STL/stl/inc/cvt/utf8

// codecvt facet for UTF-8 multibyte code, UCS wide-character code

// Copyright (c) Microsoft Corporation.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#pragma once
#ifndef _CVT_UTF8_
#define _CVT_UTF8_
#include <yvals_core.h>
#if _STL_COMPILER_PREPROCESSOR
#include <codecvt>
#include <cwchar>
#include <locale>

#pragma pack(push, _CRT_PACKING)
#pragma warning(push, _STL_WARNING_LEVEL)
#pragma warning(disable : _STL_DISABLED_WARNINGS)
_STL_DISABLE_CLANG_WARNINGS
#pragma push_macro("new")
#undef new

#if !_HAS_IF_CONSTEXPR
#pragma warning(disable : 4127) // conditional expression is constant
#endif // !_HAS_IF_CONSTEXPR

namespace stdext {
    namespace cvt {

        using _Statype = _CSTD mbstate_t;

        _STL_DISABLE_DEPRECATED_WARNING
        // CLASS TEMPLATE codecvt_utf8
        template <class _Elem, unsigned long _Maxcode = 0xffffffff, _STD codecvt_mode _Mode = _STD codecvt_mode{}>
        class codecvt_utf8
            : public _STD
                  codecvt<_Elem, char, _Statype> { // facet for converting between _Elem and UTF-8 byte sequences
        public:
            using _Mybase     = _STD codecvt<_Elem, char, _Statype>;
            using result      = typename _Mybase::result;
            using _Byte       = char;
            using intern_type = _Elem;
            using extern_type = _Byte;
            using state_type  = _Statype;

            explicit codecvt_utf8(size_t _Refs = 0) : _Mybase(_Refs) {}

            virtual ~codecvt_utf8() noexcept {}

        protected:
            virtual result do_in(_Statype& _State, const _Byte* _First1, const _Byte* _Last1, const _Byte*& _Mid1,
                _Elem* _First2, _Elem* _Last2, _Elem*& _Mid2) const override {
                // convert bytes [_First1, _Last1) to [_First2, _Last)
                char* _Pstate = reinterpret_cast<char*>(&_State);
                _Mid1         = _First1;
                _Mid2         = _First2;

                while (_Mid1 != _Last1 && _Mid2 != _Last2) { // convert a multibyte sequence
                    unsigned long _By = static_cast<unsigned char>(*_Mid1);
                    unsigned long _Ch;
                    int _Nextra;

                    if (_By < 0x80) {
                        _Ch     = _By;
                        _Nextra = 0;
                    } else if (_By < 0xc0) { // 0x80-0xbf not first byte
                        ++_Mid1;
                        return _Mybase::error;
                    } else if (_By < 0xe0) {
                        _Ch     = _By & 0x1f;
                        _Nextra = 1;
                    } else if (_By < 0xf0) {
                        _Ch     = _By & 0x0f;
                        _Nextra = 2;
                    } else if (_By < 0xf8) {
                        _Ch     = _By & 0x07;
                        _Nextra = 3;
                    } else {
                        _Ch     = _By & 0x03;
                        _Nextra = _By < 0xfc ? 4 : 5;
                    }

                    if (_Nextra == 0) {
                        ++_Mid1;
                    } else if (_Last1 - _Mid1 < _Nextra + 1) {
                        break; // not enough input
                    } else {
                        for (++_Mid1; 0 < _Nextra; --_Nextra, ++_Mid1) {
                            if ((_By = static_cast<unsigned char>(*_Mid1)) < 0x80 || 0xc0 <= _By) {
                                return _Mybase::error; // not continuation byte
                            } else {
                                _Ch = _Ch << 6 | (_By & 0x3f);
                            }
                        }
                    }

                    if (*_Pstate == 0) { // first time, maybe look for and consume header
                        *_Pstate = 1;

                        if _CONSTEXPR_IF ((_Mode & _STD consume_header) != 0) {
                            if (_Ch == 0xfeff) { // drop header and retry
                                result _Ans = do_in(_State, _Mid1, _Last1, _Mid1, _First2, _Last2, _Mid2);

