// Copyright (C) AS Sertifitseerimiskeskus
// This software is released under the BSD License (see LICENSE.BSD)
using System;

namespace NDigiDoc.Ionic.Zlib
{
    internal sealed class Tree
    {
        private static readonly int HEAP_SIZE = (2 * InternalConstants.L_CODES + 1);
                
        // extra bits for each length code
        internal static readonly int[] ExtraLengthBits = new int[]
        {
            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[] ExtraDistanceBits = new int[]
        {
            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 = new int[]{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 3, 7};
                
        internal static readonly sbyte[] bl_order = new sbyte[]{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 const int Buf_size = 8 * 2;
                
        // see definition of array dist_code below
        //internal const int DIST_CODE_LEN = 512;
                
        private static readonly sbyte[] _dist_code = new sbyte[]
        {
            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 sbyte[] LengthCode = new sbyte[]
        {
            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[] LengthBase = new int[]
        {
            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[] DistanceBase = new int[]
        {
            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
        };

        
        /// <summary>
        /// Map from a distance to a distance code.
        /// </summary>
        /// <remarks> 
        /// No side effects. _dist_code[256] and _dist_code[257] are never used.
        /// </remarks>
        internal static int DistanceCode(int dist)
        {
            return (dist < 256)
                ? _dist_code[dist]
                : _dist_code[256 + SharedUtils.URShift(dist, 7)];
        }

        internal short[] dyn_tree; // the dynamic tree
        internal int max_code; // largest code with non zero frequency
        internal StaticTree staticTree; // 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.
        internal void  gen_bitlen(DeflateManager s)
        {
            short[] tree = dyn_tree;
            short[] stree = staticTree.treeCodes;
            int[] extra = staticTree.extraBits;
            int base_Renamed = staticTree.extraBase;
            int max_length = staticTree.maxLength;
            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 <= InternalConstants.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_Renamed)
                    xbits = extra[n - base_Renamed];
                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] = (short) (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) (s.opt_len + ((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(DeflateManager s)
        {
            short[] tree  = dyn_tree;
            short[] stree = staticTree.treeCodes;
            int elems     = staticTree.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] = unchecked((short) (tree[n * 2] + tree[m * 2]));
                s.depth[node] = (sbyte) (System.Math.Max((byte) s.depth[n], (byte) 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.
                        
            gen_bitlen(s);
                        
            // The field len is now set, we can generate the bit codes
            gen_codes(tree, max_code, s.bl_count);
        }
                
        // 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.
        internal static void  gen_codes(short[] tree, int max_code, short[] bl_count)
        {
            short[] next_code = new short[InternalConstants.MAX_BITS + 1]; // next code value for each bit length
            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.
            for (bits = 1; bits <= InternalConstants.MAX_BITS; bits++)
                unchecked {
                    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] =  unchecked((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
        internal static int bi_reverse(int code, int len)
        {
            int res = 0;
            do 
            {
                res |= code & 1;
                code >>= 1; //SharedUtils.URShift(code, 1);
                res <<= 1;
            }
            while (--len > 0);
            return res >> 1;
        }
    }
}