in_file_iterator.hpp

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// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: BSD-3-Clause

 
#pragma once
 
#include <cassert>
#include <ios>
#include <ranges>
 
#include <seqan3/core/platform.hpp>
 
namespace seqan3::detail
{

template <typename file_type>
class in_file_iterator
{
    static_assert(!std::is_const_v<file_type>,
                  "You cannot iterate over const files, because the iterator changes the file.");
 
public:

    using value_type = typename file_type::value_type;
    using reference = typename file_type::reference;
    using const_reference = typename file_type::reference;
    using size_type = typename file_type::size_type;
    using difference_type = typename file_type::difference_type;
    using pointer = typename file_type::value_type *;
    using iterator_category = std::input_iterator_tag;

    constexpr in_file_iterator() = default;
    constexpr in_file_iterator(in_file_iterator const &) = default;
    constexpr in_file_iterator & operator=(in_file_iterator const &) = default;
    constexpr in_file_iterator(in_file_iterator &&) = default;
    constexpr in_file_iterator & operator=(in_file_iterator &&) = default;
    ~in_file_iterator() = default;

    constexpr in_file_iterator(file_type & _host) noexcept : host{&_host}
    {}

    in_file_iterator & operator++()
    {
        assert(host != nullptr);
        host->read_next_record();
        return *this;
    }

    void operator++(int)
    {
        assert(host != nullptr);
        ++(*this);
    }

    reference operator*() noexcept
    {
        assert(host != nullptr);
        return host->record_buffer;
    }

    reference operator*() const noexcept
    {
        assert(host != nullptr);
        return host->record_buffer;
    }


    constexpr bool operator==(std::default_sentinel_t const &) const noexcept
    {
        assert(host != nullptr);
        return host->at_end;
    }

    constexpr bool operator!=(std::default_sentinel_t const &) const noexcept
    {
        assert(host != nullptr);
        return !host->at_end;
    }

    constexpr friend bool operator==(std::default_sentinel_t const &, in_file_iterator const & it) noexcept
    {
        return (it == std::default_sentinel);
    }

    constexpr friend bool operator!=(std::default_sentinel_t const &, in_file_iterator const & it) noexcept
    {
        return (it != std::default_sentinel);
    }


    std::streampos file_position() const
    {
        assert(host != nullptr);
        return host->position_buffer;
    }

    in_file_iterator & seek_to(std::streampos const & pos)
    {
        assert(host != nullptr);
        host->secondary_stream->seekg(pos);
        if (host->secondary_stream->fail())
        {
            throw std::runtime_error{"Seeking to file position failed!"};
        }
        host->at_end = false; // iterator will not be at end if seeking to a specific record
        host->read_next_record();
        return *this;
    }
 
private:
    file_type * host{};
};
 
} // namespace seqan3::detail