// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

//JZlib 0.0.* were released under the GNU LGPL license.Later, we have switched
//over to a BSD-style license. 

//------------------------------------------------------------------------------
//Copyright (c) 2000-2011 ymnk, JCraft, Inc.All rights reserved.

//Redistribution and use in source and binary forms, with or without
//modification, are permitted provided that the following conditions are met:

//  1. Redistributions of source code must retain the above copyright notice,
//     this list of conditions and the following disclaimer.

//  2. Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in 
//     the documentation and/or other materials provided with the distribution.

//  3. The names of the authors may not be used to endorse or promote products
//     derived from this software without specific prior written permission.

//THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
//INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
//FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.IN NO EVENT SHALL JCRAFT,
//INC.OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY DIRECT, INDIRECT,
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//LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
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//EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// ReSharper disable ArrangeThisQualifier
// ReSharper disable InconsistentNaming
namespace DotNetty.Codecs.Compression
{
    using System;
    using DotNetty.Common.Utilities;

    /// <summary>
    /// https://github.com/ymnk/jzlib/blob/master/src/main/java/com/jcraft/jzlib/Tree.java
    /// </summary>
    sealed class Tree
    {
        const int MAX_BITS = 15;
        //const int BL_CODES = 19;
        //const int D_CODES = 30;
        const int LITERALS = 256;
        const int LENGTH_CODES = 29;
        const int L_CODES = (LITERALS + 1 + LENGTH_CODES);
        const int HEAP_SIZE = (2 * L_CODES + 1);

        // Bit length codes must not exceed MAX_BL_BITS bits
        internal static readonly int MAX_BL_BITS = 7;

        // end of block literal code
        internal static readonly int END_BLOCK = 256;

        // repeat previous bit length 3-6 times (2 bits of repeat count)
        internal static readonly int REP_3_6 = 16;

        // repeat a zero length 3-10 times  (3 bits of repeat count)
        internal static readonly int REPZ_3_10 = 17;

        // repeat a zero length 11-138 times  (7 bits of repeat count)
        internal static readonly int REPZ_11_138 = 18;

        // extra bits for each length code
        internal static readonly int[] extra_lbits =
        {
            0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0
        };

        // extra bits for each distance code
        internal static readonly int[] extra_dbits =
        {
            0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13
        };

        // extra bits for each bit length code
        internal static readonly int[] extra_blbits =
        {
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 3, 7
        };

        internal static readonly byte[] bl_order =
        {
            16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
        };


        // The lengths of the bit length codes are sent in order of decreasing
        // probability, to avoid transmitting the lengths for unused bit
        // length codes.

        internal static readonly int Buf_size = 8 * 2;

        // see definition of array dist_code below
        internal static readonly int DIST_CODE_LEN = 512;

        static readonly byte[] _dist_code =
        {
            0, 1, 2, 3, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8,
            8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 10,
            10, 10, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
            11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
            12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13,
            13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
            13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
            14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
            14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
            14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 15,
            15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
            15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
            15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 0, 0, 16, 17,
            18, 18, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22, 22, 22,
            23, 23, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
            24, 24, 24, 24, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
            26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
            26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27,
            27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
            27, 27, 27, 27, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
            28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
            28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28,
            28, 28, 28, 28, 28, 28, 28, 28, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
            29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
            29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
            29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29
        };

        internal static readonly byte[] _length_code =
        {
            0, 1, 2, 3, 4, 5, 6, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 12, 12,
            13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
            17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
            19, 19, 19, 19, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
            21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
            22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
            23, 23, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
            24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
            25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
            25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
            26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
            26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
            27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 28
        };

        internal static readonly int[] base_length =
        {
            0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
            64, 80, 96, 112, 128, 160, 192, 224, 0
        };

        internal static readonly int[] base_dist =
        {
            0, 1, 2, 3, 4, 6, 8, 12, 16, 24,
            32, 48, 64, 96, 128, 192, 256, 384, 512, 768,
            1024, 1536, 2048, 3072, 4096, 6144, 8192, 12288, 16384, 24576
        };

