#include "Line.h"
#include <math.h>


int lineIntersection(const LINE *la, const LINE *lb, Vertex *v) {
  double xa1 = la->v1.getX(), ya1 = la->v1.getY();
  double xa2 = la->v2.getX(), ya2 = la->v2.getY();
  double xb1 = lb->v1.getX(), yb1 = lb->v1.getY();
  double xb2 = lb->v2.getX(), yb2 = lb->v2.getY();
  double temp;
  int switched = 0;
  Vertex v2;
  
  
  if(!v) v = &v2;
  
  if(xa1 == xa2 && ya1 == ya2) return INTERSECTION_ERROR;
  if(xb1 == xb2 && yb1 == yb2) return INTERSECTION_ERROR;
  
  if(xa1 == xa2 || xb1 == xb2) {
    temp = xa1; xa1 = ya1; ya1 = temp;
    temp = xa2; xa2 = ya2; ya2 = temp;
    temp = xb1; xb1 = yb1; yb1 = temp;
    temp = xb2; xb2 = yb2; yb2 = temp;
    
    switched = 1;
  }
  
  if(xa1 == xa2 && xb1 == xb2)
    return (xa1 == xb1) ? INTERSECTION_IDENTICAL : INTERSECTION_NONE;
  
  if(xa1 == xa2) {
    v->setX(xa1);
    v->setY(yb1);
  }
  else if(xb1 == xb2) {
    v->setX(xb1);
    v->setY(ya1);
  }
  else {
    double ma = (ya2-ya1)/(xa2-xa1);
    double mb = (yb2-yb1)/(xb2-xb1);
    double ba = ya1 - ma*xa1;
    double bb = yb1 - mb*xb1;
    
    if(ma == mb) return (ba == bb) ? INTERSECTION_IDENTICAL : INTERSECTION_NONE;
    
    v->setX((bb-ba)/(ma-mb));
    v->setY(ma*v->getX() + ba);
  }
  
  if(switched) {
    temp = v->getX(); v->setX(v->getY()); v->setY(temp);
    
    //switch back everything for segment tests
    temp = xa1; xa1 = ya1; ya1 = temp;
    temp = xa2; xa2 = ya2; ya2 = temp;
    temp = xb1; xb1 = yb1; yb1 = temp;
    temp = xb2; xb2 = yb2; yb2 = temp;
  }
  
  if(v->getX() < fmin(xa1,xa2) || v->getX() > fmax(xa1, xa2) || v->getY() < fmin(ya1,ya2) || v->getY() > fmax(ya1, ya2)) {
    if(v->getX() < fmin(xb1,xb2) || v->getX() > fmax(xb1, xb2) || v->getY() < fmin(yb1,yb2) || v->getY() > fmax(yb1, yb2))
      return INTERSECTION_LINE_LINE;
    else
      return INTERSECTION_LINE_SEGMENT;
  }
  else if(v->getX() < fmin(xb1,xb2) || v->getX() > fmax(xb1, xb2) || v->getY() < fmin(yb1,yb2) || v->getY() > fmax(yb1, yb2))
    return INTERSECTION_SEGMENT_LINE;
  else
    return INTERSECTION_SEGMENT_SEGMENT;
}