/*=========================================================================
 *
 *  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 itkGPUPDEDeformableRegistrationFilter_h
#define itkGPUPDEDeformableRegistrationFilter_h

#include "itkGPUDenseFiniteDifferenceImageFilter.h"
#include "itkGPUPDEDeformableRegistrationFunction.h"
#include "itkPDEDeformableRegistrationFilter.h"

namespace itk
{
/**
 * \class GPUPDEDeformableRegistrationFilter
 * \brief Deformably register two images using a PDE algorithm.
 *
 * GPUPDEDeformableRegistrationFilter is a base case for filter implementing
 * a PDE deformable algorithm that register two images by computing the
 * deformation field which will map a moving image onto a fixed image.
 *
 * A deformation field is represented as a image whose pixel type is some
 * vector type with at least N elements, where N is the dimension of
 * the fixed image. The vector type must support element access via operator
 * []. It is assumed that the vector elements behave like floating point
 * scalars.
 *
 * This class is templated over the fixed image type, moving image type
 * and the deformation Field type.
 *
 * The input fixed and moving images are set via methods SetFixedImage
 * and SetMovingImage respectively. An initial deformation field maybe set via
 * SetInitialDisplacementField or SetInput. If no initial field is set,
 * a zero field is used as the initial condition.
 *
 * The output deformation field can be obtained via methods GetOutput
 * or GetDisplacementField.
 *
 * The PDE algorithm is run for a user defined number of iterations.
 * Typically the PDE algorithm requires period Gaussian smoothing of the
 * deformation field to enforce an elastic-like condition. The amount
 * of smoothing is governed by a set of user defined standard deviations
 * (one for each dimension).
 *
 * In terms of memory, this filter keeps two internal buffers: one for storing
 * the intermediate updates to the field and one for double-buffering when
 * smoothing the deformation field. Both buffers are the same type and size as the
 * output deformation field.
 *
 * This class make use of the finite difference solver hierarchy. Update
 * for each iteration is computed using a PDEDeformableRegistrationFunction.
 *
 * \warning This filter assumes that the fixed image type, moving image type
 * and deformation field type all have the same number of dimensions.
 *
 * \sa PDEDeformableRegistrationFunction.
 * \ingroup DeformableImageRegistration
 * \ingroup ITKPDEDeformableRegistration
 * \ingroup ITKGPUPDEDeformableRegistration
 */

/** Create a helper GPU Kernel class for GPUPDEDeformableRegistrationFilter */
itkGPUKernelClassMacro(GPUPDEDeformableRegistrationFilterKernel);

template <typename TFixedImage,
          typename TMovingImage,
          typename TDisplacementField,
          typename TParentImageFilter = PDEDeformableRegistrationFilter<TFixedImage, TMovingImage, TDisplacementField>>
class ITK_TEMPLATE_EXPORT GPUPDEDeformableRegistrationFilter
  : public GPUDenseFiniteDifferenceImageFilter<TDisplacementField, TDisplacementField, TParentImageFilter>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(GPUPDEDeformableRegistrationFilter);

  /** Standard class type aliases. */
  using Self = GPUPDEDeformableRegistrationFilter;
  using GPUSuperclass = GPUDenseFiniteDifferenceImageFilter<TDisplacementField, TDisplacementField, TParentImageFilter>;
  using CPUSuperclass = TParentImageFilter;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  /** Method for creation through the object factory. */
  itkNewMacro(Self);

  /** \see LightObject::GetNameOfClass() */
  itkOverrideGetNameOfClassMacro(GPUPDEDeformableRegistrationFilter);

  /** FixedImage image type. */
  using FixedImageType = TFixedImage;
  using FixedImagePointer = typename FixedImageType::Pointer;
  using FixedImageConstPointer = typename FixedImageType::ConstPointer;

  /** MovingImage image type. */
  using MovingImageType = TMovingImage;
  using MovingImagePointer = typename MovingImageType::Pointer;
  using MovingImageConstPointer = typename MovingImageType::ConstPointer;

  /** Deformation field type. */
  using DisplacementFieldType = TDisplacementField;
  using DisplacementFieldPointer = typename DisplacementFieldType::Pointer;
  using DeformationVectorType = typename TDisplacementField::PixelType;
  using DeformationScalarType = typename TDisplacementField::PixelType::ValueType;

  /** Types inherited from the GPUSuperclass */
  using OutputImageType = typename GPUSuperclass::OutputImageType;

