spanstream

// spanstream standard header

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

#ifndef _SPANSTREAM_
#define _SPANSTREAM_
#include <yvals.h>
#if _STL_COMPILER_PREPROCESSOR
#if !_HAS_CXX23
_EMIT_STL_WARNING(STL4038, "The contents of <spanstream> are available only with C++23 or later.");
#else // ^^^ !_HAS_CXX23 / _HAS_CXX23 vvv
#include <concepts>
#include <istream>
#include <ostream>
#include <span>
#include <streambuf>
#include <xutility>

#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

_STD_BEGIN

// In this file, _STD span is qualified to avoid ambiguity with span() member functions.
// This qualification is consistently used even when it isn't strictly necessary.

_EXPORT_STD template <class _Elem, class _Traits>
class basic_spanbuf : public basic_streambuf<_Elem, _Traits> {
private:
    using _Mysb = basic_streambuf<_Elem, _Traits>;

public:
    using char_type   = _Elem;
    using int_type    = _Traits::int_type;
    using pos_type    = _Traits::pos_type;
    using off_type    = _Traits::off_type;
    using traits_type = _Traits;

    // N4950 [spanbuf.cons], constructors
    basic_spanbuf() = default;

    explicit basic_spanbuf(ios_base::openmode _Which) : _Mysb(), _Mode(_Which) {}

    explicit basic_spanbuf(_STD span<_Elem> _Span, ios_base::openmode _Which = ios_base::in | ios_base::out)
        : _Mysb(), _Mode(_Which), _Buf() {
        this->span(_Span);
    }

    basic_spanbuf(const basic_spanbuf&) = delete;
    basic_spanbuf(basic_spanbuf&& _Right)
        : _Mysb(_STD move(_Right)), _Mode(_Right._Mode), _Buf(_STD exchange(_Right._Buf, {})) {
        _Right.setp(nullptr, nullptr, nullptr);
        _Right.setg(nullptr, nullptr, nullptr);
    }

    // N4950 [spanbuf.assign], assignment and swap
    basic_spanbuf& operator=(const basic_spanbuf&) = delete;

    basic_spanbuf& operator=(basic_spanbuf&& _Right) noexcept /* strengthened */ {
        if (this != _STD addressof(_Right)) {
            _Buf = _STD span<_Elem>{};
            this->setp(nullptr, nullptr, nullptr);
            this->setg(nullptr, nullptr, nullptr);
            this->swap(_Right);
        }
        return *this;
    }

    void swap(basic_spanbuf& _Right) noexcept /* strengthened */ {
        _Mysb::swap(_Right);
        _STD swap(_Mode, _Right._Mode);
        _STD swap(_Buf, _Right._Buf);
    }

    // N4950 [spanbuf.members], member functions
    _NODISCARD _STD span<_Elem> span() const noexcept {
        if (_Mode & ios_base::out) {
            return _STD span<_Elem>{_Mysb::pbase(), _Mysb::pptr()};
        }

        return _Buf;
    }

    void span(_STD span<_Elem> _Span) noexcept {
        _Buf              = _Span;
        const auto _First = _Buf.data();
        const auto _Last  = _First + _Buf.size();
        if (_Mode & ios_base::out) {
            if (_Mode & ios_base::ate) {
                _Mysb::setp(_First, _Last, _Last);
            } else {
                _Mysb::setp(_First, _First, _Last);
            }
        }

        if (_Mode & ios_base::in) {
            _Mysb::setg(_First, _First, _Last);
        }
    }

protected:
    // N4950 [spanbuf.virtuals], overridden virtual functions
    pos_type seekoff(
        off_type _Off, ios_base::seekdir _Way, ios_base::openmode _Which = ios_base::in | ios_base::out) override {
        const bool _Sequence_in  = _Which & ios_base::in;
        const bool _Sequence_out = _Which & ios_base::out;
        switch (_Way) {
        case ios_base::beg:
            // N4950 [spanbuf.virtuals]/4.1 baseoff = 0
            if (static_cast<size_t>(_Off) > _Buf.size()) { // negative wraparound to positive to save a compare
                return pos_type{off_type{-1}}; // N4950 [spanbuf.virtuals]/5 report failure
            }

