// Copyright (c) 2011 CNRS and LIRIS' Establishments (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v6.0.1/Linear_cell_complex/include/CGAL/Linear_cell_complex_operations.h $
// $Id: include/CGAL/Linear_cell_complex_operations.h 50cfbde3b84 $
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Guillaume Damiand <guillaume.damiand@liris.cnrs.fr>
//
#ifndef CGAL_LINEAR_CELL_COMPLEX_OPERATIONS_H
#define CGAL_LINEAR_CELL_COMPLEX_OPERATIONS_H 1

#include <CGAL/Cell_iterators.h>
#include <CGAL/Cell_const_iterators.h>
#include <CGAL/Origin.h>
#include <CGAL/assertions.h>

namespace CGAL {

  /** @file Linear_cell_complex_operations.h
   * Basic operators on  a linear cell complex.
   */
  namespace internal {
    template <class Point, class Vector>
    void newell_single_step_3_for_lcc(const Point& p, const Point& q, Vector& n)
    {
      // Compute normal of the face by using Newell's method: for each edge PQ
      // Nx += (Py - Qy) * (Pz + Qz);
      // Ny += (Pz - Qz) * (Px + Qx);
      // Nz += (Px - Qx) * (Py + Qy);
      n = Vector(n.x()+((p.y()-q.y())*(p.z()+q.z())),
                 n.y()+((p.z()-q.z())*(p.x()+q.x())),
                 n.z()+((p.x()-q.x())*(p.y()+q.y())));

      // Dot product formula
      /*n=Vector(n.x()+((p.y()*q.z())-(p.z()*q.y())),
               n.y()+((p.x()*q.z())-(p.z()*q.x())),
               n.z()+((p.x()*q.y())-(p.y()*q.x())));*/
    }
  } // End namespace internal

  /** Compute the normal of the given facet.
   * @param amap the used linear cell complex.
   * @param adart a dart incident to the facet.
   * @return the normal of the facet.
   */
  template <class LCC>
  typename LCC::Vector compute_normal_of_cell_2
  (const LCC& amap, typename LCC::Dart_const_descriptor adart)
  {
    typedef typename LCC::Point Point;
    typedef typename LCC::Vector Vector;

    typename LCC::Dart_const_descriptor start=adart;
    Vector normal(CGAL::NULL_VECTOR);

    // We go to the beginning of the face (first dart)
    while ( amap.is_previous_exist(start) && amap.previous(start)!=adart )
      start = amap.previous(start);

    // Now we advance to process each edge
    unsigned int nb = 0;
    const Point* curr = &amap.point(start);

    adart=start;
    do
    {
      if (amap.other_extremity(adart)==LCC::null_descriptor)
        adart=start; // To leave the loop, because we know that adart has no next dart
      else
      {
        const Point* next = &amap.point(amap.other_extremity(adart));
        internal::newell_single_step_3_for_lcc(*curr, *next, normal);
        ++nb;
        curr = next;
        if (amap.is_next_exist(adart) && amap.next(adart)!=start)
          adart=amap.next(adart);
        else
          adart=start;
      }
    }
    while(adart!=start);

    CGAL_assertion(nb>0);
    return (typename LCC::Traits::Construct_scaled_vector()(normal, 1.0/nb));
    //  return normal / std::sqrt(normal * normal);
  }

  /** Compute the normal of the given vertex.
   * @param amap the used linear cell complex.
   * @param adart a dart incident to the vertex.
   * @return the normal of the vertex.
   */
  template <class LCC>
  typename LCC::Vector compute_normal_of_cell_0
  (const LCC& amap, typename LCC::Dart_const_descriptor adart)
  {
    typedef typename LCC::Vector Vector;
    Vector normal(CGAL::NULL_VECTOR);
    unsigned int nb = 0;

    for ( typename LCC::template One_dart_per_incident_cell_range<2,0>::
          const_iterator it(amap, adart); it.cont(); ++it )
    {
      normal = typename LCC::Traits::Construct_sum_of_vectors()
        (normal, CGAL::compute_normal_of_cell_2(amap,it));
      ++nb;
    }

