/*=========================================================================
 *
 *  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 itkLineConstIterator_hxx
#define itkLineConstIterator_hxx


namespace itk
{
template <typename TImage>
LineConstIterator<TImage>::LineConstIterator(const ImageType * imagePtr,
                                             const IndexType & firstIndex,
                                             const IndexType & lastIndex)
{

  m_Image = imagePtr;

  m_StartIndex = firstIndex;
  m_LastIndex = lastIndex;

  IndexType difference;
  for (unsigned int i = 0; i < TImage::ImageDimension; ++i)
  {
    difference[i] = lastIndex[i] - firstIndex[i];
  }

  IndexValueType maxDistance = 0;
  unsigned int   maxDistanceDimension = 0;
  for (unsigned int i = 0; i < TImage::ImageDimension; ++i)
  {
    IndexValueType distance = itk::Math::abs(difference[i]);
    if (distance > maxDistance)
    {
      maxDistance = distance;
      maxDistanceDimension = i;
    }
    m_IncrementError[i] = 2 * distance;
    m_OverflowIncrement[i] = (difference[i] < 0 ? -1 : 1);
  }
  m_MainDirection = maxDistanceDimension;
  m_MaximalError.Fill(maxDistance);
  m_ReduceErrorAfterIncrement.Fill(2 * maxDistance);

  // Need to set m_EndIndex to be one pixel past the m_LastIndex along
  // the bresenham line. This is tricky to do.
  // m_EndIndex[m_MainDirection] is always offset by one from the
  // m_LastIndex[m_MainDirection].  The other indices may or may not
  // be incremented depending on the accumulated error to that point.
  //
  // To avoid traversing the line to determine whether the other
  // components need to be adjusted, we merely set the main direction
  // to be incremented and keep the remaining indices to be same as
  // LastIndex. Then in the test for IsAtEnd, we just check the
  // MainDirection component of the index.
  for (unsigned int i = 0; i < TImage::ImageDimension; ++i)
  {
    if (i == m_MainDirection)
    {
      m_EndIndex[i] = m_LastIndex[i] + m_OverflowIncrement[i];
    }
    else
    {
      m_EndIndex[i] = m_LastIndex[i];
    }
  }

  m_Region = m_Image->GetBufferedRegion();

  this->GoToBegin();
}

template <typename TImage>
LineConstIterator<TImage> &
LineConstIterator<TImage>::operator=(const Self & it)
{
  if (this != &it)
  {
    m_Image = it.m_Image; // copy the smart pointer
    m_Region = it.m_Region;
    m_IsAtEnd = it.m_IsAtEnd;
    m_CurrentImageIndex = it.m_CurrentImageIndex;
    m_StartIndex = it.m_StartIndex;
    m_LastIndex = it.m_LastIndex;
    m_EndIndex = it.m_EndIndex;
    m_MainDirection = it.m_MainDirection;
    m_AccumulateError = it.m_AccumulateError;
    m_IncrementError = it.m_IncrementError;
    m_MaximalError = it.m_MaximalError;
    m_OverflowIncrement = it.m_OverflowIncrement;
    m_ReduceErrorAfterIncrement = it.m_ReduceErrorAfterIncrement;
  }
  return *this;
}

template <typename TImage>
void
LineConstIterator<TImage>::GoToBegin()
{
  m_CurrentImageIndex = m_StartIndex;
  m_AccumulateError.Fill(0);
  m_IsAtEnd = (m_StartIndex[m_MainDirection] == m_EndIndex[m_MainDirection]);
}

template <typename TImage>
void
LineConstIterator<TImage>::operator++()
{
  // We need to modify m_AccumulateError, m_CurrentImageIndex, m_IsAtEnd
  for (unsigned int i = 0; i < TImage::ImageDimension; ++i)
  {
    if (i == m_MainDirection)
    {
      m_CurrentImageIndex[i] += m_OverflowIncrement[i];
    }
    else
    {
      m_AccumulateError[i] += m_IncrementError[i];
      if (m_AccumulateError[i] >= m_MaximalError[i])
      {
        m_CurrentImageIndex[i] += m_OverflowIncrement[i];
        m_AccumulateError[i] -= m_ReduceErrorAfterIncrement[i];
      }
    }
  }

  if (m_CurrentImageIndex[m_MainDirection] == m_EndIndex[m_MainDirection])
  {
    m_IsAtEnd = true;
  }
  else if (!m_Region.IsInside(m_CurrentImageIndex))
  {
    // The new index is outside the acceptable region.  We can iterate no
    // farther, call this the end.  NOTE THAT INPUT IS STILL INCREMENTED.
    m_IsAtEnd = true;
    itkWarningMacro("Line left region; unable to finish tracing it");
  }
}
} // end namespace itk

#endif
