/*

 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package jdk.internal.net.http.hpack;

import java.io.IOException;

import java.nio.ByteBuffer;

import java.util.List;

import java.util.Objects;

public final class QuickHuffman {

    /*

     * Huffman codes for encoding.

     *

     * EOS will never be matched, since there is no symbol for it, thus no need

     * to store it in the array. Thus, the length of the array is 256, not 257.

     * Code information for each character is encoded as follows:

     *

     *     MSB                             LSB

     *     +----------------+----------------+

     *     |~code           |         length~|

     *     +----------------+----------------+

     *     |<----- 32 ----->|<----- 32 ----->|

     *     |<------------- 64 -------------->|

     *

     * The leftmost 32 bits hold the code value. This value is aligned left

     * (or MSB). The rightmost 32 bits hold the length of the code value.

     * This length is aligned right (or LSB).

     */

    private static final long[] codes = new long[256];

    private static long codeValueOf(char c) {

        return codes[c] & 0xffffffff00000000L;

    }

    private static long codeLengthOf(char c) {

        return codes[c] & 0x00000000ffffffffL;

    }

    private static final int EOS_LENGTH = 30;

    private static final int EOS_LSB = 0x3fffffff;

    private static final long EOS_MSB = EOS_LSB << (64 - EOS_LENGTH);

    /*

     * Huffman codes for decoding.

     *

     * Root node contains 257 descendant nodes, including EOS.

     */

    private static final Node root;

    static {

        TemporaryNode tmpRoot = new TemporaryNode();

        addChar(tmpRoot,   0, 0x1ff8,     13);

        addChar(tmpRoot,   1, 0x7fffd8,   23);

        addChar(tmpRoot,   2, 0xfffffe2,  28);

        addChar(tmpRoot,   3, 0xfffffe3,  28);

        addChar(tmpRoot,   4, 0xfffffe4,  28);

        addChar(tmpRoot,   5, 0xfffffe5,  28);

        addChar(tmpRoot,   6, 0xfffffe6,  28);

        addChar(tmpRoot,   7, 0xfffffe7,  28);

        addChar(tmpRoot,   8, 0xfffffe8,  28);

        addChar(tmpRoot,   9, 0xffffea,   24);

        addChar(tmpRoot,  10, 0x3ffffffc, 30);

        addChar(tmpRoot,  11, 0xfffffe9,  28);

        addChar(tmpRoot,  12, 0xfffffea,  28);

        addChar(tmpRoot,  13, 0x3ffffffd, 30);

        addChar(tmpRoot,  14, 0xfffffeb,  28);

        addChar(tmpRoot,  15, 0xfffffec,  28);

        addChar(tmpRoot,  16, 0xfffffed,  28);

        addChar(tmpRoot,  17, 0xfffffee,  28);

        addChar(tmpRoot,  18, 0xfffffef,  28);

        addChar(tmpRoot,  19, 0xffffff0,  28);

        addChar(tmpRoot,  20, 0xffffff1,  28);

        addChar(tmpRoot,  21, 0xffffff2,  28);

        addChar(tmpRoot,  22, 0x3ffffffe, 30);

        addChar(tmpRoot,  23, 0xffffff3,  28);

        addChar(tmpRoot,  24, 0xffffff4,  28);

        addChar(tmpRoot,  25, 0xffffff5,  28);

        addChar(tmpRoot,  26, 0xffffff6,  28);

        addChar(tmpRoot,  27, 0xffffff7,  28);

        addChar(tmpRoot,  28, 0xffffff8,  28);

        addChar(tmpRoot,  29, 0xffffff9,  28);

        addChar(tmpRoot,  30, 0xffffffa,  28);

        addChar(tmpRoot,  31, 0xffffffb,  28);

        addChar(tmpRoot,  32, 0x14,        6);

        addChar(tmpRoot,  33, 0x3f8,      10);

        addChar(tmpRoot,  34, 0x3f9,      10);

        addChar(tmpRoot,  35, 0xffa,      12);

