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

// type_traits
// common_reference

#include <tuple>
#include <type_traits>
#include <utility>

#include "test_macros.h"

template <class T>
constexpr bool has_type = requires {
  typename T::type;
};

// A slightly simplified variation of std::tuple
template <class...>
struct UserTuple {};

template <class, class, class>
struct Tuple_helper {};
template <class... Ts, class... Us>
struct Tuple_helper<std::void_t<std::common_reference_t<Ts, Us>...>, UserTuple<Ts...>, UserTuple<Us...> > {
  using type = UserTuple<std::common_reference_t<Ts, Us>...>;
};

namespace std {
template <class... Ts, class... Us, template <class> class TQual, template <class> class UQual>
struct basic_common_reference< ::UserTuple<Ts...>, ::UserTuple<Us...>, TQual, UQual>
    : ::Tuple_helper<void, UserTuple<TQual<Ts>...>, UserTuple<UQual<Us>...> > {};
} // namespace std

struct X2 {};
struct Y2 {};
struct Z2 {};

namespace std {
template <>
struct common_type<X2, Y2> {
  using type = Z2;
};
template <>
struct common_type<Y2, X2> {
  using type = Z2;
};
} // namespace std

// (6.1)
//  -- If sizeof...(T) is zero, there shall be no member type.
static_assert(!has_type<std::common_reference<> >);

// (6.2)
//  -- Otherwise, if sizeof...(T) is one, let T0 denote the sole type in the
//     pack T. The member typedef type shall denote the same type as T0.
static_assert(std::is_same_v<std::common_reference_t<void>, void>);
static_assert(std::is_same_v<std::common_reference_t<int>, int>);
static_assert(std::is_same_v<std::common_reference_t<int&>, int&>);
static_assert(std::is_same_v<std::common_reference_t<int&&>, int&&>);
static_assert(std::is_same_v<std::common_reference_t<int const>, int const>);
static_assert(std::is_same_v<std::common_reference_t<int const&>, int const&>);
static_assert(std::is_same_v<std::common_reference_t<int const&&>, int const&&>);
static_assert(std::is_same_v<std::common_reference_t<int volatile[]>, int volatile[]>);
static_assert(std::is_same_v<std::common_reference_t<int volatile (&)[]>, int volatile (&)[]>);
static_assert(std::is_same_v<std::common_reference_t<int volatile (&&)[]>, int volatile (&&)[]>);
static_assert(std::is_same_v<std::common_reference_t<void (&)()>, void (&)()>);
static_assert(std::is_same_v<std::common_reference_t<void (&&)()>, void (&&)()>);

// (6.3)
//  -- Otherwise, if sizeof...(T) is two, let T1 and T2 denote the two types in
//     the pack T. Then
// (6.3.1)
//    -- If T1 and T2 are reference types and COMMON_REF(T1, T2) is well-formed,
//       then the member typedef type denotes that type.
struct B {};
struct D : B {};
static_assert(std::is_same_v<std::common_reference_t<B&, D&>, B&>);
static_assert(std::is_same_v<std::common_reference_t<B const&, D&>, B const&>);
static_assert(std::is_same_v<std::common_reference_t<B&, D const&>, B const&>);
static_assert(std::is_same_v<std::common_reference_t<B&, D const&, D&>, B const&>);
static_assert(std::is_same_v<std::common_reference_t<B&, D&, B&, D&>, B&>);

static_assert(std::is_same_v<std::common_reference_t<B&&, D&&>, B&&>);
static_assert(std::is_same_v<std::common_reference_t<B const&&, D&&>, B const&&>);
static_assert(std::is_same_v<std::common_reference_t<B&&, D const&&>, B const&&>);
static_assert(std::is_same_v<std::common_reference_t<B&, D&&>, B const&>);
static_assert(std::is_same_v<std::common_reference_t<B&, D const&&>, B const&>);
static_assert(std::is_same_v<std::common_reference_t<B const&, D&&>, B const&>);