            break;
        case ios_base::end:
            {
                // N4950 [spanbuf.virtuals]/4.3 baseoff =
                const auto _Baseoff = (_Mode & ios_base::out) && !(_Mode & ios_base::in)
                                        ? static_cast<off_type>(_Mysb::pptr() - _Mysb::pbase())
                                        : static_cast<off_type>(_Buf.size());
                if (_Off > (numeric_limits<off_type>::max)() - _Baseoff) { // overflow, _Baseoff is always non-negative
                    return pos_type{off_type{-1}}; // report failure
                }

                _Off += _Baseoff;
                if (static_cast<size_t>(_Off) > _Buf.size()) { // negative wraparound to positive to save a compare
                    return pos_type{off_type{-1}}; // N4950 [spanbuf.virtuals]/5 report failure
                }

                break;
            }
        case ios_base::cur:
            if (_Sequence_in && _Sequence_out) {
                return pos_type{off_type{-1}}; // report failure
            } else if (_Sequence_in || _Sequence_out) {
                const off_type _Oldoff  = _Sequence_in ? static_cast<off_type>(_Mysb::gptr() - _Mysb::eback())
                                                       : static_cast<off_type>(_Mysb::pptr() - _Mysb::pbase());
                const off_type _Oldleft = static_cast<off_type>(_Buf.size() - _Oldoff);
                if (_Off < -_Oldoff || _Off > _Oldleft) { // out of bounds
                    return pos_type{off_type{-1}};
                }

                _Off += _Oldoff;
            } else {
                return pos_type{off_type{-1}}; // report failure
            }
            break;
        default:
            return pos_type{off_type{-1}}; // report failure
        }

        // N4950 [spanbuf.virtuals]/4: For a sequence to be positioned, if its next pointer is a null pointer and newoff
        // is not equal to 0, the positioning operation fails.
        if (_Off != 0 && ((_Sequence_in && !_Mysb::gptr()) || (_Sequence_out && !_Mysb::pptr()))) {
            return pos_type{off_type{-1}}; // report failure
        }

        if (_Sequence_in) {
            _Mysb::gbump(static_cast<int>(_Off - (_Mysb::gptr() - _Mysb::eback())));
        }

        if (_Sequence_out) {
            _Mysb::pbump(static_cast<int>(_Off - (_Mysb::pptr() - _Mysb::pbase())));
        }

        return pos_type{_Off};
    }

    pos_type seekpos(pos_type _Pos, ios_base::openmode _Which = ios_base::in | ios_base::out) override {
        return seekoff(off_type{_Pos}, ios_base::beg, _Which);
    }

    _Mysb* setbuf(_Elem* _Buffer, streamsize _Count) override {
        this->span(_STD span<_Elem>{_Buffer, static_cast<size_t>(_Count)});
        return this;
    }

private:
    ios_base::openmode _Mode{ios_base::in | ios_base::out};
    _STD span<_Elem> _Buf{};
};

_EXPORT_STD template <class _Elem, class _Traits>
void swap(basic_spanbuf<_Elem, _Traits>& _Left, basic_spanbuf<_Elem, _Traits>& _Right) noexcept /* strengthened */ {
    _Left.swap(_Right);
}

_EXPORT_STD template <class _Elem, class _Traits>
class basic_ispanstream : public basic_istream<_Elem, _Traits> {
private:
    using _Mybase = basic_istream<_Elem, _Traits>;
    using _Mysb   = basic_spanbuf<_Elem, _Traits>;

public:
    using char_type   = _Elem;
    using int_type    = _Traits::int_type;
    using pos_type    = _Traits::pos_type;
    using off_type    = _Traits::off_type;
    using traits_type = _Traits;

