/*=========================================================================
 *
 *  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 itkSymmetricSecondRankTensor_h
#define itkSymmetricSecondRankTensor_h

// Undefine an eventual SymmetricSecondRankTensor macro
#ifdef SymmetricSecondRankTensor
#  undef SymmetricSecondRankTensor
#endif

#include "itkIndent.h"
#include "itkFixedArray.h"
#include "itkMatrix.h"
#include "itkSymmetricEigenAnalysis.h"

namespace itk
{
/** \class SymmetricSecondRankTensor
 * \brief Represent a symmetric tensor of second rank.
 *
 * This class implements a ND symmetric tensor of second rank.
 *
 * Since SymmetricSecondRankTensor is a subclass of FixedArray,
 * you can access its components as:
 *
 * using TensorPixelType = itk::SymmetricSecondRankTensor< float >;
 * TensorPixelType tensor;
 *
 *   tensor[0] = 1.233;
 *   tensor[1] = 1.456;
 *
 * for convenience the indexed access is also available as
 *
 *   tensor(0,0) = 1.233;
 *   tensor(2,0) = 1.233;
 *
 * The Tensor in principle represents a NxN matrix, but given that it is always
 * symmetric the representation can be compacted into a N*(N+1)/2 elements
 * array that derives from the itk::FixedArray<T>
 *
 * \author Jeffrey Duda from School of Engineering at University of Pennsylvania
 * \author Torsten Rohlfing from SRI International Neuroscience Program.
 *
 * This class was mostly based on files that Jeffrey Duda, Torsten Rohlfing and
 * Martin Styner contributed to the ITK users list during a discussion on
 * support for DiffusionTensorImages. The funding for creating this class was
 * largely provided by NAMIC (National Alliance for Medical Image Computing)
 * (https://www.na-mic.org). A discussion on the design of this class can be
 * found in the WIKI pages of NAMIC:
 *
 * https://www.na-mic.org/Wiki/index.php/NAMIC_Wiki:DTI:ITK-DiffusionTensorPixelType
 *
 * \sa DiffusionTensor3D
 *
 * \ingroup ImageObjects   TensorObjects   Geometry
 * \ingroup ITKCommon
 */

template <typename TComponent, unsigned int VDimension = 3>
class ITK_TEMPLATE_EXPORT SymmetricSecondRankTensor : public FixedArray<TComponent, VDimension *(VDimension + 1) / 2>
{
public:
  /** Standard class type aliases. */
  using Self = SymmetricSecondRankTensor;
  using Superclass = FixedArray<TComponent, VDimension *(VDimension + 1) / 2>;

  /** Dimension of the vector space. */
  static constexpr unsigned int Dimension = VDimension;
  static constexpr unsigned int InternalDimension = VDimension * (VDimension + 1) / 2;

  /** Convenience type alias. */
  using BaseArray = FixedArray<TComponent, Self::InternalDimension>;

  /** Array of eigen-values. */
  using EigenValuesArrayType = FixedArray<TComponent, VDimension>;

  /** Matrix of eigen-vectors. */
  using MatrixType = Matrix<TComponent, VDimension, VDimension>;
  using EigenVectorsMatrixType = Matrix<TComponent, VDimension, VDimension>;

  /**  Define the component type. */
  using ComponentType = TComponent;
  using typename Superclass::ValueType;
  using AccumulateValueType = typename NumericTraits<ValueType>::RealType;
  using RealValueType = typename NumericTraits<ValueType>::RealType;

  using SymmetricEigenAnalysisType =
    SymmetricEigenAnalysisFixedDimension<Dimension, MatrixType, EigenValuesArrayType, EigenVectorsMatrixType>;

  /** Default-constructor.
   * \note The other five "special member functions" are defaulted implicitly, following the C++ "Rule of Zero". */
#ifdef ITK_FUTURE_LEGACY_REMOVE
  SymmetricSecondRankTensor() = default;
#else
  SymmetricSecondRankTensor() { this->Fill(0); }
#endif

  SymmetricSecondRankTensor(const ComponentType & r) { this->Fill(r); }

  /** Constructor to enable casting...  */
  template <typename TCoordRepB>
  SymmetricSecondRankTensor(const SymmetricSecondRankTensor<TCoordRepB, VDimension> & pa)
    : BaseArray(pa)
  {}

  using ComponentArrayType = ComponentType[Self::InternalDimension];

