import draw.*;
import colors.*;
import geometry.*;
import java.util.Random;

class Star {
  Posn loc;
  private int dx;
  private int dy;
  
  Random r = new Random();
  
  private Star(Posn loc, int dx, int dy) {
    this.loc = loc;
    this.dx = dx;
    this.dy = dy;
  }
  
  public Star() {
    this.loc = new Posn(100,0);
    this.dx = this.randIn(-10,10);
    this.dy = this.randIn(-10,10);
  }
  
  // Generate a random number in [i,j].
  int randIn(int i, int j) {
    return i + r.nextInt() % ((j-i)+1) ;
  }
  
  Star move() {
    return new Star(new Posn(loc.x+dx, loc.y+dy), dx, dy);
  }
  
  boolean draw(Canvas c) {
    return c.drawDisk(this.loc, 4, new White());
  }
  
}

// to represent shooting stars in our world
interface LoStars {
  // move the stars  in this list down
  LoStars move();

  // draw the stars in this list
  boolean draw(Canvas x);
}
  
// to represent an empty list of stars
class MTLoStars implements LoStars {
  MTLoStars() {}
  
  // move the stars  in this list down
  LoStars move() {
    return this;
  }

  // draw the stars in this list
  boolean draw(Canvas x) {
    return true;
  }

}

// to represent a nonempty list of stars
class ConsLoStars implements LoStars {
  Star first;
  LoStars rest;

  ConsLoStars(Star first, LoStars rest) {
    this.first = first;
    this.rest = rest;
  }

  // move the stars  in this list down
  LoStars move() {
    return new ConsLoStars(this.first.move(),
                           this.rest.move());
  }

  // draw the stars in this list
  boolean draw(Canvas c) {
    return this.first.draw(c) &&
           this.rest.draw(c);
  }

}

// the world of shooting stars
class StarWorld extends World {
  LoStars stars;

  StarWorld(LoStars stars){
    this.stars = stars;
  }

  World onTick(){
    return new StarWorld(new ConsLoStars(new Star(), this.stars.move()));
  }

  World onKeyEvent(String ke){
    return this;
  }

  boolean draw(){
    return theCanvas.drawRect(new Posn(0, 0), 200, 300,
                              new Blue()) &&
           this.stars.draw(this.theCanvas);
  }

  boolean erase(){
    return theCanvas.drawRect(new Posn(0, 0), 200, 300, new Blue());
  }
}

class Examples {
  StarWorld sw = new StarWorld(new MTLoStars());
  boolean go = sw.bigBang(200, 300, 0.1);
}