/*=========================================================================

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkImageRegionConstIterator.txx,v $
  Language:  C++
  Date:      $Date: 2005/01/28 21:52:18 $
  Version:   $Revision: 1.5 $

  Copyright (c) Insight Software Consortium. All rights reserved.
  See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even 
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR 
     PURPOSE.  See the above copyright notices for more information.

=========================================================================*/
#ifndef _itkImageRegionConstIterator_txx
#define _itkImageRegionConstIterator_txx

#include "itkImageRegionConstIterator.h"

namespace itk
{

//----------------------------------------------------------------------------
// Begin() is the first pixel in the region.
template<class TImage>
ImageRegionConstIterator<TImage>
ImageRegionConstIterator<TImage>
::Begin() const
{
  // Copy the current iterator
  Self it( *this );

  // Set the iterator to the beginning of the region
  it.GoToBegin();
  
  return it;
}

//----------------------------------------------------------------------------
// End() is one pixel past the last pixel in the current region.
// The index of this pixel is
//          [m_StartIndex[0] + m_Size[0],
//           m_StartIndex[1] + m_Size[1]-1, ...,
//           m_StartIndex[VImageDimension-2] + m_Size[VImageDimension-2]-1,
//           m_StartIndex[VImageDimension-1] + m_Size[VImageDimension-1]-1]
//
template<class TImage>
ImageRegionConstIterator<TImage>
ImageRegionConstIterator<TImage>
::End() const
{
  // Copy the current iterator
  Self it( *this );

  // Set the iterator to the end of the region
  it.GoToEnd();
  
  return it;
}

//----------------------------------------------------------------------------
// Increment when the fastest moving direction has reached its bound.
// This method should *ONLY* be invoked from the operator++() method.
template<class TImage>
void
ImageRegionConstIterator<TImage>
::Increment() 
{
  // We have reached the end of the span (row), need to wrap around.

  // First back up one pixel, because we are going to use a different
  // algorithm to compute the next pixel
  --this->m_Offset;
  
  // Get the index of the last pixel on the span (row)
  typename ImageIterator<TImage>::IndexType
    ind = this->m_Image->ComputeIndex( static_cast<typename Superclass::OffsetValueType>(this->m_Offset) );

  const typename ImageIterator<TImage>::IndexType&
    startIndex = this->m_Region.GetIndex();
  const typename ImageIterator<TImage>::SizeType&
    size = this->m_Region.GetSize();

  // Increment along a row, then wrap at the end of the region row.
  unsigned int dim;

  // Check to see if we are past the last pixel in the region
  // Note that ++ind[0] moves to the next pixel along the row.
  ++ind[0];
  bool done = (ind[0] == startIndex[0] + static_cast<typename Superclass::IndexValueType>(size[0]));
  for (unsigned int i=1; done && i < ImageIteratorDimension; i++)
    {
    done = (ind[i] == startIndex[i] + static_cast<typename Superclass::IndexValueType>(size[i]) - 1);
    }
  
  // if the iterator is outside the region (but not past region end) then
  // we need to wrap around the region
  dim = 0;
  if (!done)
    {
    while ( ( dim+1 < ImageIteratorDimension )
      && (ind[dim] > startIndex[dim] +  static_cast<typename Superclass::IndexValueType>(size[dim]) - 1) )
      {
      ind[dim] = startIndex[dim];
      ind[++dim]++;
      }
    }
  this->m_Offset = this->m_Image->ComputeOffset( ind );
  m_SpanEndOffset = this->m_Offset + static_cast<long>(size[0]);
  m_SpanBeginOffset = this->m_Offset;
}


//----------------------------------------------------------------------------
// Decrement when the fastest moving direction has reached its bound.
// This method should *ONLY* be invoked from the operator--() method.
template<class TImage>
void
ImageRegionConstIterator<TImage>
::Decrement() 
{
  // We have pasted the beginning of the span (row), need to wrap around.

  // First move forward one pixel, because we are going to use a different
  // algorithm to compute the next pixel
  this->m_Offset++;
  
  // Get the index of the first pixel on the span (row)
  typename ImageIterator<TImage>::IndexType
    ind = this->m_Image->ComputeIndex( static_cast<typename Superclass::IndexValueType>(this->m_Offset) );

  const typename ImageIterator<TImage>::IndexType&
    startIndex = this->m_Region.GetIndex();
  const typename ImageIterator<TImage>::SizeType&
    size = this->m_Region.GetSize();

  // Deccrement along a row, then wrap at the beginning of the region row.
  bool done;
  unsigned int dim;

  // Check to see if we are past the first pixel in the region
  // Note that --ind[0] moves to the previous pixel along the row.
  done = (--ind[0] == startIndex[0] - 1);
  for (unsigned int i=1; done && i < ImageIteratorDimension; i++)
    {
    done = (ind[i] == startIndex[i]);
    }
  
  // if the iterator is outside the region (but not past region begin) then
  // we need to wrap around the region
  dim = 0;
  if (!done)
    {
    while ( (dim < ImageIteratorDimension - 1)
            && (ind[dim] < startIndex[dim]) )
      {
      ind[dim] = startIndex[dim] + static_cast<typename Superclass::IndexValueType>(size[dim]) - 1;
      ind[++dim]--;
      }
    }
  this->m_Offset = this->m_Image->ComputeOffset( ind );
  m_SpanEndOffset = this->m_Offset + 1;
  m_SpanBeginOffset = m_SpanEndOffset - static_cast<long>(size[0]);
}

} // end namespace itk

#endif
