/*=========================================================================
 *
 *  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 itkMeanReciprocalSquareDifferenceImageToImageMetric_hxx
#define itkMeanReciprocalSquareDifferenceImageToImageMetric_hxx

#include "itkImageRegionConstIteratorWithIndex.h"

namespace itk
{

template <typename TFixedImage, typename TMovingImage>
MeanReciprocalSquareDifferenceImageToImageMetric<TFixedImage,
                                                 TMovingImage>::MeanReciprocalSquareDifferenceImageToImageMetric()
{
  m_Lambda = 1.0;
  m_Delta = 0.00011;
}

template <typename TFixedImage, typename TMovingImage>
void
MeanReciprocalSquareDifferenceImageToImageMetric<TFixedImage, TMovingImage>::PrintSelf(std::ostream & os,
                                                                                       Indent         indent) const
{
  Superclass::PrintSelf(os, indent);

  os << indent << "Lambda: " << m_Lambda << std::endl;
  os << indent << "Delta: " << m_Delta << std::endl;
}

template <typename TFixedImage, typename TMovingImage>
auto
MeanReciprocalSquareDifferenceImageToImageMetric<TFixedImage, TMovingImage>::GetValue(
  const TransformParametersType & parameters) const -> MeasureType
{
  FixedImageConstPointer fixedImage = this->m_FixedImage;

  if (!fixedImage)
  {
    itkExceptionMacro("Fixed image has not been assigned");
  }

  double MovingValue;
  double FixedValue;

  using FixedIteratorType = itk::ImageRegionConstIteratorWithIndex<FixedImageType>;

  FixedIteratorType ti(fixedImage, this->GetFixedImageRegion());

  typename FixedImageType::IndexType index;

  MeasureType measure{};

  this->m_NumberOfPixelsCounted = 0;

  this->SetTransformParameters(parameters);

  while (!ti.IsAtEnd())
  {
    index = ti.GetIndex();

    InputPointType inputPoint;
    fixedImage->TransformIndexToPhysicalPoint(index, inputPoint);

    if (this->m_FixedImageMask && !this->m_FixedImageMask->IsInsideInWorldSpace(inputPoint))
    {
      ++ti;
      continue;
    }

    TransformType const * transform = this->m_Transform;
    OutputPointType       transformedPoint = transform->TransformPoint(inputPoint);

    if (this->m_MovingImageMask && !this->m_MovingImageMask->IsInsideInWorldSpace(transformedPoint))
    {
      ++ti;
      continue;
    }

    if (this->m_Interpolator->IsInsideBuffer(transformedPoint))
    {
      MovingValue = this->m_Interpolator->Evaluate(transformedPoint);
      FixedValue = ti.Get();
      this->m_NumberOfPixelsCounted++;
      const double diff = MovingValue - FixedValue;
      measure += 1.0f / (1.0f + m_Lambda * (diff * diff));
    }

    ++ti;
  }

  return measure;
}

template <typename TFixedImage, typename TMovingImage>
void
MeanReciprocalSquareDifferenceImageToImageMetric<TFixedImage, TMovingImage>::GetDerivative(
  const TransformParametersType & parameters,
  DerivativeType &                derivative) const
{
  TransformParametersType testPoint;

  testPoint = parameters;

  const unsigned int numberOfParameters = this->GetNumberOfParameters();
  derivative = DerivativeType(numberOfParameters);

  for (unsigned int i = 0; i < numberOfParameters; ++i)
  {
    testPoint[i] -= m_Delta;
    const MeasureType valuep0 = this->GetValue(testPoint);
    testPoint[i] += 2 * m_Delta;
    const MeasureType valuep1 = this->GetValue(testPoint);
    derivative[i] = (valuep1 - valuep0) / (2 * m_Delta);
    testPoint[i] = parameters[i];
  }
}

template <typename TFixedImage, typename TMovingImage>
void
MeanReciprocalSquareDifferenceImageToImageMetric<TFixedImage, TMovingImage>::GetValueAndDerivative(
  const TransformParametersType & parameters,
  MeasureType &                   Value,
  DerivativeType &                Derivative) const
{
  Value = this->GetValue(parameters);
  this->GetDerivative(parameters, Derivative);
}
} // end namespace itk

#endif
