stride_view.h

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#pragma once
 
#include "di/container/concepts/prelude.h"
#include "di/container/iterator/advance.h"
#include "di/container/iterator/default_sentinel.h"
#include "di/container/iterator/distance.h"
#include "di/container/iterator/iterator_base.h"
#include "di/container/iterator/iterator_move.h"
#include "di/container/iterator/iterator_swap.h"
#include "di/container/meta/enable_borrowed_container.h"
#include "di/container/meta/prelude.h"
#include "di/container/view/view_interface.h"
#include "di/math/divide_round_up.h"
#include "di/math/to_unsigned.h"
#include "di/meta/util.h"
 
namespace di::container {
template<concepts::InputContainer View>
requires(concepts::View<View>)
class StrideView
    : public ViewInterface<StrideView<View>>
    , public meta::EnableBorrowedContainer<StrideView<View>, concepts::BorrowedContainer<View>> {
private:
    template<bool is_const>
    using Iter = meta::ContainerIterator<meta::MaybeConst<is_const, View>>;
 
    template<bool is_const>
    using Sent = meta::ContainerSentinel<meta::MaybeConst<is_const, View>>;
 
    template<bool is_const>
    using SSizeType = meta::ContainerSSizeType<meta::MaybeConst<is_const, View>>;
 
    template<bool is_const>
    using ValueType = meta::ContainerValue<meta::MaybeConst<is_const, View>>;
 
    template<bool is_const>
    class Iterator
        : public IteratorBase<
              Iterator<is_const>,
              meta::Conditional<
                  concepts::RandomAccessIterator<Iter<is_const>>, RandomAccessIteratorTag,
                  meta::Conditional<concepts::BidirectionalIterator<Iter<is_const>>, BidirectionalIteratorTag,
                                    meta::Conditional<concepts::ForwardIterator<Iter<is_const>>, ForwardIteratorTag,
                                                      InputIteratorTag>>>,
              ValueType<is_const>, SSizeType<is_const>> {
    private:
        friend class StrideView;
 
        constexpr Iterator(meta::MaybeConst<is_const, StrideView>* parent, Iter<is_const> base,
                           SSizeType<is_const> missing = 0)
            : m_base(util::move(base))
            , m_end(container::end(parent->m_base))
            , m_stride(parent->stride())
            , m_missing(missing) {}
 
    public:
        Iterator()
        requires(concepts::DefaultInitializable<Iter<is_const>>)
        = default;
 
        constexpr Iterator(Iterator<!is_const> other)
        requires(is_const && concepts::ConvertibleTo<Iter<false>, Iter<true>> &&
                 concepts::ConvertibleTo<Sent<false>, Sent<true>>)
            : m_base(util::move(other.m_base))
            , m_end(util::move(other.m_end))
            , m_stride(other.m_stride)
            , m_missing(other.m_missing) {}
 
        Iterator(Iterator const&) = default;
        Iterator(Iterator&&) = default;
 
        auto operator=(Iterator const&) -> Iterator& = default;
        auto operator=(Iterator&&) -> Iterator& = default;
 
        Iterator(Iterator const&)
        requires(!concepts::ForwardIterator<Iter<is_const>>)
        = delete;
        auto operator=(Iterator const&) -> Iterator& requires(!concepts::ForwardIterator<Iter<is_const>>) = delete;
 
        constexpr auto base() && -> Iter<is_const> { return util::move(m_base); }
        constexpr auto base() const& -> Iter<is_const> const& { return m_base; }
 
        constexpr auto operator*() const -> decltype(auto) { return *m_base; }
 
        constexpr void advance_one() { m_missing = container::advance(m_base, m_stride, m_end); }
 
        constexpr void back_one()
        requires(concepts::BidirectionalIterator<Iter<is_const>>)
        {
            container::advance(m_base, m_missing - m_stride);
            m_missing = 0;
        }
 
        constexpr void advance_n(SSizeType<is_const> n)
        requires(concepts::RandomAccessIterator<Iter<is_const>>)
        {
            if (n > 0) {
                m_missing = container::advance(m_base, m_stride * n, m_end);
            } else if (n < 0) {
                container::advance(m_base, m_stride * n + m_missing);
                m_missing = 0;
            }
        }
 
    private:
        template<bool other_is_const>
        friend class Iterator;
 
        constexpr friend auto operator==(Iterator const& self, DefaultSentinel) -> bool {
            return self.m_base == self.m_end;
        }
        constexpr friend auto operator==(Iterator const& a, Iterator const& b) -> bool
        requires(concepts::EqualityComparable<Iter<is_const>>)
        {
            return a.m_base == b.m_base;
        }
 
