//===----------------------------------------------------------------------===//
//
// 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
// UNSUPPORTED: !c++experimental

// template<bool OtherConst>
//   requires sentinel_for<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
// friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);

#include <cassert>
#include <concepts>
#include <functional>
#include <ranges>

#include "../types.h"

template <class Iter, class Sent>
concept EqualityComparable = std::invocable<std::equal_to<>, const Iter&, const Sent&> ;

using Iterator = random_access_iterator<BufferView<int*>*>;
using ConstIterator = random_access_iterator<const BufferView<int*>*>;

template <bool Const>
struct ConstComparableSentinel {

  using Iter = std::conditional_t<Const, ConstIterator, Iterator>;
  Iter iter_;

  explicit ConstComparableSentinel() = default;
  constexpr explicit ConstComparableSentinel(const Iter& it) : iter_(it) {}

  constexpr friend bool operator==(const Iterator& i, const ConstComparableSentinel& s) {
    return base(i) == base(s.iter_);
  }

  constexpr friend bool operator==(const ConstIterator& i, const ConstComparableSentinel& s) {
    return base(i) == base(s.iter_);
  }
};

struct ConstComparableView : BufferView<BufferView<int*>*> {
  using BufferView<BufferView<int*>*>::BufferView;

  constexpr auto begin() { return Iterator(data_); }
  constexpr auto begin() const { return ConstIterator(data_); }
  constexpr auto end() { return ConstComparableSentinel<false>(Iterator(data_ + size_)); }
  constexpr auto end() const { return ConstComparableSentinel<true>(ConstIterator(data_ + size_)); }
};

static_assert(EqualityComparable<std::ranges::iterator_t<ConstComparableView>,
                                 std::ranges::sentinel_t<const ConstComparableView>>);
static_assert(EqualityComparable<std::ranges::iterator_t<const ConstComparableView>,
                                 std::ranges::sentinel_t<ConstComparableView>>);

constexpr bool test() {
  int buffer[4][4] = {{1111, 2222, 3333, 4444}, {555, 666, 777, 888}, {99, 1010, 1111, 1212}, {13, 14, 15, 16}};

  {
    ChildView children[4] = {ChildView(buffer[0]), ChildView(buffer[1]), ChildView(buffer[2]), ChildView(buffer[3])};
    auto jv = std::ranges::join_view(ParentView(children));
    assert(jv.end() == std::ranges::next(jv.begin(), 16));
    static_assert(!EqualityComparable<decltype(std::as_const(jv).begin()), decltype(jv.end())>);
    static_assert(!EqualityComparable<decltype(jv.begin()), decltype(std::as_const(jv).end())>);
  }

  {
    CopyableChild children[4] = {CopyableChild(buffer[0]), CopyableChild(buffer[1]), CopyableChild(buffer[2]),
                                 CopyableChild(buffer[3])};
    const auto jv = std::ranges::join_view(ParentView(children));
    assert(jv.end() == std::ranges::next(jv.begin(), 16));
  }

  // test iterator<Const> == sentinel<!Const>
  {
    BufferView<int*> inners[] = {buffer[0], buffer[1]};
    ConstComparableView outer(inners);
    auto jv = std::ranges::join_view(outer);
    assert(jv.end() == std::ranges::next(jv.begin(), 8));
    assert(std::as_const(jv).end() == std::ranges::next(jv.begin(), 8));
    assert(jv.end() == std::ranges::next(std::as_const(jv).begin(), 8));
  }

  return true;
}

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

  return 0;
}