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// utf8_codecvt_facet.ipp

//  Copyright (c) 2001 Ronald Garcia, Indiana University (garcia@osl.iu.edu)
//  Andrew Lumsdaine, Indiana University (lums@osl.iu.edu).
//
//  SPDX-License-Identifier: BSL-1.0
//  Use, modification and distribution is subject to the Boost Software
//  License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)

// Please see the comments in <boost/detail/utf8_codecvt_facet.hpp> to
// learn how this file should be used.

#include <hpx/program_options/config.hpp>
#include <hpx/program_options/detail/utf8_codecvt_facet.hpp>

#include <cstddef>
#include <cstdlib>    // for multi-byte conversion routines
#include <limits>

// If we don't have wstring, then Unicode support
// is not available anyway, so we don't need to even
// compile this file.

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namespace hpx::program_options::detail {

    // implementation for wchar_t

    utf8_codecvt_facet::utf8_codecvt_facet(std::size_t no_locale_manage)
      : std::codecvt<wchar_t, char, std::mbstate_t>(no_locale_manage)
    {
    }

    utf8_codecvt_facet::~utf8_codecvt_facet() = default;

    // Translate incoming UTF-8 into UCS-4
    std::codecvt_base::result utf8_codecvt_facet::do_in(
        std::mbstate_t& /*state*/, char const* from, char const* from_end,
        char const*& from_next, wchar_t* to, wchar_t* to_end,
        wchar_t*& to_next) const
    {
        // Basic algorithm:  The first octet determines how many
        // octets total make up the UCS-4 character.  The remaining
        // "continuing octets" all begin with "10". To convert, subtract the
        // amount that specifies the number of octets from the first
        // octet.  Subtract 0x80 (1000 0000) from each continuing octet,
        // then mash the whole lot together.  Note that each continuing
        // octet only uses 6 bits as unique values, so only shift by multiples
        // of 6 to combine.
        while (from != from_end && to != to_end)
        {
            // Error checking   on the first octet
            if (invalid_leading_octet(*from))
            {
                from_next = from;
                to_next = to;
                return std::codecvt_base::error;
            }

            // The first octet is   adjusted by a value dependent upon the
            // number   of "continuing octets" encoding the character
            int const cont_octet_count =
                static_cast<int>(get_cont_octet_count(*from));
            const wchar_t octet1_modifier_table[] = {
                0x00, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc};

            // The unsigned char conversion is necessary in case char is
            // signed   (I learned this the hard way)
            wchar_t ucs_result = static_cast<unsigned char>(*from++) -
                octet1_modifier_table[cont_octet_count];

            // Invariants   :
            //   1) At the start of the loop,   'i' continuing characters have been
            //    processed
            //   2) *from   points to the next continuing character to be processed.
            int i = 0;
            while (i != cont_octet_count && from != from_end)
            {
                // Error checking on continuing characters
                if (invalid_continuing_octet(*from))
                {
                    from_next = from;
                    to_next = to;
                    return std::codecvt_base::error;
                }

                ucs_result *= (1 << 6);

                // each continuing character has an extra (10xxxxxx)b attached to
                // it that must be removed.
                ucs_result += static_cast<unsigned char>(*from++) - 0x80;
                ++i;
            }

            // If   the buffer ends with an incomplete unicode character...
            if (from == from_end && i != cont_octet_count)
            {
                // rewind "from" to before the current character translation
                from_next = from - (static_cast<std::size_t>(i) + 1);
                to_next = to;
                return std::codecvt_base::partial;
            }
            *to++ = ucs_result;
        }
        from_next = from;
        to_next = to;

        // Were we done converting or did we run out of destination space?
        return from == from_end ? std::codecvt_base::ok :
                                  std::codecvt_base::partial;
    }

    std::codecvt_base::result utf8_codecvt_facet::do_out(
        std::mbstate_t& /*state*/, wchar_t const* from, wchar_t const* from_end,
        wchar_t const*& from_next, char* to, char* to_end, char*& to_next) const
    {
        // RG - consider merging this table with the other one
        const wchar_t octet1_modifier_table[] = {
            0x00, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc};

        constexpr wchar_t max_wchar = (std::numeric_limits<wchar_t>::max)();
        while (from != from_end && to != to_end)
        {
            // Check for invalid UCS-4 character
            if (*from > max_wchar)
            {
                from_next = from;
                to_next = to;
                return std::codecvt_base::error;
            }

            int const cont_octet_count = get_cont_octet_out_count(*from);

            // RG  - comment this formula better
            int shift_exponent = (cont_octet_count) *6;

