//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03, c++11, c++14, c++17

// constexpr iterator& operator-=(difference_type n)
//   requires advanceable<W>;

#include <cassert>
#include <ranges>
#include <type_traits>

#include "test_macros.h"
#include "../types.h"

constexpr bool test() {
  // When "_Start" is signed integer like.
  {
    std::ranges::iota_view<int> io(0);
    auto iter1 = std::next(io.begin(), 10);
    auto iter2 = std::next(io.begin(), 10);
    assert(iter1 == iter2);
    iter1 -= 5;
    assert(iter1 != iter2);
    assert(iter1 == std::ranges::prev(iter2, 5));

    static_assert(std::is_reference_v<decltype(iter2 -= 5)>);
  }

  // When "_Start" is not integer like.
  {
    std::ranges::iota_view io(SomeInt(0));
    auto iter1 = std::next(io.begin(), 10);
    auto iter2 = std::next(io.begin(), 10);
    assert(iter1 == iter2);
    iter1 -= 5;
    assert(iter1 != iter2);
    assert(iter1 == std::ranges::prev(iter2, 5));

    static_assert(std::is_reference_v<decltype(iter2 -= 5)>);
  }

  // When "_Start" is unsigned integer like and n is greater than or equal to zero.
  {
    std::ranges::iota_view<unsigned> io(0);
    auto iter1 = std::next(io.begin(), 10);
    auto iter2 = std::next(io.begin(), 10);
    assert(iter1 == iter2);
    iter1 -= 5;
    assert(iter1 != iter2);
    assert(iter1 == std::ranges::prev(iter2, 5));

    static_assert(std::is_reference_v<decltype(iter2 -= 5)>);
  }
  {
    std::ranges::iota_view<unsigned> io(0);
    auto iter1 = std::next(io.begin(), 10);
    auto iter2 = std::next(io.begin(), 10);
    assert(iter1 == iter2);
    iter1 -= 0;
    assert(iter1 == iter2);
  }

  // When "_Start" is unsigned integer like and n is less than zero.
  {
    std::ranges::iota_view<unsigned> io(0);
    auto iter1 = std::next(io.begin(), 10);
    auto iter2 = std::next(io.begin(), 10);
    assert(iter1 == iter2);
    iter1 -= -5;
    assert(iter1 != iter2);
    assert(iter1 == std::ranges::next(iter2, 5));

    static_assert(std::is_reference_v<decltype(iter2 -= -5)>);
  }

  return true;
}

int main(int, char**) {
  test();
  static_assert(test());

  return 0;
}