/*=========================================================================
 *
 *  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 itkLevelSetEquationChanAndVeseInternalTerm_hxx
#define itkLevelSetEquationChanAndVeseInternalTerm_hxx


namespace itk
{

template <typename TInput, typename TLevelSetContainer>
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::LevelSetEquationChanAndVeseInternalTerm()
  : m_Mean(InputPixelRealType{})
  , m_TotalValue(InputPixelRealType{})
  , m_TotalH(LevelSetOutputRealType{})
{
  this->m_TermName = "Internal Chan And Vese term";
  this->m_RequiredData.insert("Value");
}

template <typename TInput, typename TLevelSetContainer>
void
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::Update()
{
  if (this->m_TotalH > NumericTraits<LevelSetOutputRealType>::epsilon())
  {
    const LevelSetOutputRealType inv_total_h = 1. / this->m_TotalH;

    // depending on the pixel type, it may be more efficient to do
    // a multiplication than to do a division
    this->m_Mean = this->m_TotalValue * inv_total_h;
  }
  else
  {
    this->m_Mean = InputPixelRealType{};
  }
}

template <typename TInput, typename TLevelSetContainer>
void
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::InitializeParameters()
{
  this->m_TotalValue = InputPixelRealType{};
  this->m_TotalH = LevelSetOutputRealType{};
  this->SetUp();
}


template <typename TInput, typename TLevelSetContainer>
void
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::Initialize(
  const LevelSetInputIndexType & inputIndex)
{
  if (this->m_Heaviside.IsNotNull())
  {
    InputPixelType pixel = this->m_Input->GetPixel(inputIndex);

    LevelSetOutputRealType prod;
    this->ComputeProduct(inputIndex, prod);
    this->Accumulate(pixel, prod);
  }
  else
  {
    itkWarningMacro("m_Heaviside is nullptr");
  }
}


template <typename TInput, typename TLevelSetContainer>
void
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::ComputeProduct(
  const LevelSetInputIndexType & inputIndex,
  LevelSetOutputRealType &       prod)
{
  LevelSetOutputRealType value = this->m_CurrentLevelSetPointer->Evaluate(inputIndex);
  prod = this->m_Heaviside->Evaluate(-value);
}


template <typename TInput, typename TLevelSetContainer>
void
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::UpdatePixel(
  const LevelSetInputIndexType & inputIndex,
  const LevelSetOutputRealType & oldValue,
  const LevelSetOutputRealType & newValue)
{
  // For each affected h val: h val = new hval (this will dirty some cvals)
  InputPixelType input = this->m_Input->GetPixel(inputIndex);

  const LevelSetOutputRealType oldH = this->m_Heaviside->Evaluate(-oldValue);
  const LevelSetOutputRealType newH = this->m_Heaviside->Evaluate(-newValue);
  const LevelSetOutputRealType change = newH - oldH;

  // update the foreground constant for current level-set function
  this->m_TotalH += change;
  this->m_TotalValue += input * change;
}

template <typename TInput, typename TLevelSetContainer>
auto
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::Value(const LevelSetInputIndexType & inputIndex)
  -> LevelSetOutputRealType
{
  if (this->m_Heaviside.IsNotNull())
  {
    const auto value = static_cast<LevelSetOutputRealType>(this->m_CurrentLevelSetPointer->Evaluate(inputIndex));

    const LevelSetOutputRealType d_val = this->m_Heaviside->EvaluateDerivative(-value);

    const InputPixelType   pixel = this->m_Input->GetPixel(inputIndex);
    LevelSetOutputRealType prod = 1;

    this->ComputeProductTerm(inputIndex, prod);

    const LevelSetOutputRealType oValue =
      d_val * prod * static_cast<LevelSetOutputRealType>((pixel - this->m_Mean) * (pixel - this->m_Mean));

    return oValue;
  }
  else
  {
    itkWarningMacro("m_Heaviside is nullptr");
  }
  return LevelSetOutputPixelType{};
}

template <typename TInput, typename TLevelSetContainer>
auto
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::Value(const LevelSetInputIndexType & inputIndex,
                                                                           const LevelSetDataType &       data)
  -> LevelSetOutputRealType
{
  if (this->m_Heaviside.IsNotNull())
  {
    const LevelSetOutputRealType value = data.Value.m_Value;

    const LevelSetOutputRealType d_val = this->m_Heaviside->EvaluateDerivative(-value);

    const InputPixelType pixel = this->m_Input->GetPixel(inputIndex);

    LevelSetOutputRealType prod = 1;

    this->ComputeProductTerm(inputIndex, prod);

    const LevelSetOutputRealType oValue =
      d_val * prod * static_cast<LevelSetOutputRealType>((pixel - this->m_Mean) * (pixel - this->m_Mean));

    return oValue;
  }
  else
  {
    itkWarningMacro("m_Heaviside is nullptr");
  }
  return LevelSetOutputPixelType{};
}

template <typename TInput, typename TLevelSetContainer>
void
LevelSetEquationChanAndVeseInternalTerm<TInput, TLevelSetContainer>::Accumulate(
  const InputPixelType &         inputPixel,
  const LevelSetOutputRealType & heavisideValue)
{
  this->m_TotalValue +=
    static_cast<InputPixelRealType>(inputPixel) * static_cast<LevelSetOutputRealType>(heavisideValue);
  this->m_TotalH += static_cast<LevelSetOutputRealType>(heavisideValue);
}

} // namespace itk
#endif