  /** Pass-through constructor for the Array base class. */
  SymmetricSecondRankTensor(const ComponentArrayType r)
    : BaseArray(r)
  {}

  /** Templated Pass-through assignment  for the Array base class. */
  template <typename TCoordRepB>
  Self &
  operator=(const SymmetricSecondRankTensor<TCoordRepB, VDimension> & pa)
  {
    BaseArray::operator=(pa);
    return *this;
  }

  /** Pass-through assignment operator for the Array base class. */
  Self &
  operator=(const ComponentType & r);

  Self &
  operator=(const ComponentArrayType r);

  /** Arithmetic operations between pixels. Return a new
    SymmetricSecondRankTensor. */
  Self
  operator+(const Self & r) const;

  Self
  operator-(const Self & r) const;

  const Self &
  operator+=(const Self & r);

  const Self &
  operator-=(const Self & r);

  /** Arithmetic operations between tensors and scalars */
  Self operator*(const RealValueType & r) const;

  Self
  operator/(const RealValueType & r) const;

  const Self &
  operator*=(const RealValueType & r);

  const Self &
  operator/=(const RealValueType & r);

  /** Return the number of components. */
  static unsigned int
  GetNumberOfComponents()
  {
    return Self::InternalDimension;
  }

  /** Return the value for the Nth component. */
  ComponentType
  GetNthComponent(int c) const
  {
    return this->operator[](c);
  }

  /** Set the Nth component to v. */
  void
  SetNthComponent(int c, const ComponentType & v)
  {
    this->operator[](c) = v;
  }

  /** Matrix notation, in const and non-const forms. */
  ValueType &
  operator()(unsigned int row, unsigned int col);

  const ValueType &
  operator()(unsigned int row, unsigned int col) const;

  /** Set the tensor to an identity tensor. This has 1 in its diagonal elements and
   * zero elsewhere. */
  void
  SetIdentity();

  /** Get Trace value */
  AccumulateValueType
  GetTrace() const;

  /** Return an array containing EigenValues. */
  void
  ComputeEigenValues(EigenValuesArrayType & eigenValues) const;

  /** Return an array containing EigenValues, and a matrix containing Eigen
   * vectors. */
  void
  ComputeEigenAnalysis(EigenValuesArrayType & eigenValues, EigenVectorsMatrixType & eigenVectors) const;

  /** Returns the tensor rotated by the provided matrix.
   *  ResultingTensor = Matrix * ThisTensor * Matrix.GetTranspose()
   */
  template <typename TMatrixValueType>
  Self
  Rotate(const Matrix<TMatrixValueType, VDimension, VDimension> & m) const;
  template <typename TMatrixValueType>
  Self
  Rotate(const vnl_matrix_fixed<TMatrixValueType, VDimension, VDimension> & m) const
  {
    return this->Rotate(static_cast<Matrix<TMatrixValueType, VDimension, VDimension>>(m));
  }
  template <typename TMatrixValueType>
  Self
  Rotate(const vnl_matrix<TMatrixValueType> & m) const
  {
    return this->Rotate(static_cast<Matrix<TMatrixValueType>>(m));
  }

  /** Pre-Multiply by a Matrix as ResultingMatrix = Matrix * ThisTensor. */
  MatrixType
  PreMultiply(const MatrixType & m) const;

  /** Post-Multiply by a Matrix as ResultingMatrix = ThisTensor * Matrix. */
  MatrixType
  PostMultiply(const MatrixType & m) const;

private:
};

/** This extra type alias is necessary for preventing an Internal Compiler Error in
 * Microsoft Visual C++ 6.0. This type alias is not needed for any other compiler. */
using OutputStreamType = std::ostream;
using InputStreamType = std::istream;

template <typename TComponent, unsigned int VDimension>
OutputStreamType &
operator<<(OutputStreamType & os, const SymmetricSecondRankTensor<TComponent, VDimension> & c);

template <typename TComponent, unsigned int VDimension>
InputStreamType &
operator>>(InputStreamType & is, SymmetricSecondRankTensor<TComponent, VDimension> & dt);

template <typename T>
inline void
swap(SymmetricSecondRankTensor<T> & a, SymmetricSecondRankTensor<T> & b)
{
  a.swap(b);
}
} // end namespace itk

#include "itkNumericTraitsTensorPixel.h"

#ifndef ITK_MANUAL_INSTANTIATION
#  include "itkSymmetricSecondRankTensor.hxx"
#endif

#endif