/*
 * Copyright (c) 2022 NVIDIA Corporation
 *
 * Licensed under the Apache License Version 2.0 with LLVM Exceptions
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *   https://llvm.org/LICENSE.txt
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#pragma once

#include "__config.hpp"

namespace stdexec
{

//////////////////////////////////////////////////////////////////////////////////////////////////
// A very simple std::declval replacement that doesn't handle void
template <class _Tp>
_Tp&& __declval() noexcept;

//////////////////////////////////////////////////////////////////////////////////////////////////
// __decay_t: An efficient implementation for std::decay
#if STDEXEC_HAS_BUILTIN(__decay)

template <class _Ty>
using __decay_t = __decay(_Ty);

#elif STDEXEC_NVHPC()

template <class _Ty>
using __decay_t = std::decay_t<_Ty>;

#else

namespace __tt
{
struct __decay_object
{
    template <class _Ty>
    static _Ty __g(const _Ty&);
    template <class _Ty>
    using __f = decltype(__g(__declval<_Ty>()));
};

struct __decay_default
{
    template <class _Ty>
    static _Ty __g(_Ty);
    template <class _Ty>
    using __f = decltype(__g(__declval<_Ty>()));
};

struct __decay_abominable
{
    template <class _Ty>
    using __f = _Ty;
};

struct __decay_void
{
    template <class _Ty>
    using __f = void;
};

template <class _Ty>
extern __decay_object __mdecay;

template <class _Ty, class... Us>
extern __decay_default __mdecay<_Ty(Us...)>;

template <class _Ty, class... Us>
extern __decay_default __mdecay<_Ty(Us...) noexcept>;

template <class _Ty, class... Us>
extern __decay_default __mdecay<_Ty (&)(Us...)>;

template <class _Ty, class... Us>
extern __decay_default __mdecay<_Ty (&)(Us...) noexcept>;

template <class _Ty, class... Us>
extern __decay_abominable __mdecay<_Ty(Us...) const>;

template <class _Ty, class... Us>
extern __decay_abominable __mdecay<_Ty(Us...) const noexcept>;

template <class _Ty, class... Us>
extern __decay_abominable __mdecay<_Ty(Us...) const&>;

template <class _Ty, class... Us>
extern __decay_abominable __mdecay<_Ty(Us...) const & noexcept>;

template <class _Ty, class... Us>
extern __decay_abominable __mdecay<_Ty(Us...) const&&>;

template <class _Ty, class... Us>
extern __decay_abominable __mdecay<_Ty(Us...) const && noexcept>;

template <class _Ty>
extern __decay_default __mdecay<_Ty[]>;

template <class _Ty, std::size_t N>
extern __decay_default __mdecay<_Ty[N]>;

template <class _Ty, std::size_t N>
extern __decay_default __mdecay<_Ty (&)[N]>;

template <>
inline __decay_void __mdecay<void>;

template <>
inline __decay_void __mdecay<const void>;
} // namespace __tt

template <class _Ty>
using __decay_t = typename decltype(__tt::__mdecay<_Ty>)::template __f<_Ty>;

#endif

//////////////////////////////////////////////////////////////////////////////////////////////////
// __copy_cvref_t: For copying cvref from one type to another
struct __cp
{
    template <class _Tp>
    using __f = _Tp;
};

struct __cpc
{
    template <class _Tp>
    using __f = const _Tp;
};

struct __cplr
{
    template <class _Tp>
    using __f = _Tp&;
};

struct __cprr
{
    template <class _Tp>
    using __f = _Tp&&;
};

struct __cpclr
{
    template <class _Tp>
    using __f = const _Tp&;
};

struct __cpcrr
{
    template <class _Tp>
    using __f = const _Tp&&;
};

template <class>
extern __cp __cpcvr;
template <class _Tp>
extern __cpc __cpcvr<const _Tp>;
template <class _Tp>
extern __cplr __cpcvr<_Tp&>;
template <class _Tp>
extern __cprr __cpcvr<_Tp&&>;
template <class _Tp>
extern __cpclr __cpcvr<const _Tp&>;
template <class _Tp>
extern __cpcrr __cpcvr<const _Tp&&>;
template <class _Tp>
using __copy_cvref_fn = decltype(__cpcvr<_Tp>);

template <class _From, class _To>
using __copy_cvref_t = typename __copy_cvref_fn<_From>::template __f<_To>;

#if !STDEXEC_HAS_BUILTIN(__is_const)
template <class>
inline constexpr bool __is_const = false;
template <class _Up>
inline constexpr bool __is_const<const _Up> = true;
#endif

namespace __tt
{
template <class _Ty>
_Ty __remove_rvalue_reference_fn(_Ty&&);
}

template <class _Ty>
using __remove_rvalue_reference_t =
    decltype(__tt::__remove_rvalue_reference_fn(__declval<_Ty>()));

} // namespace stdexec