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

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkPathConstIterator.h,v $
  Language:  C++
  Date:      $Date: 2004/11/01 21:16:31 $
  Version:   $Revision: 1.7 $

  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 __itkPathConstIterator_h
#define __itkPathConstIterator_h

#include "itkIndex.h"
#include "itkImage.h"
#include "itkPath.h"

namespace itk
{

/**
 * \class PathConstIterator
 * \brief PathConstIterator iterates (traces) over a path through an image.
 *
 * This iterator visits only those indices of the image that are overlapped by
 * a specified 1D path.  All indicies are visited in path order.  If a path
 * crosses itself at an index, that index of the image will be visited twice.
 * An exception to this rule is that if the path is closed, i.e. its starting
 * and ending indicies are coincident.  When starting and ending indicies are
 * coincident, GoToBegin() will go to the second index, since the "first" index
 * will be visited later as the "last" index.  This is so that paths
 * (especially parametric paths) can be properly closed, without
 * double-visiting the starting/ending point.  This behavior can be overridden
 * by calling VisitStartIndexAsLastIndexIfClosed(false) before calling
 * GoToBegin().  This class is the const version of the PathIterator, and for
 * this reason it doesn't support the Set() method.
 *
 * \par MORE INFORMATION
 * For a complete description of the ITK Image Iterators and their API, please
 * see the Iterators chapter in the ITK Software Guide.  The ITK Software Guide
 * is available in print and as a free .pdf download from http://www.itk.org.
 *
 * \ingroup PathObjects \ingroup ImageIterators
 *
 * \sa ImageConstIterator \sa ConditionalConstIterator
 * \sa ConstNeighborhoodIterator \sa ConstShapedNeighborhoodIterator
 * \sa ConstSliceIterator  \sa CorrespondenceDataStructureIterator 
 * \sa FloodFilledFunctionConditionalConstIterator 
 * \sa FloodFilledImageFunctionConditionalConstIterator 
 * \sa FloodFilledImageFunctionConditionalIterator 
 * \sa FloodFilledSpatialFunctionConditionalConstIterator 
 * \sa FloodFilledSpatialFunctionConditionalIterator 
 * \sa ImageConstIterator \sa ImageConstIteratorWithIndex 
 * \sa ImageIterator \sa ImageIteratorWithIndex
 * \sa ImageLinearConstIteratorWithIndex  \sa ImageLinearIteratorWithIndex 
 * \sa ImageRandomConstIteratorWithIndex  \sa ImageRandomIteratorWithIndex 
 * \sa ImageRegionConstIterator \sa ImageRegionConstIteratorWithIndex 
 * \sa ImageRegionExclusionConstIteratorWithIndex 
 * \sa ImageRegionExclusionIteratorWithIndex 
 * \sa ImageRegionIterator  \sa ImageRegionIteratorWithIndex 
 * \sa ImageRegionReverseConstIterator  \sa ImageRegionReverseIterator 
 * \sa ImageReverseConstIterator  \sa ImageReverseIterator 
 * \sa ImageSliceConstIteratorWithIndex  \sa ImageSliceIteratorWithIndex 
 * \sa NeighborhoodIterator \sa PathIterator \sa ShapedNeighborhoodIterator
 * \sa SliceIterator \sa ImageConstIteratorWithIndex */
template<class TImage, class TPath>
class ITK_EXPORT PathConstIterator
{
public:
  /** Standard class typedefs. */
  typedef PathConstIterator Self;

  /** Dimension of the image the iterator walks.  This constant is needed so 
   * that functions that are templated over image iterator type (as opposed to
   * being templated over pixel type and dimension) can have compile time
   * access to the dimension of the image that the iterator walks. */
  itkStaticConstMacro(ImageIteratorDimension, unsigned int,
                      TImage::ImageDimension);

  /** Index typedef support. */
  typedef typename TImage::IndexType          IndexType;
  typedef typename TImage::IndexValueType     IndexValueType;

  /** Offset typedef support. */
  typedef typename TImage::OffsetType         OffsetType;
  typedef typename TImage::OffsetValueType    OffsetValueType;

  /** Size typedef support. */
  typedef typename TImage::SizeType           SizeType;
  typedef typename TImage::SizeValueType      SizeValueType;

  /** Region typedef support */
  typedef typename TImage::RegionType         RegionType;

  /** Spacing typedef support */
  typedef typename TImage::SpacingType        SpacingType;

