#include <qpdf/Pl_LZWDecoder.hh>

#include <qpdf/QIntC.hh>

#include <qpdf/QTC.hh>

#include <qpdf/Util.hh>

#include <cstring>

#include <stdexcept>

using namespace qpdf;

Pl_LZWDecoder::Pl_LZWDecoder(char const* identifier, Pipeline* next, bool early_code_change) :

    Pipeline(identifier, next),

    code_change_delta(early_code_change)

{

    util::assertion(next, "Attempt to create Pl_LZWDecoder with nullptr as next");

}

void

Pl_LZWDecoder::write(unsigned char const* bytes, size_t len)

{

    for (size_t i = 0; i < len; ++i) {

        buf[next_char_++] = bytes[i];

        if (next_char_ == 3) {

            next_char_ = 0;

        }

        bits_available += 8;

        if (bits_available >= code_size) {

            sendNextCode();

        }

    }

}

void

Pl_LZWDecoder::finish()

{

    next()->finish();

}

void

Pl_LZWDecoder::sendNextCode()

{

    unsigned int high = byte_pos;

    unsigned int med = (byte_pos + 1) % 3;

    unsigned int low = (byte_pos + 2) % 3;

    unsigned int bits_from_high = 8 - bit_pos;

    unsigned int bits_from_med = code_size - bits_from_high;

    unsigned int bits_from_low = 0;

    if (bits_from_med > 8) {

        bits_from_low = bits_from_med - 8;

        bits_from_med = 8;

    }

    unsigned int high_mask = (1U << bits_from_high) - 1U;

    unsigned int med_mask = 0xff - ((1U << (8 - bits_from_med)) - 1U);

    unsigned int low_mask = 0xff - ((1U << (8 - bits_from_low)) - 1U);

    unsigned int code = 0;

    code += (buf[high] & high_mask) << bits_from_med;

    code += ((buf[med] & med_mask) >> (8 - bits_from_med));

    if (bits_from_low) {

        code <<= bits_from_low;

        code += ((buf[low] & low_mask) >> (8 - bits_from_low));

        byte_pos = low;

        bit_pos = bits_from_low;

    } else {

        byte_pos = med;

        bit_pos = bits_from_med;

    }

    if (bit_pos == 8) {

        bit_pos = 0;

        ++byte_pos;

        byte_pos %= 3;

    }

    bits_available -= code_size;

    handleCode(code);

}

unsigned char

Pl_LZWDecoder::getFirstChar(unsigned int code)

{

    if (code < 256) {

        return static_cast<unsigned char>(code);

    }

    util::no_ci_rt_error_if(

        code <= 257,

        "Pl_LZWDecoder::getFirstChar called with invalid code (" + std::to_string(code) + ")");

    unsigned int idx = code - 258;

    util::no_ci_rt_error_if(idx >= table.size(), "Pl_LZWDecoder::getFirstChar: table overflow");

    Buffer& b = table.at(idx);

    return b.getBuffer()[0];

}

void

Pl_LZWDecoder::addToTable(unsigned char c)

{

    unsigned int last_size = 0;

    unsigned char const* last_data = nullptr;

    unsigned char tmp[1];

    if (last_code < 256) {

        tmp[0] = static_cast<unsigned char>(last_code);

        last_data = tmp;

        last_size = 1;

    } else {

        util::no_ci_rt_error_if(

            last_code <= 257,

            "Pl_LZWDecoder::addToTable called with invalid code (" + std::to_string(last_code) +

                ")");

        unsigned int idx = last_code - 258;

        util::no_ci_rt_error_if(idx >= table.size(), "Pl_LZWDecoder::addToTable: table overflow");

        Buffer& b = table.at(idx);

        last_data = b.getBuffer();

        last_size = QIntC::to_uint(b.getSize());

    }

    Buffer entry(1 + last_size);

    unsigned char* new_data = entry.getBuffer();

    memcpy(new_data, last_data, last_size);

    new_data[last_size] = c;

    table.push_back(std::move(entry));

}

void

Pl_LZWDecoder::handleCode(unsigned int code)

{

    if (eod) {

        return;

    }

    if (code == 256) {

        if (!table.empty()) {

            QTC::TC("libtests", "Pl_LZWDecoder intermediate reset");

        }

        table.clear();

        code_size = 9;

    } else if (code == 257) {

        eod = true;

    } else {

        if (last_code != 256) {

            // Add to the table from last time.  New table entry would be what we read last plus the

            // first character of what we're reading now.

            unsigned char next_c = '\0';

            unsigned int table_size = QIntC::to_uint(table.size());

            if (code < 256) {

                // just read < 256; last time's next_c was code

                next_c = static_cast<unsigned char>(code);

            } else if (code > 257) {

                size_t idx = code - 258;

                if (idx > table_size) {

                    throw std::runtime_error("LZWDecoder: bad code received");

                } else if (idx == table_size) {

                    // The encoder would have just created this entry, so the first character of

                    // this entry would have been the same as the first character of the last entry.

                    next_c = getFirstChar(last_code);

                } else {

                    next_c = getFirstChar(code);

                }

            }

            unsigned int new_idx = 258 + table_size;

            util::no_ci_rt_error_if(new_idx == 4096, "LZWDecoder: table full");

            addToTable(next_c);

            unsigned int change_idx = new_idx + code_change_delta;

            if (change_idx == 511 || change_idx == 1023 || change_idx == 2047) {

                ++code_size;

            }

        }

        if (code < 256) {

            auto ch = static_cast<unsigned char>(code);

            next()->write(&ch, 1);

        } else {

            unsigned int idx = code - 258;

            if (idx >= table.size()) {

                throw std::runtime_error("Pl_LZWDecoder::handleCode: table overflow");

            }

            Buffer& b = table.at(idx);

            next()->write(b.getBuffer(), b.getSize());

        }

    }

    last_code = code;

}