/*=========================================================================
 *
 *  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 itkImageModelEstimatorBase_h
#define itkImageModelEstimatorBase_h

#include "itkLightProcessObject.h"

namespace itk
{
/**
 * \class ImageModelEstimatorBase
 * \brief Base class for model estimation from images used for classification.
 *
 * itkImageModelEstimatorBase is the base class for the ImageModelEstimator
 * objects. It provides the basic function definitions that are inherent to
 * ImageModelEstimator objects.
 *
 * This is the Superclass for the ImageModelEstimator framework. This is an
 * abstract class defining an interface for all such objects
 * available through the ImageModelEstimator framework in the ITK toolkit.
 *
 * The basic functionality of the ImageModelEstimator framework base class is to
 * generate the models used in classification applications. It requires input
 * images and a training image to be provided by the user.
 * This object supports data handling of multiband images. The object
 * accepts the input image in vector format only, where each pixel is a
 * vector and each element of the vector corresponds to an entry from
 * 1 particular band of a multiband dataset. A single band image is treated
 * as a vector image with a single element for every vector. The classified
 * image is treated as a single band scalar image.
 *
 * EstimateModels() is a pure virtual function making this an abstract class.
 * The template parameter is the type of membership function the
 * ImageModelEstimator populates.
 *
 * A membership function represents a specific knowledge about
 * a class. In other words, it should tell us how "likely" is that a
 * measurement vector (pattern) belong to the class.
 *
 * As the method name indicates, you can have more than one membership
 * function. One for each classes. The order of the membership
 * calculator becomes the class label for the class that is represented
 * by the membership calculator.
 *
 * \ingroup ClassificationFilters
 * \ingroup ITKClassifiers
 */
template <typename TInputImage, typename TMembershipFunction>
class ITK_TEMPLATE_EXPORT ImageModelEstimatorBase : public LightProcessObject
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(ImageModelEstimatorBase);

  /** Standard class type aliases. */
  using Self = ImageModelEstimatorBase;
  using Superclass = LightProcessObject;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

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

  /** Set the number of classes. */
  itkSetMacro(NumberOfModels, unsigned int);

  /** Get the number of classes. */
  itkGetConstReferenceMacro(NumberOfModels, unsigned int);

  /** Type definitions for the membership function . */
  using MembershipFunctionPointer = typename TMembershipFunction::Pointer;

  using MembershipFunctionPointerVector = std::vector<MembershipFunctionPointer>;

  /** Type definitions for the training image. */
  using InputImageType = TInputImage;
  using InputImagePointer = typename TInputImage::Pointer;

  /** Type definitions for the training image. */
  // using TrainingImagePointer = typename TTrainingImage::Pointer;

  /** Get/Set the input image. */
  itkSetObjectMacro(InputImage, InputImageType);
  itkGetModifiableObjectMacro(InputImage, InputImageType);

  /** Set the classified image. */
  void
  SetMembershipFunctions(MembershipFunctionPointerVector membershipFunctions)
  {
    m_MembershipFunctions = membershipFunctions;
  }

  /** Method to get mean */
  const MembershipFunctionPointerVector
  GetMembershipFunctions() const
  {
    return m_MembershipFunctions;
  }

  /** Method to number of membership functions */
  unsigned int
  GetNumberOfMembershipFunctions()
  {
    return static_cast<unsigned int>(m_MembershipFunctions.size());
  }

  /** Method to reset the membership function mean */
  void
  DeleteAllMembershipFunctions()
  {
    m_MembershipFunctions.resize(0);
  }

  /** Add a membership function corresponding to the class index.
   *
   * Stores a MembershipCalculator of a class in its internal vector.
   */
  unsigned int
  AddMembershipFunction(MembershipFunctionPointer function);

  /** Define a virtual function to perform model generation from the input data
   */
  void
  Update();

protected:
  ImageModelEstimatorBase();
  ~ImageModelEstimatorBase() override = default;
  void
  PrintSelf(std::ostream & os, Indent indent) const override;

  void
  GenerateData() override;

private:
  unsigned int m_NumberOfModels{ 0 };

  /** Container to hold the membership functions */
  MembershipFunctionPointerVector m_MembershipFunctions{};

  /**Container for holding the training image */
  InputImagePointer m_InputImage{};

  /** The core virtual function to perform modeling of the input data */
  virtual void
  EstimateModels() = 0;
}; // class ImageModelEstimator
} // namespace itk

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

#endif