  /** Origin typedef support */
  typedef typename TImage::PointType          PointType;
  
  /** Image typedef support. */
  typedef TImage                              ImageType;

  /** PixelContainer typedef support. Used to refer to the container for
   * the pixel data. While this was already typdef'ed in the superclass
   * it needs to be redone here for this subclass to compile properly with gcc. */
  typedef typename TImage::PixelContainer     PixelContainer;
  typedef typename PixelContainer::Pointer    PixelContainerPointer;
  
  /** Internal Pixel Type */
  typedef typename TImage::InternalPixelType  InternalPixelType;

  /** External Pixel Type */
  typedef typename TImage::PixelType          PixelType;

  /**  Accessor type that convert data between internal and external
   *  representations. */
  typedef typename TImage::AccessorType       AccessorType;

  /** Path typedef support */
  typedef TPath                               PathType;

  /** Path 1D Input Type */
  typedef typename PathType::InputType        PathInputType;

  /** Path ND Output Type, which is not necessarily an index type */
  typedef typename PathType::OutputType       PathOutputType;
  
  /** Run-time type information (and related methods). */
  itkTypeMacro(PathConstIterator, None);
  
  /** Get the dimension (size) of the index. */
  static unsigned int GetImageIteratorDimension() 
    {
    return TImage::ImageDimension;
    }

  /** Get the input. This provides a read only reference to the input. */
  const PathInputType GetPathPosition()
    {
    return m_CurrentPathPosition;
    }

  /** Get the index. This provides a read only reference to the index. */
  const IndexType GetIndex()
    {
    return m_CurrentImageIndex;
    }

  /** Get the pixel value */
  const PixelType & Get(void) const
    {
    return m_Image->GetPixel(m_CurrentImageIndex );
    }
 
  /** Is the iterator at the end of the path?
   * Note that for a closed path, it may be possible to increment back to the
   * start of the path. */
  bool IsAtEnd()
    {
    return m_IsAtEnd;
    }

  /** Should GoToBegin() initially skip the first index of a closed path so that
   * the first index will only be visited once--at the end of the path?  If set
   * to false, then GoToBegin() will always move to the 1'st index.  The
   * constructor presets m_VisitStartIndexAsLastIndexIfClosed to true. */
  inline virtual void VisitStartIndexAsLastIndexIfClosed(bool flag)
    {
    m_VisitStartIndexAsLastIndexIfClosed = flag;
    }
  
  /** Move an iterator to the beginning of the path.  If the starting and ending
   * indicies of the path are coincident, then move to the 2'nd index of the
   * path, since the 1'st index will be visited later as the last index.
   * However, if m_VisitStartIndexAsLastIndexIfClosed is false, then GoToBegin()
   * will always move to the 1'st index. */
  void GoToBegin();

  /** Walk forward along the path to the next index in the image. */
  void operator++();

  /** operator= is provided to make sure the handles to the image and path are
   * properly reference counted. */
  Self &operator=(const Self& it);

  /** Constructor establishes an iterator to walk along a path */
  PathConstIterator(const ImageType *imagePtr, const PathType  *pathPtr);

  /** Default Destructor. */
  virtual ~PathConstIterator() {};

protected: //made protected so other iterators can access 
  // This "constant" is initialized in the constructor
  OffsetType  m_ZeroOffset; // = 0 for all dimensions

  /** Smart pointer to the source image. */
  typename ImageType::ConstWeakPointer m_Image;

  /** Smart pointer to the path we're following */
  typename PathType::ConstPointer m_Path;

  /** Region type to iterate over. */
  RegionType m_Region;

  /** The origin of the source image */
  PointType m_ImageOrigin;
  
  /** The spacing of the source image */
  SpacingType m_ImageSpacing;

  /** Size of the source image */
  const unsigned long int* m_ImageSize;
  
  /** Should GoToBegin() initially skip the first index of a closed path so that
   * the first index will only be visited once--at the end of the path?  If 
   * false, then GoToBegin() will always move to the 1'st index.  The default
   * value is true, which is set the constructor. */
  bool m_VisitStartIndexAsLastIndexIfClosed;
  
  /** Is the iterator at the end of its walk? */
  bool m_IsAtEnd;

  /** Current 1D position along the path, such as time or arc length */
  PathInputType m_CurrentPathPosition;

  /** Current ND index position in the image of the path */
  IndexType m_CurrentImageIndex;
};

} // end namespace itk

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

#endif 
