/*

Copyright (c) 2017, Andrei Kurushin

Copyright (c) 2012, 2015-2017, 2019-2020, Arvid Norberg

Copyright (c) 2017, Alden Torres

Copyright (c) 2021, AllSeeingEyeTolledEweSew

All rights reserved.

Redistribution and use in source and binary forms, with or without

modification, are permitted provided that the following conditions

are met:

    * Redistributions of source code must retain the above copyright

      notice, this list of conditions and the following disclaimer.

    * Redistributions in binary form must reproduce the above copyright

      notice, this list of conditions and the following disclaimer in

      the documentation and/or other materials provided with the distribution.

    * Neither the name of the author nor the names of its

      contributors may be used to endorse or promote products derived

      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE

LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR

CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN

CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

POSSIBILITY OF SUCH DAMAGE.

*/

#include "libtorrent/config.hpp"

#include <iterator>

#include "libtorrent/utf8.hpp"

#include "libtorrent/assert.hpp"

#include "libtorrent/error_code.hpp"

#include "libtorrent/aux_/throw.hpp"

#include "libtorrent/aux_/numeric_cast.hpp"

namespace libtorrent {

namespace {

  // return the number of bytes in the UTF-8 sequence starting with this

  // character. Returns 0 if the lead by is invalid

  int utf8_sequence_length(char const c)

  {

    auto const b = static_cast<std::uint8_t>(c);

    if (b < 0b10000000) return 1;

    if ((b >> 5) == 0b110) return 2;

    if ((b >> 4) == 0b1110) return 3;

    if ((b >> 3) == 0b11110) return 4;

    // this is an invalid prefix, but we still parse it to skip this many

    // bytes

    if ((b >> 2) == 0b111110) return 5;

    return 0;

  }

} // anonymous namespace

  std::int32_t const max_codepoint = 0x10ffff;

  std::int32_t const surrogate_start = 0xd800;

  std::int32_t const surrogate_end = 0xdfff;

  void append_utf8_codepoint(std::string& ret, std::int32_t codepoint)

  {

    if (codepoint >= surrogate_start

      && codepoint <= surrogate_end)

      codepoint = '_';

    if (codepoint > max_codepoint)

      codepoint = '_';

    int seq_len = 0;

    if (codepoint < 0x80) seq_len = 1;

    else if (codepoint < 0x800) seq_len = 2;

    else if (codepoint < 0x10000) seq_len = 3;

    else seq_len = 4;

    switch (seq_len)

    {

      case 1:

        ret.push_back(static_cast<char>(codepoint));

        break;

      case 2:

        ret.push_back(static_cast<char>(0b11000000 | (codepoint >> 6)));

        break;

      case 3:

        ret.push_back(static_cast<char>(0b11100000 | (codepoint >> 12)));

        break;

      case 4:

        ret.push_back(static_cast<char>(0b11110000 | (codepoint >> 18)));

        break;

    }

    for (int i = seq_len - 2; i >= 0; --i)

      ret.push_back(static_cast<char>(0b10000000 | ((codepoint >> (6 * i)) & 0b111111)));

  }

  // returns the unicode codepoint and the number of bytes of the utf8 sequence

  // that was parsed. The codepoint is -1 if it's invalid

  std::pair<std::int32_t, int> parse_utf8_codepoint(string_view str)

  {

    TORRENT_ASSERT(!str.empty());

    if (str.empty()) return std::make_pair(-1, 0);

    int const sequence_len = utf8_sequence_length(str[0]);

    // this is likely the most common case

    if (sequence_len == 1) return std::make_pair(std::int32_t(str[0]), sequence_len);

    // if we find an invalid sequence length, skip one byte

    if (sequence_len == 0)

      return std::make_pair(-1, 1);

    if (sequence_len > 4)

      return std::make_pair(-1, sequence_len);

    if (sequence_len > int(str.size()))

      return std::make_pair(-1, static_cast<int>(str.size()));

    std::int32_t ch = 0;

    // first byte

    switch (sequence_len)

    {

      case 1:

        ch = str[0] & 0b01111111;

        break;

      case 2:

        ch = str[0] & 0b00011111;

        break;

      case 3:

        ch = str[0] & 0b00001111;

        break;

      case 4:

        ch = str[0] & 0b00000111;

        break;

    }

    for (int i = 1; i < sequence_len; ++i)

    {

      auto const b = static_cast<std::uint8_t>(str[static_cast<std::size_t>(i)]);

      // continuation bytes must start with 10xxxxxx

      if (b > 0b10111111 || b < 0b10000000)

        return std::make_pair(-1, sequence_len);

      ch <<= 6;

      ch += b & 0b111111;

    }

    // check if the sequence is overlong, i.e. whether it has leading

    // (redundant) zeros

    switch (sequence_len)

    {

      case 2:

        if (ch < 0x80) return std::make_pair(-1, sequence_len);

        break;

      case 3:

        if (ch < 0x800) return std::make_pair(-1, sequence_len);

        break;

      case 4:

        if (ch < 0x10000) return std::make_pair(-1, sequence_len);

        break;

    }

    if (ch > max_codepoint)

      return std::make_pair(-1, sequence_len);

    // per RFC 3629, surrogates should not appear in utf-8

    if (ch >= surrogate_start && ch <= surrogate_end)

      return std::make_pair(-1, sequence_len);

    return std::make_pair(static_cast<std::int32_t>(ch), sequence_len);

  }

}