        addChar(tmpRoot,  36, 0x1ff9,     13);

        addChar(tmpRoot,  37, 0x15,        6);

        addChar(tmpRoot,  38, 0xf8,        8);

        addChar(tmpRoot,  39, 0x7fa,      11);

        addChar(tmpRoot,  40, 0x3fa,      10);

        addChar(tmpRoot,  41, 0x3fb,      10);

        addChar(tmpRoot,  42, 0xf9,        8);

        addChar(tmpRoot,  43, 0x7fb,      11);

        addChar(tmpRoot,  44, 0xfa,        8);

        addChar(tmpRoot,  45, 0x16,        6);

        addChar(tmpRoot,  46, 0x17,        6);

        addChar(tmpRoot,  47, 0x18,        6);

        addChar(tmpRoot,  48, 0x0,         5);

        addChar(tmpRoot,  49, 0x1,         5);

        addChar(tmpRoot,  50, 0x2,         5);

        addChar(tmpRoot,  51, 0x19,        6);

        addChar(tmpRoot,  52, 0x1a,        6);

        addChar(tmpRoot,  53, 0x1b,        6);

        addChar(tmpRoot,  54, 0x1c,        6);

        addChar(tmpRoot,  55, 0x1d,        6);

        addChar(tmpRoot,  56, 0x1e,        6);

        addChar(tmpRoot,  57, 0x1f,        6);

        addChar(tmpRoot,  58, 0x5c,        7);

        addChar(tmpRoot,  59, 0xfb,        8);

        addChar(tmpRoot,  60, 0x7ffc,     15);

        addChar(tmpRoot,  61, 0x20,        6);

        addChar(tmpRoot,  62, 0xffb,      12);

        addChar(tmpRoot,  63, 0x3fc,      10);

        addChar(tmpRoot,  64, 0x1ffa,     13);

        addChar(tmpRoot,  65, 0x21,        6);

        addChar(tmpRoot,  66, 0x5d,        7);

        addChar(tmpRoot,  67, 0x5e,        7);

        addChar(tmpRoot,  68, 0x5f,        7);

        addChar(tmpRoot,  69, 0x60,        7);

        addChar(tmpRoot,  70, 0x61,        7);

        addChar(tmpRoot,  71, 0x62,        7);

        addChar(tmpRoot,  72, 0x63,        7);

        addChar(tmpRoot,  73, 0x64,        7);

        addChar(tmpRoot,  74, 0x65,        7);

        addChar(tmpRoot,  75, 0x66,        7);

        addChar(tmpRoot,  76, 0x67,        7);

        addChar(tmpRoot,  77, 0x68,        7);

        addChar(tmpRoot,  78, 0x69,        7);

        addChar(tmpRoot,  79, 0x6a,        7);

        addChar(tmpRoot,  80, 0x6b,        7);

        addChar(tmpRoot,  81, 0x6c,        7);

        addChar(tmpRoot,  82, 0x6d,        7);

        addChar(tmpRoot,  83, 0x6e,        7);

        addChar(tmpRoot,  84, 0x6f,        7);

        addChar(tmpRoot,  85, 0x70,        7);

        addChar(tmpRoot,  86, 0x71,        7);

        addChar(tmpRoot,  87, 0x72,        7);

        addChar(tmpRoot,  88, 0xfc,        8);

        addChar(tmpRoot,  89, 0x73,        7);

        addChar(tmpRoot,  90, 0xfd,        8);

        addChar(tmpRoot,  91, 0x1ffb,     13);

        addChar(tmpRoot,  92, 0x7fff0,    19);

        addChar(tmpRoot,  93, 0x1ffc,     13);

        addChar(tmpRoot,  94, 0x3ffc,     14);

        addChar(tmpRoot,  95, 0x22,        6);

        addChar(tmpRoot,  96, 0x7ffd,     15);

        addChar(tmpRoot,  97, 0x3,         5);

        addChar(tmpRoot,  98, 0x23,        6);

