/*=========================================================================
 *
 *  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 itkVnlHalfHermitianToRealInverseFFTImageFilter_hxx
#define itkVnlHalfHermitianToRealInverseFFTImageFilter_hxx

#include "itkImageRegionIteratorWithIndex.h"
#include "itkProgressReporter.h"

namespace itk
{

template <typename TInputImage, typename TOutputImage>
void
VnlHalfHermitianToRealInverseFFTImageFilter<TInputImage, TOutputImage>::GenerateData()
{
  // Get pointers to the input and output.
  typename InputImageType::ConstPointer inputPtr = this->GetInput();
  typename OutputImageType::Pointer     outputPtr = this->GetOutput();

  if (!inputPtr || !outputPtr)
  {
    return;
  }

  // We don't have a nice progress to report, but at least this simple line
  // reports the beginning and the end of the process.
  ProgressReporter progress(this, 0, 1);

  const InputSizeType   inputSize = inputPtr->GetLargestPossibleRegion().GetSize();
  const InputIndexType  inputIndex = inputPtr->GetLargestPossibleRegion().GetIndex();
  const OutputSizeType  outputSize = outputPtr->GetLargestPossibleRegion().GetSize();
  const OutputIndexType outputIndex = outputPtr->GetLargestPossibleRegion().GetIndex();

  // Allocate output buffer memory
  outputPtr->SetBufferedRegion(outputPtr->GetRequestedRegion());
  outputPtr->Allocate();

  unsigned int vectorSize = 1;
  for (unsigned int i = 0; i < ImageDimension; ++i)
  {
    if (!VnlFFTCommon::IsDimensionSizeLegal(outputSize[i]))
    {
      itkExceptionMacro("Cannot compute FFT of image with size "
                        << outputSize
                        << ". VnlHalfHermitianToRealInverseFFTImageFilter operates only on images whose size in each "
                           "dimension has only a combination of 2,3, and 5 as prime factors.");
    }
    vectorSize *= outputSize[i];
  }

  // VNL requires the full complex result of the transform, so we
  // produce it here from the half complex image assumed when the output is real.
  SignalVectorType signal(vectorSize);

  OutputIndexValueType maxXIndex = inputIndex[0] + static_cast<OutputIndexValueType>(inputSize[0]);
  unsigned int         si = 0;
  for (ImageRegionIteratorWithIndex<OutputImageType> oIt(outputPtr, outputPtr->GetLargestPossibleRegion());
       !oIt.IsAtEnd();
       ++oIt)
  {
    typename OutputImageType::IndexType index = oIt.GetIndex();
    if (index[0] >= maxXIndex)
    {
      // Flip the indices in each dimension
      for (unsigned int i = 0; i < ImageDimension; ++i)
      {
        if (index[i] != outputIndex[i])
        {
          index[i] = outputSize[i] - index[i] + 2 * outputIndex[i];
        }
      }
      signal[si] = std::conj(inputPtr->GetPixel(index));
    }
    else
    {
      signal[si] = inputPtr->GetPixel(index);
    }
    ++si;
  }

  OutputPixelType * out = outputPtr->GetBufferPointer();

  // call the proper transform, based on compile type template parameter
  VnlFFTCommon::VnlFFTTransform<OutputImageType> vnlfft(outputSize);
  vnlfft.transform(signal.data_block(), 1);

  // Copy the VNL output back to the ITK image. Extract the real part
  // of the signal. Ideally, the normalization by the number of
  // elements should have been accounted for by the VNL inverse
  // Fourier transform, but it is not. So, we take care of it by
  // dividing the signal by the vectorSize.
  for (unsigned int i = 0; i < vectorSize; ++i)
  {
    out[i] = signal[i].real() / vectorSize;
  }
}

template <typename TInputImage, typename TOutputImage>
SizeValueType
VnlHalfHermitianToRealInverseFFTImageFilter<TInputImage, TOutputImage>::GetSizeGreatestPrimeFactor() const
{
  return VnlFFTCommon::GREATEST_PRIME_FACTOR;
}


} // namespace itk
#endif
