/*
 *  Copyright 2018 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.
 */

/*! \file
 *  \brief A base class for the memory resource system, similar to
 *  std::memory_resource, and related utilities.
 */

#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/config/memory_resource.h>
#ifdef THRUST_MR_STD_MR_HEADER
#  include THRUST_MR_STD_MR_HEADER
#endif

THRUST_NAMESPACE_BEGIN
/*! \brief \p thrust::mr is the namespace containing system agnostic types and functions for \p memory_resource related
 * functionalities.
 */
namespace mr
{
/** \addtogroup memory_resources Memory Resources
 *  \ingroup memory_management
 *  \{
 */

/*! \p memory_resource is the base class for all other memory resources.
 *
 *  \tparam Pointer the pointer type that is allocated and deallocated by the memory resource
 *      derived from this base class. If this is <tt>void *</tt>, this class derives from
 *      <tt>std::pmr::memory_resource</tt>.
 */
template <typename Pointer = void*>
class memory_resource
{
public:
  /*! Alias for the template parameter.
   */
  using pointer = Pointer;

  /*! Virtual destructor, defaulted when possible.
   */
  virtual ~memory_resource() = default;

  /*! Allocates memory of size at least \p bytes and alignment at least \p alignment.
   *
   *  \param bytes size, in bytes, that is requested from this allocation
   *  \param alignment alignment that is requested from this allocation
   *  \throws thrust::bad_alloc when no memory with requested size and alignment can be allocated.
   *  \return A pointer to void to the newly allocated memory.
   */
  [[nodiscard]] pointer allocate(std::size_t bytes, std::size_t alignment = THRUST_MR_DEFAULT_ALIGNMENT)
  {
    return do_allocate(bytes, alignment);
  }

  /*! Deallocates memory pointed to by \p p.
   *
   *  \param p pointer to be deallocated
   *  \param bytes the size of the allocation. This must be equivalent to the value of \p bytes that
   *      was passed to the allocation function that returned \p p.
   *  \param alignment the alignment of the allocation. This must be equivalent to the value of \p alignment
   *      that was passed to the allocation function that returned \p p.
   */
  void deallocate(pointer p, std::size_t bytes, std::size_t alignment = THRUST_MR_DEFAULT_ALIGNMENT) noexcept
  {
    do_deallocate(p, bytes, alignment);
  }

  /*! Compares this resource to the other one. The default implementation uses identity comparison,
   *      which is often the right thing to do and doesn't require RTTI involvement.
   *
   *  \param other the other resource to compare this resource to
   *  \return whether the two resources are equivalent.
   */
  _CCCL_HOST_DEVICE bool is_equal(const memory_resource& other) const noexcept
  {
    return do_is_equal(other);
  }

  /*! Allocates memory of size at least \p bytes and alignment at least \p alignment.
   *
   *  \param bytes size, in bytes, that is requested from this allocation
   *  \param alignment alignment that is requested from this allocation
   *  \throws thrust::bad_alloc when no memory with requested size and alignment can be allocated.
   *  \return A pointer to void to the newly allocated memory.
   */
  virtual pointer do_allocate(std::size_t bytes, std::size_t alignment) = 0;

  /*! Deallocates memory pointed to by \p p.
   *
   *  \param p pointer to be deallocated
   *  \param bytes the size of the allocation. This must be equivalent to the value of \p bytes that
   *      was passed to the allocation function that returned \p p.
   *  \param alignment the size of the allocation. This must be equivalent to the value of \p alignment
   *      that was passed to the allocation function that returned \p p.
   */
  virtual void do_deallocate(pointer p, std::size_t bytes, std::size_t alignment) = 0;

  /*! Compares this resource to the other one. The default implementation uses identity comparison,
   *      which is often the right thing to do and doesn't require RTTI involvement.
   *
   *  \param other the other resource to compare this resource to
   *  \return whether the two resources are equivalent.
   */
  _CCCL_HOST_DEVICE virtual bool do_is_equal(const memory_resource& other) const noexcept
  {
    return this == &other;
  }
};

template <>
class memory_resource<void*>
#ifdef THRUST_STD_MR_NS
    : THRUST_STD_MR_NS::memory_resource
#endif
{
public:
  using pointer = void*;

  virtual ~memory_resource() = default;

  [[nodiscard]] pointer allocate(std::size_t bytes, std::size_t alignment = THRUST_MR_DEFAULT_ALIGNMENT)
  {
    return do_allocate(bytes, alignment);
  }

  void deallocate(pointer p, std::size_t bytes, std::size_t alignment = THRUST_MR_DEFAULT_ALIGNMENT) noexcept
  {
    do_deallocate(p, bytes, alignment);
  }

  _CCCL_HOST_DEVICE bool is_equal(const memory_resource& other) const noexcept
  {
    return do_is_equal(other);
  }

  virtual pointer do_allocate(std::size_t bytes, std::size_t alignment)           = 0;
  virtual void do_deallocate(pointer p, std::size_t bytes, std::size_t alignment) = 0;
  _CCCL_HOST_DEVICE virtual bool do_is_equal(const memory_resource& other) const noexcept
  {
    return this == &other;
  }

#ifdef THRUST_STD_MR_NS
  // the above do_is_equal is a different function than the one from the standard memory resource
  // can't implement this reasonably without RTTI though; it's reasonable to assume false otherwise

  virtual bool do_is_equal(const THRUST_STD_MR_NS::memory_resource& other) const noexcept override
  {
#  ifndef _CCCL_NO_RTTI
    auto mr_resource = dynamic_cast<memory_resource<>*>(&other);
    return mr_resource && do_is_equal(*mr_resource);
#  else
    return this == &other;
#  endif
  }
#endif
};

/*! Compares the memory resources for equality, first by identity, then by \p is_equal.
 */
template <typename Pointer>
_CCCL_HOST_DEVICE bool operator==(const memory_resource<Pointer>& lhs, const memory_resource<Pointer>& rhs) noexcept
{
  return &lhs == &rhs || rhs.is_equal(rhs);
}

/*! Compares the memory resources for inequality, first by identity, then by \p is_equal.
 */
template <typename Pointer>
_CCCL_HOST_DEVICE bool operator!=(const memory_resource<Pointer>& lhs, const memory_resource<Pointer>& rhs) noexcept
{
  return !(lhs == rhs);
}

/*! Returns a global instance of \p MR, created as a function local static variable.
 *
 *  \tparam MR type of a memory resource to get an instance from. Must be \p DefaultConstructible.
 *  \return a pointer to a global instance of \p MR.
 */
template <typename MR>
_CCCL_HOST MR* get_global_resource()
{
  static MR resource;
  return &resource;
}

/*! \} // memory_resource
 */
} // namespace mr
THRUST_NAMESPACE_END
