// Simple spring class - fairly unrealistic but gets the job done quickly
// you can modify the stiffness but a chain of springs with a stiffness above 0.5 gets unstable

class Spring extends Line{
  float restLength;
  float stiffness;
  Point moveBy;
  // Constructor
  Spring(Point a, Point b){
    super(a, b);
    stiffness = 0.5f;
    restLength = len;
    moveBy = new Point(0.0f, 0.0f);
  }
  // Move points to new positions
  void updateSpring(){
    vx = b.x - a.x;
    vy = b.y - a.y;
    len = sqrt(vx * vx + vy * vy);
    float diff = 0.0f;
    if(len > 0.0f){
      diff = (len - restLength) / len;
    }
    float mul = diff * stiffness;
    moveBy.x = -vx*mul;
    moveBy.y = -vy*mul;
    a.x -= moveBy.x;
    a.y -= moveBy.y;
    b.x += moveBy.x;
    b.y += moveBy.y;
    updateLine();
  }
  // These two constrain methods I developed to deal with the uncontrollable length of the springs
  // The spring will lax out and then it will look like an inner cord snaps to full length - not pretty but it's a good enough workaround
  void constrainFromA(float minLength, float maxLength){
    updateLine();
    if(len < minLength){
      b.x = a.x + minLength * dx;
      b.y = a.x + minLength * dy;
      updateLine();
    } else if(len > maxLength){
      b.x = a.x + maxLength * dx;
      b.y = a.y + maxLength * dy;
      updateLine();
    }
  }
  void constrainFromB(float minLength, float maxLength){
    updateLine();
    if(len < minLength){
      a.x = b.x + minLength * dx;
      a.y = b.x + minLength * dy;
      updateLine();
    } else if(len > maxLength){
      a.x = b.x + maxLength * dx;
      a.y = b.y + maxLength * dy;
      updateLine();
    }
  }
}