/*=========================================================================
 *
 *  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 itkFEMElement1DStress_hxx
#define itkFEMElement1DStress_hxx

#include "itkFEMMaterialLinearElasticity.h"

namespace itk
{
namespace fem
{
template <typename TBaseClass>
Element1DStress<TBaseClass>::Element1DStress()
  : Superclass()
{}

// ////////////////////////////////////////////////////////////////////////
/**
 * Methods related to the physics of the problem.
 */

template <typename TBaseClass>
void
Element1DStress<TBaseClass>::GetStrainDisplacementMatrix(MatrixType & B, const MatrixType & shapeDgl) const
{
  B.set_size(1, 2);

  // Copy the shape function derivatives to the B matrix.
  B[0][0] = shapeDgl[0][0];
  B[0][1] = shapeDgl[0][1];
}

template <typename TBaseClass>
void
Element1DStress<TBaseClass>::GetMaterialMatrix(MatrixType & D) const
{
  D.set_size(1, 1);
  D.fill(0.0);

  // Material properties matrix is a scalar
  D[0][0] = m_mat->GetYoungsModulus() * m_mat->GetCrossSectionalArea();
}

template <typename TBaseClass>
void
Element1DStress<TBaseClass>::GetStiffnessMatrix(MatrixType & Ke) const
{
  const unsigned int Ndims = this->GetNumberOfSpatialDimensions();
  const unsigned int Nn = this->GetNumberOfNodes();

  // First we obtain the Ke by calling the parent's
  // GetStiffnessMatrix function. This is the stiffness matrix
  // with only one DOF per node.
  Superclass::GetStiffnessMatrix(Ke);

  // Calculate the nodal displacement transformation matrix according
  // to the number of dimensions in global coordinate system
  MatrixType T(2, 2 * Ndims, 0.0);

  VectorType d = this->GetNodeCoordinates(1) - this->GetNodeCoordinates(0);
  d = d / d.magnitude();
  for (unsigned int i = 0; i < Ndims; ++i)
  {
    for (unsigned int n = 0; n < Nn; ++n)
    {
      T[n][n * Ndims + i] = d[i];
    }
  }

  // Apply the nodal displacement transformation matrix to original
  // element stiffness matrix to obtain the element stiffness
  // matrix in global coordinates.
  Ke = T.transpose() * Ke * T;
}

template <typename TBaseClass>
void
Element1DStress<TBaseClass>::PrintSelf(std::ostream & os, Indent indent) const
{
  Superclass::PrintSelf(os, indent);
  os << indent << "Young Modulus: " << this->m_mat << std::endl;
}

} // end namespace fem
} // end namespace itk

#endif