            // assert (maxLen <= 20) : maxLen;
            // assert (minLen >= 1) : minLen;

            hbAssignCodes(code[t], len[t], minLen, maxLen, alphaSize);
        }
    }

    private void sendMTFValues4() throws IOException {
        final boolean[] inUse = this.data.inUse;
        final boolean[] inUse16 = this.data.sentMTFValues4_inUse16;

        for (int i = 16; --i >= 0;) {
            inUse16[i] = false;
            final int i16 = i * 16;
            for (int j = 16; --j >= 0;) {
                if (inUse[i16 + j]) {
                    inUse16[i] = true;
                    break;
                }
            }
        }

        for (int i = 0; i < 16; i++) {
            bsW(1, inUse16[i] ? 1 : 0);
        }

        final OutputStream outShadow = this.out;
        int bsLiveShadow = this.bsLive;
        int bsBuffShadow = this.bsBuff;

        for (int i = 0; i < 16; i++) {
            if (inUse16[i]) {
                final int i16 = i * 16;
                for (int j = 0; j < 16; j++) {
                    // inlined: bsW(1, inUse[i16 + j] ? 1 : 0);
                    while (bsLiveShadow >= 8) {
                        outShadow.write(bsBuffShadow >> 24); // write 8-bit
                        bsBuffShadow <<= 8;
                        bsLiveShadow -= 8;
                    }
                    if (inUse[i16 + j]) {
                        bsBuffShadow |= 1 << 32 - bsLiveShadow - 1;
                    }
                    bsLiveShadow++;
                }
            }
        }

        this.bsBuff = bsBuffShadow;
        this.bsLive = bsLiveShadow;
    }

    private void sendMTFValues5(final int nGroups, final int nSelectors) throws IOException {
        bsW(3, nGroups);
        bsW(15, nSelectors);

        final OutputStream outShadow = this.out;
        final byte[] selectorMtf = this.data.selectorMtf;

        int bsLiveShadow = this.bsLive;
        int bsBuffShadow = this.bsBuff;

        for (int i = 0; i < nSelectors; i++) {
            for (int j = 0, hj = selectorMtf[i] & 0xff; j < hj; j++) {
                // inlined: bsW(1, 1);
                while (bsLiveShadow >= 8) {
                    outShadow.write(bsBuffShadow >> 24);
                    bsBuffShadow <<= 8;
                    bsLiveShadow -= 8;
                }
                bsBuffShadow |= 1 << 32 - bsLiveShadow - 1;
                bsLiveShadow++;
            }

            // inlined: bsW(1, 0);
            while (bsLiveShadow >= 8) {
                outShadow.write(bsBuffShadow >> 24);
                bsBuffShadow <<= 8;
                bsLiveShadow -= 8;
            }
            // bsBuffShadow |= 0 << (32 - bsLiveShadow - 1);
            bsLiveShadow++;
        }

        this.bsBuff = bsBuffShadow;
        this.bsLive = bsLiveShadow;
    }

    private void sendMTFValues6(final int nGroups, final int alphaSize) throws IOException {
        final byte[][] len = this.data.sendMTFValues_len;
        final OutputStream outShadow = this.out;

        int bsLiveShadow = this.bsLive;
        int bsBuffShadow = this.bsBuff;

        for (int t = 0; t < nGroups; t++) {
            final byte[] len_t = len[t];
            int curr = len_t[0] & 0xff;

            // inlined: bsW(5, curr);
            while (bsLiveShadow >= 8) {
                outShadow.write(bsBuffShadow >> 24); // write 8-bit
                bsBuffShadow <<= 8;
                bsLiveShadow -= 8;
            }
            bsBuffShadow |= curr << 32 - bsLiveShadow - 5;
            bsLiveShadow += 5;

            for (int i = 0; i < alphaSize; i++) {
                final int lti = len_t[i] & 0xff;
                while (curr < lti) {
                    // inlined: bsW(2, 2);
                    while (bsLiveShadow >= 8) {
                        outShadow.write(bsBuffShadow >> 24); // write 8-bit
                        bsBuffShadow <<= 8;
                        bsLiveShadow -= 8;
                    }
                    bsBuffShadow |= 2 << 32 - bsLiveShadow - 2;
                    bsLiveShadow += 2;

                    curr++; /* 10 */
                }

                while (curr > lti) {
                    // inlined: bsW(2, 3);
                    while (bsLiveShadow >= 8) {
                        outShadow.write(bsBuffShadow >> 24); // write 8-bit
                        bsBuffShadow <<= 8;
                        bsLiveShadow -= 8;
                    }
                    bsBuffShadow |= 3 << 32 - bsLiveShadow - 2;
                    bsLiveShadow += 2;

                    curr--; /* 11 */
                }

                // inlined: bsW(1, 0);
                while (bsLiveShadow >= 8) {
                    outShadow.write(bsBuffShadow >> 24); // write 8-bit
                    bsBuffShadow <<= 8;
                    bsLiveShadow -= 8;
                }
                // bsBuffShadow |= 0 << (32 - bsLiveShadow - 1);
                bsLiveShadow++;
            }
        }

