take.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 <range/v3/algorithm/copy.hpp>

#include <seqan3/core/type_traits/iterator.hpp>
#include <seqan3/core/type_traits/range.hpp>
#include <seqan3/core/type_traits/template_inspection.hpp>
#include <seqan3/core/type_traits/transformation_trait_or.hpp>
#include <seqan3/io/exception.hpp>
#include <seqan3/range/concept.hpp>
#include <seqan3/range/shortcuts.hpp>
#include <seqan3/range/container/concept.hpp>
#include <seqan3/range/view/detail.hpp>
#include <seqan3/range/detail/inherited_iterator_base.hpp>
#include <seqan3/std/algorithm>
#include <seqan3/std/concepts>
#include <seqan3/std/iterator>
#include <seqan3/std/ranges>
#include <seqan3/std/span>
#include <seqan3/std/type_traits>

namespace seqan3::detail
{

// ============================================================================
//  view_take
// ============================================================================

template <std::ranges::View urng_t, bool exactly, bool or_throw>
class view_take : public ranges::view_interface<view_take<urng_t, exactly, or_throw>>
{
private:
    urng_t urange;

    size_t target_size;

    using sentinel_type = std::ranges::sentinel_t<urng_t>;

    template <typename rng_t>
    class iterator_type : public inherited_iterator_base<iterator_type<rng_t>, std::ranges::iterator_t<rng_t>>
    {
    private:
        using base_base_t = std::ranges::iterator_t<rng_t>;
        using base_t      = inherited_iterator_base<iterator_type, std::ranges::iterator_t<rng_t>>;

        size_t pos{};

        size_t max_pos{};

        std::conditional_t<exactly && !std::ForwardIterator<base_base_t>, view_take *, detail::ignore_t> host_ptr;

    public:
        constexpr iterator_type()                                      = default; 
        constexpr iterator_type(iterator_type const & rhs)             = default; 
        constexpr iterator_type(iterator_type && rhs)                  = default; 
        constexpr iterator_type & operator=(iterator_type const & rhs) = default; 
        constexpr iterator_type & operator=(iterator_type && rhs)      = default; 
        ~iterator_type()                                               = default; 

        constexpr iterator_type(base_base_t const & it) noexcept(noexcept(base_t{it})) :
            base_t{std::move(it)}
        {}

        constexpr iterator_type(base_base_t it, size_t const _pos, size_t const _max_pos, view_take * host = nullptr) noexcept(noexcept(base_t{it})) :
            base_t{std::move(it)}, pos{_pos}, max_pos(_max_pos)
        {
            host_ptr = host;
        }

        using difference_type       = typename std::iterator_traits<base_base_t>::difference_type;
        using value_type            = typename std::iterator_traits<base_base_t>::value_type;
        using reference             = typename std::iterator_traits<base_base_t>::reference;
        using pointer               = typename std::iterator_traits<base_base_t>::pointer;
        using iterator_category     = iterator_tag_t<base_base_t>;

        constexpr iterator_type & operator++() noexcept(noexcept(++std::declval<base_t &>()))
        {
            base_t::operator++();
            ++pos;
            if constexpr (exactly && !std::ForwardIterator<base_base_t>)
                --host_ptr->target_size;
            return *this;
        }

        constexpr iterator_type operator++(int) noexcept(noexcept(++std::declval<iterator_type &>()) &&
                                               std::is_nothrow_copy_constructible_v<iterator_type>)
        {
            iterator_type cpy{*this};
            ++(*this);
            return cpy;
        }

        constexpr iterator_type & operator--() noexcept(noexcept(--std::declval<base_base_t &>()))
            requires std::BidirectionalIterator<base_base_t>
        {
            base_t::operator--();
            --pos;
            return *this;
        }

        constexpr iterator_type operator--(int) noexcept(noexcept(--std::declval<iterator_type &>()) &&
                                               std::is_nothrow_copy_constructible_v<iterator_type>)
            requires std::BidirectionalIterator<base_base_t>
        {
            iterator_type cpy{*this};
            --(*this);
            return cpy;
        }

