import java.awt.*;
import java.util.Random;
import java.text.Format;

public class hw1 extends BufferedApplet
{
  private final int NUM_CIRCLES = 20;
  private final int CIRCLE_RADIUS = 20;

  int w = 0, h = 0;
  Circle circles[] = new Circle[NUM_CIRCLES];

  //going to be triangle covering bottom half of screen
  Polygon triangle;
  int trianglePointsX[] = {0,0,0};
  int trianglePointsY[] = {0,0,0};

  long time0;
  int lastCount = 0;

  //first time initialization
  private void init(Graphics g) {
    time0 = System.currentTimeMillis(); //start the clock

    w = bounds().width;
    h = bounds().height;

    trianglePointsX[2] = w;
    trianglePointsY[1] = h;
    trianglePointsY[2] = h;

    triangle = new Polygon(trianglePointsX, trianglePointsY, 3);

    //initialize the circles
    for (int i=0; i<NUM_CIRCLES; i++)
    {
      circles[i] = new Circle(g, CIRCLE_RADIUS, 0, 0);
      circles[i].setStartingPlace(w, h);
    }
  }

  public void render(Graphics g) {
    if (w == 0) init(g);

    //only update when the clock changes
    int count = tick();
    if (count != lastCount) update();
    lastCount = count;

    setBackground(g, Color.red);

    g.setColor(Color.white);
    for (int i=0; i<NUM_CIRCLES; i++)
      circles[i].render();

    //draw big triangle last so it covers up circles
    g.setColor(Color.blue);
    g.fillPolygon(triangle);

    animating = true;
  }

  private int tick() {
    long time = System.currentTimeMillis();

    double elapsed = (time - time0) / 1000.0;
    return (int)(30 * elapsed);
  }

  //update various positions etc
  private void update() {
    //move all the circles down-right
    for (int i=0; i<NUM_CIRCLES; i++) {
      Circle c = circles[i];

      c.move(-3, 2);
      if (c.x <= 0 || c.y >= h) //off the screen?
      c.setStartingPlace(w, h);

      //System.err.printf("Circle #%d position: (%d, %d)\n", i, c.x, c.y);
    }
  }

  private void setBackground(Graphics g, Color c) {
    g.setColor(c);
    g.fillRect(0, 0, w, h);
  }

  //helps create and render a circle
  class Circle
  {
    Graphics g;
    Random random = new Random();
    int r;
    int speed;
    public int x, y;

    Circle(Graphics g, int r, int x, int y) {
      this.g = g;
      this.r = r;
      this.x = x;
      this.y = y;

      this.speed = random.nextInt(3)+1;
    }

    //randomize the position based on screen height/width
    public void setStartingPlace(int screenWidth, int screenHeight) {
        this.x = screenWidth + random.nextInt(150);
        //lower y value is higher on screen
        this.y = random.nextInt(screenHeight) - screenHeight/3;
    }

    public void move(int dx, int dy) {
      this.x += dx * this.speed;
      this.y += dy * this.speed;
    }

    public void render() {
      g.drawOval(x, y, r*2, r*2);
    }
  }
}