// Simple Particle System
// Daniel Shiffman <http://www.shiffman.net>

// A class to describe a group of Particles
// An ArrayList is used to manage the list of Particles 

class ParticleSystem {

  ArrayList particles;    // An arraylist for all the particles

    Vector3D ac = new Vector3D(0.0,0.0);
  Vector3D ve = new Vector3D(0.0,0.0);
  Vector3D lo = new Vector3D(random(width),random(height/2,height));
  float maxMass = 50;
  float minMass = 8;

  ParticleSystem() {
    particles = new ArrayList();              // Initialize the arraylist
    for (int i = 0; i < maxThings; i++) {
      lo = new Vector3D(random(width),random(height/2,height));
      particles.add(new Thing(ac,ve,lo,random(8,13)));
    }
  }

  void run() {
    numDead = 0;
    // Cycle through the ArrayList backwards b/c we are deleting
    for (int i = particles.size()-1; i >= 0; i--) {
      Thing t = (Thing) particles.get(i);
      //println(t.getMass());
      if (t.getMass() < minMass){
        remParticle(i);
      }

      if (t.dead()){
        numDead++;
      }
      updateParticle(t);
    }
  }

  void updateParticle(Thing t){
    //Attraction between things
    for (int j = 0; j < particles.size(); j++) {        // For every Thing t[j]
      Thing tj = (Thing) particles.get(j);

      if(tj.dead()){
        tj.stop();
      }
      else{
        if (t.getX() != nx && t.getY() != ny) {     // Make sure we are not calculating gravtional pull on oneself
          Vector3D f = t.calcGravForce(tj);  // Use the function we wrote above
          t.add_force(f);                      // Add the force to the object to affect its acceleration
        }
      }
    }

    //Add forces to contain objects within screen
    if (t.getY() <= height/2){
      t.add_force(new Vector3D(0,1));
    }
    else if (t.getY() < height/2 + 50 && t.getY() > height/2){
      t.add_force(new Vector3D(0,-0.5));
    }
    else if (t.getY() > height)
      t.add_force(new Vector3D(0,-10));
    else {
      t.add_force(new Vector3D(random(-5,5),random(-1,1)));
    }

    if (t.getX() > width) {
      t.add_force(new Vector3D(-10,0));
    }
    else if (t.getX() < 0)
      t.add_force(new Vector3D(10,0));

    //Things follow mouse
    if (mousePressed) {
      Vector3D m = new Vector3D(mouseX,mouseY);
      Vector3D diff = Vector3D.sub(m,t.getLoc());
      diff.normalize();
      float factor = 1.0;  // Magnitude of Acceleration (not increasing it right now)
      diff.mult(factor);
      t.setAcc(diff);
    }

    //EATING    
    for (int j = 0; j < psF.total(); j++){
      Food fj = psF.getParticle(j);
      float nx = psF.getX(j);
      float ny = psF.getY(j);

      Vector3D dir = Vector3D.sub(fj.getLoc(), t.getLoc());     // Calculate direction of force
      float d = dir.magnitude();                        // Distance between objects
      d = constrain(d,200.0f,100.0f);                      // Limiting the distance to eliminate "extreme" results for very close or very far objects
      dir.normalize();                                  // Normalize vector (distance doesn't matter here, we just want this vector for direction)
      float force = (G * 0.05 * fj.getMass() * t.getMass()) / (d * d); // Calculate gravitional force magnitude
      dir.mult(force);                                  // Get force vector --> magnitude * direction

      t.add_force(dir);                      // Add the force to the object to affect its acceleration

      if(abs(nx - t.getX()) < t.getW()/2 && abs(ny - t.getY()) < t.getH()/2){
        if (t.getMass() < maxMass){
          if(t.dead()){
          }
          else{
            t.addMass(foodInc);
            t.add_force(new Vector3D(random(-5,5),random(-1,1)));
            t.eating();
            //println(t.getW() + "  " + t.getH());
          }
        }
        psF.remParticle(j);   
      }
      else{
        t.addMass(foodDec);
      }
    }

    t.go();                                  // Implement the rest of the object's functionality

  }

  void addParticle() {
    particles.add(new Thing(ac,ve,lo,random(8,13)));
  }

  void remParticle(int i){
    if (particles.size() > 1){
      //particles.remove(i);
      Thing t = (Thing) particles.get(i);
      t.die();
    }
  }

  void delParticle(int i){
    if (particles.size() > 1){
      particles.remove(i);
    }
  }

  void delAllParticles(int i){
    particles.remove(i);
  }

  void addParticle(Thing t) {
    particles.add(t);
  }

  // A method to test if the particle system still has particles
  boolean dead() {
    if (particles.isEmpty()) {
      return true;
    } 
    else {
      return false;
    }
  }
  int total(){
    return particles.size();    
  }
}