/*=========================================================================
 *
 *  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 itkVectorLinearInterpolateNearestNeighborExtrapolateImageFunction_hxx
#define itkVectorLinearInterpolateNearestNeighborExtrapolateImageFunction_hxx


#include "itkMath.h"

namespace itk
{
/**
 * Define the number of neighbors
 */
template <typename TInputImage, typename TCoordRep>
const unsigned int VectorLinearInterpolateNearestNeighborExtrapolateImageFunction<TInputImage, TCoordRep>::m_Neighbors =
  1 << TInputImage::ImageDimension;

template <typename TInputImage, typename TCoordRep>
auto
VectorLinearInterpolateNearestNeighborExtrapolateImageFunction<TInputImage, TCoordRep>::EvaluateAtContinuousIndex(
  const ContinuousIndexType & index) const -> OutputType
{
  unsigned int dim; // index over dimension

  //
  // Compute base index = closest index below point
  // Compute distance from point to base index
  //
  IndexType baseIndex;
  IndexType neighIndex;
  double    distance[ImageDimension];

  for (dim = 0; dim < ImageDimension; ++dim)
  {
    baseIndex[dim] = Math::Floor<IndexValueType>(index[dim]);

    if (baseIndex[dim] >= this->m_StartIndex[dim])
    {
      if (baseIndex[dim] < this->m_EndIndex[dim])
      {
        distance[dim] = index[dim] - static_cast<double>(baseIndex[dim]);
      }
      else
      {
        baseIndex[dim] = this->m_EndIndex[dim];
        distance[dim] = 0.0;
      }
    }
    else
    {
      baseIndex[dim] = this->m_StartIndex[dim];
      distance[dim] = 0.0;
    }
  }

  //
  // Interpolated value is the weight some of each of the surrounding
  // neighbors. The weight for each neighbour is the fraction overlap
  // of the neighbor pixel with respect to a pixel centered on point.
  //
  OutputType output;
  NumericTraits<OutputType>::SetLength(output, this->GetInputImage()->GetNumberOfComponentsPerPixel());
  output.Fill(0.0);

  RealType totalOverlap = 0.0;

  for (unsigned int counter = 0; counter < m_Neighbors; ++counter)
  {
    double       overlap = 1.0;   // fraction overlap
    unsigned int upper = counter; // each bit indicates upper/lower neighbour

    // get neighbor index and overlap fraction
    for (dim = 0; dim < ImageDimension; ++dim)
    {
      if (upper & 1)
      {
        neighIndex[dim] = baseIndex[dim] + 1;
        overlap *= distance[dim];
      }
      else
      {
        neighIndex[dim] = baseIndex[dim];
        overlap *= 1.0 - distance[dim];
      }

      upper >>= 1;
    }

    // get neighbor value only if overlap is not zero
    if (overlap)
    {
      const PixelType input = this->GetInputImage()->GetPixel(neighIndex);
      for (unsigned int k = 0; k < this->GetInputImage()->GetNumberOfComponentsPerPixel(); ++k)
      {
        output[k] += overlap * static_cast<RealType>(input[k]);
      }
      totalOverlap += overlap;
    }

    if (totalOverlap == 1.0)
    {
      // finished
      break;
    }
  }

  return (output);
}

/**
 * Evaluate at image index position
 */
template <typename TInputImage, typename TCoordRep>
auto
VectorLinearInterpolateNearestNeighborExtrapolateImageFunction<TInputImage, TCoordRep>::EvaluateAtIndex(
  const IndexType & index) const -> OutputType
{
  // Find the index that is closest to the requested one
  // but that lies within the image
  IndexType insideIndex;

  for (unsigned int dim = 0; dim < ImageDimension; ++dim)
  {
    if (index[dim] >= this->m_StartIndex[dim])
    {
      if (index[dim] < this->m_EndIndex[dim])
      {
        insideIndex[dim] = index[dim];
      }
      else
      {
        insideIndex[dim] = this->m_EndIndex[dim];
      }
    }
    else
    {
      insideIndex[dim] = this->m_StartIndex[dim];
    }
  }

  // Now call the superclass implementation of EvaluateAtIndex
  // since we have ensured that the index lies in the image region
  return this->Superclass::EvaluateAtIndex(insideIndex);
}
} // end namespace itk

#endif
