interleave.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 <cmath>
#include <concepts>
#include <ranges>
#include <type_traits>
 
#include <seqan3/core/range/detail/adaptor_from_functor.hpp>
#include <seqan3/core/range/detail/random_access_iterator.hpp>
#include <seqan3/utility/type_traits/detail/transformation_trait_or.hpp>
#include <seqan3/utility/views/chunk.hpp>
#include <seqan3/utility/views/join_with.hpp>
#include <seqan3/utility/views/type_reduce.hpp>
 
namespace seqan3::detail
{
 
// ============================================================================
//  view_interleave
// ============================================================================
 
template <std::ranges::random_access_range urng_t, std::ranges::random_access_range inserted_rng_t>
    requires std::ranges::view<urng_t> && std::ranges::sized_range<urng_t> && std::ranges::view<inserted_rng_t>
          && std::ranges::sized_range<inserted_rng_t>
          && std::common_reference_with<std::ranges::range_reference_t<urng_t>,
                                        std::ranges::range_reference_t<inserted_rng_t>>
class view_interleave : public std::ranges::view_interface<view_interleave<urng_t, inserted_rng_t>>
{
private:
    urng_t urange;
    size_t step_size{};
    inserted_rng_t inserted_range;
 
    using size_type = std::ranges::range_size_t<urng_t>;
    using reference =
        std::common_reference_t<std::ranges::range_reference_t<urng_t>, std::ranges::range_reference_t<inserted_rng_t>>;
    using const_reference =
        detail::transformation_trait_or_t<std::common_reference<std::ranges::range_reference_t<urng_t const>,
                                                                std::ranges::range_reference_t<inserted_rng_t const>>,
                                          void>;
    using value_type = std::ranges::range_value_t<urng_t>;
    using difference_type = std::ranges::range_difference_t<urng_t>;
    using iterator = detail::random_access_iterator<view_interleave>;
    using const_iterator = detail::random_access_iterator<view_interleave const>;
 
    template <typename range_type, template <typename...> typename derived_t_template, typename... args_t>
    friend class detail::random_access_iterator_base;
 
public:
    constexpr view_interleave() noexcept = default;                                        
    constexpr view_interleave(view_interleave const & rhs) noexcept = default;             
    constexpr view_interleave(view_interleave && rhs) noexcept = default;                  
    constexpr view_interleave & operator=(view_interleave const & rhs) noexcept = default; 
    constexpr view_interleave & operator=(view_interleave && rhs) noexcept = default;      
    ~view_interleave() noexcept = default;                                                 
 
    explicit constexpr view_interleave(urng_t && _urange, size_t const _step_size, inserted_rng_t && _inserted_range) :
        urange{_urange},
        step_size{_step_size},
        inserted_range{std::forward<inserted_rng_t>(_inserted_range)}
    {}
 
    template <typename orng_t, typename oirng_t>
        requires std::constructible_from<urng_t, decltype(views::type_reduce(std::declval<orng_t>()))>
              && std::constructible_from<inserted_rng_t, std::views::all_t<oirng_t>>
    explicit constexpr view_interleave(orng_t && _urange, size_t const _step_size, oirng_t && _inserted_range) :
        view_interleave{views::type_reduce(std::forward<orng_t>(_urange)),
                        _step_size,
                        std::views::all(std::forward<oirng_t>(_inserted_range))}
    {}
 
    iterator begin() noexcept
    {
        return {*this, 0};
    }
 
    const_iterator begin() const noexcept
    {
        return {*this, 0};
    }
 
    iterator end() noexcept
    {
        return {*this, size()};
    }
 
    const_iterator end() const noexcept
    {
        return {*this, size()};
    }
 
    size_type size()
    {
        return std::ranges::size(urange)
             + ((std::floor(std::ranges::size(urange) / step_size)
                 - (std::ranges::size(urange) % step_size == 0 ? 1 : 0))
                * std::ranges::size(inserted_range));
    }
 
    size_type size() const
    {
        return std::ranges::size(urange)
             + ((std::floor(std::ranges::size(urange) / step_size)
                 - (std::ranges::size(urange) % step_size == 0 ? 1 : 0))
                * std::ranges::size(inserted_range));
    }
 
    reference operator[](size_type const i)
    {
        size_t combined_size = step_size + std::ranges::size(inserted_range);
        assert(i < size());
        if (i % (combined_size) < step_size)
            return urange[i - (std::floor(i / (combined_size)) * std::ranges::size(inserted_range))];
        else
            return inserted_range[(i % (combined_size)) - step_size];
    }
 
    const_reference operator[](size_type const i) const
    {
        size_t combined_size = step_size + std::ranges::size(inserted_range);
        assert(i < size());
        if (i % (combined_size) < step_size)
            return urange[i - (std::floor(i / (combined_size)) * std::ranges::size(inserted_range))];
        else
            return inserted_range[(i % (combined_size)) - step_size];
    }
};
 
template <std::ranges::random_access_range urng_t, std::ranges::random_access_range inserted_rng_t>
    requires std::ranges::viewable_range<urng_t> && std::ranges::sized_range<urng_t>
              && std::ranges::sized_range<inserted_rng_t>
              && std::common_reference_with<std::ranges::range_reference_t<urng_t>,
                                            std::ranges::range_reference_t<inserted_rng_t>>
view_interleave(urng_t &&, size_t, inserted_rng_t &&)
    -> view_interleave<decltype(views::type_reduce(std::declval<urng_t>())), std::views::all_t<inserted_rng_t>>;
 
// ============================================================================
//  interleave_fn (adaptor definition)
// ============================================================================
 
struct interleave_fn
{
    template <std::ranges::forward_range inserted_rng_t, std::integral size_type>
    constexpr auto operator()(size_type const size, inserted_rng_t && i) const noexcept
    {
        return detail::adaptor_from_functor{*this, size, std::forward<inserted_rng_t>(i)};
    }
 
    template <std::ranges::range urng_t, std::ranges::range inserted_rng_t, std::integral size_type>
    constexpr auto operator()(urng_t && urange, size_type const size, inserted_rng_t && i) const noexcept
    {
        static_assert(std::ranges::forward_range<urng_t>,
                      "The underlying range parameter in views::interleave must model std::ranges::forward_range.");
        static_assert(std::ranges::viewable_range<urng_t>,
                      "The underlying range parameter in views::interleave must model std::ranges::viewable_range.");
        static_assert(std::ranges::forward_range<inserted_rng_t>,
                      "The range to be inserted by views::interleave must model std::ranges::forward_range.");
        if constexpr (std::ranges::random_access_range<urng_t> && std::ranges::sized_range<urng_t>
                      && std::ranges::random_access_range<inserted_rng_t> && std::ranges::sized_range<inserted_rng_t>)
        {
            return detail::view_interleave{std::forward<urng_t>(urange),
                                           static_cast<size_t>(size),
                                           std::forward<inserted_rng_t>(i)};
        }
        else
        {
            return std::forward<urng_t>(urange) | seqan3::views::chunk(static_cast<size_t>(size))
                 | views::join_with(std::forward<inserted_rng_t>(i));
        }
    }
};
 
} // namespace seqan3::detail
 
// ============================================================================
//  views::interleave (adaptor instance definition)
// ============================================================================
 
namespace seqan3::views
{
inline constexpr auto interleave = detail::interleave_fn{};
 
} // namespace seqan3::views