/// \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_NUMERIC_ACCUMULATE_HPP
#define RANGES_V3_NUMERIC_ACCUMULATE_HPP

#include <meta/meta.hpp>

#include <range/v3/functional/arithmetic.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/range/access.hpp>
#include <range/v3/range/concepts.hpp>
#include <range/v3/range/traits.hpp>
#include <range/v3/utility/static_const.hpp>

namespace ranges
{
    /// \addtogroup group-numerics
    /// @{
    struct accumulate_fn
    {
        template<typename I, typename S, typename T, typename Op = plus,
                 typename P = identity>
        auto operator()(I first, S last, T init, Op op = Op{},
                        P proj = P{}) const -> CPP_ret(T)( //
            requires sentinel_for<S, I> && input_iterator<I> &&
                indirectly_binary_invocable_<Op, T *, projected<I, P>> &&
                    assignable_from<T &, indirect_result_t<Op &, T *, projected<I, P>>>)
        {
            for(; first != last; ++first)
                init = invoke(op, init, invoke(proj, *first));
            return init;
        }

        template<typename Rng, typename T, typename Op = plus, typename P = identity>
        auto operator()(Rng && rng, T init, Op op = Op{},
                        P proj = P{}) const -> CPP_ret(T)( //
            requires input_range<Rng> &&
                indirectly_binary_invocable_<Op, T *, projected<iterator_t<Rng>, P>> &&
                    assignable_from<
                        T &, indirect_result_t<Op &, T *, projected<iterator_t<Rng>, P>>>)
        {
            return (*this)(
                begin(rng), end(rng), std::move(init), std::move(op), std::move(proj));
        }
    };

    RANGES_INLINE_VARIABLE(accumulate_fn, accumulate)
    /// @}
} // namespace ranges

#endif