        constexpr iterator_type & operator+=(difference_type const skip) noexcept(noexcept(std::declval<base_t &>() += skip))
            requires std::RandomAccessIterator<base_base_t>
        {
            base_t::operator+=(skip);
            pos += skip;
            return *this;
        }

        constexpr iterator_type & operator-=(difference_type const skip) noexcept(noexcept(std::declval<base_t &>() -= skip))
            requires std::RandomAccessIterator<base_base_t>
        {
            base_t::operator-=(skip);
            pos -= skip;
            return *this;
        }

        constexpr bool operator==(iterator_type const & rhs) const
            noexcept(!or_throw && noexcept(std::declval<base_base_t &>() == std::declval<base_base_t &>()))
            requires std::ForwardIterator<base_base_t>
        {
            return *base_t::this_to_base() == *rhs.this_to_base();
        }

        constexpr bool operator==(sentinel_type const & rhs) const
            noexcept(!or_throw && noexcept(std::declval<base_base_t &>() == std::declval<sentinel_type &>()))
        {
            if (pos >= max_pos)
                return true;

            if (*base_t::this_to_base() == rhs)
            {
                if constexpr (or_throw)
                    throw unexpected_end_of_input{"Reached end of input before designated size."};

                return true;
            }
            else
            {
                return false;
            }
        }

        constexpr friend bool operator==(sentinel_type const & lhs, iterator_type const & rhs) noexcept(noexcept(rhs == lhs))
        {
            return rhs == lhs;
        }

        constexpr bool operator!=(sentinel_type const & rhs) const
            noexcept(noexcept(std::declval<iterator_type &>() == rhs))
        {
            return !(*this == rhs);
        }

        constexpr bool operator!=(iterator_type const & rhs) const
            noexcept(noexcept(std::declval<iterator_type &>() == rhs))
            requires std::ForwardIterator<base_base_t>
        {
            return !(*this == rhs);
        }

        constexpr friend bool operator!=(sentinel_type const & lhs, iterator_type const & rhs) noexcept(noexcept(rhs != lhs))
        {
            return rhs != lhs;
        }

        constexpr reference operator[](std::make_unsigned_t<difference_type> const n) const
            noexcept(noexcept(std::declval<base_base_t &>()[0]))
            requires std::RandomAccessIterator<base_base_t>
        {
            return base_base_t::operator[](n);
        }
    }; // class iterator_type

public:
    using reference         = reference_t<urng_t>;
    using const_reference   = detail::transformation_trait_or_t<seqan3::reference<urng_t const>, void>;
    using value_type        = value_type_t<urng_t>;
    using size_type         = std::conditional_t<exactly,
                                                 transformation_trait_or_t<seqan3::size_type<urng_t>, size_t>,
                                                 void>;
    using difference_type   = difference_type_t<urng_t>;
    using iterator          = iterator_type<urng_t>;
    using const_iterator    = detail::transformation_trait_or_t<std::type_identity<iterator_type<urng_t const>>, void>;

    constexpr view_take()                                  = default; 
    constexpr view_take(view_take const & rhs)             = default; 
    constexpr view_take(view_take && rhs)                  = default; 
    constexpr view_take & operator=(view_take const & rhs) = default; 
    constexpr view_take & operator=(view_take && rhs)      = default; 
    ~view_take()                                           = default; 

    constexpr view_take(urng_t _urange, size_t const _size)
        : urange{std::move(_urange)}, target_size{_size}
    {
        if constexpr (exactly && or_throw && std::ranges::SizedRange<urng_t>)
        {
            if (seqan3::size(_urange) < _size)
            {
                throw std::invalid_argument{
                    "You are trying to construct a view::take_exactly_or_throw from a range that is strictly smaller."};
            }
        }
    }

