/*=========================================================================
 *
 *  Copyright Insight Software Consortium
 *
 *  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
 *
 *         http://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 itkGaussianInterpolateImageFunction_h
#define itkGaussianInterpolateImageFunction_h

#include "itkInterpolateImageFunction.h"

#include "itkConceptChecking.h"
#include "itkFixedArray.h"
#include "vnl/vnl_erf.h"

namespace itk
{

/** \class GaussianInterpolateImageFunction
 * \brief Evaluates the Gaussian interpolation of an image.
 *
 * This class defines an N-dimensional Gaussian interpolation function using
 * the vnl error function.  The two parameters associated with this function
 * are:
 *   1. Sigma - a scalar array of size ImageDimension determining the width
 *      of the interpolation function.
 *   2. Alpha - a scalar specifying the cutoff distance over which the function
 *      is calculated.
 *
 * This work was originally described in the Insight Journal article:
 * P. Yushkevich, N. Tustison, J. Gee, Gaussian interpolation.
 * \sa{https://hdl.handle.net/10380/3139}
 *
 * \author Paul Yushkevich
 * \author Nick Tustison
 *
 * \ingroup ITKImageFunction
 */

template <typename TInputImage, typename TCoordRep = double>
class ITK_TEMPLATE_EXPORT GaussianInterpolateImageFunction :
  public InterpolateImageFunction<TInputImage, TCoordRep>
{
public:
  ITK_DISALLOW_COPY_AND_ASSIGN(GaussianInterpolateImageFunction);

  /** Standard class type aliases. */
  using Self = GaussianInterpolateImageFunction;
  using Superclass = InterpolateImageFunction<TInputImage, TCoordRep>;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  /** Run-time type information (and related methods). */
  itkTypeMacro( GaussianInterpolateImageFunction, InterpolateImageFunction );

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

  /** ImageDimension constant. */
  static constexpr unsigned int ImageDimension = TInputImage::ImageDimension;


  /** OutputType type alias support */
  using OutputType = typename Superclass::OutputType;

  /** InputImageType type alias support */
  using InputImageType = typename Superclass::InputImageType;

  /** RealType type alias support */
  using RealType = typename Superclass::RealType;

  /** Index type alias support */
  using IndexType = typename Superclass::IndexType;

  /** Size type alias support */
  using SizeType = typename Superclass::SizeType;

  /** ContinuousIndex type alias support */
  using ContinuousIndexType = typename Superclass::ContinuousIndexType;

  /** Array type alias support */
  using ArrayType = FixedArray<RealType, ImageDimension>;

  /** Set input image. */
  void SetInputImage( const TInputImage *image ) override
    {
    Superclass::SetInputImage( image );
    this->ComputeBoundingBox();
    }

  /** Set/Get sigma. */
  virtual void SetSigma( const ArrayType s )
    {
    if( this->m_Sigma != s )
      {
      this->m_Sigma = s;
      this->ComputeBoundingBox();
      this->Modified();
      }
    }
  virtual void SetSigma( RealType *s )
    {
    ArrayType sigma;
    for( unsigned int d = 0; d < ImageDimension; d++ )
      {
      sigma[d] = s[d];
      }
    this->SetSigma( sigma );
    }
  itkGetConstMacro( Sigma, ArrayType );

  /** Set/Get alpha. */
  virtual void SetAlpha( const RealType a )
    {
    if( Math::NotExactlyEquals(this->m_Alpha, a) )
      {
      this->m_Alpha = a;
      this->ComputeBoundingBox();
      this->Modified();
      }
    }
  itkGetConstMacro( Alpha, RealType );

  /** Set/Get sigma and alpha. */
  virtual void SetParameters( RealType *sigma, RealType alpha )
    {
    this->SetSigma( sigma );
    this->SetAlpha( alpha );
    }

  /** Evaluate at the given index. */
  OutputType EvaluateAtContinuousIndex(
    const ContinuousIndexType & cindex ) const override
    {
    return this->EvaluateAtContinuousIndex( cindex, nullptr );
    }

#if !defined(ITKV4_COMPATIBILITY)
  SizeType GetRadius() const override;
#endif

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

  virtual void ComputeBoundingBox();

  virtual void ComputeErrorFunctionArray( unsigned int dimension, RealType cindex,
    vnl_vector<RealType> &erfArray, vnl_vector<RealType> &gerfArray,
    bool evaluateGradient = false ) const;

  /** Set/Get the bounding box starting point. */
  itkSetMacro( BoundingBoxStart, ArrayType );
  itkGetConstMacro( BoundingBoxStart, ArrayType );

  /** Set/Get the bounding box end point. */
  itkSetMacro( BoundingBoxEnd, ArrayType );
  itkGetConstMacro( BoundingBoxEnd, ArrayType );

  /** Set/Get the cut-off distance. */
  itkSetMacro( CutOffDistance, ArrayType );
  itkGetConstMacro( CutOffDistance, ArrayType );


private:
  /** Evaluate function value. */
  virtual OutputType EvaluateAtContinuousIndex(
    const ContinuousIndexType &, OutputType * ) const;

  ArrayType                                 m_Sigma;
  RealType                                  m_Alpha;

  ArrayType                                 m_BoundingBoxStart;
  ArrayType                                 m_BoundingBoxEnd;
  ArrayType                                 m_ScalingFactor;
  ArrayType                                 m_CutOffDistance;


};

} // end namespace itk

#ifndef ITK_MANUAL_INSTANTIATION
#include "itkGaussianInterpolateImageFunction.hxx"
#include "itkMath.h"
#endif

#endif
