/*
 * 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 otbAlphaBlendingFunctor_h
#define otbAlphaBlendingFunctor_h

#include "itkRGBAPixel.h"
namespace otb
{
namespace Functor
{
/**
 * \class AlphaBlendingFunctor
 * \brief Implements simple blending
 *
 * For each channel the blending function is as follows:
 * \f[ P_{o} = (1 - \alpha) P_{i1} + \alpha P_{i2} \f]
 * with
 * \f[ \alpha = \alpha_{pix} * \alpha_{glo} \f]
 * \f$ \alpha_{pix} \f$ is retrieved from the second pixel RGBA
 * \f$ \alpha_{glo} \f$ is provided by the SetAlpha() method (1.0 by default)
 *
 *
 * \ingroup OTBImageManipulation
 */

template <class TInputPixel1, class TInputPixel2, class TOutputPixel>
class ITK_EXPORT AlphaBlendingFunctorBase
{
public:
  AlphaBlendingFunctorBase() : m_Alpha(1.0)
  {
  }
  ~AlphaBlendingFunctorBase()
  {
  }

  typedef TInputPixel1 InputPixel1Type;
  typedef TInputPixel2 InputPixel2Type;
  typedef TOutputPixel OutputPixelType;

  virtual void SetAlpha(double a)
  {
    // Keep alpha between 0 and 1
    m_Alpha = a < 0.0 ? 0.0 : (a > 1.0 ? 1.0 : a);
  }

  virtual double GetAlpha() const
  {
    return m_Alpha;
  }

  virtual inline OutputPixelType operator()(InputPixel1Type input1, InputPixel2Type input2) const = 0;

protected:
  double m_Alpha;
};

template <class TInputPixel1, class TInputPixel2, class TOutputPixel>
class ITK_EXPORT AlphaBlendingFunctor : public AlphaBlendingFunctorBase<TInputPixel1, TInputPixel2, TOutputPixel>
{
public:
  AlphaBlendingFunctor()
  {
  }
  ~AlphaBlendingFunctor()
  {
  }

  typedef TInputPixel1 InputPixel1Type;
  typedef TInputPixel2 InputPixel2Type;
  typedef TOutputPixel OutputPixelType;

  inline OutputPixelType operator()(InputPixel1Type input1, InputPixel2Type input2) const
  {
    OutputPixelType resp;
    double          alpha = this->GetAlpha();

    resp = static_cast<OutputPixelType>(std::floor(0.5 + (1.0 - alpha) * static_cast<double>(input1) + alpha * static_cast<double>(input2)));
    return resp;
  }

protected:
  double m_Alpha;
};

template <class TInputInternalPixel1, class TInputInternalPixel2, class TOutputInternalPixel>
class ITK_EXPORT AlphaBlendingFunctor<itk::RGBAPixel<TInputInternalPixel1>, itk::RGBAPixel<TInputInternalPixel2>, itk::RGBAPixel<TOutputInternalPixel>>
    : public AlphaBlendingFunctorBase<itk::RGBAPixel<TInputInternalPixel1>, itk::RGBAPixel<TInputInternalPixel2>, itk::RGBAPixel<TOutputInternalPixel>>
{
public:
  AlphaBlendingFunctor()
  {
  }
  ~AlphaBlendingFunctor()
  {
  }

  typedef TInputInternalPixel1                    InternalInputPixel1Type;
  typedef itk::RGBAPixel<InternalInputPixel1Type> InputPixel1Type;
  typedef TInputInternalPixel2                    InternalInputPixel2Type;
  typedef itk::RGBAPixel<InternalInputPixel2Type> InputPixel2Type;
  typedef TOutputInternalPixel                    InternalOutputPixelType;
  typedef itk::RGBAPixel<InternalOutputPixelType> OutputPixelType;

  inline OutputPixelType operator()(InputPixel1Type input1, InputPixel2Type input2) const
  {
    OutputPixelType resp;
    resp.Fill(itk::NumericTraits<InternalOutputPixelType>::max());
    double alpha = static_cast<double>(input2.GetAlpha()) / 255.0 * this->GetAlpha();

    resp.SetRed(static_cast<InternalOutputPixelType>(
        std::floor(0.5 + (1.0 - alpha) * static_cast<double>(input1.GetRed()) + alpha * static_cast<double>(input2.GetRed()))));
    resp.SetGreen(static_cast<InternalOutputPixelType>(
        std::floor(0.5 + (1.0 - alpha) * static_cast<double>(input1.GetGreen()) + alpha * static_cast<double>(input2.GetGreen()))));
    resp.SetBlue(static_cast<InternalOutputPixelType>(
        std::floor(0.5 + (1.0 - alpha) * static_cast<double>(input1.GetBlue()) + alpha * static_cast<double>(input2.GetBlue()))));
    return resp;
  }

protected:
  double m_Alpha;
};
}
}

#endif