/// \file
// Range v3 library
//
//  Copyright Eric Niebler 2013-present
//  Copyright Gonzalo Brito Gadeschi 2014
//
//  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_NUMERIC_PARTIAL_SUM_HPP
#define RANGES_V3_NUMERIC_PARTIAL_SUM_HPP

#include <meta/meta.hpp>

#include <range/v3/algorithm/result_types.hpp>
#include <range/v3/functional/arithmetic.hpp>
#include <range/v3/functional/compose.hpp>
#include <range/v3/functional/identity.hpp>
#include <range/v3/functional/invoke.hpp>
#include <range/v3/iterator/concepts.hpp>
#include <range/v3/iterator/traits.hpp>
#include <range/v3/iterator/unreachable_sentinel.hpp>
#include <range/v3/range/access.hpp>
#include <range/v3/range/concepts.hpp>
#include <range/v3/range/dangling.hpp>
#include <range/v3/range/traits.hpp>
#include <range/v3/utility/static_const.hpp>

namespace ranges
{
    /// \addtogroup group-numerics
    /// @{

    /// \cond
    namespace detail
    {
        // Only needed for type-checking purposes:
        struct as_lvalue_fn
        {
            template<typename T>
            constexpr T & operator()(T && t) const noexcept
            {
                return t;
            }
        };
        template<typename I>
        using as_value_type_t = composed<as_lvalue_fn, coerce<iter_value_t<I>>>;
    } // namespace detail
      /// \endcond

    // axiom: BOp is associative over values of I.
    // clang-format off
    CPP_def
    (
        template(typename I, typename BOp)
        concept indirect_semigroup,
            readable<I> &&
            copyable<iter_value_t<I>> &&
            indirectly_regular_binary_invocable_<
                composed<coerce<iter_value_t<I>>, BOp>,
                iter_value_t<I>*, I>
    );

    CPP_def
    (
        template(typename I, typename O, typename BOp = plus, typename P = identity)
        (concept partial_sum_constraints)(I, O, BOp, P),
            input_iterator<I> &&
            indirect_semigroup<
                projected<projected<I, detail::as_value_type_t<I>>, P>,
                BOp> &&
            output_iterator<
                O,
                iter_value_t<
                    projected<projected<I, detail::as_value_type_t<I>>, P>> const &>
    );
    // clang-format on

    template<typename I, typename O>
    using partial_sum_result = detail::in_out_result<I, O>;

    struct partial_sum_fn
    {
        template<typename I, typename S1, typename O, typename S2, typename BOp = plus,
                 typename P = identity>
        auto operator()(I first, S1 last, O result, S2 end_result, BOp bop = BOp{},
                        P proj = P{}) const -> CPP_ret(partial_sum_result<I, O>)( //
            requires sentinel_for<S1, I> && sentinel_for<S2, O> &&
                partial_sum_constraints<I, O, BOp, P>)
        {
            using X = projected<projected<I, detail::as_value_type_t<I>>, P>;
            coerce<iter_value_t<I>> val_i;
            coerce<iter_value_t<X>> val_x;
            if(first != last && result != end_result)
            {
                auto && cur1 = val_i(*first);
                iter_value_t<X> t(invoke(proj, cur1));
                *result = t;
                for(++first, ++result; first != last && result != end_result;
                    ++first, ++result)
                {
                    auto && cur2 = val_i(*first);
                    t = val_x(invoke(bop, t, invoke(proj, cur2)));
                    *result = t;
                }
            }
            return {first, result};
        }

        template<typename I, typename S, typename O, typename BOp = plus,
                 typename P = identity>
        auto operator()(I first, S last, O result, BOp bop = BOp{}, P proj = P{}) const
            -> CPP_ret(partial_sum_result<I, O>)( //
                requires sentinel_for<S, I> && partial_sum_constraints<I, O, BOp, P>)
        {
            return (*this)(std::move(first),
                           std::move(last),
                           std::move(result),
                           unreachable,
                           std::move(bop),
                           std::move(proj));
        }

        template<typename Rng, typename ORef, typename BOp = plus, typename P = identity,
                 typename I = iterator_t<Rng>, typename O = uncvref_t<ORef>>
        auto operator()(Rng && rng, ORef && result, BOp bop = BOp{}, P proj = P{}) const
            -> CPP_ret(partial_sum_result<safe_iterator_t<Rng>, O>)( //
                requires range<Rng> && partial_sum_constraints<I, O, BOp, P>)
        {
            return (*this)(begin(rng),
                           end(rng),
                           static_cast<ORef &&>(result),
                           std::move(bop),
                           std::move(proj));
        }

        template<typename Rng, typename ORng, typename BOp = plus, typename P = identity,
                 typename I = iterator_t<Rng>, typename O = iterator_t<ORng>>
        auto operator()(Rng && rng, ORng && result, BOp bop = BOp{}, P proj = P{}) const
            -> CPP_ret(
                partial_sum_result<safe_iterator_t<Rng>, safe_iterator_t<ORng>>)( //
                requires range<Rng> && range<ORng> &&
                    partial_sum_constraints<I, O, BOp, P>)
        {
            return (*this)(begin(rng),
                           end(rng),
                           begin(result),
                           end(result),
                           std::move(bop),
                           std::move(proj));
        }
    };

    RANGES_INLINE_VARIABLE(partial_sum_fn, partial_sum)
    /// @}
} // namespace ranges

#endif