// Copyright (c) 2000
// Utrecht University (The Netherlands),
// ETH Zurich (Switzerland),
// INRIA Sophia-Antipolis (France),
// Max-Planck-Institute Saarbruecken (Germany),
// and Tel-Aviv University (Israel).  All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v6.1/Intersections_2/include/CGAL/Intersections_2/Line_2_Segment_2.h $
// $Id: include/CGAL/Intersections_2/Line_2_Segment_2.h b26b07a1242 $
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Geert-Jan Giezeman


#ifndef CGAL_INTERSECTIONS_2_SEGMENT_2_LINE_2_H
#define CGAL_INTERSECTIONS_2_SEGMENT_2_LINE_2_H

#include <CGAL/Line_2.h>
#include <CGAL/Segment_2.h>
#include <CGAL/kernel_assertions.h>
#include <CGAL/number_utils.h>
#include <CGAL/Intersections_2/Line_2_Line_2.h>
#include <CGAL/Intersection_traits_2.h>

namespace CGAL {

namespace Intersections {

namespace internal {

template <class K>
class Segment_2_Line_2_pair {
public:
    enum Intersection_results {NO_INTERSECTION, POINT, SEGMENT, UNKNOWN};
    Segment_2_Line_2_pair(typename K::Segment_2 const *seg,
                          typename K::Line_2 const *line)
      : _seg(seg), _line(line) {}

    Intersection_results intersection_type() const;

    typename K::Point_2    intersection_point() const;
    typename K::Segment_2  intersection_segment() const;
protected:
    typename K::Segment_2 const*_seg;
    typename K::Line_2 const *  _line;
    mutable Intersection_results     _result = UNKNOWN;
    mutable typename K::Point_2         _intersection_point;
};

template <class K>
inline
typename K::Boolean
do_intersect(const typename K::Segment_2& s,
             const typename K::Line_2& l,
             const K& )
{
  typedef Segment_2_Line_2_pair<K> pair_t;
  pair_t pair(&s, &l);
  return pair.intersection_type() != pair_t::NO_INTERSECTION;
}

template <class K>
inline
typename K::Boolean
do_intersect(const typename K::Line_2& l,
             const typename K::Segment_2& s,
             const K& k)
{
  return internal::do_intersect(s, l, k);
}

template <class K>
typename CGAL::Intersection_traits
<K, typename K::Segment_2, typename K::Line_2>::result_type
intersection(const typename K::Segment_2 &seg,
             const typename K::Line_2 &line,
             const K&)
{
    typedef Segment_2_Line_2_pair<K> is_t;

    is_t ispair(&seg, &line);
    switch (ispair.intersection_type()) {
    case is_t::NO_INTERSECTION:
    default:
        return intersection_return<typename K::Intersect_2, typename K::Line_2, typename K::Segment_2>();
    case is_t::POINT:
        return intersection_return<typename K::Intersect_2, typename K::Line_2, typename K::Segment_2>(ispair.intersection_point());
    case is_t::SEGMENT:
        return intersection_return<typename K::Intersect_2, typename K::Line_2, typename K::Segment_2>(seg);
    }
}

template <class K>
typename CGAL::Intersection_traits
<K, typename K::Line_2, typename K::Segment_2>::result_type
intersection(const typename K::Line_2 &line,
             const typename K::Segment_2 &seg,
             const K& k)
{
  return internal::intersection(seg, line, k);
}

template <class K>
typename Segment_2_Line_2_pair<K>::Intersection_results
Segment_2_Line_2_pair<K>::intersection_type() const
{
    if (_result!=UNKNOWN)
        return _result;
    // The non const this pointer is used to cast away const.
    const typename K::Line_2 &l1 = _seg->supporting_line();
    Line_2_Line_2_pair<K> linepair(&l1, _line);
    switch ( linepair.intersection_type()) {
    case Line_2_Line_2_pair<K>::NO_INTERSECTION:
        _result = NO_INTERSECTION;
        break;
    case Line_2_Line_2_pair<K>::POINT:
        _intersection_point = linepair.intersection_point();
        _result = (_seg->collinear_has_on(_intersection_point) )
                ? POINT : NO_INTERSECTION;
        break;
    case Line_2_Line_2_pair<K>::LINE:
        _result = SEGMENT;
        break;
    default:
      CGAL_unreachable();
    }
    return _result;
}

template <class K>
typename K::Point_2
Segment_2_Line_2_pair<K>::intersection_point() const
{
    if (_result==UNKNOWN)
        intersection_type();
    CGAL_kernel_assertion(_result == POINT);
    return _intersection_point;
}

template <class K>
typename K::Segment_2
Segment_2_Line_2_pair<K>::intersection_segment() const
{
    if (_result==UNKNOWN)
        intersection_type();
    CGAL_kernel_assertion(_result == SEGMENT);
    return *_seg;
}

} // namespace internal
} // namespace Intersections

CGAL_INTERSECTION_FUNCTION(Segment_2, Line_2, 2)
CGAL_DO_INTERSECT_FUNCTION(Segment_2, Line_2, 2)

} // namespace CGAL

#endif // CGAL_INTERSECTIONS_2_SEGMENT_2_LINE_2_H