        this.bsBuff = bsBuffShadow;
        this.bsLive = bsLiveShadow;
    }

    private void sendMTFValues7() throws IOException {
        final Data dataShadow = this.data;
        final byte[][] len = dataShadow.sendMTFValues_len;
        final int[][] code = dataShadow.sendMTFValues_code;
        final OutputStream outShadow = this.out;
        final byte[] selector = dataShadow.selector;
        final char[] sfmap = dataShadow.sfmap;
        final int nMTFShadow = this.nMTF;

        int selCtr = 0;

        int bsLiveShadow = this.bsLive;
        int bsBuffShadow = this.bsBuff;

        for (int gs = 0; gs < nMTFShadow;) {
            final int ge = Math.min(gs + G_SIZE - 1, nMTFShadow - 1);
            final int selector_selCtr = selector[selCtr] & 0xff;
            final int[] code_selCtr = code[selector_selCtr];
            final byte[] len_selCtr = len[selector_selCtr];

            while (gs <= ge) {
                final int sfmap_i = sfmap[gs];

                //
                // inlined: bsW(len_selCtr[sfmap_i] & 0xff,
                // code_selCtr[sfmap_i]);
                //
                while (bsLiveShadow >= 8) {
                    outShadow.write(bsBuffShadow >> 24);
                    bsBuffShadow <<= 8;
                    bsLiveShadow -= 8;
                }
                final int n = len_selCtr[sfmap_i] & 0xFF;
                bsBuffShadow |= code_selCtr[sfmap_i] << 32 - bsLiveShadow - n;
                bsLiveShadow += n;

                gs++;
            }

            gs = ge + 1;
            selCtr++;
        }

        this.bsBuff = bsBuffShadow;
        this.bsLive = bsLiveShadow;
    }

    @Override
    public void write(final byte[] buf, int offs, final int len) throws IOException {
        if (offs < 0) {
            throw new IndexOutOfBoundsException("offs(" + offs + ") < 0.");
        }
        if (len < 0) {
            throw new IndexOutOfBoundsException("len(" + len + ") < 0.");
        }
        if (offs + len > buf.length) {
            throw new IndexOutOfBoundsException("offs(" + offs + ") + len(" + len + ") > buf.length(" + buf.length + ").");
        }
        checkOpen();
        for (final int hi = offs + len; offs < hi;) {
            write0(buf[offs++]);
        }
    }

    @Override
    public void write(final int b) throws IOException {
        checkOpen();
        write0(b);
    }

    /**
     * Keeps track of the last bytes written and implicitly performs run-length encoding as the first step of the bzip2 algorithm.
     */
    private void write0(int b) throws IOException {
        if (this.currentChar != -1) {
            b &= 0xff;
            if (this.currentChar == b) {
                if (++this.runLength > 254) {
                    writeRun();
                    this.currentChar = -1;
                    this.runLength = 0;
                }
                // else nothing to do
            } else {
                writeRun();
                this.runLength = 1;
                this.currentChar = b;
            }
        } else {
            this.currentChar = b & 0xff;
            this.runLength++;
        }
    }

    /**
     * Writes the current byte to the buffer, run-length encoding it if it has been repeated at least four times (the first step RLEs sequences of four
     * identical bytes).
     *
     * <p>
     * Flushes the current block before writing data if it is full.
     * </p>
     *
     * <p>
     * "write to the buffer" means adding to data.buffer starting two steps "after" this.last - initially starting at index 1 (not 0) - and updating this.last
     * to point to the last index written minus 1.
     * </p>
     */
    private void writeRun() throws IOException {
        final int lastShadow = this.last;

        if (lastShadow < this.allowableBlockSize) {
            final int currentCharShadow = this.currentChar;
            final Data dataShadow = this.data;
            dataShadow.inUse[currentCharShadow] = true;
            final byte ch = (byte) currentCharShadow;

            int runLengthShadow = this.runLength;
            this.crc.update(currentCharShadow, runLengthShadow);

            switch (runLengthShadow) {
            case 1:
                dataShadow.block[lastShadow + 2] = ch;
                this.last = lastShadow + 1;
                break;

            case 2:
                dataShadow.block[lastShadow + 2] = ch;
                dataShadow.block[lastShadow + 3] = ch;
                this.last = lastShadow + 2;
                break;

            case 3: {
                final byte[] block = dataShadow.block;
                block[lastShadow + 2] = ch;
                block[lastShadow + 3] = ch;
                block[lastShadow + 4] = ch;
                this.last = lastShadow + 3;
            }
                break;

            default: {
                runLengthShadow -= 4;
                dataShadow.inUse[runLengthShadow] = true;
                final byte[] block = dataShadow.block;
                block[lastShadow + 2] = ch;
                block[lastShadow + 3] = ch;
                block[lastShadow + 4] = ch;
                block[lastShadow + 5] = ch;
                block[lastShadow + 6] = (byte) runLengthShadow;
                this.last = lastShadow + 5;
            }
                break;

            }
        } else {
            endBlock();
            initBlock();
            writeRun();
        }
    }

}
