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 *
 *  Copyright NumFOCUS
 *
 *  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
 *
 *         https://www.apache.org/licenses/LICENSE-2.0.txt
 *
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 *  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 itkNeighborhoodIterator_h
#define itkNeighborhoodIterator_h

#include <vector>
#include <cstring>
#include <iostream>
#include "itkConstNeighborhoodIterator.h"

namespace itk
{
/**
 * \class NeighborhoodIterator
 *
 * \brief Defines iteration of a local N-dimensional neighborhood of pixels
 * across an itk::Image.
 *
 * This class is a loose extension of the Standard Template Library (STL)
 * bi-directional iterator concept to \em masks of pixel neighborhoods within
 * itk::Image objects.  This NeighborhoodIterator base class defines simple
 * forward and reverse iteration of an N-dimensional neighborhood mask
 * across an image.  Elements within the mask can be accessed like elements
 * within an array.
 *
 * NeighborhoodIterators are designed to encapsulate some of the complexity of
 * working with image neighborhoods, complexity that would otherwise have to be
 * managed at the algorithmic level.  Use NeighborhoodIterators to simplify
 * writing algorithms that perform geometrically localized operations on images
 * (for example, convolution and morphological operations).
 *
 * To motivate the discussion of NeighborhoodIterators and their use in
 * Itk, consider the following code that takes directional derivatives at each
 * point in an image.
 *
\code
itk::NeighborhoodInnerProduct<ImageType> innerProduct;

itk::DerivativeOperator<ImageType> operator;
 operator->SetOrder(1);
 operator->SetDirection(0);
 operator->CreateDirectional();

itk::NeighborhoodIterator<ImageType>
  iterator(operator->GetRadius(), myImage, myImage->GetRequestedRegion());

iterator.SetToBegin();
while ( ! iterator.IsAtEnd() )
{
  std::cout << "Derivative at index " << iterator.GetIndex() << is <<
    innerProduct(iterator, operator) << std::endl;
  ++iterator;
}
\endcode
 *
 * Most of the work for the programmer in the code above is in setting up for
 * the iteration.  There are three steps.  First an inner product function
 * object is created which will be used to effect convolution with the
 * derivative kernel.  Setting up the derivative kernel, DerivativeOperator,
 * involves setting the order and direction of the derivative.  Finally, we
 * create an iterator over the RequestedRegion of the itk::Image (see Image)
 * using the radius of the derivative kernel as the size.
 *
 * Itk iterators only loosely follow STL conventions.  Notice that instead of
 * asking myImage for myImage.begin() and myImage.end(), iterator.SetToBegin()
 * and iterator.IsAtEnd() are called.  Itk iterators are typically more complex
 * objects than traditional, pointer-style STL iterators, and the increased
 * overhead required to conform to the complete STL API is not always
 * justified.
 *
 * The API for creating and manipulating a NeighborhoodIterator mimics
 * that of the itk::ImageIterators.  Like the itk::ImageIterator, a
 * ConstNeighborhoodIterator is defined on a region of interest in an itk::Image.
 * Iteration is constrained within that region of interest.
 *
 * A NeighborhoodIterator is constructed as a container of pointers (offsets)
 * to a geometric neighborhood of image pixels.  As the central pixel position
 * in the mask is moved around the image, the neighboring pixel pointers
 * (offsets) are moved accordingly.
 *
 * A \em pixel \em neighborhood is defined as a central pixel location and an
 * N-dimensional radius extending outward from that location.
 *
 * Pixels in a neighborhood can be accessed through a NeighborhoodIterator
 * like elements in an array.  For example, a 2D neighborhood with radius 2x1
 * has indices:
 *
\code
0  1  2  3  4
5  6  7  8  9
10 11 12 13 14
\endcode
 *
 * Now suppose a NeighborhoodIterator with the above dimensions is constructed
 * and positioned over a neighborhood of values in an Image:
 *
\code
1.2 1.3 1.8 1.4 1.1
1.8 1.1 0.7 1.0 1.0
2.1 1.9 1.7 1.4 2.0
\endcode
 *
 * Shown below is some sample pixel access code and the values that it returns.
 *
\code
SizeValueType c = (SizeValueType) (iterator.Size() / 2); // get offset of center pixel
SizeValueType s = iterator.GetStride(1);            // y-dimension step size

