/*=========================================================================
 *
 *  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 __itkVectorAnisotropicDiffusionFunction_hxx
#define __itkVectorAnisotropicDiffusionFunction_hxx
#include "itkVectorAnisotropicDiffusionFunction.h"

#include "itkConstNeighborhoodIterator.h"
#include "itkVectorNeighborhoodInnerProduct.h"
#include "itkNeighborhoodAlgorithm.h"
#include "itkDerivativeOperator.h"

namespace itk
{
template< typename TImage >
void
VectorAnisotropicDiffusionFunction< TImage >
::CalculateAverageGradientMagnitudeSquared(TImage *ip)
{
  typedef ConstNeighborhoodIterator< TImage >                           RNI_type;
  typedef ConstNeighborhoodIterator< TImage >                           SNI_type;
  typedef NeighborhoodAlgorithm::ImageBoundaryFacesCalculator< TImage > BFC_type;

  unsigned int i, j;
  //  ZeroFluxNeumannBoundaryCondition<TImage>  bc;
  double        accumulator;
  PixelType     val;
  SizeValueType counter;
  BFC_type      bfc;
  typename BFC_type::FaceListType faceList;
  typename RNI_type::RadiusType radius;
  typename BFC_type::FaceListType::iterator fit;

  VectorNeighborhoodInnerProduct< TImage > SIP;
  VectorNeighborhoodInnerProduct< TImage > IP;
  RNI_type                                 iterator_list[ImageDimension];
  SNI_type                                 face_iterator_list[ImageDimension];
  typedef typename PixelType::ValueType PixelValueType;
  DerivativeOperator< PixelValueType, ImageDimension > operator_list[ImageDimension];

  // Set up the derivative operators, one for each dimension
  for ( i = 0; i < ImageDimension; ++i )
    {
    operator_list[i].SetOrder(1);
    operator_list[i].SetDirection(i);
    operator_list[i].CreateDirectional();
    radius[i] = operator_list[i].GetRadius()[i];
    }

  // Get the various region "faces" that are on the data set boundary.
  faceList = bfc(ip, ip->GetRequestedRegion(), radius);
  fit      = faceList.begin();

  // Now do the actual processing
  accumulator = 0.0;
  counter     = NumericTraits<SizeValueType>::Zero;

  // First process the non-boundary region

  // Instead of maintaining a single N-d neighborhood of pointers,
  // we maintain a list of 1-d neighborhoods along each axial direction.
  // This is more efficient for higher dimensions.
  for ( i = 0; i < ImageDimension; ++i )
    {
    iterator_list[i] = RNI_type(operator_list[i].GetRadius(), ip, *fit);
    iterator_list[i].GoToBegin();
    }
  while ( !iterator_list[0].IsAtEnd() )
    {
    counter++;
    for ( i = 0; i < ImageDimension; ++i )
      {
      val = IP(iterator_list[i], operator_list[i]);
      for ( j = 0; j < VectorDimension; ++j )
        {
        accumulator += val[j] * val[j];
        }
      ++iterator_list[i];
      }
    }

  // Go on to the next region(s).  These are on the boundary faces.
  ++fit;
  while ( fit != faceList.end() )
    {
    for ( i = 0; i < ImageDimension; ++i )
      {
      face_iterator_list[i] = SNI_type(operator_list[i].GetRadius(), ip, *fit);
      face_iterator_list[i].GoToBegin();
      }

    while ( !face_iterator_list[0].IsAtEnd() )
      {
      counter++;
      for ( i = 0; i < ImageDimension; ++i )
        {
        val = SIP(face_iterator_list[i], operator_list[i]);
        for ( j = 0; j < VectorDimension; ++j )
          {
          accumulator += val[j] * val[j];
          }
        ++face_iterator_list[i];
        }
      }
    ++fit;
    }

  this->SetAverageGradientMagnitudeSquared( (double)accumulator / counter );
}
} // end namespace itk

#endif