            // Process the first character
            *to++ = static_cast<char>(octet1_modifier_table[cont_octet_count] +
                static_cast<unsigned char>(*from / (1 << shift_exponent)));

            // Process the continuation characters
            // Invariants: At   the start of the loop:
            //   1) 'i' continuing octets   have been generated
            //   2) '*to'   points to the next location to place an octet
            //   3) shift_exponent is   6 more than needed for the next octet
            int i = 0;
            while (i != cont_octet_count && to != to_end)
            {
                shift_exponent -= 6;
                *to++ = static_cast<char>(
                    0x80 + ((*from / (1 << shift_exponent)) % (1 << 6)));
                ++i;
            }
            // If   we filled up the out buffer before encoding the character
            if (to == to_end && i != cont_octet_count)
            {
                from_next = from;
                to_next = to - (static_cast<std::size_t>(i) + 1);
                return std::codecvt_base::partial;
            }
            ++from;
        }
        from_next = from;
        to_next = to;

        // Were we done or did we run out of destination space
        return from == from_end ? std::codecvt_base::ok :
                                  std::codecvt_base::partial;
    }

    // How many char objects can I process to get <= max_limit
    // wchar_t objects?
    int utf8_codecvt_facet::do_length(std::mbstate_t&, char const* from,
        char const* from_end, std::size_t max_limit) const noexcept
    {
        // RG - this code is confusing!  I need a better way to express it.
        // and test cases.

        // Invariants:
        // 1) last_octet_count has the size of the last measured character
        // 2) char_count holds the number of characters shown to fit
        // within the bounds so far (no greater than max_limit)
        // 3) from_next points to the octet 'last_octet_count' before the
        // last measured character.
        std::size_t last_octet_count = 0;
        std::size_t char_count = 0;
        char const* from_next = from;

        // Use "<" because the buffer may represent incomplete characters
        while (
            from_next + last_octet_count <= from_end && char_count <= max_limit)
        {
            from_next += last_octet_count;
            last_octet_count =
                static_cast<std::size_t>(get_octet_count(*from_next));
            ++char_count;
        }
        return static_cast<int>(from_next - from);
    }

    unsigned int utf8_codecvt_facet::get_octet_count(
        unsigned char lead_octet) noexcept
    {
        // if the 0-bit (MSB) is 0, then 1 character
        if (lead_octet <= 0x7f)
            return 1;

        // Otherwise the count number of consecutive 1 bits starting at MSB
        //    assert(0xc0 <= lead_octet && lead_octet <= 0xfd);

        if (0xc0 <= lead_octet && lead_octet <= 0xdf)
            return 2;
        else if (0xe0 <= lead_octet && lead_octet <= 0xef)
            return 3;
        else if (0xf0 <= lead_octet && lead_octet <= 0xf7)
            return 4;    // -V112
        else if (0xf8 <= lead_octet && lead_octet <= 0xfb)
            return 5;
        else
            return 6;
    }

    namespace detail {

        template <std::size_t s>
        int get_cont_octet_out_count_impl(wchar_t word) noexcept
        {
            if (word < 0x80)
            {
                return 0;
            }
            if (word < 0x800)
            {
                return 1;
            }
            return 2;
        }

        template <>
        int get_cont_octet_out_count_impl<4>(wchar_t word) noexcept
        {
            if (word < 0x80)
            {
                return 0;
            }
            if (word < 0x800)
            {
                return 1;
            }

            // Note that the following code will generate warnings on some platforms
            // where wchar_t is defined as UCS2.  The warnings are superfluous as the
            // specialization is never instantiated with such compilers, but this
            // can cause problems if warnings are being treated as errors, so we guard
            // against that.  Including <boost/detail/utf8_codecvt_facet.hpp> as we do
            // should be enough to get WCHAR_MAX defined.
            // cope with VC++ 7.1 or earlier having invalid WCHAR_MAX
#if defined(_MSC_VER) && _MSC_VER <= 1310    // 7.1 or earlier
            return 2;
#elif WCHAR_MAX > 0x10000

            if (word < 0x10000)
            {
                return 2;
            }
            if (word < 0x200000)
            {
                return 3;
            }
            if (word < 0x4000000)
            {
                return 4;
            }
            return 5;
#else
            return 2;
#endif
        }

    }    // namespace detail

    // How many "continuing octets" will be needed for this word
    // ==   total octets - 1.
    int utf8_codecvt_facet::get_cont_octet_out_count(
        wchar_t word) const noexcept
    {
        return detail::get_cont_octet_out_count_impl<sizeof(wchar_t)>(word);
    }
}    // namespace hpx::program_options::detail
