import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;
import java.util.*;
import java.io.*;

public class UFOCanvas extends GameCanvas implements Runnable {
  private Display display;
  private boolean sleeping;
  private long    frameDelay;
  private Random  rand;
  private Sprite  ufoSprite;
  private int     ufoXSpeed, ufoYSpeed;

  public UFOCanvas(Display d) {
    super(true);
    display = d;

    // Set the frame rate (30 fps)
    frameDelay = 33;
  }
  
  public void start() {
    // Set the canvas as the current screen
    display.setCurrent(this);

    // Initialize the random number generator
    rand = new Random();

    // Initialize the UFO sprite
    ufoXSpeed = ufoYSpeed = 3;
    try {
      ufoSprite = new Sprite(Image.createImage("/Saucer.png"));
      ufoSprite.setPosition(0, 0);
    }
    catch (IOException e) {
      System.err.println("Failed loading image!");
    }

    // Start the animation thread
    sleeping = false;
    Thread t = new Thread(this);
    t.start();
  }
  
  public void stop() {
    // Stop the animation
    sleeping = true;
  }
  
  public void run() {
    Graphics g = getGraphics();
    
    // The main game loop
    while (!sleeping) {
      update();
      draw(g);
      try {
        Thread.sleep(frameDelay);
      }
      catch (InterruptedException ie) {}
    }
  }
  
  private void update() {
    // Randomly alter the UFO's speed
    if (rand.nextInt() % 5 == 0) {
      ufoXSpeed = Math.min(Math.max(ufoXSpeed + rand.nextInt() % 2, -8), 8);
      ufoYSpeed = Math.min(Math.max(ufoYSpeed + rand.nextInt() % 2, -8), 8);
    }

    // Move the sprite
    ufoSprite.move(ufoXSpeed, ufoYSpeed);

    // Wrap the UFO around the screen if necessary
    if (ufoSprite.getX() < -ufoSprite.getWidth())
      ufoSprite.setPosition(getWidth(), ufoSprite.getY());
    else if (ufoSprite.getX() > getWidth())
      ufoSprite.setPosition(-ufoSprite.getWidth(), ufoSprite.getY());
    if (ufoSprite.getY() < -ufoSprite.getHeight())
      ufoSprite.setPosition(ufoSprite.getX(), getHeight());
    else if (ufoSprite.getY() > getHeight())
      ufoSprite.setPosition(ufoSprite.getX(), -ufoSprite.getHeight());
  }
  
  private void draw(Graphics g) {
    // Clear the display
    g.setColor(0x000000);
    g.fillRect(0, 0, getWidth(), getHeight());
    
    // Draw the UFO sprite
    ufoSprite.paint(g);
    
    // Flush the offscreen graphics buffer
    flushGraphics();
  }
}