/*=========================================================================
 *
 *  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 itkImageScanlineConstIterator_h
#define itkImageScanlineConstIterator_h

#include "itkImageIterator.h"
#include <type_traits> // For remove_const_t.

namespace itk
{
/** \class ImageScanlineConstIterator
 * \brief A multi-dimensional iterator templated over image type that walks a
 * region of pixels, scanline by scanline or in the direction of the
 * fastest axis.
 *
 * The itk::ImageScanlineConstIterator is optimized for iteration speed and is the
 * first choice for pixel-wise operations on an image.
 * This iterator is preferred over the older ImageRegionConstIterator even when knowledge
 * of the current line state is not desired because of its speed.
 *
 * The following is sample usage:
 *
   \code

it = ImageScanlineConstIterator()
while ( !it.IsAtEnd() )
  {
  while ( !it.IsAtEndOfLine() )
    {
    *it += 100.0;
    ++it;
    }
   it.NextLine();
   }

   \endcode
 *
 * Iterating beyond the end of a line results it undefined behavior.
 *
 *
 * \sa ImageScanlineIterator
 * \sa ImageRegionConstIterator
 * \sa ImageConstIterator
 * \ingroup ImageIterators
 * \ingroup ITKCommon
 *
 */
template <typename TImage>
class ITK_TEMPLATE_EXPORT ImageScanlineConstIterator : public ImageConstIterator<TImage>
{
public:
  /** Standard class type alias. */
  using Self = ImageScanlineConstIterator;
  using Superclass = ImageConstIterator<TImage>;

  /** 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 ImageIteratorDimension = Superclass::ImageIteratorDimension;

  /**
   * Index type alias support While these were already typedef'ed in the superclass,
   * they need to be redone here for this subclass to compile properly with gcc.
   */
  /** Types inherited from the Superclass */
  using typename Superclass::IndexType;
  using typename Superclass::SizeType;
  using typename Superclass::OffsetType;
  using typename Superclass::RegionType;
  using typename Superclass::ImageType;
  using typename Superclass::PixelContainer;
  using typename Superclass::PixelContainerPointer;
  using typename Superclass::InternalPixelType;
  using typename Superclass::PixelType;
  using typename Superclass::AccessorType;

  /** \see LightObject::GetNameOfClass() */
  itkOverrideGetNameOfClassMacro(ImageScanlineConstIterator);

  /** Default constructor. Needed since we provide a cast constructor. */
  ImageScanlineConstIterator()
    : ImageConstIterator<TImage>()
  {
    m_SpanBeginOffset = 0;
    m_SpanEndOffset = 0;
  }

  /** Constructor establishes an iterator to walk a particular image and a
   * particular region of that image. */
  ImageScanlineConstIterator(const TImage * ptr, const RegionType & region)
    : ImageConstIterator<TImage>(ptr, region)
  {
    m_SpanBeginOffset = this->m_BeginOffset;
    m_SpanEndOffset = this->m_BeginOffset + static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  /** Constructor that can be used to cast from an ImageIterator to an
   * ImageScanlineConstIterator. Many routines return an ImageIterator, but for a
   * particular task, you may want an ImageScanlineConstIterator.  Rather than
   * provide overloaded APIs that return different types of Iterators, itk
   * returns ImageIterators and uses constructors to cast from an
   * ImageIterator to a ImageScanlineConstIterator. */
  ImageScanlineConstIterator(const ImageIterator<TImage> & it)
  {
    this->ImageConstIterator<TImage>::operator=(it);

    IndexType ind = this->GetIndex();
    m_SpanEndOffset = this->m_Offset + static_cast<OffsetValueType>(this->m_Region.GetSize()[0]) -
                      (ind[0] - this->m_Region.GetIndex()[0]);
    m_SpanBeginOffset = m_SpanEndOffset - static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  /** Constructor that can be used to cast from an ImageConstIterator to an
   * ImageScanlineConstIterator. Many routines return an ImageIterator, but for a
   * particular task, you may want an ImageScanlineConstIterator.  Rather than
   * provide overloaded APIs that return different types of Iterators, itk
   * returns ImageIterators and uses constructors to cast from an
   * ImageIterator to a ImageScanlineConstIterator. */
  ImageScanlineConstIterator(const ImageConstIterator<TImage> & it)
  {
    this->ImageConstIterator<TImage>::operator=(it);