    template<std::ranges::ViewableRange rng_t>
        requires std::Constructible<rng_t, std::ranges::all_view<rng_t>>
    constexpr view_take(rng_t && _urange, size_t const _size)
        : view_take{std::view::all(std::forward<rng_t>(_urange)), _size}
    {}

    constexpr iterator begin() noexcept
    {
        return {seqan3::begin(urange), 0, target_size, &(*this)};
    }

    constexpr const_iterator begin() const noexcept
        requires ConstIterableRange<urng_t>
    {
        return {seqan3::cbegin(urange), 0, target_size};
    }

    constexpr const_iterator cbegin() const noexcept
        requires ConstIterableRange<urng_t>
    {
        return {seqan3::cbegin(urange), 0, target_size};
    }

    constexpr sentinel_type end() noexcept
    {
        return {seqan3::end(urange)};
    }

    constexpr sentinel_type end() const noexcept
        requires ConstIterableRange<urng_t>
    {
        return {seqan3::cend(urange)};
    }

    constexpr sentinel_type cend() const noexcept
        requires ConstIterableRange<urng_t>
    {
        return {seqan3::cend(urange)};
    }

    constexpr size_type size() const noexcept
        requires exactly
    {
        return target_size;
    }
};

template <typename urng_t,
          bool exactly = false,
          bool or_throw = false>
view_take(urng_t && , size_t) -> view_take<std::ranges::all_view<urng_t>, exactly, or_throw>;

// ============================================================================
//  take_fn (adaptor definition)
// ============================================================================

template <bool exactly, bool or_throw>
struct take_fn
{
    constexpr auto operator()(size_t const size) const
    {
        return adaptor_from_functor{*this, size};
    }

    template <std::ranges::Range urng_t>
    constexpr auto operator()(urng_t && urange, size_t target_size) const
    {
        static_assert(std::ranges::ViewableRange<urng_t>,
                      "The view::take adaptor can only be passed ViewableRanges, i.e. Views or &-to-non-View.");

        // safeguard against wrong size
        if constexpr (std::ranges::SizedRange<urng_t>)
        {
            if constexpr (or_throw)
            {
                if (target_size > std::ranges::size(urange))
                {
                    throw std::invalid_argument{"You are trying to construct a view::take_exactly_or_throw from a "
                                                "range that is strictly smaller."};
                }
            }
            else
            {
                target_size = std::min(target_size, std::ranges::size(urange));
            }
        }

        // string_view
        if constexpr (is_type_specialisation_of_v<remove_cvref_t<urng_t>, std::basic_string_view>)
        {
            return urange.substr(0, target_size);
        }
        // string const &
        else if constexpr (is_type_specialisation_of_v<remove_cvref_t<urng_t>, std::basic_string> &&
                           std::is_const_v<std::remove_reference_t<urng_t>>)
        {
            return std::basic_string_view{std::ranges::data(urange), target_size};
        }
        // contiguous
        else if constexpr (ForwardingRange<urng_t> &&
                           std::ranges::ContiguousRange<urng_t> &&
                           std::ranges::SizedRange<urng_t>)
        {
            return std::span{std::ranges::data(urange), target_size};
        }
        // random_access
        else if constexpr (ForwardingRange<urng_t> &&
                           std::ranges::RandomAccessRange<urng_t> &&
                           std::ranges::SizedRange<urng_t>)
        {
            return std::ranges::subrange<std::ranges::iterator_t<urng_t>, std::ranges::iterator_t<urng_t>>
            {
                std::ranges::begin(urange),
                std::ranges::begin(urange) + target_size,
                target_size
            };
        }
        // our type
        else
        {
            return view_take<std::ranges::all_view<urng_t>, exactly, or_throw>
            {
                std::forward<urng_t>(urange),
                target_size
            };
        }
    }
};

} // namespace seqan3::detail

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

namespace seqan3::view
{

inline auto constexpr take = detail::take_fn<false, false>{};


} // namespace seqan3::view