ParticleSystem ps;
int i = 0;
PImage feed;
int palette[] = new int[5]; 

void setup() {
  size(512, 512, P2D);
  colorMode(RGB, 255);
  smooth();
  ps = new ParticleSystem(1000);
  // http://www.colourlovers.com/palette/1014170
  palette[0]  = color(236,219,113);
  palette[1]  = color(153,115,74);
  palette[2]  = color(6,29,37);
  palette[3]  = color(0,80,61);
  palette[4]  = color(17,41,22);
  background(palette[4]);
}

void draw() {
  ps.run();
  // this will stretch the image and blur it, with feedback
  feed = get(1,1,width-2,height-2);
  image(feed,0,0,width,height);
  // add atraction
  if (mousePressed && this.mouseButton == LEFT){
    ps.addAttraction(mouseX,mouseY, 2.2f);
  }
  // add repulsion
  if (mousePressed && this.mouseButton == RIGHT){
    ps.addRepulsion(mouseX,mouseY,-2.2f);
  }
  ps.addFriction(-0.1f);
  if (keyPressed) {
    saveFrame();
  }
}

// A simple Particle class

class Particle {
  PVector loc;
  PVector vel;
  PVector acc;
  float timer;
  color c;
  float mass;

  // Another constructor (the one we are using here)
  Particle(PVector l) {
    acc = new PVector(0, 0, 0);
    loc = l.get();
    timer = random(255.0f);
    c = (5*(int)timer)/255;
    mass = (c+1)*5;
    float absVel = 25-(timer/10);
    vel = new PVector(random(-1,1)*absVel, random(-1,1)*absVel, 0);
  }

  void run() {
    update();
    render();
  }

  // Method to update location
  void update() {
    vel.add(acc);
    loc.add(vel);
    timer -= 0.1;
    acc.mult(0);
  }

  // Method to display
  void render() {
    stroke(palette[4-c],timer);
    displayVector(vel, loc.x, loc.y, 10);
  }

  // Is the particle still useful?
  boolean dead() {
    if (timer <= 0.0) {
      return true;
    } 
    else {
      return false;
    }
  }

  void addForce(PVector f) {
    f.div(mass);   
    acc.add(f);
  }  

  void displayVector(PVector v, float x, float y, float scayl) {
    pushMatrix();
    float arrowsize = 4;
    // Translate to location to render vector
    translate(x, y);
    // Call vector heading function to get direction (note that pointing
    // up is a heading of 0) and rotate
    rotate(v.heading2D());
    // Calculate length of vector & scale it to be bigger or smaller if
    // necessary
    float len = v.mag() * scayl;
    // Draw three lines to make an arrow (draw pointing up since we've
    // rotate to the proper direction)
    line(0, 0, len, 0);
    //line(len, 0, len - arrowsize, +arrowsize / 2);
    //line(len, 0, len - arrowsize, -arrowsize / 2);
    popMatrix();
  }
}

// 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
  PVector origin; // An origin point for where particles are born

    ParticleSystem(int num, PVector v) {
    particles = new ArrayList(); // Initialize the arraylist
    origin = v.get(); // Store the origin point
    for (int i = 0; i < num; i++) {
      particles.add(new Particle(origin)); // Add "num" amount of
    }
  }

  ParticleSystem(int num) {
    particles = new ArrayList(); // Initialize the arraylist
    // particles born at random location
    for (int i = 0; i < num; i++) {
      particles.add( new Particle(new PVector(random(0,width), random(0,height))));
    }
  }


  public void addFriction(float friction) {
    for (int i = particles.size() - 1; i >= 0; i--) {
      Particle p = (Particle) particles.get(i);
      PVector f = PVector.mult(p.vel, friction);
      p.addForce(f);				
    }
  }
  public void addAttraction(int x, int y, float attraction) {
    for (int i = particles.size() - 1; i >= 0; i--) {
      Particle p = (Particle) particles.get(i);

      PVector mouseLoc = new PVector(x,y,0); 
      PVector diff = PVector.sub(mouseLoc,p.loc); 
      diff.normalize(); 

      diff.mult(attraction); 
      p.addForce(diff);				
    }
  }

  public void addRepulsion(int x, int y, float repulsion) {
    for (int i = particles.size() - 1; i >= 0; i--) {
      Particle p = (Particle) particles.get(i);

      PVector mouseLoc = new PVector(x,y,0); 
      PVector diff = PVector.sub(mouseLoc,p.loc); 
      diff.normalize(); 

      diff.mult(repulsion); 
      p.addForce(diff);				
    }
  }

  // Method to add a force vector to all particles currently in the system
  void addForce(PVector dir) {
    for (int i = particles.size()-1; i >= 0; i--) {
      Particle p = (Particle) particles.get(i);
      p.addForce(dir);
    }
  }

  void run() {
    // Cycle through the ArrayList backwards b/c we are deleting
    for (int i = particles.size() - 1; i >= 0; i--) {
      Particle p = (Particle) particles.get(i);
      p.run();
      if (p.dead()) {
        particles.remove(i);
        ps.addParticle(random(0,width), random(0,height));
      }
    }
  }

  void addParticle() {
    particles.add(new Particle(origin));
  }

  void addParticle(float x, float y) {
    particles.add(new Particle(new PVector(x, y)));
  }

  void addParticle(Particle p) {
    particles.add(p);
  }

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

}