        constexpr friend auto operator<=>(Iterator const& a, Iterator const& b)
        requires(concepts::RandomAccessIterator<Iter<is_const>>)
        {
            return a.m_base <=> b.m_base;
        }
 
        constexpr friend auto operator-(Iterator const& a, Iterator const& b) -> SSizeType<is_const>
        requires(concepts::SizedSentinelFor<Iter<is_const>, Iter<is_const>>)
        {
            auto n = a.m_base - b.m_base;
            if constexpr (concepts::ForwardIterator<Iter<is_const>>) {
                return (n + a.m_missing - b.m_missing) / a.m_stride;
            } else if (n < 0) {
                return -math::divide_round_up(-n, a.m_stride);
            } else {
                return math::divide_round_up(n, a.m_stride);
            }
        }
 
        constexpr friend auto operator-(DefaultSentinel, Iterator const& b) -> SSizeType<is_const> {
            return math::divide_round_up(b.m_base - b.m_current, b.m_stride);
        }
        constexpr friend auto operator-(Iterator const& a, DefaultSentinel) -> SSizeType<is_const> {
            return -(default_sentinel - a);
        }
 
        constexpr friend auto tag_invoke(types::Tag<container::iterator_move>, Iterator const& a)
            -> meta::ContainerRValue<meta::MaybeConst<is_const, View>> {
            return container::iterator_move(a);
        }
 
        constexpr friend void tag_invoke(types::Tag<container::iterator_swap>, Iterator const& a, Iterator const& b)
        requires(concepts::IndirectlySwappable<Iter<is_const>>)
        {
            return container::iterator_swap(a, b);
        }
 
        Iter<is_const> m_base {};
        Sent<is_const> m_end {};
        SSizeType<is_const> m_stride { 0 };
        SSizeType<is_const> m_missing { 0 };
    };
 
public:
    constexpr explicit StrideView(View base, SSizeType<false> stride) : m_base(util::move(base)), m_stride(stride) {
        DI_ASSERT(stride > 0);
    }
 
    constexpr auto base() const& -> View
    requires(concepts::CopyConstructible<View>)
    {
        return m_base;
    }
    constexpr auto base() && -> View { return util::move(m_base); }
 
    constexpr auto stride() const { return m_stride; }
 
    constexpr auto begin()
    requires(!concepts::SimpleView<View>)
    {
        return Iterator<false>(this, container::begin(m_base));
    }
 
    constexpr auto begin() const
    requires(concepts::Container<View const>)
    {
        return Iterator<true>(this, container::begin(m_base));
    }
 
    constexpr auto end()
    requires(!concepts::SimpleView<View>)
    {
        if constexpr (concepts::CommonContainer<View> && concepts::SizedContainer<View> &&
                      concepts::ForwardContainer<View>) {
            auto missing = (m_stride - container::distance(m_base) % m_stride) % m_stride;
            return Iterator<false>(this, container::end(m_base), missing);
        } else if constexpr (concepts::CommonContainer<View> && !concepts::BidirectionalContainer<View>) {
            return Iterator<false>(this, container::end(m_base));
        } else {
            return default_sentinel;
        }
    }
 
    constexpr auto end() const
    requires(concepts::Container<View const>)
    {
        if constexpr (concepts::CommonContainer<View const> && concepts::SizedContainer<View const> &&
                      concepts::ForwardContainer<View const>) {
            auto missing = (m_stride - container::distance(m_base) % m_stride) % m_stride;
            return Iterator<true>(this, container::end(m_base), missing);
        } else if constexpr (concepts::CommonContainer<View const> && !concepts::BidirectionalContainer<View const>) {
            return Iterator<true>(this, container::end(m_base));
        } else {
            return default_sentinel;
        }
    }
 
    constexpr auto size()
    requires(concepts::SizedContainer<View>)
    {
        return math::to_unsigned(math::divide_round_up(container::distance(m_base), m_stride));
    }
 
    constexpr auto size() const
    requires(concepts::SizedContainer<View const>)
    {
        return math::to_unsigned(math::divide_round_up(container::distance(m_base), m_stride));
    }
 
private:
    View m_base;
    SSizeType<false> m_stride;
};
 
template<typename Con>
StrideView(Con&&, meta::ContainerSSizeType<Con>) -> StrideView<meta::AsView<Con>>;
}