        addChar(tmpRoot,  99, 0x4,         5);

        addChar(tmpRoot, 100, 0x24,        6);

        addChar(tmpRoot, 101, 0x5,         5);

        addChar(tmpRoot, 102, 0x25,        6);

        addChar(tmpRoot, 103, 0x26,        6);

        addChar(tmpRoot, 104, 0x27,        6);

        addChar(tmpRoot, 105, 0x6,         5);

        addChar(tmpRoot, 106, 0x74,        7);

        addChar(tmpRoot, 107, 0x75,        7);

        addChar(tmpRoot, 108, 0x28,        6);

        addChar(tmpRoot, 109, 0x29,        6);

        addChar(tmpRoot, 110, 0x2a,        6);

        addChar(tmpRoot, 111, 0x7,         5);

        addChar(tmpRoot, 112, 0x2b,        6);

        addChar(tmpRoot, 113, 0x76,        7);

        addChar(tmpRoot, 114, 0x2c,        6);

        addChar(tmpRoot, 115, 0x8,         5);

        addChar(tmpRoot, 116, 0x9,         5);

        addChar(tmpRoot, 117, 0x2d,        6);

        addChar(tmpRoot, 118, 0x77,        7);

        addChar(tmpRoot, 119, 0x78,        7);

        addChar(tmpRoot, 120, 0x79,        7);

        addChar(tmpRoot, 121, 0x7a,        7);

        addChar(tmpRoot, 122, 0x7b,        7);

        addChar(tmpRoot, 123, 0x7ffe,     15);

        addChar(tmpRoot, 124, 0x7fc,      11);

        addChar(tmpRoot, 125, 0x3ffd,     14);

        addChar(tmpRoot, 126, 0x1ffd,     13);

        addChar(tmpRoot, 127, 0xffffffc,  28);

        addChar(tmpRoot, 128, 0xfffe6,    20);

        addChar(tmpRoot, 129, 0x3fffd2,   22);

        addChar(tmpRoot, 130, 0xfffe7,    20);

        addChar(tmpRoot, 131, 0xfffe8,    20);

        addChar(tmpRoot, 132, 0x3fffd3,   22);

        addChar(tmpRoot, 133, 0x3fffd4,   22);

        addChar(tmpRoot, 134, 0x3fffd5,   22);

        addChar(tmpRoot, 135, 0x7fffd9,   23);

        addChar(tmpRoot, 136, 0x3fffd6,   22);

        addChar(tmpRoot, 137, 0x7fffda,   23);

        addChar(tmpRoot, 138, 0x7fffdb,   23);

        addChar(tmpRoot, 139, 0x7fffdc,   23);

        addChar(tmpRoot, 140, 0x7fffdd,   23);

        addChar(tmpRoot, 141, 0x7fffde,   23);

        addChar(tmpRoot, 142, 0xffffeb,   24);

        addChar(tmpRoot, 143, 0x7fffdf,   23);

        addChar(tmpRoot, 144, 0xffffec,   24);

        addChar(tmpRoot, 145, 0xffffed,   24);

        addChar(tmpRoot, 146, 0x3fffd7,   22);

        addChar(tmpRoot, 147, 0x7fffe0,   23);

        addChar(tmpRoot, 148, 0xffffee,   24);

        addChar(tmpRoot, 149, 0x7fffe1,   23);

        addChar(tmpRoot, 150, 0x7fffe2,   23);

        addChar(tmpRoot, 151, 0x7fffe3,   23);

        addChar(tmpRoot, 152, 0x7fffe4,   23);

        addChar(tmpRoot, 153, 0x1fffdc,   21);

        addChar(tmpRoot, 154, 0x3fffd8,   22);

        addChar(tmpRoot, 155, 0x7fffe5,   23);

        addChar(tmpRoot, 156, 0x3fffd9,   22);

        addChar(tmpRoot, 157, 0x7fffe6,   23);

        addChar(tmpRoot, 158, 0x7fffe7,   23);

