// Copyright (c) 2014  INRIA Sophia-Antipolis (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v6.1/Convex_hull_3/include/CGAL/Convex_hull_3/dual/halfspace_intersection_3.h $
// $Id: include/CGAL/Convex_hull_3/dual/halfspace_intersection_3.h b26b07a1242 $
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Jocelyn Meyron
//

#ifndef CGAL_HALFSPACE_INTERSECTION_3_H
#define CGAL_HALFSPACE_INTERSECTION_3_H

#include <CGAL/license/Convex_hull_3.h>

#include <CGAL/disable_warnings.h>

#include <CGAL/HalfedgeDS_default.h>
#include <CGAL/Convex_hull_3/dual/Convex_hull_traits_dual_3.h>
#include <CGAL/Origin.h>
#include <CGAL/convex_hull_3.h>
#include <CGAL/intersections.h>
#include <CGAL/assertions.h>
#include <CGAL/boost/graph/Euler_operations.h>
// For interior_polyhedron_3
#ifndef CGAL_CH3_DUAL_WITHOUT_QP_SOLVER
#include <CGAL/Convex_hull_3/dual/halfspace_intersection_interior_point_3.h>
#endif
#include <CGAL/Number_types/internal/Exact_type_selector.h>

#include <unordered_map>
#include <deque>

namespace CGAL
{
    namespace Convex_hull_3
    {
        namespace internal
        {
            // Build the primal polyhedron associated to a dual polyhedron
            // We also need the `origin` which represents a point inside the primal polyhedron
          template <class Polyhedron_dual, class Polyhedron, class Point_3>
            void
            build_primal_polyhedron(Polyhedron& primal,
                                    const Polyhedron_dual & _dual,
                                    const Point_3& origin)
            {
              typedef typename Kernel_traits<Point_3>::Kernel Kernel;
              typedef typename Kernel::RT RT;

              // Typedefs for dual

              typedef typename boost::graph_traits<Polyhedron_dual>::face_descriptor
                Facet_const_handle;
              typedef typename boost::graph_traits<Polyhedron_dual>::vertex_descriptor
                Vertex_const_descriptor;
              typedef typename boost::graph_traits<Polyhedron_dual>::halfedge_descriptor
                Halfedge_const_descriptor;

              // typedef and type for primal
              typedef typename boost::graph_traits<Polyhedron>::vertex_descriptor vertex_descriptor;
              typename boost::property_map<Polyhedron, vertex_point_t>::type vpm  =
                get(CGAL::vertex_point, primal);

              // Typedefs for intersection
              typedef typename Kernel::Plane_3 Plane_3;
              typedef typename Kernel::Line_3 Line_3;
              typedef std::optional< std::variant< Point_3,
                                                       Line_3,
                                                       Plane_3 > > result_inter;


              std::unordered_map <Facet_const_handle, vertex_descriptor> primal_vertices;

              // First, computing the primal vertices
              for(Facet_const_handle fd : faces(_dual)){
                Halfedge_const_descriptor h = fd->halfedge();
                // Build the dual plane corresponding to the current facet
                Plane_3 p1 = h->vertex()->point();
                Plane_3 p2 = h->next()->vertex()->point();
                Plane_3 p3 = h->next()->next()->vertex()->point();

                RT dp1 = p1.d() + origin.x() * p1.a()
                  + origin.y() * p1.b() + origin.z() * p1.c();
                RT dp2 = p2.d() + origin.x() * p2.a()
                  + origin.y() * p2.b() + origin.z() * p2.c();
                RT dp3 = p3.d() + origin.x() * p3.a()
                  + origin.y() * p3.b() + origin.z() * p3.c();

                Plane_3 pp1(p1.a(), p1.b(), p1.c(), dp1);
                Plane_3 pp2(p2.a(), p2.b(), p2.c(), dp2);
                Plane_3 pp3(p3.a(), p3.b(), p3.c(), dp3);

