// Copyright (c) 2003  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/Intersections_3/include/CGAL/Intersections_3/internal/Ray_3_Triangle_3_do_intersect.h $
// $Id: include/CGAL/Intersections_3/internal/Ray_3_Triangle_3_do_intersect.h b26b07a1242 $
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Philippe Guigue

#ifndef CGAL_INTERNAL_INTERSECTIONS_RAY_3_TRIANGLE_3_DO_INTERSECT_H
#define CGAL_INTERNAL_INTERSECTIONS_RAY_3_TRIANGLE_3_DO_INTERSECT_H

#include <CGAL/enum.h>
#include <CGAL/kernel_assertions.h>

namespace CGAL {
namespace Intersections {
namespace internal {

namespace R3T3_intersection {

enum type {
  COPLANAR_RAY = 3,
  ENDPOINT_IN_TRIANGLE = 4,
  CROSS_SEGMENT = 1,
  CROSS_VERTEX = 2,
  CROSS_FACET = 0
};

} // namespace R3T3_intersection

struct r3t3_do_intersect_empty_visitor
{
  typedef bool result_type;
  result_type result(bool b){ return b; }
  void update(Orientation){}
  void ray_coplanar(){}
  void end_point_in_triangle(){}
};

struct r3t3_do_intersect_endpoint_position_visitor
{
  int m_intersection_type;

  r3t3_do_intersect_endpoint_position_visitor() : m_intersection_type(0) { }

  typedef std::pair<bool,R3T3_intersection::type> result_type;
  result_type result(bool b)
  {
    CGAL_assertion(m_intersection_type>-1 && m_intersection_type<5);
    return std::make_pair(b,enum_cast<R3T3_intersection::type>(m_intersection_type));
  }

  void update(Orientation orient)
  {
    if (orient==ZERO)
      ++m_intersection_type;
  }

  void ray_coplanar(){ m_intersection_type = 3; }
  void end_point_in_triangle(){ m_intersection_type = 4; }
};

//the template parameter Visitor here is used to offer the possibility to use
//r3t3_do_intersect_endpoint_position_visitor to track whether the endpoint of
//the ray lies inside the plane of the triangle or not. It is used for example
//in the function that checks whether a point is inside a polyhedron; if the ray
//is on an edge of the triangle, we try with another random ray (as this case does not
//happen often in practice).
//By default an empty visitor is used to avoid penalizing the running time.

template <class K,class Visitor>
typename Visitor::result_type
do_intersect_coplanar(const typename K::Triangle_3& t,
                      const typename K::Ray_3& r,
                      const K& k,
                      Visitor visitor)
{
  visitor.ray_coplanar();
  CGAL_kernel_precondition(!k.is_degenerate_3_object()(t));
  CGAL_kernel_precondition(!k.is_degenerate_3_object()(r));

  typedef typename K::Point_3 Point_3;

  typename K::Construct_point_on_3 point_on = k.construct_point_on_3_object();
  typename K::Construct_vertex_3 vertex_on = k.construct_vertex_3_object();
  typename K::Coplanar_orientation_3 coplanar_orientation = k.coplanar_orientation_3_object();

  const Point_3& p = point_on(r,0);
  const Point_3& q = point_on(r,1);

  const Point_3& A = vertex_on(t,0);
  const Point_3& B = vertex_on(t,1);
  const Point_3& C = vertex_on(t,2);

  const Point_3* a = &A;
  const Point_3* b = &B;
  const Point_3* c = &C;

  // Determine the orientation of the triangle in the common plane
  if (coplanar_orientation(A,B,C) != POSITIVE)
    {
      // The triangle is not counterclockwise oriented
      // swap two vertices.
      b = &C;
      c = &B;
    }

