// ============================================================================
//
// Copyright (c) 2000 The CGAL Consortium
//
// This software and related documentation is part of an INTERNAL release
// of the Computational Geometry Algorithms Library (CGAL). It is not
// intended for general use.
//
// ----------------------------------------------------------------------------
//
// release       : $CGAL_Revision $
// release_date  : $CGAL_Date $
//
// file          : include/CGAL/is_degenerate_polygon_2.h
// package       : $CGAL_Package: Partition_2 $
// maintainer    : Susan Hert <hert@mpi-sb.mpg.de>
// chapter       : Planar Polygon Partitioning
//
// revision      : $Revision$
// revision_date : $Date$
//
// author(s)     : Susan Hert <hert@mpi-sb.mpg.de>
//
// coordinator   : MPI (Susan Hert <hert@mpi-sb.mpg.de>)
//
// implementation: test for degenerate polygon with collinear vertices 
// ============================================================================

#ifndef CGAL_IS_DEGENERATE_POLYGON_2_H
#define CGAL_IS_DEGENERATE_POLYGON_2_H

namespace CGAL {

// tests if a sequence of points represents a degenerate polygon (i.e.
// one of zero area)
template<class BidirectionalIterator, class Traits>
bool 
is_degenerate_polygon_2(BidirectionalIterator first, 
                        BidirectionalIterator last,
                        const Traits& traits)
{
   if (first == last) return true;

   BidirectionalIterator prev = last;
   prev--;
   BidirectionalIterator curr = first;
   BidirectionalIterator next = first;
   next++;

   // fewer than three vertices
   if (prev == first) return true; 
   if (next == last) return true; 

   typedef typename Traits::Orientation_2                Orientation_2;

   Orientation_2 orientation = traits.orientation_2_object();

   while (curr != last)
   {
     if (orientation(*prev, *curr, *next) != COLLINEAR)
        return false;

     prev++;
     if (prev == last)
        prev = first;
     next++;   
     if (next == last)
       next = first;
     curr++;
   }
   return true;

}

template<class InputIterator>
bool 
is_degenerate_polygon_2(InputIterator first, InputIterator last)
{
   if (first == last) return true;

   typedef typename std::iterator_traits<InputIterator>::value_type Point_2;
   typedef typename Kernel_traits<Point_2>::Kernel  K;
   return is_degenerate_polygon_2(first, last, K());
}

}

#endif // CGAL_IS_DEGENERATE_POLYGON_2_H