                // Compute the intersection
                result_inter result = CGAL::intersection(pp1, pp2, pp3);
                CGAL_assertion_msg(bool(result),
                                   "halfspace_intersection_3: no intersection");
                CGAL_assertion_msg(std::get_if<Point_3>(& *result) != nullptr,
                                   "halfspace_intersection_3: intersection is not a point");

                const Point_3* pp = std::get_if<Point_3>(& *result);

                // Primal vertex associated to the current dual plane
                Point_3 ppp(origin.x() + pp->x(),
                            origin.y() + pp->y(),
                            origin.z() + pp->z());

                vertex_descriptor vd = add_vertex(primal);
                primal_vertices[fd] = vd;
                put(vpm, vd, ppp);
              }

              // Then, add facets to the primal polyhedron
              // To do this, for each dual vertex, we circulate around this vertex
              // and we add an edge between each facet we encounter

              for(Vertex_const_descriptor vd : vertices( _dual)) {
                std::deque<vertex_descriptor> vertices;
                for(Halfedge_const_descriptor hd : halfedges_around_target(vd, _dual)){
                  vertices.push_front(primal_vertices[face(hd, _dual)]);
                }
                Euler::add_face(vertices,primal);
              }
            }

            // Test if a point is inside a convex polyhedron
          template <class Polyhedron, class Point>
            bool point_inside_convex_polyhedron (const Polyhedron &P,
                                                 Point const& p) {
            // Compute the equations of the facets of the polyhedron
            typedef typename boost::graph_traits<Polyhedron>::face_descriptor face_descriptor;
            typedef typename boost::graph_traits<Polyhedron>::halfedge_descriptor halfedge_descriptor;

            typename boost::property_map<Polyhedron, vertex_point_t>::const_type vpmap  = get(CGAL::vertex_point, P);

            for(face_descriptor fd : faces(P))
                {
                  halfedge_descriptor h = halfedge(fd,P), done(h);
                  Point const& p1 = get(vpmap, target(h,P));
                  h = next(h,P);
                  Point const& p2 = get(vpmap, target(h,P));
                  h = next(h,P);
                  Point p3 = get(vpmap, target(h,P));

                  while( h!=done && collinear(p1,p2,p3) )
                  {
                    h = next(h,P);
                    p3 = get(vpmap, target(h,P));
                  }
                  if (h==done) continue; //degenerate facet, skip it

                  if ( orientation (p1, p2, p3, p) != CGAL::NEGATIVE ) return false;
                }

                return true;
            }

            template <class Plane>
            bool collinear_plane (Plane u, Plane v) {
                typedef typename Kernel_traits<Plane>::Kernel Kernel;
                typedef typename Kernel::Vector_3 Vector;

                Vector uu = u.orthogonal_vector();
                Vector vv = v.orthogonal_vector();

                return CGAL::cross_product(uu, vv) == Vector(0, 0, 0);
            }

            template <class Plane>
            bool coplanar_plane (Plane u, Plane v, Plane w) {
                typedef typename Kernel_traits<Plane>::Kernel Kernel;
                typedef typename Kernel::Vector_3 Vector;

                Vector uu = u.orthogonal_vector();
                Vector vv = v.orthogonal_vector();
                Vector ww = w.orthogonal_vector();

                return CGAL::orientation(uu, vv, ww) == CGAL::COPLANAR;
            }

            // Checks if the dimension of intersection of the planes
            // is a polyhedron (dimension == 3)
            template <class InputPlaneIterator>
            bool is_intersection_dim_3 (InputPlaneIterator begin,
                                        InputPlaneIterator end) {
                typedef typename std::iterator_traits<InputPlaneIterator>::value_type Plane;
                typedef typename std::vector<Plane>::iterator PlaneIterator;

                std::vector<Plane> planes(begin, end);
                // Remove same planes
                std::size_t size = planes.size();

                // At least 4 points
                if (size < 4)
                    return false;