    // N4950 [ispanstream.cons], constructors
    explicit basic_ispanstream(_STD span<_Elem> _Span, ios_base::openmode _Which = ios_base::in)
        : _Mybase(_STD addressof(_Buf)), _Buf(_Span, _Which | ios_base::in) {}

    basic_ispanstream(const basic_ispanstream&) = delete;

    basic_ispanstream(basic_ispanstream&& _Right) : _Mybase(_STD move(_Right)), _Buf(_STD move(_Right._Buf)) {
        _Mybase::set_rdbuf(_STD addressof(_Buf));
    }

    template <_RANGES borrowed_range _ReadOnlyRange>
        requires (
            !convertible_to<_ReadOnlyRange, _STD span<_Elem>> && convertible_to<_ReadOnlyRange, _STD span<const _Elem>>)
    explicit basic_ispanstream(_ReadOnlyRange&& _Range)
        : basic_ispanstream(
            _STD span<_Elem>{const_cast<_Elem*>(_RANGES data(_Range)), static_cast<size_t>(_RANGES size(_Range))}) {}

    basic_ispanstream& operator=(const basic_ispanstream&) = delete;

    basic_ispanstream& operator=(basic_ispanstream&& _Right) noexcept /* strengthened */ {
        _Mybase::swap(_Right);
        _Buf.swap(_Right._Buf);
        return *this;
    }

    // N4950 [ispanstream.swap], swap
    void swap(basic_ispanstream& _Right) noexcept /* strengthened */ {
        _Mybase::swap(_Right);
        _Buf.swap(_Right._Buf);
    }

    // N4950 [ispanstream.members], member functions
    _NODISCARD _Mysb* rdbuf() const noexcept {
        return const_cast<_Mysb*>(_STD addressof(_Buf));
    }

    _NODISCARD _STD span<const _Elem> span() const noexcept {
        return rdbuf()->span();
    }

    void span(_STD span<_Elem> _Span) noexcept {
        rdbuf()->span(_Span);
    }

    template <_RANGES borrowed_range _ReadOnlyRange>
        requires (
            !convertible_to<_ReadOnlyRange, _STD span<_Elem>> && convertible_to<_ReadOnlyRange, _STD span<const _Elem>>)
    void span(_ReadOnlyRange&& _Range) noexcept {
        this->span(
            _STD span<_Elem>{const_cast<_Elem*>(_RANGES data(_Range)), static_cast<size_t>(_RANGES size(_Range))});
    }

private:
    _Mysb _Buf;
};

_EXPORT_STD template <class _Elem, class _Traits>
void swap(basic_ispanstream<_Elem, _Traits>& _Left, basic_ispanstream<_Elem, _Traits>& _Right) noexcept
/* strengthened */ {
    _Left.swap(_Right);
}

_EXPORT_STD template <class _Elem, class _Traits>
class basic_ospanstream : public basic_ostream<_Elem, _Traits> {
private:
    using _Mybase = basic_ostream<_Elem, _Traits>;
    using _Mysb   = basic_spanbuf<_Elem, _Traits>;

public:
    using char_type   = _Elem;
    using int_type    = _Traits::int_type;
    using pos_type    = _Traits::pos_type;
    using off_type    = _Traits::off_type;
    using traits_type = _Traits;

    // N4950 [ospanstream.cons], constructors
    explicit basic_ospanstream(_STD span<_Elem> _Span, ios_base::openmode _Which = ios_base::out)
        : _Mybase(_STD addressof(_Buf)), _Buf(_Span, _Which | ios_base::out) {}

    basic_ospanstream(const basic_ospanstream&) = delete;

    basic_ospanstream(basic_ospanstream&& _Right) : _Mybase(_STD move(_Right)), _Buf(_STD move(_Right._Buf)) {
        _Mybase::set_rdbuf(_STD addressof(_Buf));
    }

    basic_ospanstream& operator=(const basic_ospanstream&) = delete;

    basic_ospanstream& operator=(basic_ospanstream&& _Right) noexcept /* strengthened */ {
        _Mybase::swap(_Right);
        _Buf.swap(_Right._Buf);
        return *this;
    }

