/*=========================================================================
 *
 *  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 itkCumulativeGaussianCostFunction_h
#define itkCumulativeGaussianCostFunction_h

#include "itkMultipleValuedCostFunction.h"
#include "ITKOptimizersExport.h"

namespace itk
{
/** \class CumulativeGaussianCostFunction
 * \brief Cost function for the Cumulative Gaussian Optimizer.
 *
 * The Cumulative Gaussian is defined as the integral of
 * a normalized Gaussian over the domain \f$ [-\infty, \infty] \f$.
 *
 * \par Let G(x) be the normalized Gaussian defined as
 * \f$ G(x) = \frac{1}{{\sigma \sqrt {2\pi } }}e^{ - \frac{{\left( {x -
 * \mu } \right)^2 }}{{2\sigma ^2 }}} \f$.
 * The Cumulative Gaussian, is acquired by integrating G(x) then scaling and
 * offsetting it by the lower asymptotes \f$ I_1 \f$ and upper \f$ I_2 \f$:
 * \f$ C\left( x \right) = I_1  + \frac{{I_2  - I_1 }}{2}\left( {1 +
 * erf\left( {\frac{{x - \mu }}{{\sigma \sqrt 2 }}} \right)} \right) \f$, where
 * \f$ C\left( { - \infty } \right) = I_1 \f$ and
 * \f$ C\left( \infty  \right) = I_2 \f$.
 *
 * \par C(x) can only be tabulated since it's a variation of the
 * error function. It is included in this class
 * as the function EvaluateCumulativeGaussian, where the argument
 * of the function is \f$ {\frac{{x - \mu }}{{\sigma \sqrt 2 }}} \f$.
 *
 * \ingroup Numerics Cost Functions
 * \ingroup ITKOptimizers
 */

class ITKOptimizers_EXPORT CumulativeGaussianCostFunction : public MultipleValuedCostFunction
{
public:
  /** Standard type alias. */
  using Self = CumulativeGaussianCostFunction;
  using Superclass = MultipleValuedCostFunction;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

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

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

  /** Array Typedefs. */
  using ParametersType = Superclass::ParametersType;
  using MeasureType = Superclass::MeasureType;
  using DerivativeType = Superclass::DerivativeType;

  /** The dimensions of parameter space; mean, standard deviation, lower and
    upper asymptotes. */
  enum
  {
    SpaceDimension = 4
  };

  /** Not necessary for this optimizer. */
  void
  GetDerivative(const ParametersType & itkNotUsed(parameters), DerivativeType & itkNotUsed(derivative)) const override
  {}

  /** Return the values evaluated for the given parameters. */
  MeasureType
  GetValue(const ParametersType & parameters) const override;

  /** Return a pointer of values evaluated for the given parameters. */
  MeasureType *
  GetValuePointer(ParametersType & parameters);

  /** Calculate a fit error between the data and the fit curve. */
  double
  CalculateFitError(MeasureType * setTestArray);

  /** Given the argument of a Cumulative Gaussian, return its value. */
  double
  EvaluateCumulativeGaussian(double argument) const;

  /** Get the SpaceDimension. */
  unsigned int
  GetNumberOfParameters() const override;

  /** Get the number Range Dimension. */
  unsigned int
  GetNumberOfValues() const override;

  /** Initialize the arrays. */
  void
  Initialize(unsigned int rangeDimension);

  /** Set the original data array. */
  void
  SetOriginalDataArray(MeasureType * setOriginalDataArray);

protected:
  CumulativeGaussianCostFunction();
  ~CumulativeGaussianCostFunction() override;

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

private:
  /** The original data array. */
  MeasureType m_OriginalDataArray{};

  /** Number of data samples. */
  unsigned int m_RangeDimension{ 0 };

  /** Different arrays. */
  mutable MeasureType    m_Measure{};
  mutable MeasureType    m_MeasurePointer{};
  mutable ParametersType m_Parameters{};
};
} // end namespace itk

#endif