
#ifndef itkCorrelationImageToImageMetricv4HelperThreader_h
#define itkCorrelationImageToImageMetricv4HelperThreader_h

#include "itkImageToImageMetricv4GetValueAndDerivativeThreader.h"

namespace itk
{

/** \class CorrelationImageToImageMetricv4GetValueAndDerivativeThreader
 * \brief Helper class for CorrelationImageToImageMetricv4 \c
 * To compute the average pixel intensities of the fixed image and the moving image
 * on the sampled points or inside the virtual image region:
 * \f$ \bar f (CorrelationImageToImageMetricv4::m_AverageFix ) \f$
 * \f$ \bar m (CorrelationImageToImageMetricv4::m_AverageMov ) \f$
 *
 * \ingroup ITKMetricsv4
 */
template < typename TDomainPartitioner, typename TImageToImageMetric, typename TCorrelationMetric >
class ITK_TEMPLATE_EXPORT CorrelationImageToImageMetricv4HelperThreader
  : public ImageToImageMetricv4GetValueAndDerivativeThreader< TDomainPartitioner, TImageToImageMetric >
{
public:
  ITK_DISALLOW_COPY_AND_ASSIGN(CorrelationImageToImageMetricv4HelperThreader);

  /** Standard class type aliases. */
  using Self = CorrelationImageToImageMetricv4HelperThreader;
  using Superclass = ImageToImageMetricv4GetValueAndDerivativeThreader< TDomainPartitioner, TImageToImageMetric >;
  using Pointer = SmartPointer< Self >;
  using ConstPointer = SmartPointer< const Self >;

  itkTypeMacro( CorrelationImageToImageMetricv4HelperThreader, ImageToImageMetricv4GetValueAndDerivativeThreader );

  itkNewMacro( Self );

  using DomainType = typename Superclass::DomainType;
  using AssociateType = typename Superclass::AssociateType;

  using ImageToImageMetricv4Type = typename Superclass::ImageToImageMetricv4Type;
  using VirtualIndexType = typename Superclass::VirtualIndexType;
  using VirtualPointType = typename Superclass::VirtualPointType;
  using FixedImagePointType = typename Superclass::FixedImagePointType;
  using FixedImagePixelType = typename Superclass::FixedImagePixelType;
  using FixedImageGradientType = typename Superclass::FixedImageGradientType;
  using MovingImagePointType = typename Superclass::MovingImagePointType;
  using MovingImagePixelType = typename Superclass::MovingImagePixelType;
  using MovingImageGradientType = typename Superclass::MovingImageGradientType;
  using MeasureType = typename Superclass::MeasureType;
  using DerivativeType = typename Superclass::DerivativeType;
  using DerivativeValueType = typename Superclass::DerivativeValueType;

  using InternalComputationValueType = typename Superclass::InternalComputationValueType;
  using NumberOfParametersType = typename Superclass::NumberOfParametersType;

  using FixedOutputPointType = typename Superclass::FixedOutputPointType;
  using MovingOutputPointType = typename Superclass::MovingOutputPointType;

protected:
  CorrelationImageToImageMetricv4HelperThreader();
  ~CorrelationImageToImageMetricv4HelperThreader() override;

  /** Overload: Resize and initialize per thread objects. */
  void BeforeThreadedExecution() override;

  /** Overload:
   * Collects the results from each thread and sums them.  Results are stored
   * in the enclosing class \c m_Value and \c m_DerivativeResult.  Behavior
   * depends on m_AverageValueAndDerivativeByNumberOfValuePoints,
   * m_NumberOfValidPoints, to average the value sum, and to average
   * derivative sums for global transforms only (i.e. transforms without local
   * support).  */
  void AfterThreadedExecution() override;


  /* Overload: don't need to compute the image gradients and store derivatives
   *
   * Method called by the threaders to process the given virtual point.  This
   * in turn calls \c TransformAndEvaluateFixedPoint, \c
   * TransformAndEvaluateMovingPoint, and \c ProcessPoint.
   */
  bool ProcessVirtualPoint( const VirtualIndexType & virtualIndex,
                                    const VirtualPointType & virtualPoint,
                                    const ThreadIdType threadId ) override;


  /**
   * Not using. All processing is done in ProcessVirtualPoint.
   */
  bool ProcessPoint(
        const VirtualIndexType &          ,
        const VirtualPointType &          ,
        const FixedImagePointType &       ,
        const FixedImagePixelType &       ,
        const FixedImageGradientType &    ,
        const MovingImagePointType &      ,
        const MovingImagePixelType &      ,
        const MovingImageGradientType &   ,
        MeasureType &                     ,
        DerivativeType &                  ,
        const ThreadIdType                 ) const override
  {
    return false;
  }

private:
  struct CorrelationMetricPerThreadStruct
    {
    InternalComputationValueType FixSum;
    InternalComputationValueType MovSum;
    };
  itkPadStruct( ITK_CACHE_LINE_ALIGNMENT, CorrelationMetricPerThreadStruct,
                                          PaddedCorrelationMetricPerThreadStruct);
  itkAlignedTypedef( ITK_CACHE_LINE_ALIGNMENT, PaddedCorrelationMetricPerThreadStruct,
                                               AlignedCorrelationMetricPerThreadStruct );
  /* per thread variables for correlation and its derivatives */
  mutable AlignedCorrelationMetricPerThreadStruct * m_CorrelationMetricPerThreadVariables;

  /** Internal pointer to the metric object in use by this threader.
   *  This will avoid costly dynamic casting in tight loops. */
  TCorrelationMetric * m_CorrelationAssociate;
};

} // end namespace itk

#ifndef ITK_MANUAL_INSTANTIATION
#include "itkCorrelationImageToImageMetricv4HelperThreader.hxx"
#endif

#endif