        addChar(tmpRoot, 159, 0xffffef,   24);

        addChar(tmpRoot, 160, 0x3fffda,   22);

        addChar(tmpRoot, 161, 0x1fffdd,   21);

        addChar(tmpRoot, 162, 0xfffe9,    20);

        addChar(tmpRoot, 163, 0x3fffdb,   22);

        addChar(tmpRoot, 164, 0x3fffdc,   22);

        addChar(tmpRoot, 165, 0x7fffe8,   23);

        addChar(tmpRoot, 166, 0x7fffe9,   23);

        addChar(tmpRoot, 167, 0x1fffde,   21);

        addChar(tmpRoot, 168, 0x7fffea,   23);

        addChar(tmpRoot, 169, 0x3fffdd,   22);

        addChar(tmpRoot, 170, 0x3fffde,   22);

        addChar(tmpRoot, 171, 0xfffff0,   24);

        addChar(tmpRoot, 172, 0x1fffdf,   21);

        addChar(tmpRoot, 173, 0x3fffdf,   22);

        addChar(tmpRoot, 174, 0x7fffeb,   23);

        addChar(tmpRoot, 175, 0x7fffec,   23);

        addChar(tmpRoot, 176, 0x1fffe0,   21);

        addChar(tmpRoot, 177, 0x1fffe1,   21);

        addChar(tmpRoot, 178, 0x3fffe0,   22);

        addChar(tmpRoot, 179, 0x1fffe2,   21);

        addChar(tmpRoot, 180, 0x7fffed,   23);

        addChar(tmpRoot, 181, 0x3fffe1,   22);

        addChar(tmpRoot, 182, 0x7fffee,   23);

        addChar(tmpRoot, 183, 0x7fffef,   23);

        addChar(tmpRoot, 184, 0xfffea,    20);

        addChar(tmpRoot, 185, 0x3fffe2,   22);

        addChar(tmpRoot, 186, 0x3fffe3,   22);

        addChar(tmpRoot, 187, 0x3fffe4,   22);

        addChar(tmpRoot, 188, 0x7ffff0,   23);

        addChar(tmpRoot, 189, 0x3fffe5,   22);

        addChar(tmpRoot, 190, 0x3fffe6,   22);

        addChar(tmpRoot, 191, 0x7ffff1,   23);

        addChar(tmpRoot, 192, 0x3ffffe0,  26);

        addChar(tmpRoot, 193, 0x3ffffe1,  26);

        addChar(tmpRoot, 194, 0xfffeb,    20);

        addChar(tmpRoot, 195, 0x7fff1,    19);

        addChar(tmpRoot, 196, 0x3fffe7,   22);

        addChar(tmpRoot, 197, 0x7ffff2,   23);

        addChar(tmpRoot, 198, 0x3fffe8,   22);

        addChar(tmpRoot, 199, 0x1ffffec,  25);

        addChar(tmpRoot, 200, 0x3ffffe2,  26);

        addChar(tmpRoot, 201, 0x3ffffe3,  26);

        addChar(tmpRoot, 202, 0x3ffffe4,  26);

        addChar(tmpRoot, 203, 0x7ffffde,  27);

        addChar(tmpRoot, 204, 0x7ffffdf,  27);

        addChar(tmpRoot, 205, 0x3ffffe5,  26);

        addChar(tmpRoot, 206, 0xfffff1,   24);

        addChar(tmpRoot, 207, 0x1ffffed,  25);

        addChar(tmpRoot, 208, 0x7fff2,    19);

        addChar(tmpRoot, 209, 0x1fffe3,   21);

        addChar(tmpRoot, 210, 0x3ffffe6,  26);

        addChar(tmpRoot, 211, 0x7ffffe0,  27);

        addChar(tmpRoot, 212, 0x7ffffe1,  27);

        addChar(tmpRoot, 213, 0x3ffffe7,  26);

        addChar(tmpRoot, 214, 0x7ffffe2,  27);

        addChar(tmpRoot, 215, 0xfffff2,   24);

