#ifndef __itkWarpSmoothnessCalculator_h
#define __itkWarpSmoothnessCalculator_h

#include "itkObject.h"
#include "itkObjectFactory.h"
#include "itkConstNeighborhoodIterator.h"
#include "itkImage.h"
#include "itkVector.h"

namespace itk
{

/** \class WarpSmoothnessCalculator
 *
 * \brief Compute the harmonic energy of a deformation field
 *
 * This class computes the harmonic energy of a deformation
 * field which is a measure inversely related to the smoothness
 * of the deformation field
 *
 * \author Tom Vercauteren, INRIA & Mauna Kea Technologies
 *
 * \ingroup Operators
 */
template <class TInputImage>            
class ITK_EXPORT WarpSmoothnessCalculator : public Object 
{
public:
  /** Standard class typedefs. */
  typedef WarpSmoothnessCalculator Self;
  typedef Object  Superclass;
  typedef SmartPointer<Self>   Pointer;
  typedef SmartPointer<const Self>  ConstPointer;

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

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

  /** Type definition for the input image. */
  typedef TInputImage  ImageType;

  /** Pointer type for the image. */
  typedef typename TInputImage::Pointer  ImagePointer;
  
  /** Const Pointer type for the image. */
  typedef typename TInputImage::ConstPointer ImageConstPointer;

  /** Type definition for the input image pixel type. */
  typedef typename TInputImage::PixelType PixelType;
  
  /** Type definition for the input image index type. */
  typedef typename TInputImage::IndexType IndexType;
  
  /** Type definition for the input image region type. */
  typedef typename TInputImage::RegionType RegionType;

  /** The dimensionality of the input image. */
  itkStaticConstMacro(ImageDimension, unsigned int,
                      TInputImage::ImageDimension);
  
  /** Length of the vector pixel type of the input image. */
  itkStaticConstMacro(VectorDimension, unsigned int,
                      PixelType::Dimension);

  /** Type of the iterator that will be used to move through the image.  Also
      the type which will be passed to the evaluate function */
  typedef ConstNeighborhoodIterator<ImageType> ConstNeighborhoodIteratorType;
  typedef typename ConstNeighborhoodIteratorType::RadiusType RadiusType;

  /** Set the derivative weights according to the spacing of the input image
      (1/spacing). Use this option if you want to calculate the Jacobian
      determinant in the space in which the data was acquired.*/
  void SetUseImageSpacingOn()
  { this->SetUseImageSpacing(true); }

  /** Reset the derivative weights to ignore image spacing.  Use this option if
      you want to calculate the Jacobian determinant in the image space.  
      Default is ImageSpacingOn. */
  void SetUseImageSpacingOff()
  { this->SetUseImageSpacing(false); }

  /** Set/Get whether or not the filter will use the spacing of the input
      image in its calculations */
  void SetUseImageSpacing(bool);                         
  itkGetMacro(UseImageSpacing, bool);

  /** Directly Set/Get the array of weights used in the gradient calculations.
      Note that calling UseImageSpacingOn will clobber these values.*/
  void SetDerivativeWeights(double data[]);
  itkGetVectorMacro(DerivativeWeights, const double, itk::GetImageDimension<TInputImage>::ImageDimension);
  
  /** Set the input image. */
  itkSetConstObjectMacro(Image,ImageType);

  /** Compute the minimum value of intensity of the input image. */
  void ComputeMinimum(void);

  /** Compute the maximum value of intensity of the input image. */
  void ComputeMaximum(void);

  /** Compute the minimum and maximum values of intensity of the input image. */
  void Compute(void);

  /** Return the smoothness value. */
  itkGetMacro(Smoothness,double);

  /** Set the region over which the values will be computed */
  void SetRegion( const RegionType & region );

protected:
  WarpSmoothnessCalculator();
  virtual ~WarpSmoothnessCalculator() {};
  void PrintSelf(std::ostream& os, Indent indent) const;

  /** Get/Set the neighborhood radius used for gradient computation */
  itkGetConstReferenceMacro( NeighborhoodRadius, RadiusType );
  itkSetMacro( NeighborhoodRadius, RadiusType );
  
  double EvaluateAtNeighborhood
     (ConstNeighborhoodIteratorType &it) const;

private:
  WarpSmoothnessCalculator(const Self&); //purposely not implemented
  void operator=(const Self&); //purposely not implemented
  
  double               m_Smoothness;
  ImageConstPointer    m_Image;

  RegionType           m_Region;
  bool                 m_RegionSetByUser;

  bool m_UseImageSpacing;

  /** The weights used to scale partial derivatives during processing */
  double m_DerivativeWeights[itk::GetImageDimension<TInputImage>::ImageDimension];

  RadiusType    m_NeighborhoodRadius;
};

} // end namespace itk


#ifndef ITK_MANUAL_INSTANTIATION
#include "itkWarpSmoothnessCalculator.txx"
#endif

#endif /* __itkWarpSmoothnessCalculator_h */