istreambuf.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2019, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2019, Knut Reinert & MPI für molekulare Genetik
// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
// -----------------------------------------------------------------------------------------------------

#pragma once

#include <iosfwd>

#include <seqan3/io/stream/concept.hpp>
#include <seqan3/std/iterator>
#include <seqan3/std/ranges>

namespace seqan3::detail
{

// ============================================================================
//  fast_istreambuf_iterator
// ============================================================================

template <typename char_t, typename traits_t = std::char_traits<char_t>>
struct stream_buffer_exposer : public std::basic_streambuf<char_t, traits_t>
{
    using base_t = std::basic_streambuf<char_t, traits_t>;

    // Expose protected members:
    using base_t::eback;
    using base_t::gptr;
    using base_t::egptr;
    using base_t::gbump;
    using base_t::underflow;

    using base_t::pbase;
    using base_t::pptr;
    using base_t::epptr;
    using base_t::pbump;
    using base_t::overflow;
};

template <typename char_t, typename traits_t = std::char_traits<char_t>>
class fast_istreambuf_iterator
{
private:
    stream_buffer_exposer<char_t, traits_t> * stream_buf = nullptr;

public:
    using difference_type   = ptrdiff_t;               
    using value_type        = char_t;                  
    using reference         = char_t;                  
    using pointer           = void;                    
    using iterator_category = std::input_iterator_tag; 

    fast_istreambuf_iterator()                                              noexcept = default; 
    fast_istreambuf_iterator(fast_istreambuf_iterator const &)              noexcept = default; 
    fast_istreambuf_iterator(fast_istreambuf_iterator &&)                   noexcept = default; 
    fast_istreambuf_iterator & operator=(fast_istreambuf_iterator const &)  noexcept = default; 
    fast_istreambuf_iterator & operator=(fast_istreambuf_iterator &&)       noexcept = default; 
    ~fast_istreambuf_iterator()                                             noexcept = default; 

    explicit fast_istreambuf_iterator(std::basic_streambuf<char_t, traits_t> & ibuf) :
        stream_buf{reinterpret_cast<stream_buffer_exposer<char_t, traits_t> *>(&ibuf)}
    {
        assert(stream_buf != nullptr);
        stream_buf->underflow(); // ensure the stream buffer has content on construction
    }

    fast_istreambuf_iterator & operator++()
    {
        assert(stream_buf != nullptr);
        stream_buf->snextc(); // move to then right, then underflow()
        return *this;
    }

    void operator++(int)
    {
        ++(*this);
    }

    reference operator*() const
    {
        assert(stream_buf != nullptr);
        return *stream_buf->gptr();
    }

    friend bool operator==(fast_istreambuf_iterator const & lhs, std::ranges::default_sentinel_t const &) noexcept
    {
        assert(lhs.stream_buf != nullptr);
        // compare size of remaining buffer; since ++ always resizes if possible, safe to compare pointers here
        return (lhs.stream_buf->gptr() == lhs.stream_buf->egptr());
    }

    friend bool operator!=(fast_istreambuf_iterator const & lhs, std::ranges::default_sentinel_t const &) noexcept
    {
        return !(lhs == std::ranges::default_sentinel);
    }

    friend bool operator==(std::ranges::default_sentinel_t const &, fast_istreambuf_iterator const & rhs) noexcept
    {
        return rhs == std::ranges::default_sentinel;
    }

    friend bool operator!=(std::ranges::default_sentinel_t const &, fast_istreambuf_iterator const & rhs) noexcept
    {
        return !(rhs == std::ranges::default_sentinel);
    }
};

// ============================================================================
//  istreambuf_fn (adaptor definition)
// ============================================================================

struct istreambuf_fn
{
    template <typename stream_char_t, typename stream_traits_t>
    constexpr auto operator()(std::basic_streambuf<stream_char_t, stream_traits_t> & s) const
    {
        return std::ranges::subrange<detail::fast_istreambuf_iterator<stream_char_t, stream_traits_t>,
                                     std::ranges::default_sentinel_t>
        {
            detail::fast_istreambuf_iterator<stream_char_t, stream_traits_t>{s},
            std::ranges::default_sentinel_t{}
        };
    }

    template <IStream2 stream_t>
    constexpr auto operator()(stream_t & s) const
    {
        return this->operator()(*s.rdbuf());
    }
};

} // namespace seqan3::detail

// ============================================================================
//  view::istreambuf (adaptor instance definition)
// ============================================================================

namespace seqan3::view
{

inline constexpr auto istreambuf = detail::istreambuf_fn{};

} // namespace seqan3::view