        addChar(tmpRoot, 216, 0x1fffe4,   21);

        addChar(tmpRoot, 217, 0x1fffe5,   21);

        addChar(tmpRoot, 218, 0x3ffffe8,  26);

        addChar(tmpRoot, 219, 0x3ffffe9,  26);

        addChar(tmpRoot, 220, 0xffffffd,  28);

        addChar(tmpRoot, 221, 0x7ffffe3,  27);

        addChar(tmpRoot, 222, 0x7ffffe4,  27);

        addChar(tmpRoot, 223, 0x7ffffe5,  27);

        addChar(tmpRoot, 224, 0xfffec,    20);

        addChar(tmpRoot, 225, 0xfffff3,   24);

        addChar(tmpRoot, 226, 0xfffed,    20);

        addChar(tmpRoot, 227, 0x1fffe6,   21);

        addChar(tmpRoot, 228, 0x3fffe9,   22);

        addChar(tmpRoot, 229, 0x1fffe7,   21);

        addChar(tmpRoot, 230, 0x1fffe8,   21);

        addChar(tmpRoot, 231, 0x7ffff3,   23);

        addChar(tmpRoot, 232, 0x3fffea,   22);

        addChar(tmpRoot, 233, 0x3fffeb,   22);

        addChar(tmpRoot, 234, 0x1ffffee,  25);

        addChar(tmpRoot, 235, 0x1ffffef,  25);

        addChar(tmpRoot, 236, 0xfffff4,   24);

        addChar(tmpRoot, 237, 0xfffff5,   24);

        addChar(tmpRoot, 238, 0x3ffffea,  26);

        addChar(tmpRoot, 239, 0x7ffff4,   23);

        addChar(tmpRoot, 240, 0x3ffffeb,  26);

        addChar(tmpRoot, 241, 0x7ffffe6,  27);

        addChar(tmpRoot, 242, 0x3ffffec,  26);

        addChar(tmpRoot, 243, 0x3ffffed,  26);

        addChar(tmpRoot, 244, 0x7ffffe7,  27);

        addChar(tmpRoot, 245, 0x7ffffe8,  27);

        addChar(tmpRoot, 246, 0x7ffffe9,  27);

        addChar(tmpRoot, 247, 0x7ffffea,  27);

        addChar(tmpRoot, 248, 0x7ffffeb,  27);

        addChar(tmpRoot, 249, 0xffffffe,  28);

        addChar(tmpRoot, 250, 0x7ffffec,  27);

        addChar(tmpRoot, 251, 0x7ffffed,  27);

        addChar(tmpRoot, 252, 0x7ffffee,  27);

        addChar(tmpRoot, 253, 0x7ffffef,  27);

        addChar(tmpRoot, 254, 0x7fffff0,  27);

        addChar(tmpRoot, 255, 0x3ffffee,  26);

        addEOS (tmpRoot, 256, EOS_LSB, EOS_LENGTH);

        // The difference in performance can always be checked by not using

        // the immutable trie:

        //     root = tmpRoot;

        root = ImmutableNode.copyOf(tmpRoot);

    }

    private QuickHuffman() { }

    private static void addChar(Node root, int symbol, int code, int bitLength)

    {

        addLeaf(root, (char) symbol, code, bitLength, false);

        long value = ((long) code) << (64 - bitLength); // re-align MSB <- LSB

        codes[symbol] = value | bitLength;

    }

    private static void addEOS(Node root, int symbol, int code, int bitLength)

    {

        addLeaf(root, (char) symbol, code, bitLength, true);

    }

    private static void addLeaf(Node root,

                                char symbol,

                                int code,

                                int bitLength,

                                boolean isEOS)

    {

        assert 0 < bitLength && bitLength <= 32 : bitLength;

        Node curr = root;

        int nBytes = bytesForBits(bitLength);

        // The number of bits the code needs to be shifted to the left in order

        // to align with the byte #nBytes boundary:

        int align = (nBytes << 3) - bitLength;

        code <<= align;