    // N4950 [ospanstream.swap], swap
    void swap(basic_ospanstream& _Right) noexcept /* strengthened */ {
        _Mybase::swap(_Right);
        _Buf.swap(_Right._Buf);
    }

    // N4950 [ospanstream.members], member functions
    _NODISCARD _Mysb* rdbuf() const noexcept {
        return const_cast<_Mysb*>(_STD addressof(_Buf));
    }

    _NODISCARD _STD span<_Elem> span() const noexcept {
        return rdbuf()->span();
    }

    void span(_STD span<_Elem> _Span) noexcept {
        rdbuf()->span(_Span);
    }

private:
    _Mysb _Buf;
};

_EXPORT_STD template <class _Elem, class _Traits>
void swap(basic_ospanstream<_Elem, _Traits>& _Left, basic_ospanstream<_Elem, _Traits>& _Right) noexcept
/* strengthened */ {
    _Left.swap(_Right);
}

_EXPORT_STD template <class _Elem, class _Traits>
class basic_spanstream : public basic_iostream<_Elem, _Traits> {
private:
    using _Mybase = basic_iostream<_Elem, _Traits>;
    using _Mysb   = basic_spanbuf<_Elem, _Traits>;

public:
    using char_type   = _Elem;
    using int_type    = _Traits::int_type;
    using pos_type    = _Traits::pos_type;
    using off_type    = _Traits::off_type;
    using traits_type = _Traits;

    // N4950 [spanstream.cons], constructors
    explicit basic_spanstream(_STD span<_Elem> _Span, ios_base::openmode _Which = ios_base::out | ios_base::in)
        : _Mybase(_STD addressof(_Buf)), _Buf(_Span, _Which) {}

    basic_spanstream(const basic_spanstream&) = delete;

    basic_spanstream(basic_spanstream&& _Right) : _Mybase(_STD move(_Right)), _Buf(_STD move(_Right._Buf)) {
        _Mybase::set_rdbuf(_STD addressof(_Buf));
    }

    basic_spanstream& operator=(const basic_spanstream&) = delete;

    basic_spanstream& operator=(basic_spanstream&& _Right) noexcept /* strengthened */ {
        _Mybase::swap(_Right);
        _Buf.swap(_Right._Buf);
        return *this;
    }

    // N4950 [spanstream.swap], swap
    void swap(basic_spanstream& _Right) noexcept /* strengthened */ {
        _Mybase::swap(_Right);
        _Buf.swap(_Right._Buf);
    }

    // N4950 [spanstream.members], member functions
    _NODISCARD _Mysb* rdbuf() const noexcept {
        return const_cast<_Mysb*>(_STD addressof(_Buf));
    }

    _NODISCARD _STD span<_Elem> span() const noexcept {
        return rdbuf()->span();
    }

    void span(_STD span<_Elem> _Span) noexcept {
        rdbuf()->span(_Span);
    }

private:
    _Mysb _Buf;
};

_EXPORT_STD template <class _Elem, class _Traits>
void swap(basic_spanstream<_Elem, _Traits>& _Left, basic_spanstream<_Elem, _Traits>& _Right) noexcept
/* strengthened */ {
    _Left.swap(_Right);
}

_STD_END

#pragma pop_macro("new")
_STL_RESTORE_CLANG_WARNINGS
#pragma warning(pop)
#pragma pack(pop)
#endif // ^^^ _HAS_CXX23 ^^^
#endif // _STL_COMPILER_PREPROCESSOR
#endif // _SPANSTREAM_