/*=========================================================================
 *
 *  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
 *
 *  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 itkImageConstIteratorWithOnlyIndex_h
#define itkImageConstIteratorWithOnlyIndex_h

#include "itkIndex.h"
#include "itkImage.h"
#include <memory>

namespace itk
{
/** \class ImageConstIteratorWithOnlyIndex
 * \brief A base class for multi-dimensional iterators templated over image
 * type that are designed to provide only index information, and no pixel
 * access.
 *
 * ImageConstIteratorWithOnlyIndex is a templated class to represent a
 * multi-dimensional iterator, and is templated over the dimension of
 * the image.
 *
 * The "WithOnlyIndex" family of iterators differs from the "WithIndex"
 * family of iterators in that *only* index information is available. The
 * iterator does not access image data at all, and thus can be safely used with
 * images of type ImageBase.
 *
 * ImageConstIteratorWithOnlyIndex is a base class for the "WithOnlyIndex" family of
 * ITK image iterators, which are designed to efficiently keep track of the
 * image index position of the iterator during increment and decrement
 * operations.  This iterator is a base class and provides only the basic
 * construction and comparison operations. It does not provide mechanisms for
 * moving the iterator.  A subclass of ImageConstIteratorWithOnlyIndex must be used
 * to move the iterator.
 *
 * ImageConstIteratorWithOnlyIndex is a multi-dimensional iterator, requiring
 * more information be specified before the iterator can be used than
 * conventional iterators.  Whereas the std::vector::iterator from the
 * STL only needs to be passed a pointer to establish the iterator,
 * the multi-dimensional image iterator needs a pointer, the size of the region,
 * and the start index of the region. To gain access to this
 * information, ImageConstIteratorWithOnlyIndex holds a reference to the image
 * over which it is traversing.
 *
 * \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 ImageRegionConstIteratorWithOnlyIndex
 * \sa ImageRandomConstIteratorWithOnlyIndex
 * \sa ConstNeighborhoodIteratorWithOnlyIndex
 *
 * \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
 *
 * \ingroup ImageIterators
 * \ingroup ITKCommon
 */
template <typename TImage>
class ITK_TEMPLATE_EXPORT ImageConstIteratorWithOnlyIndex
{
public:
  /** Standard class type aliases. */
  using Self = ImageConstIteratorWithOnlyIndex;

  /** Dimension of the image that the iterator walks.  This constant is needed so
   * 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. */
  static constexpr unsigned int ImageDimension = TImage::ImageDimension;

  /** Index type alias support */
  using IndexType = typename TImage::IndexType;
  using IndexValueType = typename IndexType::IndexValueType;

  /** Size type alias support */
  using SizeType = typename TImage::SizeType;
  using SizeValueType = typename SizeType::SizeValueType;

  /** Region type alias support */
  using RegionType = typename TImage::RegionType;

  /** Image type alias support */
  using ImageType = TImage;

  /** Type of the Offset taken from the image */
  using OffsetType = typename TImage::OffsetType;
  using OffsetValueType = typename OffsetType::OffsetValueType;

  /** Default Constructor. Need to provide a default constructor since we
   * provide a copy constructor. */
  ImageConstIteratorWithOnlyIndex() = default;

  /** Copy Constructor. The copy constructor is provided to make sure the
   * handle to the image is properly reference counted. */
  ImageConstIteratorWithOnlyIndex(const Self & it);

  /** Constructor establishes an iterator to walk a particular image and a
   * particular region of that image. */
  ImageConstIteratorWithOnlyIndex(const TImage * ptr, const RegionType & region);

  /** Default Destructor. */
  virtual ~ImageConstIteratorWithOnlyIndex() = default;

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

  /** Get the dimension (size) of the index. */
  static unsigned int
  GetImageDimension()
  {
    return ImageDimension;
  }

  /** Comparison operator. Two iterators are the same if they "point to" the
   * same memory location */
  bool
  operator==(const Self & it) const
  {
    // two iterators are the same if they "point to" the same memory location
    return (m_PositionIndex) == (it.m_PositionIndex);
  }

  ITK_UNEQUAL_OPERATOR_MEMBER_FUNCTION(Self);

  /** Comparison operator. An iterator is "less than" another if it "points to"
   * a lower memory location. */
  bool
  operator<=(const Self & it) const
  {
    // an iterator is "less than" another if it "points to" a lower
    // memory location
    return (m_PositionIndex) <= (it.m_PositionIndex);
  }

  /** Comparison operator. An iterator is "less than" another if it "points to"
   * a lower memory location. */
  bool
  operator<(const Self & it) const
  {
    // an iterator is "less than" another if it "points to" a lower
    // memory location
    return (m_PositionIndex) < (it.m_PositionIndex);
  }

  /** Comparison operator. An iterator is "greater than" another if it
   * "points to" a higher location. */
  bool
  operator>=(const Self & it) const
  {
    // an iterator is "greater than" another if it "points to" a higher
    // memory location
    return (m_PositionIndex) >= (it.m_PositionIndex);
  }

  /** Comparison operator. An iterator is "greater than" another if it
   * "points to" a higher location. */
  bool
  operator>(const Self & it) const
  {
    // an iterator is "greater than" another if it "points to" a higher
    // memory location
    return (m_PositionIndex) > (it.m_PositionIndex);
  }

  /** Get the index. This provides a read only reference to the index.
   * \sa SetIndex */
  const IndexType &
  GetIndex() const
  {
    return m_PositionIndex;
  }

  /** Get the region that this iterator walks. ImageIterators know the
   * beginning and the end of the region of the image to iterate over. */
  const RegionType &
  GetRegion() const
  {
    return m_Region;
  }

  /** Set the index. No bounds checking is performed.
   * \sa GetIndex */
  void
  SetIndex(const IndexType & ind)
  {
    m_PositionIndex = ind;
  }

  /** Move an iterator to the beginning of the region. */
  void
  GoToBegin();

  /** Move an iterator to the End of the region. */
  void
  GoToReverseBegin();

  /** Is the iterator at the beginning of the region? */
  bool
  IsAtReverseEnd() const
  {
    return !m_Remaining;
  }

  /** Is the iterator at the end of the region? */
  bool
  IsAtEnd() const
  {
    return !m_Remaining;
  }

  /** Are there data remaining in the region ? */
  bool
  Remaining()
  {
    return m_Remaining;
  }

protected: // made protected so other iterators can access
  typename TImage::ConstPointer m_Image{};

  IndexType m_PositionIndex{ { 0 } }; // Index where we currently are
  IndexType m_BeginIndex{ { 0 } };    // Index to start iterating over
  IndexType m_EndIndex{ { 0 } };      // Index to finish iterating:
                                      // one pixel past the end of each
                                      // row, col, slice, etc....

  RegionType m_Region{}; // region to iterate over

  OffsetValueType m_OffsetTable[ImageDimension + 1]{};

  bool m_Remaining{ false };
};
} // end namespace itk

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

#endif