/*=========================================================================
 *
 *  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 itkFEMElement2DC0LinearLine_h
#define itkFEMElement2DC0LinearLine_h

#include "itkFEMElementStd.h"
#include "ITKFEMExport.h"

namespace itk
{
namespace fem
{
/**
 * \class Element2DC0LinearLine
 * \brief 2-noded, linear, C0 continuous line element in 2D space.
 *  takes loads only along the length of the axis
 * \ingroup ITKFEM
 */
class ITKFEM_EXPORT Element2DC0LinearLine : public ElementStd<2, 2>
{
public:
  /** Standard class type aliases. */
  using Self = Element2DC0LinearLine;
  using TemplatedParentClass = ElementStd<2, 2>;
  using Superclass = TemplatedParentClass;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  /** \see LightObject::GetNameOfClass() */
  itkOverrideGetNameOfClassMacro(Element2DC0LinearLine);

  // ////////////////////////////////////////////////////////////////////////
  /**
   * Methods related to numeric integration
   */

  enum
  {
    DefaultIntegrationOrder = 1
  };

  /** Get the Integration point and weight */
  void
  GetIntegrationPointAndWeight(unsigned int i, VectorType & pt, Float & w, unsigned int order) const override;

  /** Get the number of integration points */
  unsigned int
  GetNumberOfIntegrationPoints(unsigned int order) const override;

  // ////////////////////////////////////////////////////////////////////////
  /**
   * Methods related to the geometry of an element
   */

  /** Return the shape functions used to interpolate across the element */
  VectorType
  ShapeFunctions(const VectorType & pt) const override;

  /** Return the shape functions derivatives in the shapeD matrix */
  void
  ShapeFunctionDerivatives(const VectorType & pt, MatrixType & shapeD) const override;

  /**
   * Get parametric/local coordinates given global coordinates. The function returns true if the
   * global coordinate is within the element else returns false.
   * For a line, line length*1e-4 is used as the tolerance
   */
  bool
  GetLocalFromGlobalCoordinates(const VectorType & globalPt, VectorType & localPt) const override;

  /**
   * We need to provide our own implementation of calculating Jacobian,
   * because the element lives in 2D space and has only one dimension.
   * The default implementation of Jacobian in the Element base class
   * is not correct since it assumes that the number of element dimensions
   * is equal to the number of spatial dimensions.
   *
   * Jacobian is a scalar for this element.
   */
  void
  Jacobian(const VectorType & pt, MatrixType & J, const MatrixType * pshapeD = nullptr) const override;

  /**
   * Distance of a point to a line.(Used in GetLocalFromGlobalCoordinates ).
   */
  Float
  DistanceToLine(const VectorType & x,
                 const VectorType & p1,
                 const VectorType & p2,
                 Float &            t,
                 VectorType &       closestPoint) const;

protected:
  void
  PrintSelf(std::ostream & os, Indent indent) const override;

  void
  PopulateEdgeIds() override; // HACK:  Should PopulateEdgeIds
                              // be const or not in this
                              // hierarchy. Sometimes it is,
                              // sometimes it is not.
};
} // end namespace fem
} // end namespace itk

#endif // itkFEMElement2DC0LinearLine_h