  // Test whether the ray's supporting line intersects the
  // triangle in the common plane

  const Orientation pqa = coplanar_orientation(p,q,*a);
  const Orientation pqb = coplanar_orientation(p,q,*b);
  const Orientation pqc = coplanar_orientation(p,q,*c);

  switch ( pqa ) {
  case POSITIVE:
    switch ( pqb ) {
    case POSITIVE:
       if (pqc == POSITIVE)
         // the triangle lies in the positive halfspace
         // defined by the ray's supporting line.
         return visitor.result(false);
       // c is isolated on the negative side
       return visitor.result(coplanar_orientation(*a,*c,p) != POSITIVE);

    case NEGATIVE:
      if (pqc == POSITIVE) // b is isolated on the negative side
        return visitor.result(coplanar_orientation(*c,*b,p) != POSITIVE);
      // a is isolated on the positive side
      return visitor.result(coplanar_orientation(*a,*c,p) != POSITIVE);

    case COLLINEAR:
      if (pqc == POSITIVE) // b is isolated on the negative side
        return visitor.result(coplanar_orientation(*c,*b,p) != POSITIVE);
      // a is isolated on the positive side
      return visitor.result(coplanar_orientation(*a,*c,p) != POSITIVE);

    default: // should not happen.
      CGAL_kernel_assertion(false);
      return visitor.result(false);
    }

  case NEGATIVE:
    switch ( pqb ) {
    case POSITIVE:
      if (pqc == POSITIVE)         // a is isolated on the negative side
        return visitor.result(coplanar_orientation(*b,*a,p) != POSITIVE);
      // b is isolated on the positive side
      return visitor.result(coplanar_orientation(*b,*a,p) != POSITIVE);

    case NEGATIVE:
      if (pqc == NEGATIVE)
        // the triangle lies in the negative halfspace
        // defined by the ray's supporting line.
        return visitor.result( false);
      // c is isolated on the positive side
      return visitor.result(coplanar_orientation(*c,*b,p) != POSITIVE);
    case COLLINEAR:
      if (pqc == NEGATIVE) // b is isolated on the positive side
        return visitor.result(coplanar_orientation(*b,*a,p) != POSITIVE);
      // a is isolated on the negative side
      return visitor.result(coplanar_orientation(*b,*a,p) != POSITIVE);

    default: // should not happen.
      CGAL_kernel_assertion(false);
      return visitor.result(false);
    }

  case COLLINEAR:
    switch ( pqb ) {
    case POSITIVE:
      if (pqc == POSITIVE) // a is isolated on the negative side
        return visitor.result(coplanar_orientation(*b,*a,p) != POSITIVE);
      // b is isolated on the positive side
      return visitor.result(coplanar_orientation(*b,*a,p) != POSITIVE);
    case NEGATIVE:
      if (pqc == NEGATIVE) // a is isolated on the positive side
        return visitor.result(coplanar_orientation(*a,*c,p) != POSITIVE);
      // b is isolated on the negative side
      return visitor.result(coplanar_orientation(*c,*b,p) != POSITIVE);

    case COLLINEAR:
      if (pqc == POSITIVE) // c is isolated on the positive side
        return visitor.result(coplanar_orientation(*c,*b,p) != POSITIVE);
      // c is isolated on the negative side
      return visitor.result(coplanar_orientation(*a,*c,p) != POSITIVE);
      // case pqc == COLLINEAR is imposiible

    default: // should not happen.
      CGAL_kernel_assertion(false);
      return visitor.result(false);
    }

  default: // should not happen.
    CGAL_kernel_assertion(false);
    return visitor.result(false);
  }
}

template <class K,class Visitor>
typename Visitor::result_type
do_intersect(const typename K::Triangle_3& t,
             const typename K::Ray_3 &r,
             const K& k,
             Visitor visitor)
{
  CGAL_kernel_precondition(!k.is_degenerate_3_object()(t));
  CGAL_kernel_precondition(!k.is_degenerate_3_object()(r));

  typedef typename K::Point_3 Point_3;

  typename K::Construct_vertex_3 vertex_on = k.construct_vertex_3_object();
  typename K::Orientation_3 orientation = k.orientation_3_object();

  const Point_3& a = vertex_on(t,0);
  const Point_3& b = vertex_on(t,1);
  const Point_3& c = vertex_on(t,2);

