// -*- C++ -*-
//===-- execution_defs.h --------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#ifndef __PSTL_execution_policy_defs_H
#define __PSTL_execution_policy_defs_H

#include <type_traits>

namespace __pstl
{
namespace execution
{
inline namespace v1
{

// 2.4, Sequential execution policy
class sequenced_policy
{
  public:
    // For internal use only
    static constexpr std::false_type
    __allow_unsequenced()
    {
        return std::false_type{};
    }
    static constexpr std::false_type
    __allow_vector()
    {
        return std::false_type{};
    }
    static constexpr std::false_type
    __allow_parallel()
    {
        return std::false_type{};
    }
};

#if __PSTL_USE_PAR_POLICIES
// 2.5, Parallel execution policy
class parallel_policy
{
  public:
    // For internal use only
    static constexpr std::false_type
    __allow_unsequenced()
    {
        return std::false_type{};
    }
    static constexpr std::false_type
    __allow_vector()
    {
        return std::false_type{};
    }
    static constexpr std::true_type
    __allow_parallel()
    {
        return std::true_type{};
    }
};

// 2.6, Parallel+Vector execution policy
class parallel_unsequenced_policy
{
  public:
    // For internal use only
    static constexpr std::true_type
    __allow_unsequenced()
    {
        return std::true_type{};
    }
    static constexpr std::true_type
    __allow_vector()
    {
        return std::true_type{};
    }
    static constexpr std::true_type
    __allow_parallel()
    {
        return std::true_type{};
    }
};
#endif

class unsequenced_policy
{
  public:
    // For internal use only
    static constexpr std::true_type
    __allow_unsequenced()
    {
        return std::true_type{};
    }
    static constexpr std::true_type
    __allow_vector()
    {
        return std::true_type{};
    }
    static constexpr std::false_type
    __allow_parallel()
    {
        return std::false_type{};
    }
};

// 2.8, Execution policy objects
constexpr sequenced_policy seq{};
#if __PSTL_USE_PAR_POLICIES
constexpr parallel_policy par{};
constexpr parallel_unsequenced_policy par_unseq{};
#endif
constexpr unsequenced_policy unseq{};

// 2.3, Execution policy type trait
template <class T>
struct is_execution_policy : std::false_type
{
};

template <>
struct is_execution_policy<sequenced_policy> : std::true_type
{
};
#if __PSTL_USE_PAR_POLICIES
template <>
struct is_execution_policy<parallel_policy> : std::true_type
{
};
template <>
struct is_execution_policy<parallel_unsequenced_policy> : std::true_type
{
};
#endif
template <>
struct is_execution_policy<unsequenced_policy> : std::true_type
{
};

#if __PSTL_CPP14_VARIABLE_TEMPLATES_PRESENT
template <class T>
constexpr bool is_execution_policy_v = is_execution_policy<T>::value;
#endif

} // namespace v1
} // namespace execution

namespace internal
{
template <class ExecPolicy, class T>
using enable_if_execution_policy =
    typename std::enable_if<__pstl::execution::is_execution_policy<typename std::decay<ExecPolicy>::type>::value,
                            T>::type;
} // namespace internal

} // namespace __pstl

#endif /* __PSTL_execution_policy_defs_H */