#include "line.h"

// Returns 1 lines cross & 0 if not.
// Parallel lines won't be detected, even if they share
// the same coordinates
int LineCollision(Line a, Line b) {
	long swapTemp;
	long ay, by, cy, dy;
	
	// Ensure coords are defined in correct order
	if (a.sx > a.ex) {
		swapTemp=a.sx; a.sx=a.ex; a.ex=swapTemp;
		swapTemp=a.sy; a.sy=a.ey; a.ey=swapTemp;
	}
	if (b.sx > b.ex) {
		swapTemp=b.sx; b.sx=b.ex; b.ex=swapTemp;
		swapTemp=b.sy; b.sy=b.ey; b.ey=swapTemp;
	}
	
	// Clip lines
	if (a.sx < b.sx) {
		if (a.ex <= b.sx)
			return 0;
		ay = ((a.ey-a.sy)*(b.sx-a.sx)) / (a.ex-a.sx) + a.sy;
		cy = b.sy;
		if (b.ex < a.ex) {
			by = ((a.ey-a.sy)*(b.ex-a.sx)) / (a.ex-a.sx) + a.sy;
			dy = b.ey;
		}
		else {
			by = a.ey;
			dy = ((b.ey-b.sy)*(a.ex-b.sx)) / (b.ex-b.sx) + b.sy;
		}
	}
	else {
		if (b.ex <= a.sx)
			return 0;
		ay = a.sy;
		cy = ((b.ey-b.sy)*(a.sx-b.sx)) / (b.ex-b.sx) + b.sy;
		if (a.ex < b.ex) {
			by = a.ey;
			dy = ((b.ey-b.sy)*(a.ex-b.sx)) / (b.ex-b.sx) + b.sy;
		}
		else {
			by = ((a.ey-a.sy)*(b.ex-a.sx)) / (a.ex-a.sx) + a.sy;
			dy = b.ey;
		}
	}
	
	// Check that they cross
	return (Sgn(cy-ay) != Sgn(dy-by));
}