/*
 *  Copyright 2008-2018 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 thrust/iterator/transform_output_iterator.h
 *  \brief An output iterator which adapts another output iterator by applying a
 *         function to the result of its dereference before writing it.
 */

#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/iterator/detail/transform_output_iterator.inl>

THRUST_NAMESPACE_BEGIN

/*! \addtogroup iterators
 *  \{
 */

/*! \addtogroup fancyiterator Fancy Iterators
 *  \ingroup iterators
 *  \{
 */

/*! \p transform_output_iterator is a special kind of output iterator which
 * transforms a value written upon dereference. This iterator is useful
 * for transforming an output from algorithms without explicitly storing the
 * intermediate result in the memory and applying subsequent transformation,
 * thereby avoiding wasting memory capacity and bandwidth.
 * Using \p transform_iterator facilitates kernel fusion by deferring execution
 * of transformation until the value is written while saving both memory
 * capacity and bandwidth.
 *
 * The following code snippet demonstrated how to create a
 * \p transform_output_iterator which applies \c sqrtf to the assigning value.
 *
 * \code
 * #include <thrust/iterator/transform_output_iterator.h>
 * #include <thrust/device_vector.h>
 *
 * // note: functor inherits form unary function
 *  // note: functor inherits from unary_function
 *  struct square_root : public thrust::unary_function<float,float>
 *  {
 *    __host__ __device__
 *    float operator()(float x) const
 *    {
 *      return sqrtf(x);
 *    }
 *  };
 *
 *  int main()
 *  {
 *    thrust::device_vector<float> v(4);
 *
 *    using FloatIterator = thrust::device_vector<float>::iterator;
 *    thrust::transform_output_iterator<square_root, FloatIterator> iter(v.begin(), square_root());
 *
 *    iter[0] =  1.0f;    // stores sqrtf( 1.0f)
 *    iter[1] =  4.0f;    // stores sqrtf( 4.0f)
 *    iter[2] =  9.0f;    // stores sqrtf( 9.0f)
 *    iter[3] = 16.0f;    // stores sqrtf(16.0f)
 *    // iter[4] is an out-of-bounds error
 *
 *    v[0]; // returns 1.0f;
 *    v[1]; // returns 2.0f;
 *    v[2]; // returns 3.0f;
 *    v[3]; // returns 4.0f;
 *
 *  }
 *  \endcode
 *
 *  \see make_transform_output_iterator
 */

template <typename UnaryFunction, typename OutputIterator>
class transform_output_iterator : public detail::transform_output_iterator_base<UnaryFunction, OutputIterator>::type
{
  /*! \cond
   */

public:
  using super_t = typename detail::transform_output_iterator_base<UnaryFunction, OutputIterator>::type;

  friend class iterator_core_access;
  /*! \endcond
   */

  transform_output_iterator() = default;

  /*! This constructor takes as argument an \c OutputIterator and an \c
   * UnaryFunction and copies them to a new \p transform_output_iterator
   *
   * \param out An \c OutputIterator pointing to the output range whereto the result of
   *            \p transform_output_iterator's \c UnaryFunction will be written.
   * \param fun An \c UnaryFunction used to transform the objects assigned to
   *            this \p transform_output_iterator.
   */
  THRUST_HOST_DEVICE transform_output_iterator(OutputIterator const& out, UnaryFunction fun)
      : super_t(out)
      , fun(fun)
  {}

  /*! \cond
   */

private:
  THRUST_HOST_DEVICE typename super_t::reference dereference() const
  {
    return detail::transform_output_iterator_proxy<UnaryFunction, OutputIterator>(this->base_reference(), fun);
  }

  UnaryFunction fun;

  /*! \endcond
   */
}; // end transform_output_iterator

/*! \p make_transform_output_iterator creates a \p transform_output_iterator from
 *  an \c OutputIterator and \c UnaryFunction.
 *
 *  \param out The \c OutputIterator pointing to the output range of the newly
 *            created \p transform_output_iterator
 *  \param fun The \c UnaryFunction transform the object before assigning it to
 *            \c out by the newly created \p transform_output_iterator
 *  \see transform_output_iterator
 */
template <typename UnaryFunction, typename OutputIterator>
transform_output_iterator<UnaryFunction, OutputIterator> THRUST_HOST_DEVICE
make_transform_output_iterator(OutputIterator out, UnaryFunction fun)
{
  return transform_output_iterator<UnaryFunction, OutputIterator>(out, fun);
} // end make_transform_output_iterator

/*! \} // end fancyiterators
 */

/*! \} // end iterators
 */

THRUST_NAMESPACE_END