static_assert(std::is_same_v<std::common_reference_t<B&&, D&>, B const&>);
static_assert(std::is_same_v<std::common_reference_t<B&&, D const&>, B const&>);
static_assert(std::is_same_v<std::common_reference_t<B const&&, D&>, B const&>);

static_assert(std::is_same_v<std::common_reference_t<int const&, int volatile&>, int const volatile&>);
static_assert(std::is_same_v<std::common_reference_t<int const volatile&&, int volatile&&>, int const volatile&&>);

static_assert(std::is_same_v<std::common_reference_t<int (&)[10], int (&&)[10]>, int const (&)[10]>);
static_assert(std::is_same_v<std::common_reference_t<int const (&)[10], int volatile (&)[10]>, int const volatile (&)[10]>);

// (6.3.2)
//    -- Otherwise, if basic_common_reference<remove_cvref_t<T1>,
//       remove_cvref_t<T2>, XREF(T1), XREF(T2)>::type is well-formed, then the
//       member typedef type denotes that type.
static_assert(std::is_same_v<std::common_reference_t<const UserTuple<int, short>&, UserTuple<int&, short volatile&>>,
                             UserTuple<const int&, const volatile short&>>);

static_assert(std::is_same_v<std::common_reference_t<volatile UserTuple<int, short>&, const UserTuple<int, short>&>,
                             const volatile UserTuple<int, short>&>);

// (6.3.3)
//    -- Otherwise, if COND_RES(T1, T2) is well-formed, then the member typedef
//       type denotes that type.
static_assert(std::is_same_v<std::common_reference_t<void, void>, void>);
static_assert(std::is_same_v<std::common_reference_t<int, short>, int>);
static_assert(std::is_same_v<std::common_reference_t<int, short&>, int>);
static_assert(std::is_same_v<std::common_reference_t<int&, short&>, int>);
static_assert(std::is_same_v<std::common_reference_t<int&, short>, int>);

// tricky volatile reference case
static_assert(std::is_same_v<std::common_reference_t<int&&, int volatile&>, int>);
static_assert(std::is_same_v<std::common_reference_t<int volatile&, int&&>, int>);

static_assert(std::is_same_v<std::common_reference_t<int (&)[10], int (&)[11]>, int*>);

// https://github.com/ericniebler/stl2/issues/338
struct MyIntRef {
  MyIntRef(int&);
};
static_assert(std::is_same_v<std::common_reference_t<int&, MyIntRef>, MyIntRef>);

// (6.3.4)
//    -- Otherwise, if common_type_t<T1, T2> is well-formed, then the member
//       typedef type denotes that type.
struct moveonly {
  moveonly() = default;
  moveonly(moveonly&&) = default;
  moveonly& operator=(moveonly&&) = default;
};
struct moveonly2 : moveonly {};

static_assert(std::is_same_v<std::common_reference_t<moveonly const&, moveonly>, moveonly>);
static_assert(std::is_same_v<std::common_reference_t<moveonly2 const&, moveonly>, moveonly>);
static_assert(std::is_same_v<std::common_reference_t<moveonly const&, moveonly2>, moveonly>);

static_assert(std::is_same_v<std::common_reference_t<X2&, Y2 const&>, Z2>);

// (6.3.5)
//    -- Otherwise, there shall be no member type.
static_assert(!has_type<std::common_reference<volatile UserTuple<short>&, const UserTuple<int, short>&> >);

// (6.4)
//  -- Otherwise, if sizeof...(T) is greater than two, let T1, T2, and Rest,
//     respectively, denote the first, second, and (pack of) remaining types
//     comprising T. Let C be the type common_reference_t<T1, T2>. Then:
// (6.4.1)
//    -- If there is such a type C, the member typedef type shall denote the
//       same type, if any, as common_reference_t<C, Rest...>.
static_assert(std::is_same_v<std::common_reference_t<int, int, int>, int>);
static_assert(std::is_same_v<std::common_reference_t<int&&, int const&, int volatile&>, int const volatile&>);
static_assert(std::is_same_v<std::common_reference_t<int&&, int const&, float&>, float>);

