// -*- 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
// SPDX-FileCopyrightText: Copyright (c) 2023 NVIDIA CORPORATION & AFFILIATES.
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCUDACXX___RANGES_EMPTY_H
#define _LIBCUDACXX___RANGES_EMPTY_H

#include <cuda/std/detail/__config>

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

#include <cuda/std/__concepts/class_or_enum.h>
#include <cuda/std/__iterator/concepts.h>
#include <cuda/std/__ranges/access.h>
#include <cuda/std/__ranges/size.h>

_LIBCUDACXX_BEGIN_NAMESPACE_RANGES

// [range.prim.empty]

_LIBCUDACXX_BEGIN_NAMESPACE_CPO(__empty)

#if !defined(_CCCL_NO_CONCEPTS)
template <class _Tp>
concept __member_empty = __workaround_52970<_Tp> && requires(_Tp&& __t) { bool(__t.empty()); };

template <class _Tp>
concept __can_invoke_size = !__member_empty<_Tp> && requires(_Tp&& __t) { _CUDA_VRANGES::size(__t); };

template <class _Tp>
concept __can_compare_begin_end = !__member_empty<_Tp> && !__can_invoke_size<_Tp> && requires(_Tp&& __t) {
  bool(_CUDA_VRANGES::begin(__t) == _CUDA_VRANGES::end(__t));
  { _CUDA_VRANGES::begin(__t) } -> forward_iterator;
};
#else // ^^^ !_CCCL_NO_CONCEPTS ^^^ / vvv _CCCL_NO_CONCEPTS vvv
template <class _Tp>
_CCCL_CONCEPT_FRAGMENT(__member_empty_, requires(_Tp&& __t)(requires(__workaround_52970<_Tp>), (bool(__t.empty()))));

template <class _Tp>
_CCCL_CONCEPT __member_empty = _CCCL_FRAGMENT(__member_empty_, _Tp);

template <class _Tp>
_CCCL_CONCEPT_FRAGMENT(__can_invoke_size_,
                       requires(_Tp&& __t)(requires(!__member_empty<_Tp>), ((void) _CUDA_VRANGES::size(__t))));

template <class _Tp>
_CCCL_CONCEPT __can_invoke_size = _CCCL_FRAGMENT(__can_invoke_size_, _Tp);

template <class _Tp>
_CCCL_CONCEPT_FRAGMENT(
  __can_compare_begin_end_,
  requires(_Tp&& __t)(requires(!__member_empty<_Tp>),
                      requires(!__can_invoke_size<_Tp>),
                      (bool(_CUDA_VRANGES::begin(__t) == _CUDA_VRANGES::end(__t))),
                      requires(forward_iterator<decltype(_CUDA_VRANGES::begin(__t))>)));

template <class _Tp>
_CCCL_CONCEPT __can_compare_begin_end = _CCCL_FRAGMENT(__can_compare_begin_end_, _Tp);
#endif // _CCCL_NO_CONCEPTS

struct __fn
{
  _CCCL_TEMPLATE(class _Tp)
  _CCCL_REQUIRES(__member_empty<_Tp>)
  _CCCL_NODISCARD _LIBCUDACXX_HIDE_FROM_ABI constexpr bool operator()(_Tp&& __t) const
    noexcept(noexcept(bool(__t.empty())))
  {
    return bool(__t.empty());
  }

  _CCCL_TEMPLATE(class _Tp)
  _CCCL_REQUIRES(__can_invoke_size<_Tp>)
  _CCCL_NODISCARD _LIBCUDACXX_HIDE_FROM_ABI constexpr bool operator()(_Tp&& __t) const
    noexcept(noexcept(_CUDA_VRANGES::size(__t)))
  {
    return _CUDA_VRANGES::size(__t) == 0;
  }

  _CCCL_TEMPLATE(class _Tp)
  _CCCL_REQUIRES(__can_compare_begin_end<_Tp>)
  _CCCL_NODISCARD _LIBCUDACXX_HIDE_FROM_ABI constexpr bool operator()(_Tp&& __t) const
    noexcept(noexcept(bool(_CUDA_VRANGES::begin(__t) == _CUDA_VRANGES::end(__t))))
  {
    return _CUDA_VRANGES::begin(__t) == _CUDA_VRANGES::end(__t);
  }
};
_LIBCUDACXX_END_NAMESPACE_CPO

inline namespace __cpo
{
_CCCL_GLOBAL_CONSTANT auto empty = __empty::__fn{};
} // namespace __cpo

_LIBCUDACXX_END_NAMESPACE_RANGES

#endif // _LIBCUDACXX___RANGES_EMPTY_H
