/// \file
// Range v3 library
//
//  Copyright Eric Niebler 2013-present
//
//  Use, modification and distribution is subject to the
//  Boost Software License, Version 1.0. (See accompanying
//  file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)
//
// Project home: https://github.com/ericniebler/range-v3
//

#ifndef RANGES_V3_VIEW_DROP_HPP
#define RANGES_V3_VIEW_DROP_HPP

#include <type_traits>

#include <meta/meta.hpp>

#include <range/v3/range_fwd.hpp>

#include <range/v3/algorithm/min.hpp>
#include <range/v3/functional/bind_back.hpp>
#include <range/v3/iterator/operations.hpp>
#include <range/v3/iterator/traits.hpp>
#include <range/v3/range/concepts.hpp>
#include <range/v3/range/traits.hpp>
#include <range/v3/utility/box.hpp>
#include <range/v3/utility/optional.hpp>
#include <range/v3/utility/static_const.hpp>
#include <range/v3/view/all.hpp>
#include <range/v3/view/interface.hpp>
#include <range/v3/view/subrange.hpp>
#include <range/v3/view/view.hpp>

namespace ranges
{
    /// \addtogroup group-views
    /// @{
    template<typename Rng>
    struct RANGES_EMPTY_BASES drop_view
      : view_interface<drop_view<Rng>,
                       is_finite<Rng>::value ? finite : range_cardinality<Rng>::value>
      , private detail::non_propagating_cache<iterator_t<Rng>, drop_view<Rng>,
                                              !random_access_range<Rng>>
    {
    private:
        using difference_type_ = range_difference_t<Rng>;
        Rng rng_;
        difference_type_ n_;

        template<bool Const = true>
        auto get_begin_(std::true_type, std::true_type) const
            -> CPP_ret(iterator_t<meta::const_if_c<Const, Rng>>)( //
                requires Const && range<meta::const_if_c<Const, Rng>>)
        {
            CPP_assert(random_access_range<meta::const_if_c<Const, Rng>>);
            return next(ranges::begin(rng_), n_, ranges::end(rng_));
        }
        iterator_t<Rng> get_begin_(std::true_type, std::false_type)
        {
            CPP_assert(random_access_range<Rng>);
            return next(ranges::begin(rng_), n_, ranges::end(rng_));
        }
        iterator_t<Rng> get_begin_(std::false_type, detail::ignore_t)
        {
            CPP_assert(!random_access_range<Rng>);
            using cache_t =
                detail::non_propagating_cache<iterator_t<Rng>, drop_view<Rng>>;
            auto & begin_ = static_cast<cache_t &>(*this);
            if(!begin_)
                begin_ = next(ranges::begin(rng_), n_, ranges::end(rng_));
            return *begin_;
        }

    public:
        drop_view() = default;
        drop_view(Rng rng, difference_type_ n)
          : rng_(std::move(rng))
          , n_(n)
        {
            RANGES_EXPECT(n >= 0);
        }
        iterator_t<Rng> begin()
        {
            return this->get_begin_(meta::bool_<random_access_range<Rng>>{},
                                    std::false_type{});
        }
        sentinel_t<Rng> end()
        {
            return ranges::end(rng_);
        }
        template<bool Const = true>
        auto begin() const -> CPP_ret(iterator_t<meta::const_if_c<Const, Rng>>)( //
            requires Const && random_access_range<meta::const_if_c<Const, Rng>>)
        {
            return this->get_begin_(std::true_type{}, std::true_type{});
        }
        template<bool Const = true>
        auto end() const -> CPP_ret(sentinel_t<meta::const_if_c<Const, Rng>>)( //
            requires Const && random_access_range<meta::const_if_c<Const, Rng>>)
        {
            return ranges::end(rng_);
        }
        CPP_member
        auto CPP_fun(size)()(const requires sized_range<Rng const>)
        {
            auto const s = ranges::size(rng_);
            auto const n = static_cast<range_size_t<Rng const>>(n_);
            return s < n ? 0 : s - n;
        }
        CPP_member
        auto CPP_fun(size)()(requires sized_range<Rng>)
        {
            auto const s = ranges::size(rng_);
            auto const n = static_cast<range_size_t<Rng>>(n_);
            return s < n ? 0 : s - n;
        }
        Rng base() const
        {
            return rng_;
        }
    };

#if RANGES_CXX_DEDUCTION_GUIDES >= RANGES_CXX_DEDUCTION_GUIDES_17
    template<typename Rng>
    drop_view(Rng &&, range_difference_t<Rng>)->drop_view<views::all_t<Rng>>;
#endif

    namespace views
    {
        struct drop_fn
        {
        private:
            friend view_access;
            template<typename Int>
            static constexpr auto CPP_fun(bind)(drop_fn drop, Int n)( //
                requires integral<Int>)
            {
                return make_pipeable(bind_back(drop, n));
            }
            template<typename Rng>
            static auto impl_(Rng && rng, range_difference_t<Rng> n, input_range_tag)
                -> drop_view<all_t<Rng>>
            {
                return {all(static_cast<Rng &&>(rng)), n};
            }
            template<typename Rng>
            static auto impl_(Rng && rng, range_difference_t<Rng> n,
                              random_access_range_tag)
                -> CPP_ret(subrange<iterator_t<Rng>, sentinel_t<Rng>>)( //
                    requires forwarding_range_<Rng> && sized_range<Rng>)
            {
                return {begin(rng) + ranges::min(n, distance(rng)), end(rng)};
            }

        public:
            template<typename Rng>
            auto CPP_fun(operator())(Rng && rng, range_difference_t<Rng> n)(
                const requires viewable_range<Rng> && input_range<Rng>)
            {
                return drop_fn::impl_(static_cast<Rng &&>(rng), n, range_tag_of<Rng>{});
            }
        };

        /// \relates drop_fn
        /// \ingroup group-views
        RANGES_INLINE_VARIABLE(view<drop_fn>, drop)
    } // namespace views

    namespace cpp20
    {
        namespace views
        {
            using ranges::views::drop;
        }
        CPP_template(typename Rng)( //
            requires view_<Rng>)    //
            using drop_view = ranges::drop_view<Rng>;
    } // namespace cpp20
    /// @}
} // namespace ranges

#include <range/v3/detail/satisfy_boost_range.hpp>
RANGES_SATISFY_BOOST_RANGE(::ranges::drop_view)

#endif