    if ( nb<2 ) return normal;
    return (typename LCC::Traits::Construct_scaled_vector()(normal, 1.0/nb));
  }
  // Compute the barycenter of a given i-cell
  // General case, 1<i<=dimension
  template<class LCC, unsigned int i, unsigned int dim=LCC::dimension>
  struct Barycenter_functor
  {
    static typename LCC::Point run(const LCC& amap,
                                   typename LCC::Dart_const_descriptor adart)
    {
      static_assert(0<i && i<=LCC::dimension);
      CGAL_assertion(adart != LCC::null_descriptor);

      typename LCC::Vector vec
        (typename LCC::Traits::Construct_vector()(CGAL::ORIGIN,
                                                  amap.point(adart)));
      unsigned int nb = 1;

      typename LCC::template One_dart_per_incident_cell_range<0, i, i>::
          const_iterator it(amap, adart);
      for ( ++it; it.cont(); ++it)
      {
        vec = typename LCC::Traits::Construct_sum_of_vectors()
          (vec, typename LCC::Traits::Construct_vector()(CGAL::ORIGIN,
                                                    amap.point(it) ));
        ++nb;
      }

      return typename LCC::Traits::Construct_translated_point()
        (CGAL::ORIGIN, typename LCC::Traits::Construct_scaled_vector()
         (vec, 1.0/nb));
    }
  };

  // Compute the barycenter of a given 1-cell
  template<class LCC, unsigned int dim>
  struct Barycenter_functor<LCC, 1, dim>
  {
    static typename LCC::Point run(const LCC& amap,
                                   typename LCC::Dart_const_descriptor adart)
    {
      static_assert(1<=LCC::dimension);
      CGAL_assertion(adart != LCC::null_descriptor);
      typename LCC::Dart_const_descriptor d2=amap.other_extremity(adart);
      if (d2==amap.null_descriptor) return amap.point(adart);
      return typename LCC::Traits::Construct_midpoint()
        (amap.point(adart),
         amap.point(d2));
    }
  };

  // Compute the barycenter of a given 2-cell
  template<class LCC, unsigned int dim>
  struct Barycenter_functor<LCC, 2, dim>
  {
    static typename LCC::Point run(const LCC& amap,
                                   typename LCC::Dart_const_descriptor adart)
    {
      static_assert(2<=LCC::dimension);
      CGAL_assertion(adart != LCC::null_descriptor);

      // We go to the beginning of the face (first dart, case of open face)
      typename LCC::Dart_const_descriptor start=adart;
      while ( amap.is_previous_exist(start) && amap.previous(start)!=adart )
        start = amap.previous(start);

      typename LCC::Vector vec
        (typename LCC::Traits::Construct_vector()(CGAL::ORIGIN,
                                                  amap.point(start)));

      if ((!amap.is_previous_exist(adart) && !amap.is_next_exist(adart)) ||
          amap.next(adart)==adart)
        return typename LCC::Traits::Construct_translated_point()
            (CGAL::ORIGIN, vec);  // case of face with only one edge

      unsigned int nb = 1;

      // Now we advance to process each edge
      adart=amap.next(start); // Because the first vertex was already sum up
      do
      {
        vec = typename LCC::Traits::Construct_sum_of_vectors()
          (vec, typename LCC::Traits::Construct_vector()(CGAL::ORIGIN,
                                                         amap.point(adart)));
        ++nb;
        if (amap.is_next_exist(adart) && amap.next(adart)!=start)
          adart=amap.next(adart);
        else
          adart=start;
      }
      while(adart!=start);

      CGAL_assertion(nb>1);
      return typename LCC::Traits::Construct_translated_point()
        (CGAL::ORIGIN, typename LCC::Traits::Construct_scaled_vector()
         (vec, 1.0/nb));
    }
  };

} // namespace CGAL

#endif // CGAL_LINEAR_CELL_COMPLEX_OPERATIONS_H //
// EOF //

