import java.awt.*;

public class WallSeg
{
   Ball pt0, pt1;
   Color color;
   String str;
   double kx, ky, scl;
   WallSeg() {
      pt0 = new Ball(250, 200);
      pt1 = new Ball(150, 50);
      color = Color.black;
      setup();
   }
   WallSeg(Ball pt1, Ball pt2) {
     this.pt0 = pt1;
     this.pt1 = pt2;
     color = Color.BLACK;
     setup();
   }
   public void setup()
   {
      kx = pt1.px-pt0.px;
      ky = pt1.py-pt0.py;
      scl = Math.hypot(kx,ky);
      kx = kx/scl;
      ky = ky/scl;
   }

   public void draw(Graphics g) {
      g.setColor(color);
      g.drawLine((int)pt0.px,(int)pt0.py,(int)pt1.px,(int)pt1.py);
   }
   public double intersect(Ball ball, double tstep) {
        // distance to pt0
	double px = ball.px - pt0.px;
	double py = ball.py - pt0.py;
	double dist, radius, q;
	double d[] = new double[3];
	radius = ball.radius;
	d[0] = Math.hypot(px,py);
	// distance to pt1
	double qx = ball.px - pt1.px;
	double qy = ball.py - pt1.py;
	d[1] = Math.hypot(qx,qy);
	// distance to line
	d[2] = (kx*py - ky*px);
	q = (px*kx+py*ky)/scl;
	if (d[2]<0) {
	   d[0] = -d[0];
           d[1] = -d[1];
        }
	if (q>1) dist = d[1];
	else if (q<0) dist = d[0];
	else dist = d[2];
	str = String.format("dist %6.1f q %6.1f",dist/radius,q);
	// calculate time to intersection
	double t;
	if (q>0 && q<1) {
	    double vperp = kx*ball.vy - ky*ball.vx;
	    t = (radius-dist)/vperp;
	    if (dist<0) t = -(radius+dist)/vperp;
	    str = str + String.format("  t %6.2f",t);
	}
	else t = -1;
        if (Math.abs(dist)<=radius)  ball.color = Color.RED;
	else ball.color = Color.YELLOW;
	ball.t = t-1;
	return t;
   }

}