std::cout << iterator.GetPixel(7)      << std::endl;
std::cout << iterator.GetCenterPixel() << std::endl;
std::cout << iterator.GetPixel(c)      << std::endl;
std::cout << iterator.GetPixel(c-1)    << std::endl;
std::cout << iterator.GetPixel(c-s)    << std::endl;
std::cout << iterator.GetPixel(c-s-1)  << std::endl;
std::cout << *iterator[c]              << std::endl;
\endcode
 *
 * Results:
 *
\code
0.7
0.7
0.7
1.1
1.8
1.3
0.7
\endcode
 *
 * Use of GetPixel() is preferred over the *iterator[] form, and can be used
 * without loss of efficiency in most cases. Some variations (subclasses) of
 * NeighborhoodIterators may exist which do not support the latter
 * API. Corresponding SetPixel() methods exist to modify pixel values in
 * non-const NeighborhoodIterators.
 *
 * NeighborhoodIterators are "bidirectional iterators". They move only in two
 * directions through the data set.  These directions correspond to the layout
 * of the image data in memory and not to spatial directions of the
 * N-dimensional itk::Image.  Iteration always proceeds along the fastest
 * increasing dimension (as defined by the layout of the image data).  For
 * itk::Image this is the first dimension specified (i.e. for 3-dimensional
 * (x,y,z) NeighborhoodIterator proceeds along the x-dimension) (For random
 * access iteration through N-dimensional indices, use
 * RandomAccessNeighborhoodIterator).
 *
 * Each subclass of a ConstNeighborhoodIterator may also define its own
 * mechanism for iteration through an image.  In general, the Iterator does not
 * directly keep track of its spatial location in the image, but uses a set of
 * internal loop variables and offsets to trigger wraps at itk::Image region
 * boundaries, and to identify the end of the itk::Image region.
 *
 * \todo Better support for regions with negative indices.
 * \todo Add Begin() and End() methods?
 *
 * \sa DerivativeOperator \sa NeighborhoodInnerProduct
 *
 * \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 https://www.itk.org.
 *
 * \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 PathConstIterator  \sa PathIterator
 * \sa ShapedNeighborhoodIterator  \sa SliceIterator
 * \sa ImageConstIteratorWithIndex
 * \sa ShapedImageNeighborhoodRange
 *
 * \ingroup Operators
 * \ingroup ITKCommon
 *
 * \sphinx
 * \sphinxexample{Core/Common/IterateRegionWithNeighborhood,Iterate Region In Image With Neighborhood}
 * \sphinxexample{Core/Common/NeighborhoodIteratorOnVectorImage,Neighborhood Iterator On Vector Image}
 * \endsphinx
 */
template <typename TImage, typename TBoundaryCondition = ZeroFluxNeumannBoundaryCondition<TImage>>
class ITK_TEMPLATE_EXPORT NeighborhoodIterator : public ConstNeighborhoodIterator<TImage, TBoundaryCondition>
{
public:
  /** Standard class type aliases. */
  using Self = NeighborhoodIterator;
  using Superclass = ConstNeighborhoodIterator<TImage, TBoundaryCondition>;

  /** Extract type alias from superclass. */
  using typename Superclass::InternalPixelType;
  using typename Superclass::PixelType;
  using typename Superclass::SizeType;
  using typename Superclass::ImageType;
  using typename Superclass::RegionType;
  using typename Superclass::IndexType;
  using typename Superclass::OffsetType;
  using typename Superclass::RadiusType;
  using typename Superclass::NeighborhoodType;
  using typename Superclass::Iterator;
  using typename Superclass::ConstIterator;
  using typename Superclass::ImageBoundaryConditionPointerType;

