/*
 *  Copyright 2008-2013 NVIDIA Corporation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  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 <thrust/detail/config.h>

#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 <thrust/detail/raw_pointer_cast.h>
#include <thrust/detail/tuple_transform.h>
#include <thrust/detail/type_traits.h>
#include <thrust/detail/type_traits/has_nested_type.h>

#if !_THRUST_HAS_DEVICE_SYSTEM_STD
#  include <type_traits>
#endif

// the order of declarations and definitions in this file is totally goofy
// this header defines raw_reference_cast, which has a few overloads towards the bottom of the file
// raw_reference_cast depends on metafunctions such as is_unwrappable and raw_reference
// we need to be sure that these metafunctions are completely defined (including specializations) before they are
// instantiated by raw_reference_cast

THRUST_NAMESPACE_BEGIN
namespace detail
{

template <typename... Ts>
class tuple_of_iterator_references;

__THRUST_DEFINE_HAS_NESTED_TYPE(is_wrapped_reference, wrapped_reference_hint)

// wrapped reference-like things which aren't strictly wrapped references
// (e.g. tuples of wrapped references) are considered unwrappable
template <typename T>
struct is_unwrappable : is_wrapped_reference<T>
{};

// specialize is_unwrappable
// a tuple is_unwrappable if any of its elements is_unwrappable
template <typename... Ts>
struct is_unwrappable<thrust::tuple<Ts...>> : _THRUST_STD::disjunction<is_unwrappable<Ts>...>
{};

// specialize is_unwrappable
// a tuple_of_iterator_references is_unwrappable if any of its elements is_unwrappable
template <typename... Ts>
struct is_unwrappable<thrust::detail::tuple_of_iterator_references<Ts...>>
    : _THRUST_STD::disjunction<is_unwrappable<Ts>...>
{};

template <typename T, typename Result = void>
struct enable_if_unwrappable : _THRUST_STD::enable_if<is_unwrappable<T>::value, Result>
{};

namespace raw_reference_detail
{

template <typename T, typename Enable = void>
struct raw_reference_impl : _THRUST_STD::add_lvalue_reference<T>
{};

template <typename T>
struct raw_reference_impl<T, _THRUST_STD::enable_if_t<is_wrapped_reference<_THRUST_STD::remove_cv_t<T>>::value>>
{
  using type = _THRUST_STD::add_lvalue_reference_t<typename pointer_element<typename T::pointer>::type>;
};

} // namespace raw_reference_detail

template <typename T>
struct raw_reference : raw_reference_detail::raw_reference_impl<T>
{};

namespace raw_reference_detail
{

// unlike raw_reference,
// raw_reference_tuple_helper needs to return a value
// when it encounters one, rather than a reference
// upon encountering tuple, recurse
//
// we want the following behavior:
//  1. T                                -> T
//  2. T&                               -> T&
//  3. null_type                        -> null_type
//  4. reference<T>                     -> T&
//  5. tuple_of_iterator_references<T>  -> tuple_of_iterator_references<raw_reference_tuple_helper<T>::type>

// wrapped references are unwrapped using raw_reference, otherwise, return T
template <typename T>
struct raw_reference_tuple_helper
    : eval_if<is_unwrappable<_THRUST_STD::remove_cv_t<T>>::value, raw_reference<T>, identity_<T>>
{};

// recurse on tuples
template <typename... Ts>
struct raw_reference_tuple_helper<thrust::tuple<Ts...>>
{
  using type = thrust::tuple<typename raw_reference_tuple_helper<Ts>::type...>;
};

template <typename... Ts>
struct raw_reference_tuple_helper<thrust::detail::tuple_of_iterator_references<Ts...>>
{
  using type = thrust::detail::tuple_of_iterator_references<typename raw_reference_tuple_helper<Ts>::type...>;
};

} // namespace raw_reference_detail

// a couple of specializations of raw_reference for tuples follow

// if a tuple "tuple_type" is_unwrappable,
//   then the raw_reference of tuple_type is a tuple of its members' raw_references
//   else the raw_reference of tuple_type is tuple_type &
template <typename... Ts>
struct raw_reference<thrust::tuple<Ts...>>
{
private:
  using tuple_type = thrust::tuple<Ts...>;

public:
  using type = typename eval_if<is_unwrappable<tuple_type>::value,
                                raw_reference_detail::raw_reference_tuple_helper<tuple_type>,
                                _THRUST_STD::add_lvalue_reference<tuple_type>>::type;
};

template <typename... Ts>
struct raw_reference<thrust::detail::tuple_of_iterator_references<Ts...>>
{
private:
  using tuple_type = detail::tuple_of_iterator_references<Ts...>;

public:
  using type = typename raw_reference_detail::raw_reference_tuple_helper<tuple_type>::type;
};

} // namespace detail

// provide declarations of raw_reference_cast's overloads for raw_reference_caster below
template <typename T>
THRUST_HOST_DEVICE typename detail::raw_reference<T>::type raw_reference_cast(T& ref);

template <typename T>
THRUST_HOST_DEVICE typename detail::raw_reference<const T>::type raw_reference_cast(const T& ref);

template <typename... Ts>
THRUST_HOST_DEVICE typename detail::enable_if_unwrappable<
  thrust::detail::tuple_of_iterator_references<Ts...>,
  typename detail::raw_reference<thrust::detail::tuple_of_iterator_references<Ts...>>::type>::type
raw_reference_cast(thrust::detail::tuple_of_iterator_references<Ts...> t);

namespace detail
{

struct raw_reference_caster
{
  template <typename T>
  THRUST_HOST_DEVICE typename detail::raw_reference<T>::type operator()(T& ref)
  {
    return thrust::raw_reference_cast(ref);
  }

  template <typename T>
  THRUST_HOST_DEVICE typename detail::raw_reference<const T>::type operator()(const T& ref)
  {
    return thrust::raw_reference_cast(ref);
  }

  template <typename... Ts>
  THRUST_HOST_DEVICE typename detail::raw_reference<thrust::detail::tuple_of_iterator_references<Ts...>>::type
  operator()(thrust::detail::tuple_of_iterator_references<Ts...> t,
             _THRUST_STD::enable_if_t<is_unwrappable<thrust::detail::tuple_of_iterator_references<Ts...>>::value>* = 0)
  {
    return thrust::raw_reference_cast(t);
  }
}; // end raw_reference_caster

} // namespace detail

template <typename T>
THRUST_HOST_DEVICE typename detail::raw_reference<T>::type raw_reference_cast(T& ref)
{
  return *thrust::raw_pointer_cast(&ref);
} // end raw_reference_cast

template <typename T>
THRUST_HOST_DEVICE typename detail::raw_reference<const T>::type raw_reference_cast(const T& ref)
{
  return *thrust::raw_pointer_cast(&ref);
} // end raw_reference_cast

template <typename... Ts>
THRUST_HOST_DEVICE typename detail::enable_if_unwrappable<
  thrust::detail::tuple_of_iterator_references<Ts...>,
  typename detail::raw_reference<thrust::detail::tuple_of_iterator_references<Ts...>>::type>::type
raw_reference_cast(thrust::detail::tuple_of_iterator_references<Ts...> t)
{
  thrust::detail::raw_reference_caster f;

  // note that we pass raw_reference_tuple_helper, not raw_reference as the unary metafunction
  // the different way that raw_reference_tuple_helper unwraps tuples is important
  return thrust::detail::tuple_host_device_transform<detail::raw_reference_detail::raw_reference_tuple_helper>(t, f);
} // end raw_reference_cast

THRUST_NAMESPACE_END
