// Copyright (c) 2017-2021 Advanced Micro Devices, Inc. All rights reserved.
//
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// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
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// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
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// THE SOFTWARE.

#ifndef ROCPRIM_TYPES_FUTURE_VALUE_HPP_
#define ROCPRIM_TYPES_FUTURE_VALUE_HPP_

#include "../config.hpp"

/// \addtogroup utilsmodule
/// @{

BEGIN_ROCPRIM_NAMESPACE

/**
 * \brief Allows passing values that are not yet known at launch time as paramters to device algorithms.
 *
 * \note It is the users responsibility to ensure that value is available when the algorithm executes.
 * This can be guaranteed with stream dependencies or explicit external synchronization.
 *
 * \code
 * int* intermediate_result = nullptr;
 * hipMalloc(reinterpret_cast<void**>(&intermediate_result), sizeof(intermediate_result));
 * hipLaunchKernelGGL(compute_intermediate, blocks, threads, 0, stream, arg1, arg2, itermediate_result);
 * const auto initial_value = rocprim::future_value<int>{intermediate_result};
 * rocprim::exclusive_scan(temporary_storage,
 *                         storage_size,
 *                         input,
 *                         output,
 *                         initial_value,
 *                         size);
 * hipFree(intermediate_result)
 * \endcode
 *
 * \tparam T
 * \tparam Iter
 */
template <typename T, typename Iter = T*>
class future_value
{
public:
    using value_type    = T; ///< The type of the value this future will store.
    using iterator_type = Iter; ///< An iterator type that can point at the \p value_type.

    /// \brief Constructs a future value
    /// \param iter - An iterator that will point to the value when it becomes available.
    explicit ROCPRIM_HOST_DEVICE future_value(const Iter iter)
        : iter_ {iter}
    {
    }

    /// \brief Returns the value by dereferencing the iterator that the constructor was passed.
    /// \note The value must be available at the point this is called.
    ROCPRIM_HOST_DEVICE operator T()
    {
        return *iter_;
    }

    /// \brief Returns the value by dereferencing the iterator that the constructor was passed.
    /// \note The value must be available at the point this is called.
    ROCPRIM_HOST_DEVICE operator T() const
    {
        return *iter_;
    }
private:
    Iter iter_;
};

namespace detail
{
    /// \brief Used for unpacking a future_value, basically just a cast but its more explicit
    /// this way.
    template <typename T>
    ROCPRIM_HOST_DEVICE T get_input_value(const T value)
    {
        return value;
    }

    template <typename T, typename Iter>
    ROCPRIM_HOST_DEVICE T get_input_value(::rocprim::future_value<T, Iter> future) {
        return future;
    }

    template <class T>
    struct input_value_traits {
        using value_type = T;
    };

    template <class T, typename Iter> 
    struct input_value_traits<::rocprim::future_value<T, Iter>>
    {
        using value_type    = T;
        using iterator_type = Iter;
    };

    template <typename T>
    using input_type_t = typename input_value_traits<T>::value_type;

    template <typename T>
    using input_iterator_t = typename input_value_traits<T>::iterator_type;
}

END_ROCPRIM_NAMESPACE

/// @}
// end of group utilsmodule

#endif
