/*=========================================================================
 *
 *  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 itkGaussianExponentialDiffeomorphicTransform_hxx
#define itkGaussianExponentialDiffeomorphicTransform_hxx


#include "itkAddImageFilter.h"
#include "itkImageDuplicator.h"
#include "itkImportImageFilter.h"
#include "itkMultiplyImageFilter.h"

namespace itk
{

template <typename TParametersValueType, unsigned int VDimension>
GaussianExponentialDiffeomorphicTransform<TParametersValueType, VDimension>::GaussianExponentialDiffeomorphicTransform()
  : m_GaussianSmoothingVarianceForTheUpdateField(0.5)
  , m_GaussianSmoothingVarianceForTheConstantVelocityField(0.5)
{}

template <typename TParametersValueType, unsigned int VDimension>
void
GaussianExponentialDiffeomorphicTransform<TParametersValueType, VDimension>::UpdateTransformParameters(
  const DerivativeType & update,
  ScalarType             factor)
{
  //
  // Smooth the update field
  //
  bool smoothUpdateField = true;
  if (this->m_GaussianSmoothingVarianceForTheUpdateField <= 0.0)
  {
    itkDebugMacro("Not smooothing the update field.");
    smoothUpdateField = false;
  }

  ConstantVelocityFieldPointer velocityField = this->GetModifiableConstantVelocityField();
  if (!velocityField)
  {
    itkExceptionMacro("The velocity field has not been set.");
  }

  const typename ConstantVelocityFieldType::RegionType & bufferedRegion = velocityField->GetBufferedRegion();
  const SizeValueType                                    numberOfPixels = bufferedRegion.GetNumberOfPixels();

  auto * updateFieldPointer =
    reinterpret_cast<DisplacementVectorType *>(const_cast<DerivativeType &>(update).data_block());

  using ImporterType = ImportImageFilter<DisplacementVectorType, VDimension>;
  const bool importFilterWillReleaseMemory = false;

  auto importer = ImporterType::New();
  importer->SetImportPointer(updateFieldPointer, numberOfPixels, importFilterWillReleaseMemory);
  importer->SetRegion(velocityField->GetBufferedRegion());
  importer->SetOrigin(velocityField->GetOrigin());
  importer->SetSpacing(velocityField->GetSpacing());
  importer->SetDirection(velocityField->GetDirection());

  ConstantVelocityFieldPointer updateField = importer->GetOutput();
  updateField->Update();
  updateField->DisconnectPipeline();

  if (smoothUpdateField)
  {
    itkDebugMacro("Smoothing the update field.");

    ConstantVelocityFieldPointer updateSmoothField =
      this->GaussianSmoothConstantVelocityField(updateField, this->m_GaussianSmoothingVarianceForTheUpdateField);

    updateField = updateSmoothField;
  }

  using RealImageType = Image<ScalarType, VDimension>;

  using MultiplierType = MultiplyImageFilter<ConstantVelocityFieldType, RealImageType, ConstantVelocityFieldType>;
  auto multiplier = MultiplierType::New();
  multiplier->SetInput(updateField);
  multiplier->SetConstant(factor);
  multiplier->Update();

  using AdderType = AddImageFilter<ConstantVelocityFieldType, ConstantVelocityFieldType, ConstantVelocityFieldType>;
  auto adder = AdderType::New();
  adder->SetInput1(velocityField);
  adder->SetInput2(multiplier->GetOutput());

  ConstantVelocityFieldPointer updatedVelocityField = adder->GetOutput();
  updatedVelocityField->Update();
  updatedVelocityField->DisconnectPipeline();

  //
  // Smooth the velocity field
  //
  bool smoothVelocityField = true;
  if (this->m_GaussianSmoothingVarianceForTheConstantVelocityField <= 0)
  {
    itkDebugMacro("Not smoothing the velocity field.");
    smoothVelocityField = false;
  }

  if (smoothVelocityField)
  {
    itkDebugMacro("Smoothing the velocity field.");

    // The update field is the velocity field but since it's constant
    // we smooth it using the parent class smoothing functionality

