/*
 * Copyright (C) 2005-2019 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 otbSpectralAngleFunctor_h
#define otbSpectralAngleFunctor_h

#include "otbMath.h"
#include <algorithm>

namespace otb
{
/** \class SpectralAngleFunctor
 *  \brief This functor computes the spectral angle according to a reference pixel.
 *
 * \ingroup OTBImageManipulation
 */
namespace Functor
{
template <class TInput, class TOutputValue>
class SpectralAngleFunctor
{
public:
  SpectralAngleFunctor()
  {
    m_ReferencePixel.SetSize(4);
    m_ReferencePixel.Fill(1);
  }

  virtual ~SpectralAngleFunctor()
  {
  }
  // Binary operator
  inline TOutputValue operator()(const TInput& inPix) const
  {
    return this->Evaluate(inPix);
  }

  void SetReferencePixel(TInput ref)
  {
    m_ReferencePixel = ref;
    m_RefNorm        = 0.0;
    for (unsigned int i = 0; i < ref.Size(); ++i)
    {
      m_RefNorm += ref[i] * ref[i];
    }
    m_RefNorm = std::sqrt(static_cast<double>(m_RefNorm));
  }
  TInput GetReferencePixel() const
  {
    return m_ReferencePixel;
  }

protected:
  // This method can be reimplemented in subclasses to actually
  // compute the index value
  virtual TOutputValue Evaluate(const TInput& inPix) const
  {
    TOutputValue out;

    double dist         = 0.0;
    double scalarProd   = 0.0;
    double normProd     = 0.0;
    double normProd1    = 0.0;
    double sqrtNormProd = 0.0;
    for (unsigned int i = 0; i < std::min(inPix.Size(), m_ReferencePixel.Size()); ++i)
    {
      scalarProd += inPix[i] * m_ReferencePixel[i];
      normProd1 += inPix[i] * inPix[i];
    }
    normProd     = normProd1 * m_RefNorm * m_RefNorm;
    sqrtNormProd = std::sqrt(normProd);
    if ((sqrtNormProd == 0.0) || (scalarProd / sqrtNormProd > 1))
    {
      dist = 0.0;
    }
    else
    {
      dist = std::acos(scalarProd / sqrtNormProd);
    }

    out = static_cast<TOutputValue>(dist);
    return out;
  }

  TInput m_ReferencePixel;
  double m_RefNorm;
};

} // end namespace functor
} // end namespace otb

#endif