/*=========================================================================
 *
 *  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 itkShapedFloodFilledFunctionConditionalConstIterator_h
#define itkShapedFloodFilledFunctionConditionalConstIterator_h

#include <queue>
#include <vector>

#include "itkSize.h"
#include "itkConditionalConstIterator.h"
#include "itkConnectedComponentAlgorithm.h"

namespace itk
{
/**
 * \class ShapedFloodFilledFunctionConditionalConstIterator
 * \brief Iterates over a flood-filled spatial function with read-only access
 *        to pixels.
 *
 * Contributed as a paper to the Insight Journal:
 * https://doi.org/10.54294/iei8xt
 *
 * \ingroup ImageIterators
 *
 * \ingroup ITKCommon
 */
template <typename TImage, typename TFunction>
class ITK_TEMPLATE_EXPORT ShapedFloodFilledFunctionConditionalConstIterator : public ConditionalConstIterator<TImage>
{
public:
  /** Standard class type aliases. */
  using Self = ShapedFloodFilledFunctionConditionalConstIterator;

  /** Type of function */
  using FunctionType = TFunction;

  /** Type of vector used to store location info in the spatial function */
  using FunctionInputType = typename TFunction::InputType;

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

  /** Index Container Type */
  using SeedsContainerType = typename std::vector<IndexType>;

  /** Offset type alias support */
  using OffsetType = typename TImage::OffsetType;

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

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

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

  /** Internal Pixel Type */
  using InternalPixelType = typename TImage::InternalPixelType;

  /** External Pixel Type */
  using PixelType = typename TImage::PixelType;

  /** Internal Neighborhood Iterator Type */
  using NeighborhoodIteratorType = typename itk::ShapedNeighborhoodIterator<ImageType>;

  /** 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. */
  static constexpr unsigned int NDimensions = TImage::ImageDimension;

  /** Constructor establishes an iterator to walk a particular image and a
   * particular region of that image. This version of the constructor uses
   * an explicit seed pixel for the flood fill, the "startIndex" */
  ShapedFloodFilledFunctionConditionalConstIterator(const ImageType * imagePtr,
                                                    FunctionType *    fnPtr,
                                                    IndexType         startIndex);

  /** Constructor establishes an iterator to walk a particular image and a
   * particular region of that image. This version of the constructor uses
   * a list of seed pixels for the flood fill */
  ShapedFloodFilledFunctionConditionalConstIterator(const ImageType *        imagePtr,
                                                    FunctionType *           fnPtr,
                                                    std::vector<IndexType> & startIndex);

  /** Constructor establishes an iterator to walk a particular image and a
   * particular region of that image. This version of the constructor
   * should be used when the seed pixel is unknown */
  ShapedFloodFilledFunctionConditionalConstIterator(const ImageType * imagePtr, FunctionType * fnPtr);

  /** Automatically find a seed pixel and set m_StartIndex. Does nothing
   * if a seed pixel isn't found. A seed pixel is determined by
   * traversing the input image's LargestPossibleRegion and
   * applying the IsPixelIncluded() test. */
  void
  FindSeedPixel();

  /** Automatically find all seed pixels. */
  void
  FindSeedPixels();

  /** Initializes the iterator, called from constructor */
  void
  InitializeIterator();

  /** Default Destructor. */
  ~ShapedFloodFilledFunctionConditionalConstIterator() override = default;

  /** Compute whether the index of interest should be included in the flood */
  bool
  IsPixelIncluded(const IndexType & index) const override = 0;

  /** operator= is provided to make sure the handle to the image is properly
   * reference counted. */
  Self &
  operator=(const Self & it)
  {
    this->m_Image = it.m_Image; // copy the smart pointer
    this->m_Region = it.m_Region;
    return *this;
  }

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

  /** Get the index. This provides a read only reference to the index.
   * This causes the index to be calculated from pointer arithmetic and is
   * therefore an expensive operation.
   * \sa SetIndex */
  const IndexType
  GetIndex() override
  {
    return m_IndexStack.front();
  }

