#include <qpdf/Pl_Base64.hh>

#include <qpdf/QIntC.hh>

#include <qpdf/Util.hh>

#include <cstring>

#include <stdexcept>

using namespace qpdf;

static char

to_c(unsigned int ch)

{

    return static_cast<char>(ch);

}

static unsigned char

to_uc(int ch)

{

    return static_cast<unsigned char>(ch);

}

static int

to_i(int i)

{

    return static_cast<int>(i);

}

Pl_Base64::Pl_Base64(char const* identifier, Pipeline* next, action_e action) :

    Pipeline(identifier, next),

    action(action)

{

}

void

Pl_Base64::write(unsigned char const* data, size_t len)

{

    in_buffer.append(reinterpret_cast<const char*>(data), len);

}

std::string

Pl_Base64::decode(std::string_view data)

{

    Pl_Base64 p("base64-decode", nullptr, a_decode);

    p.decode_internal(data);

    return std::move(p.out_buffer);

}

std::string

Pl_Base64::encode(std::string_view data)

{

    Pl_Base64 p("base64-encode", nullptr, a_encode);

    p.encode_internal(data);

    return std::move(p.out_buffer);

}

void

Pl_Base64::decode_internal(std::string_view data)

{

    auto len = data.size();

    auto res = (len / 4u + 1u) * 3u;

    out_buffer.reserve(res);

    unsigned char const* p = reinterpret_cast<const unsigned char*>(data.data());

    while (len > 0) {

        if (!util::is_space(to_c(*p))) {

            buf[pos++] = *p;

            if (pos == 4) {

                flush_decode();

            }

        }

        ++p;

        --len;

    }

    if (pos > 0) {

        for (size_t i = pos; i < 4; ++i) {

            buf[i] = '=';

        }

        flush_decode();

    }

    qpdf_assert_debug(out_buffer.size() <= res);

}

void

Pl_Base64::encode_internal(std::string_view data)

{

    auto len = data.size();

    static const size_t max_len = (std::string().max_size() / 4u - 1u) * 3u;

    // Change to constexpr once AppImage is build with GCC >= 12

    if (len > max_len) {

        throw std::length_error(getIdentifier() + ": base64 decode: data exceeds maximum length");

    }

    auto res = (len / 3u + 1u) * 4u;

    out_buffer.reserve(res);

    unsigned char const* p = reinterpret_cast<const unsigned char*>(data.data());

    while (len > 0) {

        buf[pos++] = *p;

        if (pos == 3) {

            flush_encode();

        }

        ++p;

        --len;

    }

    if (pos > 0) {

        flush_encode();

    }

    qpdf_assert_debug(out_buffer.size() <= res);

}

void

Pl_Base64::flush_decode()

{

    if (end_of_data) {

        throw std::runtime_error(getIdentifier() + ": base64 decode: data follows pad characters");

    }

    size_t pad = 0;

    int shift = 18;

    int outval = 0;

    for (size_t i = 0; i < 4; ++i) {

        int v = 0;

        char ch = to_c(buf[i]);

        if (ch >= 'A' && ch <= 'Z') {

            v = ch - 'A';

        } else if (ch >= 'a' && ch <= 'z') {

            v = ch - 'a' + 26;

        } else if (ch >= '0' && ch <= '9') {

            v = ch - '0' + 52;

        } else if (ch == '+' || ch == '-') {

            v = 62;

        } else if (ch == '/' || ch == '_') {

            v = 63;

        } else if (ch == '=' && (i == 3 || (i == 2 && buf[3] == '='))) {

            ++pad;

            end_of_data = true;

            v = 0;

        } else {

            throw std::runtime_error(getIdentifier() + ": base64 decode: invalid input");

        }

        outval |= v << shift;

        shift -= 6;

    }

    unsigned char out[3] = {

        to_uc(outval >> 16),

        to_uc(0xff & (outval >> 8)),

        to_uc(0xff & outval),

    };

    out_buffer.append(reinterpret_cast<const char*>(out), 3u - pad);

    reset();

}

void

Pl_Base64::flush_encode()

{

    int outval = ((buf[0] << 16) | (buf[1] << 8) | buf[2]);

    unsigned char out[4] = {

        to_uc(outval >> 18),

        to_uc(0x3f & (outval >> 12)),

        to_uc(0x3f & (outval >> 6)),

        to_uc(0x3f & outval),

    };

    for (size_t i = 0; i < 4; ++i) {

        int ch = to_i(out[i]);

        if (ch < 26) {

            ch += 'A';

        } else if (ch < 52) {

            ch -= 26;

            ch += 'a';

        } else if (ch < 62) {

            ch -= 52;

            ch += '0';

        } else if (ch == 62) {

            ch = '+';

        } else if (ch == 63) {

            ch = '/';

        }

        out[i] = to_uc(ch);

    }

    for (size_t i = 0; i < 3 - pos; ++i) {

        out[3 - i] = '=';

    }

    out_buffer.append(reinterpret_cast<const char*>(out), 4);

    reset();

}

void

Pl_Base64::finish()

{

    if (action == a_decode) {

        decode_internal(in_buffer);

    } else {

        encode_internal(in_buffer);

    }

    if (next()) {

        in_buffer.clear();

        in_buffer.shrink_to_fit();

        next()->write(reinterpret_cast<unsigned char const*>(out_buffer.data()), out_buffer.size());

        out_buffer.clear();

        out_buffer.shrink_to_fit();

        next()->finish();

    }

}

void

Pl_Base64::reset()

{

    pos = 0;

    memset(buf, 0, 4);

}