// (6.4.2)
//    -- Otherwise, there shall be no member type.
static_assert(!has_type<std::common_reference<int, short, int, char*> >);

#if TEST_STD_VER > 20
static_assert(std::is_same_v<std::common_reference_t<std::tuple<int, int>>, std::tuple<int, int>>);
static_assert(std::is_same_v<std::common_reference_t<std::tuple<int, long>, std::tuple<long, int>>, std::tuple<long, long>>);
static_assert(std::is_same_v<std::common_reference_t<std::tuple<int&, const int&>, std::tuple<const int&, int>>,
                             std::tuple<const int&, int>>);
static_assert(std::is_same_v<std::common_reference_t<std::tuple<int&, volatile int&>, std::tuple<volatile int&, int>>,
                             std::tuple<volatile int&, int>>);
static_assert(std::is_same_v<std::common_reference_t<std::tuple<int&, const volatile int&>, std::tuple<const volatile int&, int>>,
                             std::tuple<const volatile int&, int>>);
static_assert(!has_type<std::common_reference_t<std::tuple<const int&, volatile int&>, std::tuple<volatile int&, const int&>>>);

static_assert(std::is_same_v<std::common_reference_t<std::tuple<int, X2>, std::tuple<int, Y2>>, std::tuple<int, Z2>>);
static_assert(std::is_same_v<std::common_reference_t<std::tuple<int, X2>, std::tuple<int, Y2>>, std::tuple<int, Z2>>);
static_assert(!has_type<std::common_reference<std::tuple<int, const X2>, std::tuple<float, const Z2>>>);
static_assert(!has_type<std::common_reference<std::tuple<int, X2>, std::tuple<float, Z2>>>);
static_assert(!has_type<std::common_reference<std::tuple<int, X2>, int, X2>>);

struct A {};
template <template<class> class TQual, template<class> class UQual>
struct std::basic_common_reference<A, std::tuple<B>, TQual, UQual> {
  using type = tuple<UQual<B>>;
};

static_assert(std::is_same_v<std::common_reference_t<A, std::tuple<B>, std::tuple<D>>, std::tuple<B>>);


static_assert(std::is_same_v<std::common_reference_t<std::pair<int, int>>,
                             std::pair<int, int>>);
static_assert(std::is_same_v<std::common_reference_t<std::pair<int, long>, std::pair<long, int>>,
                             std::pair<long, long>>);
static_assert(std::is_same_v<std::common_reference_t<std::pair<int&, const int&>, std::pair<const int&, int>>,
                             std::pair<const int&, int>>);
static_assert(std::is_same_v<std::common_reference_t<std::pair<int&, volatile int&>, std::pair<volatile int&, int>>,
                             std::pair<volatile int&, int>>);
static_assert(std::is_same_v<std::common_reference_t<std::pair<int&, const volatile int&>, std::pair<const volatile int&, int>>,
                             std::pair<const volatile int&, int>>);
static_assert(!has_type<std::common_reference_t<std::pair<const int&, volatile int&>,
                        std::pair<volatile int&, const int&>>>);

static_assert(std::is_same_v<std::common_reference_t<std::pair<int, X2>, std::pair<int, Y2>>, std::pair<int, Z2>>);
static_assert(std::is_same_v<std::common_reference_t<std::pair<int, X2>, std::pair<int, Y2>>, std::pair<int, Z2>>);
static_assert(!has_type<std::common_reference<std::pair<int, const X2>, std::pair<float, const Z2>>>);
static_assert(!has_type<std::common_reference<std::pair<int, X2>, std::pair<float, Z2>>>);
static_assert(!has_type<std::common_reference<std::pair<int, X2>, int, X2>>);
#endif