// Copyright (C) 2010, Guy Barrand. All rights reserved.
// See the file tools.license for terms.

#ifndef tools_geom2
#define tools_geom2

#include <vector>
#include <cstddef>

namespace tools {

template <class VEC2>
inline double is_left(const VEC2& P0,const VEC2& P1,const VEC2& P2){
  return ( (P1.v0() - P0.v0()) * (P2.v1() - P0.v1())
         - (P2.v0() - P0.v0()) * (P1.v1() - P0.v1()) );
}

template <class VEC2>
inline bool is_inside(const VEC2& a_P,const std::vector<VEC2>& a_V) {
  // V[] = vertex points of a polygon V[n+1] with V[n]=V[0]

  // From :
  //   http://softsurfer.com/Archive/algorithm_0103/algorithm_0103.htm
  // Copyright 2001, softSurfer (www.softsurfer.com)
  // This code may be freely used and modified for any purpose
  // providing that this copyright notice is included with it.
  // SoftSurfer makes no warranty for this code, and cannot be held
  // liable for any real or imagined damage resulting from its use.
  // Users of this code must verify correctness for their application.

  size_t n = a_V.size()-1;

  int    wn = 0;    // the winding number counter

  // loop through all edges of the polygon
  for (size_t i=0; i<n; i++) {   // edge from V[i] to V[i+1]
    if (a_V[i].v1() <= a_P.v1()) {         // start y <= P[1]
      if (a_V[i+1].v1() > a_P.v1())      // an upward crossing
        if (is_left( a_V[i], a_V[i+1], a_P) > 0)  // P left of edge
          ++wn;            // have a valid up intersect
    } else {                       // start y > P[1] (no test needed)
      if (a_V[i+1].v1() <= a_P.v1())     // a downward crossing
        if (is_left( a_V[i], a_V[i+1], a_P) < 0)  // P right of edge
          --wn;            // have a valid down intersect
    }
  }
  
  return ((wn!=0)?true:false);
}

// the same done with std::pair.

template <class T>
inline double is_left(const std::pair<T,T>& P0,const std::pair<T,T>& P1,const std::pair<T,T>& P2){
  return ( (P1.first - P0.first) * (P2.second - P0.second)
         - (P2.first - P0.first) * (P1.second - P0.second) );
}

template <class T>
inline bool inside(const std::pair<T,T>& a_P,const std::vector< std::pair<T,T> >& a_V) {
  // V[] = vertex points of a polygon V[n+1] with V[n]=V[0]

  // From :
  //   http://softsurfer.com/Archive/algorithm_0103/algorithm_0103.htm
  // Copyright 2001, softSurfer (www.softsurfer.com)
  // This code may be freely used and modified for any purpose
  // providing that this copyright notice is included with it.
  // SoftSurfer makes no warranty for this code, and cannot be held
  // liable for any real or imagined damage resulting from its use.
  // Users of this code must verify correctness for their application.

  size_t n = a_V.size()-1;

  int    wn = 0;    // the winding number counter

  // loop through all edges of the polygon
  for (size_t i=0; i<n; i++) {   // edge from V[i] to V[i+1]
    if (a_V[i].second <= a_P.second) {         // start y <= P[1]
      if (a_V[i+1].second > a_P.second)      // an upward crossing
        if (is_left( a_V[i], a_V[i+1], a_P) > 0)  // P left of edge
          ++wn;            // have a valid up intersect
    } else {                       // start y > P[1] (no test needed)
      if (a_V[i+1].second <= a_P.second)     // a downward crossing
        if (is_left( a_V[i], a_V[i+1], a_P) < 0)  // P right of edge
          --wn;            // have a valid down intersect
    }
  }
  
  return ((wn!=0)?true:false);
}

}

#endif