/*=========================================================================
 *
 *  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 itkQuadEdgeMeshEulerOperatorDeleteCenterVertexFunction_hxx
#define itkQuadEdgeMeshEulerOperatorDeleteCenterVertexFunction_hxx


namespace itk
{
template <typename TMesh, typename TQEType>
auto
QuadEdgeMeshEulerOperatorDeleteCenterVertexFunction<TMesh, TQEType>::Evaluate(QEType * g) -> OutputType
{
  if (!g)
  {
    itkDebugMacro("Input is not an edge.");
    return (QEType *)nullptr;
  }

  if (!this->m_Mesh)
  {
    itkDebugMacro("No mesh present.");
    return (QEType *)nullptr;
  }

  if (!g->IsInternal())
  {
    itkDebugMacro("The edge is either border or wire.");
    return (QEType *)nullptr;
  }

  // None of the incident facets of g->GetDestination() is a hole.

  // one-ring
  std::vector<PointIdentifier> pList;
  QEType *                     g_sym = g->GetSym();
  using QEIterator = typename QEType::IteratorGeom;
  for (QEIterator it = g_sym->BeginGeomOnext(); it != g_sym->EndGeomOnext(); ++it)
  {
    QEType * one_edge = it.Value();
    if (!one_edge->IsInternal())
    {
      itkDebugMacro("DeleteVertex requires a full one-ring, i.e. no holes.");
      return (QEType *)nullptr;
    }
    pList.push_back(one_edge->GetDestination());
  }

  // Condition: There are at least two distinct facets incident to the facets
  // that are incident to g->GetDestination().(This prevents the operation
  // from collapsing a volume into two facets glued together with opposite
  // orientations, such as would happen with any vertex of a tetrahedron.)
  PointIdentifier PointId1;
  PointId1 = pList.back();
  pList.pop_back();
  PointIdentifier PointId2;
  PointId2 = pList.back();
  pList.pop_back();
  const FaceRefType FirstFace = this->m_Mesh->FindEdge(PointId1, PointId2)->GetLeft();
  bool              SecondFaceFound = false;
  while ((pList.size()) && (!SecondFaceFound))
  {
    PointId1 = PointId2;
    PointId2 = pList.back();
    pList.pop_back();
    if (this->m_Mesh->FindEdge(PointId1, PointId2)->GetLeft() != FirstFace)
    {
      SecondFaceFound = true;
    }
  }
  if (!SecondFaceFound)
  {
    itkDebugMacro("DeleteVertex requires at least two distinct facets incident to the facets that are incident to "
                  "g->GetDestination().");
    return (QEType *)nullptr;
  }

  // let's do the job now.
  QEType * h = g->GetLprev();
  this->m_OldPointID = g->GetDestination();
  this->m_Mesh->LightWeightDeleteEdge(g);
  g = h->GetLnext();
  while (g != h)
  {
    while ((g->GetDestination() != this->m_OldPointID) && (g != h))
    {
      g = g->GetLnext();
    }
    if (g != h)
    {
      QEType * temp = g->GetLprev();
      this->m_Mesh->LightWeightDeleteEdge(g);
      g = temp;
    }
  }
  this->m_Mesh->AddFace(h);

  return h;
}

} // end namespace itk

#endif