  /** Default constructor. */
  NeighborhoodIterator()
    : Superclass()
  {}

  /** Copy constructor */
  NeighborhoodIterator(const NeighborhoodIterator & n)
    : Superclass(n)
  {}

  /** Assignment operator */
  Self &
  operator=(const Self & orig)
  {
    Superclass::operator=(orig);
    return *this;
  }

  /** Constructor which establishes the region size, neighborhood, and image
   * over which to walk. */
  NeighborhoodIterator(const SizeType & radius, ImageType * ptr, const RegionType & region)
    : Superclass(radius, ptr, region)
  {}

  /** Returns the central memory pointer of the neighborhood. */
  InternalPixelType *
  GetCenterPointer()
  {
    return (this->operator[]((this->Size()) >> 1));
  }

  /** Returns the central pixel of the neighborhood. */
  ITK_ITERATOR_VIRTUAL void
  SetCenterPixel(const PixelType & p) ITK_ITERATOR_FINAL
  {
    this->m_NeighborhoodAccessorFunctor.Set(this->operator[]((this->Size()) >> 1), p);
  }

  /** Virtual function that replaces the pixel values in the image
   * neighborhood that are pointed to by this NeighborhoodIterator with
   * the pixel values contained in a Neighborhood. */
  ITK_ITERATOR_VIRTUAL void
  SetNeighborhood(const NeighborhoodType &) ITK_ITERATOR_FINAL;

  /** Special SetPixel method which quietly ignores out-of-bounds attempts.
   *  Sets status TRUE if pixel has been set, FALSE otherwise.  */
  ITK_ITERATOR_VIRTUAL void
  SetPixel(const unsigned int i, const PixelType & v, bool & status) ITK_ITERATOR_FINAL;

  /** Set the pixel at the ith location. */
  ITK_ITERATOR_VIRTUAL void
  SetPixel(const unsigned int i, const PixelType & v) ITK_ITERATOR_FINAL;

  //  { *(this->operator[](i)) = v; }

  /** Set the pixel at offset o from the neighborhood center */
  ITK_ITERATOR_VIRTUAL void
  SetPixel(const OffsetType o, const PixelType & v) ITK_ITERATOR_FINAL
  {
    this->SetPixel(this->GetNeighborhoodIndex(o), v);
  }
  //  { *(this->operator[](o)) = v; }

  /** Sets the pixel value located i pixels distant from the neighborhood center in
      the positive specified "axis" direction. No bounds checking is done on
      the size of the neighborhood. */
  ITK_ITERATOR_VIRTUAL void
  SetNext(const unsigned int axis, const unsigned int i, const PixelType & v) ITK_ITERATOR_FINAL
  {
    this->SetPixel(this->GetCenterNeighborhoodIndex() + (i * this->GetStride(axis)), v);
  }

  /** Sets the pixel value located one pixel distant from the neighborhood center in
      the specified positive axis direction. No bounds checking is done on the
      size of the neighborhood. */
  ITK_ITERATOR_VIRTUAL void
  SetNext(const unsigned int axis, const PixelType & v) ITK_ITERATOR_FINAL
  {
    this->SetPixel(this->GetCenterNeighborhoodIndex() + this->GetStride(axis), v);
  }

  /** Sets the pixel value located i pixels distant from the neighborhood center in
      the negative specified "axis" direction. No bounds checking is done on
      the size of the neighborhood. */
  ITK_ITERATOR_VIRTUAL void
  SetPrevious(const unsigned int axis, const unsigned int i, const PixelType & v) ITK_ITERATOR_FINAL
  {
    this->SetPixel(this->GetCenterNeighborhoodIndex() - (i * this->GetStride(axis)), v);
  }

  /** Sets the pixel value located one pixel distant from the neighborhood center in
      the specified negative axis direction. No bounds checking is done on the
      size of the neighborhood. */
  ITK_ITERATOR_VIRTUAL void
  SetPrevious(const unsigned int axis, const PixelType & v) ITK_ITERATOR_FINAL
  {
    this->SetPixel(this->GetCenterNeighborhoodIndex() - this->GetStride(axis), v);
  }
};
} // namespace itk

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

#endif