//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// <numeric>

// Became constexpr in C++20
// template <InputIterator Iter, MoveConstructible T,
//           Callable<auto, const T&, Iter::reference> BinaryOperation>
//   requires HasAssign<T, BinaryOperation::result_type>
//         && CopyConstructible<BinaryOperation>
//   T
//   accumulate(Iter first, Iter last, T init, BinaryOperation binary_op);

#include <numeric>
#include <functional>
#include <string>
#include <cassert>

#include "test_macros.h"
#include "test_iterators.h"

#if TEST_STD_VER > 17
struct rvalue_addable
{
    bool correctOperatorUsed = false;

    // make sure the predicate is passed an rvalue and an lvalue (so check that the first argument was moved)
    constexpr rvalue_addable operator()(rvalue_addable&& r, rvalue_addable const&) {
        r.correctOperatorUsed = true;
        return std::move(r);
    }
};

constexpr rvalue_addable operator+(rvalue_addable& lhs, rvalue_addable const&)
{
    lhs.correctOperatorUsed = false;
        return lhs;
}

constexpr rvalue_addable operator+(rvalue_addable&& lhs, rvalue_addable const&)
{
    lhs.correctOperatorUsed = true;
    return std::move(lhs);
}

constexpr void
test_use_move()
{
    rvalue_addable arr[100];
    auto res1 = std::accumulate(arr, arr + 100, rvalue_addable());
    auto res2 = std::accumulate(arr, arr + 100, rvalue_addable(), /*predicate=*/rvalue_addable());
    assert(res1.correctOperatorUsed);
    assert(res2.correctOperatorUsed);
}
#endif // TEST_STD_VER > 17

TEST_CONSTEXPR_CXX20 void test_string() {
    std::string sa[] = {"a", "b", "c"};
    assert(std::accumulate(sa, sa + 3, std::string()) == "abc");
    assert(std::accumulate(sa, sa + 3, std::string(), std::plus<std::string>()) == "abc");
}

template <class Iter, class T>
TEST_CONSTEXPR_CXX20 void
test(Iter first, Iter last, T init, T x)
{
    assert(std::accumulate(first, last, init, std::multiplies<T>()) == x);
}

template <class Iter>
TEST_CONSTEXPR_CXX20 void
test()
{
    int ia[] = {1, 2, 3, 4, 5, 6};
    unsigned sa = sizeof(ia) / sizeof(ia[0]);
    test(Iter(ia), Iter(ia), 1, 1);
    test(Iter(ia), Iter(ia), 10, 10);
    test(Iter(ia), Iter(ia+1), 1, 1);
    test(Iter(ia), Iter(ia+1), 10, 10);
    test(Iter(ia), Iter(ia+2), 1, 2);
    test(Iter(ia), Iter(ia+2), 10, 20);
    test(Iter(ia), Iter(ia+sa), 1, 720);
    test(Iter(ia), Iter(ia+sa), 10, 7200);
}

TEST_CONSTEXPR_CXX20 bool
test()
{
    test<cpp17_input_iterator<const int*> >();
    test<forward_iterator<const int*> >();
    test<bidirectional_iterator<const int*> >();
    test<random_access_iterator<const int*> >();
    test<const int*>();

#if TEST_STD_VER > 17
    test_use_move();
#endif // TEST_STD_VER > 17

    test_string();

    return true;
}

int main(int, char**)
{
    test();
#if TEST_STD_VER > 17
    static_assert(test());
#endif
    return 0;
}