  typename K::Construct_vector_3  construct_vector = k.construct_vector_3_object();
  typename K::Construct_ray_3 construct_ray = k.construct_ray_3_object();
  typename K::Construct_point_on_3 point_on = k.construct_point_on_3_object();

  const Point_3& p = point_on(r,0);
  const Point_3& q = point_on(r,1);

  const Orientation ray_direction =
    orientation(a,b,c,point_on(construct_ray(a, construct_vector(r)),1));

  if (ray_direction == COPLANAR ) {
    if (orientation(a,b,c,p) == COPLANAR)
      return do_intersect_coplanar(t,r,k,visitor);
    else return visitor.result(false);
  }

  const Orientation abcp = orientation(a,b,c,p);

  switch ( abcp ) {
  case POSITIVE:
    switch ( ray_direction ) {
    case POSITIVE:
      // the ray lies in the positive open halfspaces defined by the
      // triangle's supporting plane
      return visitor.result(false);

    case NEGATIVE:{
      // The ray straddles the triangle's plane
      // p sees the triangle in counterclockwise order
      Orientation
      orient=orientation(p,q,a,b);
      if (orient == POSITIVE ) return visitor.result(false);
      visitor.update(orient);
      orient=orientation(p,q,b,c);
      if (orient == POSITIVE ) return visitor.result(false);
      visitor.update(orient);
      orient=orientation(p,q,c,a);
      if (orient == POSITIVE ) return visitor.result(false);
      visitor.update(orient);
      return visitor.result(true);
    }
    // case COPLANAR: should not happen
    default: // should not happen.
      CGAL_kernel_assertion(false);
      return visitor.result(false);
    }

  case NEGATIVE:
    switch ( ray_direction ) {
    case POSITIVE:{
      // The ray straddles the triangle's plane
      // q sees the triangle in counterclockwise order
      Orientation
      orient=orientation(q,p,a,b);
      if (orient == POSITIVE ) return visitor.result(false);
      visitor.update(orient);
      orient=orientation(q,p,b,c);
      if (orient == POSITIVE ) return visitor.result(false);
      visitor.update(orient);
      orient=orientation(q,p,c,a);
      if (orient == POSITIVE ) return visitor.result(false);
      visitor.update(orient);
      return visitor.result(true);

    }
    case NEGATIVE:
      // the ray lies in the negative open halfspaces defined by the
      // triangle's supporting plane
      return visitor.result(false);

      // case COPLANAR: should not happen

    default: // should not happen.
      CGAL_kernel_assertion(false);
      return visitor.result(false);
    }

  case COPLANAR: // p belongs to the triangle's supporting plane
    visitor.end_point_in_triangle();
    switch ( ray_direction ) {
    case POSITIVE:
      // q sees the triangle in counterclockwise order
      return visitor.result(
           orientation(q,p,a,b) != POSITIVE
        && orientation(q,p,b,c) != POSITIVE
        && orientation(q,p,c,a) != POSITIVE);

    case NEGATIVE:
      // q sees the triangle in clockwise order
      return visitor.result(
           orientation(p,q,a,b) != POSITIVE
        && orientation(p,q,b,c) != POSITIVE
        && orientation(p,q,c,a) != POSITIVE);

      // case COPLANAR: should not happen

    default: // should not happen.
      CGAL_kernel_assertion(false);
      return visitor.result(false);
    }

  default: // should not happen.
    CGAL_kernel_assertion(false);
    return visitor.result(false);
  }
}

template <class K>
typename K::Boolean
do_intersect(const typename K::Triangle_3& t,
             const typename K::Ray_3& r,
             const K& k)
{
  return do_intersect(t, r, k, r3t3_do_intersect_empty_visitor());
}

template <class K>
inline
typename K::Boolean
do_intersect(const typename K::Ray_3& r,
             const typename K::Triangle_3& t,
             const K& k)
{
  return do_intersect(t, r, k);
}

} // namespace internal
} // namespace Intersections
} // namespace CGAL

#endif // CGAL_INTERNAL_INTERSECTIONS_RAY_3_TRIANGLE_3_DO_INTERSECT_H

