/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  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
 *
 *         https://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  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.
 *
 *=========================================================================*/
#ifndef itkVectorImageNeighborhoodAccessorFunctor_h
#define itkVectorImageNeighborhoodAccessorFunctor_h

#include "itkVariableLengthVector.h"
#include "itkImageBoundaryCondition.h"
#include "itkImageBase.h"

namespace itk
{
/** \class VectorImageNeighborhoodAccessorFunctor
 * \brief Provides accessor interfaces to Access pixels and is meant to be
 * used on pointers to pixels held by the Neighborhood class.
 *
 * A typical user should not need to use this class. The class is internally
 * used by the neighborhood iterators.
 *
 * \note
 * This work is part of the National Alliance for Medical Image Computing
 * (NAMIC), funded by the National Institutes of Health through the NIH Roadmap
 * for Medical Research, Grant U54 EB005149.
 * \ingroup ITKCommon
 */
template <typename TImage>
class VectorImageNeighborhoodAccessorFunctor
{
public:
  using ImageType = TImage;
  using PixelType = typename ImageType::PixelType;
  using InternalPixelType = typename ImageType::InternalPixelType;
  using VectorLengthType = unsigned int;
  using OffsetType = typename ImageType::OffsetType;

  using NeighborhoodType = Neighborhood<InternalPixelType *, TImage::ImageDimension>;

  template <typename TOutput = ImageType>
  using ImageBoundaryConditionType = ImageBoundaryCondition<ImageType, TOutput>;

  VectorImageNeighborhoodAccessorFunctor(VectorLengthType length)
    : m_VectorLength(length)
    , m_OffsetMultiplier(length - 1)
  {}
  VectorImageNeighborhoodAccessorFunctor() = default;

  /** Set the pointer index to the start of the buffer.
   * This must be set by the iterators to the starting location of the buffer.
   * Typically a neighborhood iterator iterating on a neighborhood of an Image,
   * say \c image will set this in its constructor. For instance:
   *
     \code
     ConstNeighborhoodIterator( radius, image, )
       {
       ...
       m_NeighborhoodAccessorFunctor.SetBegin( image->GetBufferPointer() );
       }
     \endcode
   */
  inline void
  SetBegin(const InternalPixelType * begin)
  {
    this->m_Begin = const_cast<InternalPixelType *>(begin);
  }

  /** Method to dereference a pixel pointer. This is used from the
   * ConstNeighborhoodIterator as the equivalent operation to (*it).
   * This method should be preferred over the former *it notation.
   * The reason is that dereferencing a pointer to a location of
   * VectorImage pixel involves a different operation that simply
   * dereferencing the pointer. Here a PixelType (array of InternalPixelType s)
   * is created on the stack and returned.  */
  inline PixelType
  Get(const InternalPixelType * pixelPointer) const
  {
    return PixelType(pixelPointer + (pixelPointer - m_Begin) * m_OffsetMultiplier, m_VectorLength);
  }

  /** Method to set the pixel value at a certain pixel pointer */
  inline void
  Set(InternalPixelType * const pixelPointer, const PixelType & p) const
  {
    InternalPixelType * const truePixelPointer = pixelPointer + (pixelPointer - m_Begin) * m_OffsetMultiplier;

    for (VectorLengthType i = 0; i < m_VectorLength; ++i)
    {
      truePixelPointer[i] = p[i];
    }
  }


  template <typename TOutput>
  inline typename ImageBoundaryConditionType<TOutput>::OutputPixelType
  BoundaryCondition(const OffsetType &                          point_index,
                    const OffsetType &                          boundary_offset,
                    const NeighborhoodType *                    data,
                    const ImageBoundaryConditionType<TOutput> * boundaryCondition) const
  {
    return boundaryCondition->operator()(point_index, boundary_offset, data, *this);
  }

  /** Methods to Set/Get vector length. This should be the length of a block of
   * pixels in the VectorImage. */
  void
  SetVectorLength(VectorLengthType length)
  {
    m_VectorLength = length;
    m_OffsetMultiplier = length - 1;
  }

  /** Methods to Set/Get vector length. This should be the length of a block of
   * pixels in the VectorImage. */
  VectorLengthType
  GetVectorLength()
  {
    return m_VectorLength;
  }

private:
  VectorLengthType m_VectorLength{ 0 };
  VectorLengthType m_OffsetMultiplier{ 0 }; // m_OffsetMultiplier = m_VectorLength-1
                                            // (precomputed for speedup).
  InternalPixelType * m_Begin{ nullptr };   // Begin of the buffer.
};
} // end namespace itk
#endif
