//============================================================================
//  Copyright (c) Kitware, Inc.
//  All rights reserved.
//  See LICENSE.txt for details.
//
//  This software is distributed WITHOUT ANY WARRANTY; without even
//  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
//  PURPOSE.  See the above copyright notice for more information.
//============================================================================
#ifndef vtk_m_cont_ExecutionAndControlObjectBase_h
#define vtk_m_cont_ExecutionAndControlObjectBase_h

#include <vtkm/cont/ExecutionObjectBase.h>

namespace vtkm
{
namespace cont
{

/// Base `ExecutionAndControlObjectBase` class. These are objects that behave
/// as execution objects but can also be use din the control environment.
/// Any subclass of `ExecutionAndControlObjectBase` must implement a
/// `PrepareForExecution` method that takes a device adapter tag and a
/// `vtkm::cont::Token` reference and returns
/// an object for that device. It also must implement `PrepareForControl` that simply
/// returns an object that works in the control environment.
///
struct ExecutionAndControlObjectBase : vtkm::cont::ExecutionObjectBase
{
};

namespace internal
{

namespace detail
{

struct CheckPrepareForControl
{
  template <typename T>
  static auto check(T* p) -> decltype(p->PrepareForControl(), std::true_type());

  template <typename T>
  static auto check(...) -> std::false_type;
};

} // namespace detail

template <typename T>
using IsExecutionAndControlObjectBase =
  std::is_base_of<vtkm::cont::ExecutionAndControlObjectBase, typename std::decay<T>::type>;

template <typename T>
struct HasPrepareForControl
  : decltype(detail::CheckPrepareForControl::check<typename std::decay<T>::type>(nullptr))
{
};

/// Checks that the argument is a proper execution object.
///
#define VTKM_IS_EXECUTION_AND_CONTROL_OBJECT(execObject)                                          \
  static_assert(::vtkm::cont::internal::IsExecutionAndControlObjectBase<execObject>::value,       \
                "Provided type is not a subclass of vtkm::cont::ExecutionAndControlObjectBase."); \
  static_assert(::vtkm::cont::internal::HasPrepareForExecution<execObject>::value,                \
                "Provided type does not have requisite PrepareForExecution method.");             \
  static_assert(::vtkm::cont::internal::HasPrepareForControl<execObject>::value,                  \
                "Provided type does not have requisite PrepareForControl method.")

/// \brief Gets the object to use in the control environment from an ExecutionAndControlObject.
///
/// An execution and control object (that is, an object inheriting from
/// `vtkm::cont::ExecutionAndControlObjectBase`) is really a control object factory that generates
/// a objects to be used in either the execution environment or the control environment. This
/// function takes a subclass of `ExecutionAndControlObjectBase` and returns the control object.
///
template <typename T>
VTKM_CONT auto CallPrepareForControl(T&& execObject) -> decltype(execObject.PrepareForControl())
{
  VTKM_IS_EXECUTION_AND_CONTROL_OBJECT(T);

  return execObject.PrepareForControl();
}

/// \brief Gets the object to use in the control environment from an ExecutionAndControlObject.
///
/// An execution and control object (that is, an object inheriting from
/// `vtkm::cont::ExecutionAndControlObjectBase`) is really a control object factory that generates
/// a objects to be used in either the execution environment or the control environment. This
/// templated type gives the type for the class used in the control environment for a given
/// ExecutionAndControlObject.
///
template <typename ExecutionAndControlObject>
using ControlObjectType =
  decltype(CallPrepareForControl(std::declval<ExecutionAndControlObject>()));

} // namespace internal
}
} // namespace vtkm::cont

#endif //vtk_m_cont_ExecutionAndControlObjectBase_h
