/*=========================================================================
 *
 *  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 itkTriangleThresholdCalculator_hxx
#define itkTriangleThresholdCalculator_hxx

#include "itkProgressReporter.h"
#include "itkMath.h"

#include <algorithm>

namespace itk
{

template <typename THistogram, typename TOutput>
void
TriangleThresholdCalculator<THistogram, TOutput>::GenerateData()
{
  const HistogramType * histogram = this->GetInput();

  if (histogram->GetTotalFrequency() == 0)
  {
    itkExceptionMacro("Histogram is empty");
  }
  ProgressReporter progress(this, 0, histogram->GetSize(0));
  if (histogram->GetSize(0) == 1)
  {
    this->GetOutput()->Set(static_cast<OutputType>(histogram->GetMeasurement(0, 0)));
  }

  SizeValueType size = histogram->GetSize(0);

  // Create a histogram
  std::vector<double> cumSum(size, 0.0);
  std::vector<double> triangle(size, 0.0);

  // Triangle method needs the maximum and minimum indexes
  // Minimum indexes for this purpose are poorly defined - can't just
  // take an index with zero entries.
  double         Mx = itk::NumericTraits<double>::min();
  IndexValueType MxIdx = 0;

  for (SizeValueType j = 0; j < size; ++j)
  {
    if (histogram->GetFrequency(j, 0) > Mx)
    {
      MxIdx = j;
      Mx = histogram->GetFrequency(j, 0);
    }
  }


  cumSum[0] = histogram->GetFrequency(0, 0);
  for (SizeValueType j = 1; j < size; ++j)
  {
    cumSum[j] = histogram->GetFrequency(j, 0) + cumSum[j - 1];
  }

  typename HistogramType::MeasurementVectorType onePC(1), nnPC(1);
  onePC.Fill(histogram->Quantile(0, 0.01));
  typename HistogramType::IndexType localIndex;
  histogram->GetIndex(onePC, localIndex);
  const IndexValueType onePCIdx = localIndex[0];
  nnPC.Fill(histogram->Quantile(0, 0.99));
  histogram->GetIndex(nnPC, localIndex);
  const IndexValueType nnPCIdx = localIndex[0];

  // Figure out which way we are looking - we want to construct our
  // line between the max index and the further of 1% and 99%
  IndexValueType ThreshIdx = 0;
  if (itk::Math::abs(static_cast<float>(MxIdx) - static_cast<float>(onePCIdx)) >
      itk::Math::abs(static_cast<float>(MxIdx) - static_cast<float>(nnPCIdx)))
  {
    // line to 1 %
    double slope = Mx / (MxIdx - onePCIdx);
    for (IndexValueType k = onePCIdx; k < MxIdx; ++k)
    {
      float line = slope * (k - onePCIdx);
      triangle[k] = line - histogram->GetFrequency(k);
    }

    ThreshIdx =
      onePCIdx + std::distance(&(triangle[onePCIdx]), std::max_element(&(triangle[onePCIdx]), &(triangle[MxIdx])));
  }
  else
  {
    // line to 99 %
    double slope = -Mx / (nnPCIdx - MxIdx);
    for (IndexValueType k = MxIdx; k < nnPCIdx; ++k)
    {
      float line = slope * (k - MxIdx) + Mx;
      triangle[k] = line - histogram->GetFrequency(k);
    }
    ThreshIdx = MxIdx + std::distance(&(triangle[MxIdx]), std::max_element(&(triangle[MxIdx]), &(triangle[nnPCIdx])));
  }

  this->GetOutput()->Set(static_cast<OutputType>(histogram->GetMeasurement(ThreshIdx + 1, 0)));
}

} // end namespace itk

#endif
