/*=========================================================================
 *
 *  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 itkLevelSetEquationTermBase_h
#define itkLevelSetEquationTermBase_h

#include "itkObject.h"
#include "itkHeavisideStepFunctionBase.h"
#include <unordered_set>

namespace itk
{
/**
 *  \class LevelSetEquationTermBase
 *  \brief Abstract class to represents a term in the level-set evolution PDE
 *
 *  \tparam TInput Input Image Type
 *  \tparam TLevelSetContainer Level set function container type
 *
 *  Evolving single level-set function \f$ \phi \f$ can be expressed as follows:
 *  \f[
 *  \frac{\partial \phi(p)}{\partial \tau} = \sum\limits_{i=1}^{N} \alpha_{i} \cdot \omega_i(p)
 *  \f]
 *  where \f$\omega_i\f$ is a term which could depend on the level-set function,
 *  the input image; and \f$\alpha_i\f$ is a weight to balance the contribution of
 *  each term in the PDE.
 *
 *  \sa LevelSetEquationContainer
 *
 *  \ingroup ITKLevelSetsv4
 */
template <typename TInputImage, // Input image
          typename TLevelSetContainer>
class ITK_TEMPLATE_EXPORT LevelSetEquationTermBase : public Object
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(LevelSetEquationTermBase);

  using Self = LevelSetEquationTermBase;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;
  using Superclass = Object;

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

  using InputImageType = TInputImage;
  using InputImagePointer = typename InputImageType::Pointer;
  using InputPixelType = typename InputImageType::PixelType;
  using InputPixelRealType = typename NumericTraits<InputPixelType>::RealType;

  /** Level-set function container type */
  using LevelSetContainerType = TLevelSetContainer;
  using LevelSetIdentifierType = typename LevelSetContainerType::LevelSetIdentifierType;
  using LevelSetContainerPointer = typename LevelSetContainerType::Pointer;
  using LevelSetType = typename LevelSetContainerType::LevelSetType;
  using LevelSetPointer = typename LevelSetContainerType::LevelSetPointer;
  using LevelSetOutputPixelType = typename LevelSetContainerType::OutputType;
  using LevelSetOutputRealType = typename LevelSetContainerType::OutputRealType;
  using LevelSetInputIndexType = typename LevelSetContainerType::InputIndexType;
  using LevelSetGradientType = typename LevelSetContainerType::GradientType;
  using LevelSetHessianType = typename LevelSetContainerType::HessianType;
  using LevelSetDataType = typename LevelSetContainerType::LevelSetDataType;

  using DomainMapImageFilterType = typename LevelSetContainerType::DomainMapImageFilterType;
  using CacheImageType = typename LevelSetContainerType::CacheImageType;

  using HeavisideType = HeavisideStepFunctionBase<LevelSetOutputRealType, LevelSetOutputRealType>;
  //  using HeavisidePointer = typename HeavisideType::Pointer;
  using HeavisideConstPointer = typename HeavisideType::ConstPointer;

  /** Set/Get the image to be segmented */
  itkSetObjectMacro(Input, InputImageType);
  itkGetModifiableObjectMacro(Input, InputImageType);

  itkSetMacro(Coefficient, LevelSetOutputRealType);
  itkGetMacro(Coefficient, LevelSetOutputRealType);

  itkSetMacro(CurrentLevelSetId, LevelSetIdentifierType);
  itkGetMacro(CurrentLevelSetId, LevelSetIdentifierType);

  itkGetModifiableObjectMacro(CurrentLevelSetPointer, LevelSetType);

  virtual void
  SetLevelSetContainer(LevelSetContainerType * iContainer);
  itkGetModifiableObjectMacro(LevelSetContainer, LevelSetContainerType);

  /** Returns the weighted term contribution at the given location iP, i.e.
   *  \f$ \alpha_i \cdot \omega_i( p ) \f$
   */
  virtual LevelSetOutputRealType
  Evaluate(const LevelSetInputIndexType & iP);

  virtual LevelSetOutputRealType
  Evaluate(const LevelSetInputIndexType & iP, const LevelSetDataType & iData);

  /** \todo to be documented. */
  virtual void
  Initialize(const LevelSetInputIndexType & iP) = 0;

  /** Initialize the parameters in the terms prior to an iteration */
  virtual void
  InitializeParameters() = 0;

  /** Supply updates at pixels to keep the term parameters always updated */
  virtual void
  UpdatePixel(const LevelSetInputIndexType & iP,
              const LevelSetOutputRealType & oldValue,
              const LevelSetOutputRealType & newValue) = 0;

  /** Get the CFL contribution for the given term */
  itkGetConstMacro(CFLContribution, LevelSetOutputRealType);

  /** Set/Get the term name */
  itkSetStringMacro(TermName);
  itkGetStringMacro(TermName);

  /** Update the term parameter values at end of iteration */
  virtual void
  Update() = 0;

  using RequiredDataType = std::unordered_set<std::string>;

  const RequiredDataType &
  GetRequiredData() const;

protected:
  /** Default Constructor */
  LevelSetEquationTermBase();

  /** Destructor */
  ~LevelSetEquationTermBase() override = default;

  void
  SetUp();

  /** Returns the term contribution for a given location iP, i.e.
   *  \f$ \omega_i( p ) \f$. This method must be implemented in all
   *  class which inherits from this class.
   */
  virtual LevelSetOutputRealType
  Value(const LevelSetInputIndexType & iP) = 0;

  virtual LevelSetOutputRealType
  Value(const LevelSetInputIndexType & iP, const LevelSetDataType & iData) = 0;

  /** Input image */
  InputImagePointer m_Input{};

  /** Container of level-set function */
  LevelSetContainerPointer m_LevelSetContainer{};

  /** Id of the current level-set function */
  LevelSetIdentifierType m_CurrentLevelSetId{};

  LevelSetPointer m_CurrentLevelSetPointer{};

  /** Coefficient \f$ \alpha_i \f$ */
  LevelSetOutputRealType m_Coefficient{};

  /** Contribution to the CFL condition (which will be used to compute the
   *  the time step at the next iteration
   */
  LevelSetOutputRealType m_CFLContribution{};

  /** Heaviside function to be used. Depending on the term expression,
   *  this one may need to be provided
   */
  HeavisideConstPointer m_Heaviside{};

  /** Name to be given to the term. Note by default, one name is provided,
   *  but end-users may rename differently each term.
   */
  std::string m_TermName{};

  RequiredDataType m_RequiredData{};
};
} // namespace itk

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

#endif
