/*=========================================================================
 *
 *  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 itkValuedRegionalExtremaImageFilter_hxx
#define itkValuedRegionalExtremaImageFilter_hxx

#include "itkImageRegionIterator.h"
#include "itkNumericTraits.h"
#include "itkProgressReporter.h"
#include "itkConnectedComponentAlgorithm.h"


namespace itk
{

template <typename TInputImage, typename TOutputImage, typename TFunction1, typename TFunction2>
ValuedRegionalExtremaImageFilter<TInputImage, TOutputImage, TFunction1, TFunction2>::ValuedRegionalExtremaImageFilter()
  : m_MarkerValue(0)

{}


template <typename TInputImage, typename TOutputImage, typename TFunction1, typename TFunction2>
void
ValuedRegionalExtremaImageFilter<TInputImage, TOutputImage, TFunction1, TFunction2>::GenerateInputRequestedRegion()
{
  // call the superclass' implementation of this method
  Superclass::GenerateInputRequestedRegion();

  // We need all the input.
  auto * input = const_cast<InputImageType *>(this->GetInput());
  if (!input)
  {
    return;
  }
  input->SetRequestedRegion(input->GetLargestPossibleRegion());
}


template <typename TInputImage, typename TOutputImage, typename TFunction1, typename TFunction2>
void
ValuedRegionalExtremaImageFilter<TInputImage, TOutputImage, TFunction1, TFunction2>::EnlargeOutputRequestedRegion(
  DataObject *)
{
  OutputImageType * output = this->GetOutput();
  output->SetRequestedRegion(output->GetLargestPossibleRegion());
}


template <typename TInputImage, typename TOutputImage, typename TFunction1, typename TFunction2>
void
ValuedRegionalExtremaImageFilter<TInputImage, TOutputImage, TFunction1, TFunction2>::GenerateData()
{
  // Allocate the output
  this->AllocateOutputs();

  const InputImageType * input = this->GetInput();
  OutputImageType *      output = this->GetOutput();

  // 2 phases
  ProgressReporter progress(this, 0, this->GetOutput()->GetRequestedRegion().GetNumberOfPixels() * 2);

  // copy input to output - isn't there a better way?
  using InputIterator = ImageRegionConstIterator<TInputImage>;
  using OutputIterator = ImageRegionIterator<TOutputImage>;

  InputIterator  inIt(input, output->GetRequestedRegion());
  OutputIterator outIt(output, output->GetRequestedRegion());

  InputImagePixelType firstValue = inIt.Get();
  this->m_Flat = true;

  while (!outIt.IsAtEnd())
  {
    InputImagePixelType currentValue = inIt.Get();
    outIt.Set(static_cast<OutputImagePixelType>(currentValue));
    if (currentValue != firstValue)
    {
      this->m_Flat = false;
    }
    ++inIt;
    ++outIt;
    progress.CompletedPixel();
  }

  // if the image is flat, there is no need to do the work:
  // the image will be unchanged
  if (!this->m_Flat)
  {
    // Now for the real work!
    // More iterators - use shaped ones so that we can set connectivity
    // Note : all comments refer to finding regional minima, because
    // it is briefer and clearer than trying to describe both regional
    // maxima and minima processes at the same time
    ISizeType kernelRadius;
    kernelRadius.Fill(1);
    NOutputIterator outNIt(kernelRadius, output, output->GetRequestedRegion());
    setConnectivity(&outNIt, m_FullyConnected);

    ConstInputIterator inNIt(kernelRadius, input, output->GetRequestedRegion());
    setConnectivity(&inNIt, m_FullyConnected);

    ConstantBoundaryCondition<OutputImageType> iBC;
    iBC.SetConstant(m_MarkerValue);
    inNIt.OverrideBoundaryCondition(&iBC);

    ConstantBoundaryCondition<OutputImageType> oBC;
    oBC.SetConstant(m_MarkerValue);
    outNIt.OverrideBoundaryCondition(&oBC);

    TFunction1 compareIn;
    TFunction2 compareOut;

    outIt.GoToBegin();
    // set up the stack and neighbor list
    IndexStack                              IS;
    typename NOutputIterator::IndexListType IndexList;
    IndexList = outNIt.GetActiveIndexList();

    while (!outIt.IsAtEnd())
    {
      OutputImagePixelType V = outIt.Get();
      // if the output pixel value = the marker value then we have
      // already visited this pixel and don't need to do so again
      if (compareOut(V, m_MarkerValue))
      {
        // reposition the input iterator
        inNIt += outIt.GetIndex() - inNIt.GetIndex();

        auto Cent = static_cast<InputImagePixelType>(V);

        // check each neighbor of the input pixel
        typename ConstInputIterator::ConstIterator sIt;
        for (sIt = inNIt.Begin(); !sIt.IsAtEnd(); ++sIt)
        {
          InputImagePixelType Adjacent = sIt.Get();
          if (compareIn(Adjacent, Cent))
          {
            // The centre pixel cannot be part of a regional minima
            // because one of its neighbors is smaller.
            // Set all pixels in the output image that are connected to
            // the centre pixel and have the same value to
            // m_MarkerValue
            // This is the flood filling step. It is a simple, stack
            // based, procedure. The original value (V) of the pixel is
            // recorded and the pixel index in the output image
            // is set to the marker value. The stack is initialized
            // with the pixel index. The flooding procedure pops the
            // stack, sets that index to the marker value and places the
            // indexes of all neighbors with value V on the stack. The
            // process terminates when the stack is empty.

            outNIt += outIt.GetIndex() - outNIt.GetIndex();

            OutputImagePixelType NVal;
            OutIndexType         idx;
            // Initialize the stack
            IS.push(outNIt.GetIndex());
            outNIt.SetCenterPixel(m_MarkerValue);

            typename NOutputIterator::IndexListType::const_iterator LIt;

            while (!IS.empty())
            {
              // Pop the stack
              idx = IS.top();
              IS.pop();
              // position the iterator
              outNIt += idx - outNIt.GetIndex();
              // check neighbors
              for (LIt = IndexList.begin(); LIt != IndexList.end(); ++LIt)
              {
                NVal = outNIt.GetPixel(*LIt);
                if (NVal == V)
                {
                  // still in a flat zone
                  IS.push(outNIt.GetIndex(*LIt));

                  // set the output as the marker value
                  outNIt.SetPixel(*LIt, m_MarkerValue);
                }
              }
            }
            // end flooding
            break;
          }
        }
      }
      ++outIt;
      progress.CompletedPixel();
    }
  }
}


template <typename TInputImage, typename TOutputImage, typename TFunction1, typename TFunction2>
void
ValuedRegionalExtremaImageFilter<TInputImage, TOutputImage, TFunction1, TFunction2>::PrintSelf(std::ostream & os,
                                                                                               Indent indent) const
{
  Superclass::PrintSelf(os, indent);

  os << indent << "FullyConnected: " << (m_FullyConnected ? "On" : "Off") << std::endl;
  os << indent << "Flat: " << m_Flat << std::endl;
  os << indent << "MarkerValue: " << m_MarkerValue << std::endl;
}

} // end namespace itk

#endif
