import javax.swing.*;
import java.awt.*;
import java.util.*;

// a snow flake is a simple game object which can move around and be drawn
class Flake {
    // position and speed are now doubles
    private double x, y, dx, dy;

    // position the snow flake randomly
    public Flake() {
        Random r = new Random();
        x = r.nextFloat() * 500;
        y = r.nextFloat() * 500;

        // these are now pixels / second instead of pixels per frame
        dx = r.nextFloat() * 50 - 25;
        dy = r.nextFloat() * 50 + 100;
    }

    // draw the snow flake at its position casted as an int
    public void draw(Graphics g) {
        g.fillRect((int) x, (int) y, 3, 3);
    }

    // update takes the seconds since the last update
    public void update(double dt) {
        x += (dx * dt);
        y += (dy * dt);

        if (y < 0) {
            y = 500;
        }
        if (y > 500) {
            y = 0;
        }
        if (x < 0) {
            x = 500;
        }
        if (x > 500) {
            x = 0;
        }
    }
}

class GameWorld extends JComponent {
    // the array of snow flakes
    private ArrayList<Flake> snow;

    // the time the last time the update runs
    private long last_time;

    // build the game world with a certain number of flakes
    public GameWorld(int count) {
        // store the current time
        last_time = new Date().getTime();

        // initialize snow flakes
        snow = new ArrayList<>(count);
        for (int i = 0; i < count; i++) {
            snow.add(new Flake());
        }
    }

    @Override
    public void paintComponent(Graphics g) {
        // set the color to light blue and draw the sky
        g.setColor(new Color(100, 150, 255));
        g.fillRect(0, 0, 500, 500);

        // draw each of the snow flakes to the screen
        g.setColor(Color.white);
        for (Flake f : snow) {
            f.draw(g);
        }

        // calculate the number of seconds since the last update
        long time_now = new Date().getTime();
        long elapsed_ms = time_now - last_time;
        double dt = elapsed_ms / 1000.0;

        // update each flake with this elapsed time
        for (Flake f : snow) {
            f.update(dt);
        }

        // save the current time as the last time
        last_time = time_now;

        // force an update
        revalidate();
        repaint();
    }
}

public class Snow {

    public static void main(String args[]) {
        // create and set up the window.
        JFrame frame = new JFrame("Snow!");

        // make the program close when the window closes
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // add the GameWorld component
        frame.add(new GameWorld(250));

        // display the window.
        frame.setSize(500, 500);
        frame.setVisible(true);
    }
}