        // Mapping from a distance to a distance code. dist is the distance - 1 and
        // must not have side effects. _dist_code[256] and _dist_code[257] are never
        // used.
        internal static int D_code(int dist) => 
            (dist < 256 ? _dist_code[dist] : _dist_code[256 + dist.RightUShift(7)]);

        internal short[] dyn_tree; // the dynamic tree
        internal int max_code; // largest code with non zero frequency
        internal StaticTree stat_desc; // the corresponding static tree

        // Compute the optimal bit lengths for a tree and update the total bit length
        // for the current block.
        // IN assertion: the fields freq and dad are set, heap[heap_max] and
        //    above are the tree nodes sorted by increasing frequency.
        // OUT assertions: the field len is set to the optimal bit length, the
        //     array bl_count contains the frequencies for each bit length.
        //     The length opt_len is updated; static_len is also updated if stree is
        //     not null.
        void Gen_bitlen(Deflate s)
        {
            short[] tree = dyn_tree;
            short[] stree = stat_desc.static_tree;
            int[] extra = stat_desc.extra_bits;
            int _base = stat_desc.extra_base;
            int max_length = stat_desc.max_length;
            int h; // heap index
            int n, m; // iterate over the tree elements
            int bits; // bit length
            int xbits; // extra bits
            short f; // frequency
            int overflow = 0; // number of elements with bit length too large

            for (bits = 0; bits <= MAX_BITS; bits++)
                s.bl_count[bits] = 0;

            // In a first pass, compute the optimal bit lengths (which may
            // overflow in the case of the bit length tree).
            tree[s.heap[s.heap_max] * 2 + 1] = 0; // root of the heap

            for (h = s.heap_max + 1; h < HEAP_SIZE; h++)
            {
                n = s.heap[h];
                bits = tree[tree[n * 2 + 1] * 2 + 1] + 1;
                if (bits > max_length)
                {
                    bits = max_length;
                    overflow++;
                }
                tree[n * 2 + 1] = (short)bits;
                // We overwrite tree[n*2+1] which is no longer needed

                if (n > max_code)
                    continue; // not a leaf node

                s.bl_count[bits]++;
                xbits = 0;
                if (n >= _base)
                    xbits = extra[n - _base];
                f = tree[n * 2];
                s.opt_len += f * (bits + xbits);
                if (stree != null)
                    s.static_len += f * (stree[n * 2 + 1] + xbits);
            }
            if (overflow == 0)
                return;

            // This happens for example on obj2 and pic of the Calgary corpus
            // Find the first bit length which could increase:
            do
            {
                bits = max_length - 1;
                while (s.bl_count[bits] == 0)
                    bits--;
                s.bl_count[bits]--; // move one leaf down the tree
                s.bl_count[bits + 1] += 2; // move one overflow item as its brother
                s.bl_count[max_length]--;
                // The brother of the overflow item also moves one step up,
                // but this does not affect bl_count[max_length]
                overflow -= 2;
            }
            while (overflow > 0);

            for (bits = max_length; bits != 0; bits--)
            {
                n = s.bl_count[bits];
                while (n != 0)
                {
                    m = s.heap[--h];
                    if (m > max_code)
                        continue;
                    if (tree[m * 2 + 1] != bits)
                    {
                        s.opt_len += (int)(((long)bits - (long)tree[m * 2 + 1]) * (long)tree[m * 2]);
                        tree[m * 2 + 1] = (short)bits;
                    }
                    n--;
                }
            }
        }

        // Construct one Huffman tree and assigns the code bit strings and lengths.
        // Update the total bit length for the current block.
        // IN assertion: the field freq is set for all tree elements.
        // OUT assertions: the fields len and code are set to the optimal bit length
        //     and corresponding code. The length opt_len is updated; static_len is
        //     also updated if stree is not null. The field max_code is set.
        internal void Build_tree(Deflate s)
        {
            short[] tree = dyn_tree;
            short[] stree = stat_desc.static_tree;
            int elems = stat_desc.elems;
            int n, m; // iterate over heap elements
            int max_code = -1; // largest code with non zero frequency
            int node; // new node being created

