/*
Copyright (c) 2015 Timur Gafarov

Boost Software License - Version 1.0 - August 17th, 2003

Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
this license (the "Software") to use, reproduce, display, distribute,
execute, and transmit the Software, and to prepare derivative works of the
Software, and to permit third-parties to whom the Software is furnished to
do so, all subject to the following:

The copyright notices in the Software and this entire statement, including
the above license grant, this restriction and the following disclaimer,
must be included in all copies of the Software, in whole or in part, and
all derivative works of the Software, unless such copies or derivative
works are solely in the form of machine-executable object code generated by
a source language processor.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/

// dimage is actually stripped out part of dlib - just to support reading PNG and JPEG
module dimage.huffman;

import dimage.memory;
import dimage.bitio;

//import dlib.core.memory;
//import dlib.core.bitio;

struct HuffmanTreeNode
{
    HuffmanTreeNode* parent;
    HuffmanTreeNode* left;
    HuffmanTreeNode* right;
    ubyte ch;
    uint freq;
    bool blank = true;

    this(
        HuffmanTreeNode* leftNode,
        HuffmanTreeNode* rightNode,
        ubyte symbol,
        uint frequency,
        bool isBlank)
    {
        parent = null;
        left = leftNode;
        right = rightNode;

        if (left !is null)
            left.parent = &this;
        if (right !is null)
            right.parent = &this;

        ch = symbol;
        freq = frequency;
        blank = isBlank;
    }

    bool isLeaf()
    {
        return (left is null && right is null);
    }

    void free()
    {
        if (left !is null)
        {
            left.free();
            Delete(left);
        }

        if (right !is null)
        {
            right.free();
            Delete(right);
        }
    }

/*
    // TODO: implement this without GC

    void getCodes(ref string[ubyte] table, string code = "")
    {
        if (isLeaf())
        {
            table[ch] = code;
        }
        else
        {
            if (left !is null)
                left.getCodes(table, code ~ '0');
            if (right !is null)
                right.getCodes(table, code ~ '1');
        }
    }

    void print(string indent = "")
    {
        writefln("%s<%s>%x", indent, freq, ch);
        indent ~= " ";
        if (left !is null)
            left.print(indent);
        if (right !is null)
            right.print(indent);
    }
*/
}

/*
// TODO: implement this without GC

HuffmanTreeNode* buildHuffmanTree(ubyte[] data)
{
    // Count frequencies
    uint[ubyte] freqs;
    foreach(s; data)
    {
        if (s in freqs)
            freqs[s] += 1;
        else
            freqs[s] = 1;
    }

    // Sort in descending order
    ubyte[] symbols = freqs.keys;
    sort!((a, b) => freqs[a] > freqs[b])(symbols);

    // Create node list
    auto nodeList = new HuffmanTreeNode*[symbols.length];
    foreach(i, s; symbols)
        nodeList[i] = new HuffmanTreeNode(null, null, s, freqs[s], false);

    // Build tree
    while (nodeList.length > 1)
    {
        // Pop two nodes with minimal frequencies
        auto n1 = nodeList[$-1];
        auto n2 = nodeList[$-2];
        nodeList.popBack;
        nodeList.popBack;

        // Insert a new parent node
        uint fsum = n1.freq + n2.freq;
        auto parent = new HuffmanTreeNode(n1, n2, 0, fsum, false);
        nodeList ~= parent;
        sort!((a, b) => a.freq > b.freq)(nodeList);
    }

    auto root = nodeList[0];

    return root;
}

void packHuffmanTree(HuffmanTreeNode* node, BitWriter* bw)
{
    if (node.isLeaf)
    {
        bw.writeBit(true);
        bw.writeByte(node.ch);
    }
    else
    {
        bw.writeBit(false);
        packHuffmanTree(node.left, bw);
        packHuffmanTree(node.right, bw);
    }
}

HuffmanTreeNode* unpackHuffmanTree(BitReader* br)
{
    if (!br.end)
    {
        bool bit = br.readBit();
        if (bit)
        {
            byte ch = br.readByte();
            return new HuffmanTreeNode(null, null, ch, 0, false);
        }
        else
        {
            HuffmanTreeNode* left = unpackHuffmanTree(br);
            HuffmanTreeNode* right = unpackHuffmanTree(br);
            return new HuffmanTreeNode(left, right, 0, 0, false);
        }
    }
    else return null;
}

ubyte[] encodeHuffman(ubyte[] data, out HuffmanTreeNode* tree)
{
    // Build Huffman tree
    tree = buildHuffmanTree(data);

    // Generate binary codes
    string[ubyte] huffTable;
    tree.getCodes(huffTable);

    // Encode data
    string bitStr;
    foreach(s; data)
        bitStr ~= huffTable[s];

    // Pack bits to byte array
    uint octetsLen = 0;
    ubyte lastBits = 0;
    if (bitStr.length == 8)
    {
        octetsLen = 1;
    }
    else if (bitStr.length > 8)
    {
        octetsLen = cast(uint)bitStr.length / 8;
        lastBits = cast(ubyte)(bitStr.length % 8);
        if (lastBits != 0)
            octetsLen++;
    }
    else
    {
        octetsLen = 1;
        lastBits = cast(ubyte)(bitStr.length);
    }

    octetsLen++;
    auto octets = new ubyte[octetsLen];
    octets[0] = lastBits;

    uint bitPos = 0;
    uint bytePos = 1;

    foreach(bit; bitStr)
    {
        bool state;
        if (bit == '0')
            state = false;
        else
            state = true;

        octets[bytePos] = setBit(octets[bytePos], bitPos, state);
        bitPos++;

        if (bitPos == 8)
        {
            bitPos = 0;
            bytePos++;
        }
    }

    return octets;
}

ubyte[] decodeHuffman(ubyte[] data, HuffmanTreeNode* tree)
{
    // Generate binary codes
    string[ubyte] huffTable;
    tree.getCodes(huffTable);

    //Unpack bits from array
    ubyte[] result;
    bool appendNext = true;
    string code = "";
    ubyte lastBits = data[0];
    foreach(i, b; data[1..$])
    {
        uint len;
        if ((lastBits != 0) && (i == data.length-1))
            len = lastBits;
        else
            len = 8;

        foreach(bp; 0..len)
        {
            char bitChr = getBit(b, bp)? '1':'0';
            if (appendNext)
            {
                code ~= bitChr;
                foreach(key, val; huffTable)
                {
                    if (code == val)
                    {
                        result ~= key;
                        appendNext = false;
                        break;
                    }
                }
            }
            else
            {
                code = "";
                code ~= bitChr;
                appendNext = true;
            }
        }
    }

    return result;
}

*/