/*=========================================================================
 *
 *  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 itkDiscreteGaussianDerivativeImageFunction_hxx
#define itkDiscreteGaussianDerivativeImageFunction_hxx

#include "itkNeighborhoodOperatorImageFilter.h"

namespace itk
{
/** Set the Input Image */
template <typename TInputImage, typename TOutput>
DiscreteGaussianDerivativeImageFunction<TInputImage, TOutput>::DiscreteGaussianDerivativeImageFunction()
{
  m_Variance.Fill(1.0);
  m_Order.Fill(0);
  m_Order[0] = 1; // by default calculate derivative in x
  m_OperatorImageFunction = OperatorImageFunctionType::New();
}

/** Print self method */
template <typename TInputImage, typename TOutput>
void
DiscreteGaussianDerivativeImageFunction<TInputImage, TOutput>::PrintSelf(std::ostream & os, Indent indent) const
{
  this->Superclass::PrintSelf(os, indent);
  os << indent << "UseImageSpacing: " << (m_UseImageSpacing ? "On" : "Off") << std::endl;
  os << indent << "NormalizeAcrossScale: " << m_NormalizeAcrossScale << std::endl;
  os << indent << "Variance: " << m_Variance << std::endl;
  os << indent << "Order: " << m_Order << std::endl;
  os << indent << "MaximumError: " << m_MaximumError << std::endl;
  os << indent << "MaximumKernelWidth: " << m_MaximumKernelWidth << std::endl;
  os << indent << "InterpolationMode: " << m_InterpolationMode << std::endl;
  os << indent << "OperatorArray: " << m_OperatorArray << std::endl;
  os << indent << "DerivativeKernel: " << m_DerivativeKernel << std::endl;
  os << indent << "OperatorImageFunction: " << m_OperatorImageFunction << std::endl;
}

/** Set the input image */
template <typename TInputImage, typename TOutput>
void
DiscreteGaussianDerivativeImageFunction<TInputImage, TOutput>::SetInputImage(const InputImageType * ptr)
{
  Superclass::SetInputImage(ptr);
  m_OperatorImageFunction->SetInputImage(ptr);
}

/** Recompute the gaussian kernel used to evaluate indexes
 *  This should use a fastest Derivative Gaussian operator */
template <typename TInputImage, typename TOutput>
void
DiscreteGaussianDerivativeImageFunction<TInputImage, TOutput>::RecomputeGaussianKernel()
{
  // Create N operators (N=ImageDimension) with the order specified in m_Order
  unsigned int idx;

  for (unsigned int direction = 0; direction < Self::ImageDimension2; ++direction)
  {
    m_OperatorArray[direction].SetDirection(direction);
    m_OperatorArray[direction].SetMaximumKernelWidth(m_MaximumKernelWidth);
    m_OperatorArray[direction].SetMaximumError(m_MaximumError);

    if (m_UseImageSpacing && (this->GetInputImage()))
    {
      if (this->GetInputImage()->GetSpacing()[direction] == 0.0)
      {
        itkExceptionMacro("Pixel spacing cannot be zero");
      }
      else
      {
        m_OperatorArray[direction].SetSpacing(this->GetInputImage()->GetSpacing()[direction]);
      }
    }

    // GaussianDerivativeOperator modifies the variance when setting
    // image spacing
    m_OperatorArray[direction].SetVariance(m_Variance[direction]);
    m_OperatorArray[direction].SetOrder(m_Order[direction]);
    m_OperatorArray[direction].SetNormalizeAcrossScale(m_NormalizeAcrossScale);
    m_OperatorArray[direction].CreateDirectional();
  }

  // Now precompute the n-dimensional kernel. This fastest as we don't
  // have to perform N convolutions for each point we calculate but
  // only one.

  using KernelImageType = itk::Image<TOutput, Self::ImageDimension2>;
  auto kernelImage = KernelImageType::New();

  using RegionType = typename KernelImageType::RegionType;
  RegionType region;

  typename RegionType::SizeType size;
  size.Fill(4 * m_OperatorArray[0].GetRadius()[0] + 1);
  region.SetSize(size);

  kernelImage->SetRegions(region);
  kernelImage->AllocateInitialized();

  // Initially the kernel image will be an impulse at the center
  typename KernelImageType::IndexType centerIndex;
  centerIndex.Fill(2 * m_OperatorArray[0].GetRadius()[0]); // include also
                                                           // boundaries
  kernelImage->SetPixel(centerIndex, itk::NumericTraits<TOutput>::OneValue());