    IndexType ind = this->GetIndex();
    m_SpanEndOffset = this->m_Offset + static_cast<OffsetValueType>(this->m_Region.GetSize()[0]) -
                      (ind[0] - this->m_Region.GetIndex()[0]);
    m_SpanBeginOffset = m_SpanEndOffset - static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  /** Move an iterator to the beginning of the region. "Begin" is
   * defined as the first pixel in the region. */
  void
  GoToBegin()
  {
    Superclass::GoToBegin();

    // reset the span offsets
    m_SpanBeginOffset = this->m_BeginOffset;
    m_SpanEndOffset = this->m_BeginOffset + static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  /** Move an iterator to the end of the region.
   *
   * "End" is defined as
   * one pixel past the last pixel of the region.
   */
  void
  GoToEnd()
  {
    Superclass::GoToEnd();

    // reset the span offsets
    m_SpanEndOffset = this->m_EndOffset;
    m_SpanBeginOffset = m_SpanEndOffset - static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  /** Go to the beginning pixel of the current line.
   *
   * \sa operator++
   * \sa operator--
   * \sa NextLine
   * \sa IsAtEndOfLine
   */
  void
  GoToBeginOfLine()
  {
    this->m_Offset = m_SpanBeginOffset;
  }

  /** Go to the past end pixel of the current line.
   *
   * \sa GoToBeginOfLine
   * \sa operator++
   * \sa operator--
   * \sa NextLine
   * \sa IsAtEndOfLine
   */
  void
  GoToEndOfLine()
  {
    this->m_Offset = m_SpanEndOffset;
  }

  /** Test if the index is at the end of line
   */
  inline bool
  IsAtEndOfLine() const
  {
    return this->m_Offset >= m_SpanEndOffset;
  }


  /** Set the index without bounds checking.
   *
   * This is overridden from the parent because we have an extra ivar.
   * \sa GetIndex
   */
  void
  SetIndex(const IndexType & ind) override
  {
    Superclass::SetIndex(ind);
    m_SpanEndOffset = this->m_Offset + static_cast<OffsetValueType>(this->m_Region.GetSize()[0]) -
                      (ind[0] - this->m_Region.GetIndex()[0]);
    m_SpanBeginOffset = m_SpanEndOffset - static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  /** Go to the next line.
   *
   * The iterator always moves to the beginning of the next line. If
   * the iterator is on the last scanline then no action is performed.
   *
   * \sa operator++
   * \sa IsAtEndOfLine
   */
  void
  NextLine();

  /** Increment (prefix) along the scanline the iterator's index.
   *
   * If the iterator is at the end of the scanline ( one past the last
   * valid element in the row ), then the results are undefined. Which
   * means is may assert in debug mode or result in an undefined
   * iterator which may have unknown consequences if used.
   */
  Self &
  operator++()
  {
    itkAssertInDebugAndIgnoreInReleaseMacro(!this->IsAtEndOfLine());
    ++this->m_Offset;
    return *this;
  }

  /** decrement (prefix) along the scanline the iterator's index.
   *
   */
  Self &
  operator--()
  {
    itkAssertInDebugAndIgnoreInReleaseMacro(!this->IsAtEndOfLine());
    --this->m_Offset;
    return *this;
  }


protected:
  OffsetValueType m_SpanBeginOffset{}; // one pixel the beginning of the scanline
  OffsetValueType m_SpanEndOffset{};   // one pixel past the end of the scanline
};

// Deduction guide for class template argument deduction (CTAD).
template <typename TImage>
ImageScanlineConstIterator(SmartPointer<TImage>, const typename TImage::RegionType &)
  ->ImageScanlineConstIterator<std::remove_const_t<TImage>>;

} // end namespace itk

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

#endif