  /** FiniteDifferenceFunction type. */
  using FiniteDifferenceFunctionType = typename GPUSuperclass::FiniteDifferenceFunctionType;

  /** PDEDeformableRegistrationFilterFunction type. */
  /** GPUPDEDeformableRegistrationFilterFunction type. */
  using GPUPDEDeformableRegistrationFunctionType =
    GPUPDEDeformableRegistrationFunction<FixedImageType, MovingImageType, DisplacementFieldType>;

  /** Inherit some enums and type alias from the GPUSuperclass. */
  static constexpr unsigned int ImageDimension = GPUSuperclass::ImageDimension;

  /** Get OpenCL Kernel source as a string, creates a GetOpenCLSource method */
  itkGetOpenCLSourceFromKernelMacro(GPUPDEDeformableRegistrationFilterKernel);

  /** Get output deformation field. */
  DisplacementFieldType *
  GetDisplacementField()
  {
    return this->GetOutput();
  }

  using StandardDeviationsType = FixedArray<double, ImageDimension>;

protected:
  GPUPDEDeformableRegistrationFilter();
  ~GPUPDEDeformableRegistrationFilter() override = default;

  void
  PrintSelf(std::ostream & os, Indent indent) const override;

  /** Copy the data from the input to the output.
   *
   * If the input does not exist, a zero field is written to the output. */
  void
  CopyInputToOutput() override;

  /** Initialize the state of filter and equation before each iteration.
   * Progress feedback is implemented as part of this method. */
  void
  InitializeIteration() override;

  /** Utility to smooth the deformation field (represented in the Output)
   * using a separable Gaussian kernel. The amount of smoothing can be specified
   * by setting the StandardDeviations. */
  void
  SmoothDisplacementField() override;

  /** Smooth a vector field using a separable Gaussian kernel.
   *
   * The smoothed field may be m_DisplacementField or m_UpdateBuffer.
   */
  virtual void
  GPUSmoothVectorField(DisplacementFieldPointer         field,
                       typename GPUDataManager::Pointer GPUSmoothingKernels[],
                       int                              GPUSmoothingKernelSizes[]);

  virtual void
  AllocateSmoothingBuffer();

  /** Smooth the UpdateBuffer using a separable Gaussian kernel.
   * The amount of smoothing can be specified by setting the
   * UpdateFieldStandardDeviations. */
  void
  SmoothUpdateField() override;

  /** Release the memory of the internal buffers.
   *
   * Called after the solution has been generated.
   */
  void
  PostProcessOutput() override;

  /** Initialize flags.
   *
   * Called before iterating the solution.
   */
  void
  Initialize() override;

  /** By default the output deformation field has the same Spacing, Origin
   * and LargestPossibleRegion as the input/initial deformation field.  If
   * the initial deformation field is not set, the output information is
   * copied from the fixed image. */
  void
  GenerateOutputInformation() override;

  /** It is difficult to compute in advance the input moving image region
   * required to compute the requested output region. Thus the safest
   * thing to do is to request for the whole moving image.
   *
   * For the fixed image and deformation field, the input requested region
   * set to be the same as that of the output requested region. */
  void
  GenerateInputRequestedRegion() override;

private:
  /** Temporary deformation field use for smoothing the
   * the deformation field. */
  DisplacementFieldPointer m_TempField{};

private:
  /** Memory buffer for smoothing kernels of the displacement field. */
  int                              m_SmoothingKernelSizes[ImageDimension]{};
  DeformationScalarType *          m_SmoothingKernels[ImageDimension]{};
  typename GPUDataManager::Pointer m_GPUSmoothingKernels[ImageDimension]{};

  /** Memory buffer for smoothing kernels of the update field. */
  int                              m_UpdateFieldSmoothingKernelSizes[ImageDimension]{};
  DeformationScalarType *          m_UpdateFieldSmoothingKernels[ImageDimension]{};
  typename GPUDataManager::Pointer m_UpdateFieldGPUSmoothingKernels[ImageDimension]{};

  int *                            m_ImageSizes{};
  typename GPUDataManager::Pointer m_GPUImageSizes{};

  /* GPU kernel handle for GPUSmoothDisplacementField */
  int m_SmoothDisplacementFieldGPUKernelHandle{};
};
} // end namespace itk

#ifndef ITK_MANUAL_INSTANTIATION
#  include "itkGPUPDEDeformableRegistrationFilter.hxx"
#endif

#endif
