/*
 * Copyright (C) 2005-2020 Centre National d'Etudes Spatiales (CNES)
 *
 * This file is part of Orfeo Toolbox
 *
 *     https://www.orfeo-toolbox.org/
 *
 * 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
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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 otbSavitzkyGolayInterpolationFunctor_h
#define otbSavitzkyGolayInterpolationFunctor_h

#include "otbTimeSeries.h"
#include "otbTimeSeriesLeastSquareFittingFunctor.h"


namespace otb
{
namespace Functor
{

/** \class otbSavitzkyGolayInterpolationFunctor
 *
 *  \brief: This functor implements a local polynomial regression (of
 *  degree k) on a series of values (of at least k+1 points which are
 *  treated as being equally spaced in the series) to determine the
 *  smoothed value for each point.
 *
 *  In this implementation, the interpolation is performed by least
 *  squares fitting. The size of the moving window for the
 *  interpolation can be set using the radius variable. If needed,
 *  weights for each value of the series to be used by the least
 *  squares estimation can be set (the higher the weight, the lower the
 *  confidence in the value).
 *
 *  Savitzky, A.; Golay, M.J.E. (1964). "Smoothing and Differentiation of
 *  Data by Simplified Least Squares Procedures". Analytical Chemistry 36
 *  (8): 1627-1639. doi:10.1021/ac60214a047
 *
 * \sa otbTimeSeriesLeastSquareFittingFunctor
 *
 *
 * \ingroup OTBTimeSeries
 */
template <unsigned int Radius, class TSeries, class TDates, class TWeight = TSeries, unsigned int Degree = 2>
class SavitzkyGolayInterpolationFunctor
{
public:
  typedef typename TSeries::ValueType ValueType;
  typedef typename TDates::ValueType  DateType;
  typedef typename TWeight::ValueType WeightType;
  typedef double                      CoefficientPrecisionType;
  typedef otb::PolynomialTimeSeries<Degree, CoefficientPrecisionType> TSFunctionType;
  static const unsigned int nbDates            = TSeries::Dimension;
  static const unsigned int InterpolatedLength = 2 * Radius + 1;

  typedef itk::FixedArray<ValueType, InterpolatedLength>  InterpolatedSeriesType;
  typedef itk::FixedArray<DateType, InterpolatedLength>   InterpolatedDatesType;
  typedef itk::FixedArray<WeightType, InterpolatedLength> InterpolatedWeightType;

  typedef otb::Functor::TimeSeriesLeastSquareFittingFunctor<InterpolatedSeriesType, TSFunctionType, InterpolatedDatesType, InterpolatedWeightType>
      TLSFunctorType;

  /// Constructor
  SavitzkyGolayInterpolationFunctor()
  {
  }
  /// Destructor
  virtual ~SavitzkyGolayInterpolationFunctor()
  {
  }

  inline void SetWeights(const TWeight weights)
  {
    for (unsigned int i = 0; i < m_WeightSeries.Size(); ++i)
      m_WeightSeries[i] = weights[i];
  }

  inline void SetDates(const TDates doy)
  {
    for (unsigned int i = 0; i < m_DoySeries.Size(); ++i)
      m_DoySeries[i]    = doy[i];
  }

  inline TSeries operator()(const TSeries& series) const
  {
    TSeries outSeries;

    unsigned int firstSample = Radius;
    unsigned int lastSample  = nbDates - Radius - 1;

    for (unsigned int i = 0; i < firstSample; ++i)
      outSeries[i]      = series[i];
    for (unsigned int i = lastSample + 1; i < nbDates; ++i)
      outSeries[i]      = series[i];

    for (unsigned int i = firstSample; i <= lastSample; ++i)
    {
      InterpolatedSeriesType tmpInSeries;
      InterpolatedDatesType  tmpDates;
      InterpolatedWeightType tmpWeights;

      for (unsigned int j = 0; j <= 2 * Radius; ++j)
      {
        tmpInSeries[j] = series[i + j - Radius];
        tmpDates[j]    = m_DoySeries[i + j - Radius];
        tmpWeights[j]  = m_WeightSeries[i + j - Radius];
      }

      TLSFunctorType f;
      f.SetDates(tmpDates);
      f.SetWeights(tmpWeights);
      InterpolatedSeriesType tmpOutSeries = f(tmpInSeries);
      outSeries[i]                        = tmpOutSeries[Radius];
    }

    return outSeries;
  }

private:
  TWeight m_WeightSeries;
  TDates  m_DoySeries;
};
}
} // namespace otb
#endif
