// Manager object for particles moved with Verlet Integration methods

// Methods are kept separate for optimisation
// Call verlet(), then springs(), then attractions(), then pin particles, then constrain any springs, then manage collisions
// this order is usually fairly stable - instability explosions can happen but this ain't RK4 so live with it - plus check for typos, they are a common cause of instability

class Physics{
  float gravityX, gravityY, damping;
  ArrayList p;
  ArrayList s;
  ArrayList g;
  // Constructor
  Physics(){
    p = new ArrayList();
    s = new ArrayList();
    g = new ArrayList();
    damping = 0.99f;
    gravityX = 0.0f;
    gravityY = 0.0f;
  }
  // Move particles
  void verlet(){
    for(int i = 0; i < p.size(); i++){
      Particle temp = (Particle)p.get(i);
      temp.verlet();
    }
  }
  // Update springs
  void springs(){
    for(int i = 0; i < s.size(); i++){
      Spring temp = (Spring)s.get(i);
      temp.updateSpring();
    }
  }
  // Add a particle to the system and return a reference
  Particle addParticle(float x, float y){
    Particle temp = new Particle(x, y, this);
    p.add(temp);
    return temp;
  }
  // Add a spring to the system and return a reference
  Spring addSpring(Point a, Point b){
    Spring temp = new Spring(a, b);
    s.add(temp);
    return temp;
  }
  // Debug drawings
  void drawParticles(){
    for(int i = 0; i < p.size(); i++){
      Particle temp = (Particle)p.get(i);
      ellipse(temp.x, temp.y, 10, 10);
    }
  }
  void drawSprings(){
    for(int i = 0; i < s.size(); i++){
      Spring temp = (Spring)s.get(i);
      line(temp.a.x, temp.a.y, temp.b.x, temp.b.y);
    }
  }
}