/*=========================================================================
 *
 *  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 itkSinRegularizedHeavisideStepFunction_hxx
#define itkSinRegularizedHeavisideStepFunction_hxx

#include "itkMath.h"

namespace itk
{
template <typename TInput, typename TOutput>
auto
SinRegularizedHeavisideStepFunction<TInput, TOutput>::Evaluate(const InputType & input) const -> OutputType
{
  if (static_cast<RealType>(input) >= this->GetEpsilon())
  {
    return NumericTraits<OutputType>::OneValue();
  }

  if (static_cast<RealType>(input) <= -this->GetEpsilon())
  {
    return OutputType{};
  }
  else
  {
    const RealType angleFactor = 0.5 * itk::Math::pi * this->GetOneOverEpsilon();
    const RealType angle = input * angleFactor;

    return static_cast<OutputType>(0.5 * (1.0 + std::sin(angle)));
  }
}

template <typename TInput, typename TOutput>
auto
SinRegularizedHeavisideStepFunction<TInput, TOutput>::EvaluateDerivative(const InputType & input) const -> OutputType
{
  if (itk::Math::Absolute(static_cast<RealType>(input)) >= this->GetEpsilon())
  {
    return OutputType{};
  }

  const RealType angleFactor = 0.5 * itk::Math::pi * this->GetOneOverEpsilon();
  const RealType angle = input * angleFactor;

  return static_cast<OutputType>(0.5 * angleFactor * std::cos(angle));
}

} // namespace itk

#endif
