@Override
    public void intersect( Ray ray, IntersectResult result ) {

        // TODO: Objective 2: finish this class

        // at^2 + bt + c = 0

        double A = ray.viewDirection.dot(ray.viewDirection);

        Vector3d centerToEye = new Vector3d();
        center.scale(-1);
        centerToEye.add(center, ray.eyePoint);
        center.scale(-1);

        double B = 2 * ray.viewDirection.dot(centerToEye);

        double C = centerToEye.dot(centerToEye) - Math.pow(radius, 2);

        double discriminant = Math.sqrt( Math.pow(B, 2) - 4 * A * C);

        if (discriminant < 0) {
            return;
        }

        double t0 = (-B + discriminant) / (2 * A);
        double t1 = (-B - discriminant) / (2 * A);
        if (!Double.isNaN(t0) || !Double.isNaN(t1)) {

            double firstT = Math.min(t0, t1);

            if (!Double.isInfinite(result.t) && result.t < firstT) {
                return;
            }

            ray.getPoint(firstT, result.p);

            Vector3d normal = new Vector3d();
            normal.x = result.p.x - center.x;
            normal.y = result.p.y - center.y;
            normal.z = result.p.z - center.z;
            normal.normalize();
            result.n = normal;
            result.t = firstT;
            result.material = material;

        }
    }