// -*- 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___ITERATOR_INCREMENTABLE_TRAITS_H
#define _LIBCUDACXX___ITERATOR_INCREMENTABLE_TRAITS_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/arithmetic.h>
#include <cuda/std/__concepts/same_as.h>
#include <cuda/std/__fwd/iterator_traits.h>
#include <cuda/std/__type_traits/conditional.h>
#include <cuda/std/__type_traits/enable_if.h>
#include <cuda/std/__type_traits/is_const.h>
#include <cuda/std/__type_traits/is_object.h>
#include <cuda/std/__type_traits/is_pointer.h>
#include <cuda/std/__type_traits/is_primary_template.h>
#include <cuda/std/__type_traits/make_signed.h>
#include <cuda/std/__type_traits/remove_cvref.h>
#include <cuda/std/__type_traits/void_t.h>
#include <cuda/std/__utility/declval.h>
#include <cuda/std/cstddef>

_LIBCUDACXX_BEGIN_NAMESPACE_STD

#if !defined(_CCCL_NO_CONCEPTS)

// [incrementable.traits]
template <class>
struct incrementable_traits
{};

template <class _Tp>
  requires is_object_v<_Tp>
struct incrementable_traits<_Tp*>
{
  using difference_type = ptrdiff_t;
};

template <class _Ip>
struct incrementable_traits<const _Ip> : incrementable_traits<_Ip>
{};

template <class _Tp>
concept __has_member_difference_type = requires { typename _Tp::difference_type; };

template <__has_member_difference_type _Tp>
struct incrementable_traits<_Tp>
{
  using difference_type = typename _Tp::difference_type;
};

template <class _Tp>
concept __has_integral_minus = requires(const _Tp& __x, const _Tp& __y) {
  { __x - __y } -> integral;
};

template <__has_integral_minus _Tp>
  requires(!__has_member_difference_type<_Tp>)
struct incrementable_traits<_Tp>
{
  using difference_type = make_signed_t<decltype(declval<_Tp>() - declval<_Tp>())>;
};

// Let `RI` be `remove_cvref_t<I>`. The type `iter_difference_t<I>` denotes
// `incrementable_traits<RI>::difference_type` if `iterator_traits<RI>` names a specialization
// generated from the primary template, and `iterator_traits<RI>::difference_type` otherwise.
template <class _Ip>
using iter_difference_t =
  typename __select_traits<remove_cvref_t<_Ip>, incrementable_traits<remove_cvref_t<_Ip>>>::difference_type;

#else // ^^^ !_CCCL_NO_CONCEPTS ^^^ / vvv _CCCL_NO_CONCEPTS vvv

// [incrementable.traits]
template <class, class = void>
struct incrementable_traits
{};

template <class _Tp>
struct incrementable_traits<_Tp*, enable_if_t<_CCCL_TRAIT(is_object, _Tp)>>
{
  using difference_type = ptrdiff_t;
};

template <class _Ip>
struct incrementable_traits<const _Ip> : incrementable_traits<_Ip>
{};

template <class _Tp, class = void>
_CCCL_INLINE_VAR constexpr bool __has_member_difference_type = false;

template <class _Tp>
_CCCL_INLINE_VAR constexpr bool __has_member_difference_type<_Tp, void_t<typename _Tp::difference_type>> = true;

template <class _Tp, class = void, class = void>
_CCCL_INLINE_VAR constexpr bool __has_integral_minus = false;

// In C++17 we get issues trying to bind void* to a const& so special case it here
template <class _Tp>
_CCCL_INLINE_VAR constexpr bool
  __has_integral_minus<_Tp,
                       enable_if_t<!same_as<_Tp, void*>>,
                       void_t<decltype(_CUDA_VSTD::declval<const _Tp&>() - _CUDA_VSTD::declval<const _Tp&>())>> =
    integral<decltype(_CUDA_VSTD::declval<const _Tp&>() - _CUDA_VSTD::declval<const _Tp&>())>;

template <class _Tp>
struct incrementable_traits<
  _Tp,
  enable_if_t<!_CCCL_TRAIT(is_pointer, _Tp) && !_CCCL_TRAIT(is_const, _Tp) && __has_member_difference_type<_Tp>>>
{
  using difference_type = typename _Tp::difference_type;
};

template <class _Tp>
struct incrementable_traits<_Tp,
                            enable_if_t<!_CCCL_TRAIT(is_pointer, _Tp) && !_CCCL_TRAIT(is_const, _Tp)
                                        && !__has_member_difference_type<_Tp> && __has_integral_minus<_Tp>>>
{
  using difference_type = make_signed_t<decltype(declval<_Tp>() - declval<_Tp>())>;
};

// Let `RI` be `remove_cvref_t<I>`. The type `iter_difference_t<I>` denotes
// `incrementable_traits<RI>::difference_type` if `iterator_traits<RI>` names a specialization
// generated from the primary template, and `iterator_traits<RI>::difference_type` otherwise.
template <class _Ip>
using iter_difference_t =
  typename __select_traits<remove_cvref_t<_Ip>, incrementable_traits<remove_cvref_t<_Ip>>>::difference_type;

#endif // _CCCL_NO_CONCEPTS

_LIBCUDACXX_END_NAMESPACE_STD

#endif // _LIBCUDACXX___ITERATOR_INCREMENTABLE_TRAITS_H