                                if (_Ans == _Mybase::partial) { // roll back header determination
                                    *_Pstate = 0;
                                    _Mid1    = _First1;
                                }
                                return _Ans;
                            }
                        }
                    }

                    if (_Maxcode < _Ch) {
                        return _Mybase::error; // code too large
                    }
                    *_Mid2++ = static_cast<_Elem>(_Ch);
                }

                return _First1 == _Mid1 ? _Mybase::partial : _Mybase::ok;
            }

            virtual result do_out(_Statype& _State, const _Elem* _First1, const _Elem* _Last1, const _Elem*& _Mid1,
                _Byte* _First2, _Byte* _Last2, _Byte*& _Mid2) const override {
                // convert [_First1, _Last1) to bytes [_First2, _Last)
                char* _Pstate = reinterpret_cast<char*>(&_State);
                _Mid1         = _First1;
                _Mid2         = _First2;

                while (_Mid1 != _Last1 && _Mid2 != _Last2) { // convert and put a wide char
                    _Byte _By;
                    int _Nextra;
                    unsigned long _Ch = static_cast<unsigned long>(*_Mid1);

                    if (_Maxcode < _Ch) {
                        return _Mybase::error;
                    }

                    if (_Ch < 0x0080) {
                        _By     = static_cast<_Byte>(_Ch);
                        _Nextra = 0;
                    } else if (_Ch < 0x0800) {
                        _By     = static_cast<_Byte>(0xc0 | _Ch >> 6);
                        _Nextra = 1;
                    } else if (_Ch < 0x00010000) {
                        _By     = static_cast<_Byte>(0xe0 | _Ch >> 12);
                        _Nextra = 2;
                    } else if (_Ch < 0x00200000) {
                        _By     = static_cast<_Byte>(0xf0 | _Ch >> 18);
                        _Nextra = 3;
                    } else if (_Ch < 0x04000000) {
                        _By     = static_cast<_Byte>(0xf8 | _Ch >> 24);
                        _Nextra = 4;
                    } else {
                        _By     = static_cast<_Byte>(0xfc | (_Ch >> 30 & 0x03));
                        _Nextra = 5;
                    }

                    if (*_Pstate == 0) { // first time, maybe generate header
                        *_Pstate = 1;

                        if _CONSTEXPR_IF ((_Mode & _STD generate_header) != 0) {
                            if (_Last2 - _Mid2 < 3 + 1 + _Nextra) {
                                return _Mybase::partial; // not enough room for both
                            }

                            // prepend header
                            *_Mid2++ = '\xef';
                            *_Mid2++ = '\xbb';
                            *_Mid2++ = '\xbf';
                        }
                    }

                    if (_Last2 - _Mid2 < 1 + _Nextra) {
                        break; // not enough room for output
                    }

                    ++_Mid1;
                    for (*_Mid2++ = _By; 0 < _Nextra;) {
                        *_Mid2++ = static_cast<_Byte>((_Ch >> 6 * --_Nextra & 0x3f) | 0x80);
                    }
                }
                return _First1 == _Mid1 ? _Mybase::partial : _Mybase::ok;
            }

            virtual result do_unshift(_Statype&, _Byte* _First2, _Byte*, _Byte*& _Mid2) const override {
                // generate bytes to return to default shift state
                _Mid2 = _First2;
                return _Mybase::ok;
            }

            virtual int do_length(
                _Statype& _State, const _Byte* _First1, const _Byte* _Last1, size_t _Count) const noexcept override {
                // return min(_Count, converted length of bytes [_First1, _Last1))
                size_t _Wchars    = 0;
                _Statype _Mystate = _State;

                while (_Wchars < _Count && _First1 != _Last1) { // convert another wide character
                    const _Byte* _Mid1;
                    _Elem* _Mid2;
                    _Elem _Ch;

                    switch (do_in(_Mystate, _First1, _Last1, _Mid1, &_Ch, &_Ch + 1,
                        _Mid2)) { // test result of single wide-char conversion
                    case _Mybase::noconv:
                        return static_cast<int>(_Wchars + (_Last1 - _First1));

                    case _Mybase::ok:
                        if (_Mid2 == &_Ch + 1) {
                            ++_Wchars; // replacement do_in might not convert one
                        }

                        _First1 = _Mid1;
                        break;

                    default:
                        return static_cast<int>(_Wchars); // error or partial
                    }
                }

                return static_cast<int>(_Wchars);
            }

            virtual bool do_always_noconv() const noexcept override { // return true if conversions never change input
                return false;
            }

            virtual int do_max_length() const noexcept override { // return maximum length required for a conversion
                if _CONSTEXPR_IF ((_Mode & (_STD consume_header | _STD generate_header)) != 0) {
                    return 9;
                } else {
                    return 6;
                }
            }

            virtual int do_encoding() const noexcept override { // return length of code sequence (from codecvt)
                if _CONSTEXPR_IF ((_Mode & (_STD consume_header | _STD generate_header)) != 0) {
                    return -1; // -1 => state dependent
                } else {
                    return 0; // 0 => varying length
                }
            }
        };
        _STL_RESTORE_DEPRECATED_WARNING
    } // namespace cvt
} // namespace stdext

#pragma pop_macro("new")
_STL_RESTORE_CLANG_WARNINGS
#pragma warning(pop)
#pragma pack(pop)

#endif // _STL_COMPILER_PREPROCESSOR
#endif // _CVT_UTF8_