        // descend the trie until the last element

        int l = 0;

        for (int i = 0, probe = 0xff << ((nBytes - 1) << 3);

             i < nBytes - 1;

             i++, probe >>>= 8)

        {

            curr.setEOSPath(curr.isEOSPath() | isEOS);

            int idx = (code & probe) >>> ((nBytes - 1 - i) << 3);

            curr = curr.getOrCreateChild(idx);

            curr.setLength(8);

            l += 8;

        }

        // Assign the same char to all byte variants. For example, if the code

        // and its length are 00011b and 5 respectively (letter 'a') then, in

        // order to be able to match any byte starting with 00011b prefix,

        // the following nodes need to be created:

        //

        //     00011000b, 00011001b, 00011010b, 00011011b, 00011100b, 00011101b,

        //     00011110b and 00011111b

        int idx = code & 0xff;

        curr.setEOSPath(curr.isEOSPath() | isEOS);

        for (int i = 0; i < (1 << align); i++) {

            Node child = curr.getOrCreateChild(idx | i);

            child.setSymbol(symbol);

            child.setEOSPath(child.isEOSPath() | isEOS);

            child.setLength(bitLength - l);

        }

    }

    /*

     * A node in the Huffman trie.

     */

    interface Node {

        boolean isEOSPath();

        void setEOSPath(boolean value);

        boolean isLeaf();

        Node getChild(int index);

        Node getOrCreateChild(int index);

        Node[] getChildren();

        char getSymbol();

        void setSymbol(char symbol);

        int getLength();

        void setLength(int value);

    }

    /*

     * Mutable nodes used for initial construction of the Huffman trie.

     * (These nodes are perfectly ok to be used after that.)

     */

    static final class TemporaryNode implements Node {

        private char symbol;

        private boolean eosPath;

        private TemporaryNode[] children;

        private int length;

        @Override

        public TemporaryNode getOrCreateChild(int index) {

            ensureChildrenExist();

            if (children[index] == null) {

                children[index] = new TemporaryNode();

            }

            return children[index];

        }

        private void ensureChildrenExist() {

            if (children == null) {

                children = new TemporaryNode[256];

            }

        }

        @Override

        public boolean isLeaf() {

            return children == null;

        }

        @Override

        public boolean isEOSPath() {

            return eosPath;

        }

        @Override

        public void setEOSPath(boolean value) {

            eosPath = value;

        }

        @Override

        public TemporaryNode getChild(int index) {

            ensureChildrenExist();

            return children[index];

        }

        @Override

        public Node[] getChildren() {

            if (children == null) {

                return new Node[0];

            }

            return children;

        }

        @Override

        public char getSymbol() {

            return symbol;

        }

        @Override

        public int getLength() {

            return length;

        }

        @Override

        public void setSymbol(char value) {

            this.symbol = value;

        }

        @Override

        public void setLength(int value) {

            this.length = value;

        }

    }

    /*

     * Immutable node used to construct traversal-only Huffman trie.

     *

     * Once the trie has been built, the support of modifications is no longer

     * required. An immutable trie should be used. Not only it will help to

     * catch possible bugs, but hopefully speedup the traversal operations.

     */

    static final class ImmutableNode implements Node {

        private final char symbol;

        private final boolean eosPath;

        private final int length;

        private final List<ImmutableNode> children;

        public static ImmutableNode copyOf(Node node) {

            if (node.isLeaf()) {

                return new ImmutableNode(node.getSymbol(), node.isEOSPath(),

                                         node.getLength());

            }

            Node[] children = node.getChildren();

            ImmutableNode[] immutableChildren = new ImmutableNode[children.length];

            for (int i = 0; i < children.length; i++) {

                immutableChildren[i] = copyOf(children[i]);

            }

            return new ImmutableNode(node.isEOSPath(), node.getLength(),

                                     immutableChildren);

        }

        /* Creates a leaf node */

        private ImmutableNode(char symbol,

                              boolean eosPath,