  /** Get the pixel value */
  const PixelType
  Get() const override
  {
    return this->m_Image->GetPixel(m_IndexStack.front());
  }

  /** Is the iterator at the end of the region? */
  [[nodiscard]] bool
  IsAtEnd() const override
  {
    return this->m_IsAtEnd;
  }

  /** Put more seeds on the list */
  void
  AddSeed(const IndexType seed)
  {
    m_Seeds.push_back(seed);
  }

  /** Clear all the seeds */
  void
  ClearSeeds()
  {
    m_Seeds.clear();
  }

  /** Move an iterator to the beginning of the region. "Begin" is
   * defined as the first pixel in the region. */
  void
  GoToBegin()
  {
    // Clear the queue
    while (!m_IndexStack.empty())
    {
      m_IndexStack.pop();
    }

    this->m_IsAtEnd = true;
    // Initialize the temporary image
    m_TempPtr->FillBuffer(typename TTempImage::PixelType{});

    for (unsigned int i = 0; i < m_Seeds.size(); ++i)
    {
      if (this->m_Image->GetBufferedRegion().IsInside(m_Seeds[i]) && this->IsPixelIncluded(m_Seeds[i]))
      {
        // Push the seed onto the queue
        m_IndexStack.push(m_Seeds[i]);

        // Obviously, we're at the beginning
        this->m_IsAtEnd = false;

        // Mark the start index in the temp image as inside the
        // function, neighbor check incomplete
        m_TempPtr->SetPixel(m_Seeds[i], 2);
      }
    }
  }

  /** Walk forward one index */
  void
  operator++() override
  {
    this->DoFloodStep();
  }

  void
  DoFloodStep();

  virtual SmartPointer<FunctionType>
  GetFunction() const
  {
    return m_Function;
  }

  /** When m_FullyConnected is set to true, the neighborhood
   * iterator will inspect an 8 respectively 26 neighborhood.
   * When the value is set to false, the neighborhood will be
   * 4 in 2D and 6 in 3D. */
  void
  SetFullyConnected(const bool _arg);

  [[nodiscard]] bool
  GetFullyConnected() const;

  itkBooleanMacro(FullyConnected);

  virtual const SeedsContainerType &
  GetSeeds() const
  {
    return m_Seeds;
  }

protected: // made protected so other iterators can access
  /** Smart pointer to the function we're evaluating */
  SmartPointer<FunctionType> m_Function{};

  /** A temporary image used for storing info about indices
   * 0 = pixel has not yet been processed
   * 1 = pixel is not inside the function
   * 2 = pixel is inside the function, neighbor check incomplete
   * 3 = pixel is inside the function, neighbor check complete */
  using TTempImage = Image<unsigned char, Self::NDimensions>;

  typename TTempImage::Pointer m_TempPtr{};

  /** A list of locations to start the recursive fill */
  SeedsContainerType m_Seeds{};

  /** The origin of the source image */
  typename ImageType::PointType m_ImageOrigin{};

  /** The spacing of the source image */
  typename ImageType::SpacingType m_ImageSpacing{};

  /** The neighborhood iterator */
  NeighborhoodIteratorType m_NeighborhoodIterator{};

  /** Region of the source image */
  RegionType m_ImageRegion{};

  /** Stack used to hold the path of the iterator through the image */
  std::queue<IndexType> m_IndexStack{};

  /** Location vector used in the flood algorithm */
  FunctionInputType m_LocationVector{};

  /** Indicates whether or not we've found a neighbor that needs to be
   * checked.  */
  bool m_FoundUncheckedNeighbor{};

  /** Indicates whether or not an index is valid (inside an image)/ */
  bool m_IsValidIndex{};

  /** Defines the connectivity of the neighborhood iterator.
   * In case of 2D the default connectivity is 4 (6 in 3D) and
   * when m_FullyConnected is set to true the connectivity is
   * 8 (26 in 3D).
   */
  bool m_FullyConnected{};
};
} // end namespace itk

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

#endif