  // Create an image region to be used later that does not include boundaries
  RegionType kernelRegion;
  size.Fill(2 * m_OperatorArray[0].GetRadius()[0] + 1);
  typename RegionType::IndexType origin;
  origin.Fill(m_OperatorArray[0].GetRadius()[0]);
  kernelRegion.SetSize(size);
  kernelRegion.SetIndex(origin);

  // Now create an image filter to perform successive convolutions
  using NeighborhoodFilterType = itk::NeighborhoodOperatorImageFilter<KernelImageType, KernelImageType>;
  auto convolutionFilter = NeighborhoodFilterType::New();

  for (unsigned int direction = 0; direction < Self::ImageDimension2; ++direction)
  {
    convolutionFilter->SetInput(kernelImage);
    convolutionFilter->SetOperator(m_OperatorArray[direction]);
    convolutionFilter->Update();
    kernelImage = convolutionFilter->GetOutput();
    kernelImage->DisconnectPipeline();
  }

  // Set the size of the kernel
  m_DerivativeKernel.SetRadius(m_OperatorArray[0].GetRadius()[0]);

  // Copy kernel image to neighborhood. Do not copy boundaries.
  ImageRegionConstIterator<KernelImageType> it(kernelImage, kernelRegion);
  it.GoToBegin();
  idx = 0;

  while (!it.IsAtEnd())
  {
    m_DerivativeKernel[idx] = it.Get();
    ++idx;
    ++it;
  }
}

/** Evaluate the function at the specified index */
template <typename TInputImage, typename TOutput>
auto
DiscreteGaussianDerivativeImageFunction<TInputImage, TOutput>::EvaluateAtIndex(const IndexType & index) const
  -> OutputType
{
  OutputType derivative;

  m_OperatorImageFunction->SetOperator(m_DerivativeKernel);
  derivative = m_OperatorImageFunction->EvaluateAtIndex(index);


  return derivative;
}

/** Evaluate the function at the specified point */
template <typename TInputImage, typename TOutput>
auto
DiscreteGaussianDerivativeImageFunction<TInputImage, TOutput>::Evaluate(const PointType & point) const -> OutputType
{
  if (m_InterpolationMode == InterpolationModeEnum::NearestNeighbourInterpolation)
  {
    IndexType index;
    this->ConvertPointToNearestIndex(point, index);
    return this->EvaluateAtIndex(index);
  }
  else
  {
    ContinuousIndexType cindex;
    this->ConvertPointToContinuousIndex(point, cindex);
    return this->EvaluateAtContinuousIndex(cindex);
  }
}

/** Evaluate the function at specified ContinuousIndex position.*/
template <typename TInputImage, typename TOutput>
auto
DiscreteGaussianDerivativeImageFunction<TInputImage, TOutput>::EvaluateAtContinuousIndex(
  const ContinuousIndexType & cindex) const -> OutputType
{
  if (m_InterpolationMode == InterpolationModeEnum::NearestNeighbourInterpolation)
  {
    IndexType index;
    this->ConvertContinuousIndexToNearestIndex(cindex, index);
    return this->EvaluateAtIndex(index);
  }
  else
  {
    using NumberOfNeighborsType = unsigned int;

    unsigned int          dim; // index over dimension
    NumberOfNeighborsType numberOfNeighbors = 1 << ImageDimension2;

    // Compute base index = closet index below point
    // Compute distance from point to base index
    IndexType baseIndex;
    double    distance[ImageDimension2];

    for (dim = 0; dim < ImageDimension2; ++dim)
    {
      baseIndex[dim] = Math::Floor<IndexValueType>(cindex[dim]);
      distance[dim] = cindex[dim] - static_cast<double>(baseIndex[dim]);
    }

    // Interpolated value is the weighted sum of each of the surrounding
    // neighbors. The weight for each neighbor is the fraction overlap
    // of the neighbor pixel with respect to a pixel centered on point.
    TOutput value{};
    TOutput totalOverlap{};

    for (NumberOfNeighborsType counter = 0; counter < numberOfNeighbors; ++counter)
    {
      double                overlap = 1.0;   // fraction overlap
      NumberOfNeighborsType upper = counter; // each bit indicates upper/lower neighbour
      IndexType             neighIndex;

      // get neighbor index and overlap fraction
      for (dim = 0; dim < ImageDimension2; ++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)
      {
        value += overlap * static_cast<TOutput>(this->EvaluateAtIndex(neighIndex));
        totalOverlap += overlap;
      }

      if (totalOverlap == 1.0)
      {
        // finished
        break;
      }
    }
    return (static_cast<OutputType>(value));
  }
}
} // end namespace itk

#endif