stuff-from-scratch/src/compression/Lz77Encoder.cpp

#include "Lz77Encoder.h"

#include "StringUtils.h"
#include "BitStream.h"

Lz77Encoder::Lz77Encoder(BitStream* inputStream, BitStream* outputStream)
    : AbstractEncoder(inputStream, outputStream)
{

}


unsigned Lz77Encoder::lookAheadForMatchingChars(std::vector<char>& matchBuffer, unsigned searchIndex, unsigned hitOffset, const std::string& stream, unsigned streamLoc)
{
    auto remaining_size = stream.size() - streamLoc;

    unsigned num_hits{1};
    for (unsigned jdx=1; jdx< remaining_size; jdx++)
    {
        char buffer_char{0};
        if (searchIndex + jdx < mSearchBuffer.size())
        {
            buffer_char = mSearchBuffer[searchIndex + jdx];
        }
        else
        {
            buffer_char = stream[jdx - hitOffset];
        }

        auto lookahead_char = stream[streamLoc + jdx];
        if (lookahead_char == buffer_char)
        {
            matchBuffer.push_back(buffer_char);
            num_hits++;
        }
        else
        {
            break;
        }
    }
    return num_hits;
}

void Lz77Encoder::lookThroughSearchBuffer(char searchChar, unsigned& hitLength, unsigned& hitOffset, const std::string& stream, unsigned streamLoc)
{
    for(unsigned idx=0; idx<mSearchBuffer.size(); idx++)
    {
        auto search_index = mSearchBuffer.size() - idx - 1;

        if (auto buffer_char = mSearchBuffer[search_index]; buffer_char == searchChar)
        {
            std::vector<char> match_buffer{buffer_char};
            auto num_hits = lookAheadForMatchingChars(match_buffer, search_index, idx, stream, streamLoc);

            if (num_hits >= hitLength)
            {
                hitLength = num_hits;
                hitOffset = idx + 1;
            }
        }
    }
}

bool Lz77Encoder::encode()
{
    /*
    unsigned loc{0};
    std::string ret;

    while(!mInputStream->isFinished())
    {
        auto search_char = stream[loc];

        unsigned hit_length{0};
        unsigned hit_offset{0};
        lookThroughSearchBuffer(search_char, hit_length, hit_offset, stream, loc);

        if (hit_length > 0)
        {
            ret += "@" + std::to_string(hit_offset) + "L" + std::to_string(hit_length);
            loc+=hit_length;

            auto hit_loc = mSearchBuffer.size() - hit_offset;
            for(unsigned idx=hit_loc; idx<hit_loc + hit_length; idx++)
            {
                mSearchBuffer.push_back(mSearchBuffer[idx]);
            }
        }
        else
        {
            ret += search_char;
            mSearchBuffer.push_back(search_char);
            loc++;
        }
    }

    return ret;
    */
    return false;
}

bool Lz77Encoder::decode()
{
    /*
    std::string ret;

    unsigned loc{0};
    while(loc < stream.size())
    {
        auto working_char = stream[loc];
        if (working_char == '@')
        {
            unsigned loc_working = loc;

            auto remainder = stream.size() - loc;
            std::string offset;

            unsigned length_loc{0};
            for(unsigned jdx=0; jdx< remainder; jdx++)
            {
                loc++;

                auto offset_char = stream[loc];
                if (offset_char == 'L')
                {
                    loc++;
                    break;
                }
                else
                {
                    offset += offset_char;
                }
            }
            unsigned offset_amount = std::stoul(offset);

            std::string length;
            remainder = stream.size() - loc;

            for(unsigned jdx=0; jdx< remainder; jdx++)
            {
                auto length_char = stream[loc];
                if (StringUtils::IsAlphabetical(length_char) || length_char == '@')
                {
                    break;
                }
                else
                {
                    loc++;
                    length += length_char;
                }
            }

            unsigned length_amount = std::stoul(length);

            auto buffer_index = ret.size() - offset_amount;
            for(unsigned jdx=buffer_index;jdx<buffer_index+length_amount; jdx++)
            {
                ret += ret[jdx];
            }
        }
        else
        {
            loc++;
            ret += working_char;
        }
    }
    return ret;
    */
    return false;
}