/*=========================================================================
 *
 *  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 itkNthElementPixelAccessor_h
#define itkNthElementPixelAccessor_h

#include "itkMacro.h"
#include "itkDefaultConvertPixelTraits.h"
#include "itkVariableLengthVector.h"
#include "itkDefaultVectorPixelAccessor.h"

namespace itk
{
/**
 * \class NthElementPixelAccessor
 * \brief Give access to the N-th of a Container type
 *
 * This class is intended to be used as parameter of
 * an ImageAdaptor to make a  Container appears as being
 * of scalar type T, showing only the N-th component.
 *
 * This class is templated over the container type.
 * Any container type that provides a method:
 * operator[]( unsigned int ) can be used here,
 * for example: itkPoint, itkVector, itkVectorContainer,
 *              and std::vector.
 *
 * For performance, no bound checking is performed during
 * access to the n-th element.
 *
 * \sa ImageAdaptor
 * \sa PixelAccessor
 *
 * \ingroup ImageAdaptors
 * \ingroup ITKImageAdaptors
 */

template <typename T, typename TContainer>
class NthElementPixelAccessor
{
public:
  /** Standard class type aliases. */
  using Self = NthElementPixelAccessor;

  /** that this class will exhibit */
  using ExternalType = T;

  /** Internal type alias. It defines the internal real
   * representation of data */
  using InternalType = TContainer;

  /** Write access to the NthElement component */
  inline void
  Set(InternalType & output, const ExternalType & input) const
  {
    DefaultConvertPixelTraits<InternalType>::SetNthComponent(m_ElementNumber, output, input);
  }

  /** Read access to the NthElement component */
  inline ExternalType
  Get(const InternalType & input) const
  {
    return static_cast<ExternalType>(DefaultConvertPixelTraits<InternalType>::GetNthComponent(m_ElementNumber, input));
  }

  /** Get the element number to access in the container */
  unsigned int
  GetElementNumber() const
  {
    return m_ElementNumber;
  }

  /** Set the element number to access in the container */
  void
  SetElementNumber(unsigned int nth)
  {
    m_ElementNumber = nth;
  }

  /** This is needed to convert a pixel accessor to a functor.
   * \sa AdaptImageFilter */
  bool
  operator==(const Self & accessor) const
  {
    return m_ElementNumber == accessor.m_ElementNumber;
  }

  ITK_UNEQUAL_OPERATOR_MEMBER_FUNCTION(Self);

  /** Assignment operator */
  NthElementPixelAccessor &
  operator=(const NthElementPixelAccessor & accessor)
  {
    m_ElementNumber = accessor.m_ElementNumber;
    return *this;
  }

  /** Constructor */
  NthElementPixelAccessor() { m_ElementNumber = 0; }

private:
  // Identifier of the N-th element to be accessed
  unsigned int m_ElementNumber;
};


template <typename TOutputPixelType, typename TPixelType>
class NthElementPixelAccessor<TOutputPixelType, itk::VariableLengthVector<TPixelType>>
  : private DefaultVectorPixelAccessor<TPixelType>
{
public:
  /** Standard class type aliases. */
  using Self = NthElementPixelAccessor;

  using VectorLengthType = unsigned int;

  /** External type alias. It defines the external aspect
   * that this class will exhibit. */
  using ExternalType = TOutputPixelType;

  /** Internal type alias used by the ImageAdaptor for the buffer pointer */
  using InternalType = TPixelType;

  using ActualPixelType = VariableLengthVector<TPixelType>;

  inline void
  Set(ActualPixelType & output, const ExternalType & input) const
  {
    output[m_ElementNumber] = input;
  }

  inline void
  Set(InternalType & output, const ExternalType & input, const unsigned long offset) const
  {
    // note: v is a reference to the internal buffer, this method of
    // access relies on return value optimization to work
    ActualPixelType v = Superclass::Get(output, offset);

    return Set(v, input);
  }

  inline ExternalType
  Get(const ActualPixelType & input) const
  {
    ExternalType output;

    output = static_cast<ExternalType>(input[m_ElementNumber]);
    return output;
  }

  inline ExternalType
  Get(const InternalType & input, const SizeValueType offset) const
  {
    return Get(Superclass::Get(input, offset));
  }


  /** Get the element number to access in the container */
  unsigned int
  GetElementNumber() const
  {
    return m_ElementNumber;
  }

  /** Set the element number to access in the container */
  void
  SetElementNumber(unsigned int nth)
  {
    m_ElementNumber = nth;
  }

  /** Set the length of each vector in the VectorImage */
  void
  SetVectorLength(VectorLengthType l)
  {
    Superclass::SetVectorLength(l);
  }

  /** Get Vector lengths */
  VectorLengthType
  GetVectorLength() const
  {
    return Superclass::GetVectorLength();
  }

  NthElementPixelAccessor(unsigned int length = 1) { Superclass::SetVectorLength(length); }

  /** This is needed to convert a pixel accessor to a functor.
   * \sa AdaptImageFilter */
  bool
  operator==(const Self & accessor) const
  {
    return m_ElementNumber == accessor.m_ElementNumber;
  }

  ITK_UNEQUAL_OPERATOR_MEMBER_FUNCTION(Self);

  /** Assignment operator */
  NthElementPixelAccessor &
  operator=(const NthElementPixelAccessor & accessor)
  {
    m_ElementNumber = accessor.m_ElementNumber;
    this->SetVectorLength(accessor.GetVectorLength());
    return *this;
  }

protected:
  using Superclass = DefaultVectorPixelAccessor<TPixelType>;

private:
  VectorLengthType m_ElementNumber{ 0 };
};

} // end namespace itk

#endif