            // Construct the initial heap, with least frequent element in
            // heap[1]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
            // heap[0] is not used.
            s.heap_len = 0;
            s.heap_max = HEAP_SIZE;

            for (n = 0; n < elems; n++)
            {
                if (tree[n * 2] != 0)
                {
                    s.heap[++s.heap_len] = max_code = n;
                    s.depth[n] = 0;
                }
                else
                {
                    tree[n * 2 + 1] = 0;
                }
            }

            // The pkzip format requires that at least one distance code exists,
            // and that at least one bit should be sent even if there is only one
            // possible code. So to avoid special checks later on we force at least
            // two codes of non zero frequency.
            while (s.heap_len < 2)
            {
                node = s.heap[++s.heap_len] = (max_code < 2 ? ++max_code : 0);
                tree[node * 2] = 1;
                s.depth[node] = 0;
                s.opt_len--;
                if (stree != null)
                    s.static_len -= stree[node * 2 + 1];
                // node is 0 or 1 so it does not have extra bits
            }
            this.max_code = max_code;

            // The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
            // establish sub-heaps of increasing lengths:

            for (n = s.heap_len / 2; n >= 1; n--)
                s.Pqdownheap(tree, n);

            // Construct the Huffman tree by repeatedly combining the least two
            // frequent nodes.

            node = elems; // next internal node of the tree
            do
            {
                // n = node of least frequency
                n = s.heap[1];
                s.heap[1] = s.heap[s.heap_len--];
                s.Pqdownheap(tree, 1);
                m = s.heap[1]; // m = node of next least frequency

                s.heap[--s.heap_max] = n; // keep the nodes sorted by frequency
                s.heap[--s.heap_max] = m;

                // Create a new node father of n and m
                tree[node * 2] = (short)(tree[n * 2] + tree[m * 2]);
                s.depth[node] = (byte)(Math.Max(s.depth[n], s.depth[m]) + 1);
                tree[n * 2 + 1] = tree[m * 2 + 1] = (short)node;

                // and insert the new node in the heap
                s.heap[1] = node++;
                s.Pqdownheap(tree, 1);
            }
            while (s.heap_len >= 2);

            s.heap[--s.heap_max] = s.heap[1];

            // At this point, the fields freq and dad are set. We can now
            // generate the bit lengths.

            this.Gen_bitlen(s);

            // The field len is now set, we can generate the bit codes
            Gen_codes(tree, max_code, s.bl_count, s.next_code);
        }

        // Generate the codes for a given tree and bit counts (which need not be
        // optimal).
        // IN assertion: the array bl_count contains the bit length statistics for
        // the given tree and the field len is set for all tree elements.
        // OUT assertion: the field code is set for all tree elements of non
        //     zero code length.
        static void Gen_codes(
            short[] tree, // the tree to decorate
            int max_code, // largest code with non zero frequency
            short[] bl_count, // number of codes at each bit length
            short[] next_code)
        {
            short code = 0; // running code value
            int bits; // bit index
            int n; // code index

            // The distribution counts are first used to generate the code values
            // without bit reversal.
            next_code[0] = 0;
            for (bits = 1; bits <= MAX_BITS; bits++)
            {
                next_code[bits] = code = (short)((code + bl_count[bits - 1]) << 1);
            }

            // Check that the bit counts in bl_count are consistent. The last code
            // must be all ones.
            //Assert (code + bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1,
            //        "inconsistent bit counts");
            //Tracev((stderr,"\ngen_codes: max_code %d ", max_code));

            for (n = 0; n <= max_code; n++)
            {
                int len = tree[n * 2 + 1];
                if (len == 0)
                    continue;
                // Now reverse the bits
                tree[n * 2] = (short)(Bi_reverse(next_code[len]++, len));
            }
        }

        // Reverse the first len bits of a code, using straightforward code (a faster
        // method would use a table)
        // IN assertion: 1 <= len <= 15
        static int Bi_reverse(
            int code, // the value to invert
            int len // its bit length
        )
        {
            int res = 0;
            do
            {
                res |= code & 1;
                code = code.RightUShift(1);
                res <<= 1;
            }
            while (--len > 0);
            return res.RightUShift(1);
        }
    }
}
