// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___FUNCTIONAL_PERFECT_FORWARD_H
#define _LIBCPP___FUNCTIONAL_PERFECT_FORWARD_H

#include <__config>
#include <__utility/declval.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <tuple>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 17

template <class _Op, class _Indices, class... _BoundArgs>
struct __perfect_forward_impl;

template <class _Op, size_t... _Idx, class... _BoundArgs>
struct __perfect_forward_impl<_Op, index_sequence<_Idx...>, _BoundArgs...> {
private:
  tuple<_BoundArgs...> __bound_args_;

public:
  template <class... _Args, class = enable_if_t<
    is_constructible_v<tuple<_BoundArgs...>, _Args&&...>
  >>
  explicit constexpr __perfect_forward_impl(_Args&&... __bound_args)
    : __bound_args_(_VSTD::forward<_Args>(__bound_args)...) {}

  __perfect_forward_impl(__perfect_forward_impl const&) = default;
  __perfect_forward_impl(__perfect_forward_impl&&) = default;

  __perfect_forward_impl& operator=(__perfect_forward_impl const&) = default;
  __perfect_forward_impl& operator=(__perfect_forward_impl&&) = default;

  template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs&..., _Args...>>>
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) &
    noexcept(noexcept(_Op()(_VSTD::get<_Idx>(__bound_args_)..., _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op()(_VSTD::get<_Idx>(__bound_args_)..., _VSTD::forward<_Args>(__args)...))
    { return          _Op()(_VSTD::get<_Idx>(__bound_args_)..., _VSTD::forward<_Args>(__args)...); }

  template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs&..., _Args...>>>
  auto operator()(_Args&&...) & = delete;

  template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs const&..., _Args...>>>
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const&
    noexcept(noexcept(_Op()(_VSTD::get<_Idx>(__bound_args_)..., _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op()(_VSTD::get<_Idx>(__bound_args_)..., _VSTD::forward<_Args>(__args)...))
    { return          _Op()(_VSTD::get<_Idx>(__bound_args_)..., _VSTD::forward<_Args>(__args)...); }

  template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs const&..., _Args...>>>
  auto operator()(_Args&&...) const& = delete;

  template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs..., _Args...>>>
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) &&
    noexcept(noexcept(_Op()(_VSTD::get<_Idx>(_VSTD::move(__bound_args_))..., _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op()(_VSTD::get<_Idx>(_VSTD::move(__bound_args_))..., _VSTD::forward<_Args>(__args)...))
    { return          _Op()(_VSTD::get<_Idx>(_VSTD::move(__bound_args_))..., _VSTD::forward<_Args>(__args)...); }

  template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs..., _Args...>>>
  auto operator()(_Args&&...) && = delete;

  template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs const..., _Args...>>>
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const&&
    noexcept(noexcept(_Op()(_VSTD::get<_Idx>(_VSTD::move(__bound_args_))..., _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op()(_VSTD::get<_Idx>(_VSTD::move(__bound_args_))..., _VSTD::forward<_Args>(__args)...))
    { return          _Op()(_VSTD::get<_Idx>(_VSTD::move(__bound_args_))..., _VSTD::forward<_Args>(__args)...); }

  template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs const..., _Args...>>>
  auto operator()(_Args&&...) const&& = delete;
};

// __perfect_forward implements a perfect-forwarding call wrapper as explained in [func.require].
template <class _Op, class ..._Args>
using __perfect_forward = __perfect_forward_impl<_Op, index_sequence_for<_Args...>, _Args...>;

#endif // _LIBCPP_STD_VER >= 17

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___FUNCTIONAL_PERFECT_FORWARD_H