#include <qpdf/Pl_RunLength.hh>

#include <qpdf/QTC.hh>

#include <qpdf/Util.hh>

using namespace qpdf;

namespace

{

    unsigned long long memory_limit{0};

} // namespace

class Pl_RunLength::Members

{

  public:

    Members(action_e action) :

        action(action)

    {

    }

    Members(Members const&) = delete;

    ~Members() = default;

    action_e action;

    state_e state{st_top};

    unsigned char buf[128];

    unsigned int length{0};

    std::string out;

};

Pl_RunLength::Pl_RunLength(char const* identifier, Pipeline* next, action_e action) :

    Pipeline(identifier, next),

    m(std::make_unique<Members>(action))

{

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

}

void

Pl_RunLength::setMemoryLimit(unsigned long long limit)

{

    memory_limit = limit;

}

Pl_RunLength::~Pl_RunLength() = default;

void

Pl_RunLength::write(unsigned char const* data, size_t len)

{

    if (m->action == a_encode) {

        encode(data, len);

    } else {

        decode(data, len);

    }

}

void

Pl_RunLength::encode(unsigned char const* data, size_t len)

{

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

        util::assertion(

            (m->state == st_top) == (m->length <= 1),

            "Pl_RunLength::encode: state/length inconsistency");

        unsigned char ch = data[i];

        if (m->length > 0 && (m->state == st_copying || m->length < 128) &&

            ch == m->buf[m->length - 1]) {

            QTC::TC("libtests", "Pl_RunLength: switch to run", (m->length == 128) ? 0 : 1);

            if (m->state == st_copying) {

                --m->length;

                flush_encode();

                m->buf[0] = ch;

                m->length = 1;

            }

            m->state = st_run;

            m->buf[m->length] = ch;

            ++m->length;

        } else {

            if (m->length == 128 || m->state == st_run) {

                flush_encode();

            } else if (m->length > 0) {

                m->state = st_copying;

            }

            m->buf[m->length] = ch;

            ++m->length;

        }

    }

}

void

Pl_RunLength::decode(unsigned char const* data, size_t len)

{

    util::no_ci_rt_error_if(

        memory_limit && (len + m->out.size()) > memory_limit, "Pl_RunLength memory limit exceeded");

    m->out.reserve(len);

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

        unsigned char const& ch = data[i];

        switch (m->state) {

        case st_top:

            if (ch < 128) {

                // length represents remaining number of bytes to copy

                m->length = 1U + ch;

                m->state = st_copying;

            } else if (ch > 128) {

                // length represents number of copies of next byte

                m->length = 257U - ch;

                m->state = st_run;

            } else // ch == 128

            {

                // EOD; stay in this state

            }

            break;

        case st_copying:

            m->out.append(1, static_cast<char>(ch));

            if (--m->length == 0) {

                m->state = st_top;

            }

            break;

        case st_run:

            m->out.append(m->length, static_cast<char>(ch));

            m->state = st_top;

            break;

        }

    }

}

void

Pl_RunLength::flush_encode()

{

    if (m->length == 128) {

        QTC::TC(

            "libtests",

            "Pl_RunLength flush full buffer",

            (m->state == st_copying   ? 0

                 : m->state == st_run ? 1

                                      : -1));

    }

    if (m->length == 0) {

        QTC::TC("libtests", "Pl_RunLength flush empty buffer");

    }

    if (m->state == st_run) {

        util::assertion(

            !(m->length < 2 || m->length > 128),

            "Pl_RunLength: invalid length in flush_encode for run");

        auto ch = static_cast<unsigned char>(257 - m->length);

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

        next()->write(&m->buf[0], 1);

    } else if (m->length > 0) {

        auto ch = static_cast<unsigned char>(m->length - 1);

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

        next()->write(m->buf, m->length);

    }

    m->state = st_top;

    m->length = 0;

}

void

Pl_RunLength::finish()

{

    // When decoding, we might have read a length byte not followed by data, which means the stream

    // was terminated early, but we will just ignore this case since this is the only sensible thing

    // to do.

    if (m->action == a_encode) {

        flush_encode();

        unsigned char ch = 128;

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

    } else {

        if (memory_limit && (m->out.size()) > memory_limit) {

            throw std::runtime_error("Pl_RunLength memory limit exceeded");

        }

        next()->writeString(m->out);

    }

    next()->finish();

}