                // Look for two non-parallel planes
                PlaneIterator plane1_it = planes.begin();
                PlaneIterator plane2_it = std::next(planes.begin());

                while (plane2_it != planes.end() &&
                       collinear_plane(*plane1_it, *plane2_it)) {
                    ++plane2_it;
                }

                if (plane2_it == planes.end()) return false;

                PlaneIterator plane3_it = std::next(plane2_it);

                // Look for a triple of planes intersecting in a point
                while (plane3_it != planes.end() &&
                       coplanar_plane(*plane1_it, *plane2_it, *plane3_it)) {
                    ++plane3_it;
                }

                if (plane3_it == planes.end()) return false;

                return true;
            }
        } // namespace internal
    } // namespace Convex_hull_3

    // Compute the intersection of halfspaces.
    // If the user gives an origin then the function used it, otherwise, it is
    // computed using a linear program.
    template <class PlaneIterator, class Polyhedron>
    void halfspace_intersection_3 (PlaneIterator begin, PlaneIterator end,
                                   Polyhedron &P,
                                   std::optional<typename Kernel_traits<typename std::iterator_traits<PlaneIterator>::value_type>::Kernel::Point_3> origin
#ifndef CGAL_CH3_DUAL_WITHOUT_QP_SOLVER
                                   = std::nullopt
#endif
    ) {
        // Checks whether the intersection is a polyhedron
        CGAL_assertion_msg(Convex_hull_3::internal::is_intersection_dim_3(begin, end), "halfspace_intersection_3: intersection not a polyhedron");

        // Types
        typedef typename Kernel_traits<typename std::iterator_traits<PlaneIterator>::value_type>::Kernel K;
        typedef Convex_hull_3::Convex_hull_traits_dual_3<K> Hull_traits_dual_3;
        typedef HalfedgeDS_default<Hull_traits_dual_3, HalfedgeDS_items_3 > Polyhedron_dual_3;

        // if a point inside is not provided find one using linear programming
        if (!origin) {
#ifndef CGAL_CH3_DUAL_WITHOUT_QP_SOLVER
          // find a point inside the intersection
          origin = halfspace_intersection_interior_point_3(begin, end);
#endif

          CGAL_assertion_msg(origin!=std::nullopt, "halfspace_intersection_3: problem when determining a point inside the intersection");
          if (origin==std::nullopt)
            return;
        }

        // make sure the origin is on the negative side of all the planes
        CGAL_assertion_code(for(PlaneIterator pit=begin;pit!=end;++pit))
          CGAL_assertion(pit->has_on_negative_side(*origin));

        // compute the intersection of the half-space using the dual formulation
        Hull_traits_dual_3 dual_traits(*origin);
        Polyhedron_dual_3 dual_convex_hull;
        CGAL::convex_hull_3(begin, end, dual_convex_hull, dual_traits);
        Convex_hull_3::internal::build_primal_polyhedron(P, dual_convex_hull, *origin);

        // Posterior check if the origin is inside the computed polyhedron
        // The check is done only if the number type is not float or double because in that
        // case we know the construction of dual points is not exact
        CGAL_assertion_msg(
          std::is_floating_point<typename K::FT>::value ||
          Convex_hull_3::internal::point_inside_convex_polyhedron(P, *origin),
          "halfspace_intersection_3: origin not in the polyhedron"
        );
    }

  #ifndef CGAL_NO_DEPRECATED_CODE
  // Compute the intersection of halfspaces (an interior point is given.)
  template <class PlaneIterator, class Polyhedron>
  void halfspace_intersection_3 (PlaneIterator begin, PlaneIterator end,
                                 Polyhedron &P,
                                 typename Kernel_traits<typename std::iterator_traits<PlaneIterator>::value_type>::Kernel::Point_3 const& origin) {
    halfspace_intersection_3(begin, end , P, std::make_optional(origin));
  }
  #endif
} // namespace CGAL

#include <CGAL/enable_warnings.h>

#endif // CGAL_HALFSPACE_INTERSECTION_3_H