    ConstantVelocityFieldPointer velocitySmoothField = this->GaussianSmoothConstantVelocityField(
      updatedVelocityField, this->m_GaussianSmoothingVarianceForTheConstantVelocityField);

    this->SetConstantVelocityField(velocitySmoothField);
  }
  else
  {
    this->SetConstantVelocityField(updatedVelocityField);
  }

  this->IntegrateVelocityField();
}

template <typename TParametersValueType, unsigned int VDimension>
auto
GaussianExponentialDiffeomorphicTransform<TParametersValueType, VDimension>::GaussianSmoothConstantVelocityField(
  ConstantVelocityFieldType * field,
  ScalarType                  variance) -> ConstantVelocityFieldPointer
{
  if (variance <= 0.0)
  {
    return field;
  }

  using DuplicatorType = ImageDuplicator<ConstantVelocityFieldType>;
  auto duplicator = DuplicatorType::New();
  duplicator->SetInputImage(field);
  duplicator->Update();

  ConstantVelocityFieldPointer smoothField = duplicator->GetOutput();

  auto smoother = GaussianSmoothingSmootherType::New();

  for (unsigned int dimension = 0; dimension < Superclass::Dimension; ++dimension)
  {
    // smooth along this dimension
    this->m_GaussianSmoothingOperator.SetDirection(dimension);
    this->m_GaussianSmoothingOperator.SetVariance(variance);
    this->m_GaussianSmoothingOperator.SetMaximumError(0.001);
    this->m_GaussianSmoothingOperator.SetMaximumKernelWidth(smoothField->GetRequestedRegion().GetSize()[dimension]);
    this->m_GaussianSmoothingOperator.CreateDirectional();

    // todo: make sure we only smooth within the buffered region
    smoother->SetOperator(this->m_GaussianSmoothingOperator);
    smoother->SetInput(smoothField);
    try
    {
      smoother->Update();
    }
    catch (const ExceptionObject & exc)
    {
      std::string msg("Caught exception: ");
      msg += exc.what();
      itkExceptionMacro(<< msg);
    }

    smoothField = smoother->GetOutput();
    smoothField->Update();
    smoothField->DisconnectPipeline();
  }

  constexpr DisplacementVectorType zeroVector{};

  // make sure boundary does not move
  ScalarType weight1 = 1.0;
  if (variance < 0.5)
  {
    weight1 = 1.0 - 1.0 * (variance / 0.5);
  }
  ScalarType weight2 = 1.0 - weight1;

  const typename ConstantVelocityFieldType::RegionType region = field->GetLargestPossibleRegion();
  const typename ConstantVelocityFieldType::SizeType   size = region.GetSize();
  const typename ConstantVelocityFieldType::IndexType  startIndex = region.GetIndex();

  ImageRegionIteratorWithIndex<ConstantVelocityFieldType>      fieldIt(field, field->GetLargestPossibleRegion());
  ImageRegionConstIteratorWithIndex<ConstantVelocityFieldType> smoothedFieldIt(smoothField,
                                                                               smoothField->GetLargestPossibleRegion());
  for (fieldIt.GoToBegin(), smoothedFieldIt.GoToBegin(); !fieldIt.IsAtEnd(); ++fieldIt, ++smoothedFieldIt)
  {
    typename ConstantVelocityFieldType::IndexType index = fieldIt.GetIndex();
    bool                                          isOnBoundary = false;
    for (unsigned int dimension = 0; dimension < Dimension; ++dimension)
    {
      if (index[dimension] == startIndex[dimension] ||
          index[dimension] == static_cast<IndexValueType>(size[dimension]) - startIndex[dimension] - 1)
      {
        isOnBoundary = true;
        break;
      }
    }
    if (isOnBoundary)
    {
      fieldIt.Set(zeroVector);
    }
    else
    {
      fieldIt.Set(smoothedFieldIt.Get() * weight1 + fieldIt.Get() * weight2);
    }
  }

  return field;
}

template <typename TParametersValueType, unsigned int VDimension>
void
GaussianExponentialDiffeomorphicTransform<TParametersValueType, VDimension>::PrintSelf(std::ostream & os,
                                                                                       Indent         indent) const
{
  Superclass::PrintSelf(os, indent);

  os << indent << "GaussianSmoothingVarianceForTheConstantVelocityField: "
     << static_cast<typename NumericTraits<ScalarType>::PrintType>(
          m_GaussianSmoothingVarianceForTheConstantVelocityField)
     << std::endl;
  os << indent << "GaussianSmoothingVarianceForTheUpdateField: "
     << static_cast<typename NumericTraits<ScalarType>::PrintType>(m_GaussianSmoothingVarianceForTheUpdateField)
     << std::endl;
}

} // namespace itk

#endif