import greenfoot.*;  // (World, Actor, GreenfootImage, and Greenfoot)
import java.awt.Color;

/**
 * Space. Something for rockets to fly in.
 * 
 * 
 * @version 1.0
 */
public class Space extends World
{
    private Counter scoreCounter;
    private int startAsteroids = 3;

    public Space() 
    {
        super(800, 700, 1);
        GreenfootImage background = getBackground();
        background.setColor(Color.BLACK);
        background.fill();
        createStars(300);
        
        Rocket rocket = new Rocket();
        addObject(rocket, getWidth()/2 + 100, getHeight()/2);
        
        addAsteroids(startAsteroids);
        
        scoreCounter = new Counter("Score: ");
        addObject(scoreCounter, 60, 380);

        Explosion.initializeImages();
        ProtonWave.initializeImages();
   
    }
    
    /**
     * Add a given number of asteroids to our world. Asteroids are only added into
     * the left half of the world.
     */
    private void addAsteroids(int count) 
    {
        for(int i = 0; i < count; i++) 
        {
            int x = Greenfoot.getRandomNumber(getWidth()/2);
            int y = Greenfoot.getRandomNumber(getHeight()/2);
            addObject(new Asteroid(), x, y);
        }
    } 
     private void createStars(int number)
    {
        GreenfootImage background = getBackground();
        for(int i = 0; i < number; i++) {
          int x = Greenfoot.getRandomNumber( getWidth() );
          int y = Greenfoot.getRandomNumber(getHeight() );
          int color = 120 - Greenfoot.getRandomNumber(100);
          background.setColor(new Color(color,color,color));
          background.fillOval(x,y, 2, 2);
        }
    }
    /**
     * This method is called when the game is over to display the final score.
     */
    public void gameOver() 
    {
        addObject(new ScoreBoard(getCounter().getValue()), getWidth()/2, getHeight()/2);
    }
    public Counter getCounter()
    {
        
       return scoreCounter;
     }

}

import greenfoot.*;  // (World, Actor, GreenfootImage, and Greenfoot)

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics;
/**
 * Counter that displays a text and number.
 * 
 * 
 * @version 1.0.1
 */
public class Counter extends Actor
{
    private static final Color textColor = new Color(255, 180, 150);
    
    private int value = 0;
    private static int target = 0;
    private String text;
    private int stringLength;

    public Counter()
    {
        this("0");
    }

    public Counter(String prefix)
    {
        text = prefix;
        stringLength = (text.length() + 2) * 10;

        setImage(new GreenfootImage(stringLength, 16));
        GreenfootImage image = getImage();
        image.setColor(textColor);

        updateImage();
    }
    
    public void act() {
       
        if(value < target) {
            value++;
            updateImage();
        }
        else if(value > target) {
            value--;
            updateImage();
        }
    }

    public static void add(int score)
    {
        target += score;
    }

    public int getValue()
    {
        return value;
    }
   
    /**
     * Make the image
     */
    private void updateImage()
    {
        GreenfootImage image = getImage();
        image.clear();
        image.drawString(text + value, 1, 12);
    }
}

import greenfoot.*;  // (World, Actor, GreenfootImage, and Greenfoot)

/**
 * An explosion. It starts by expanding and then collapsing. 
 * The explosion will explode other obejcts that the explosion intersects.
 * 
 * 
 * @version 1.0.1
 */
public class Explosion extends Actor
{
    /** How many images should be used in the animation of the explostion */
    private final static int IMAGE_COUNT= 12;
    
    /** 
     * The images in the explosion. This is static so the images are not
     * recreated for every object (improves performance significantly).
     */
    private static GreenfootImage images;
    
    /** Current size of the explosion */
    private int imageNo = 0;
    
    /** How much do we increment the index in the explosion animation. */
    private int increment=1;
    
    /**
     * Create a new explosion.
     */
    public Explosion() 
    {
        initializeImages();
        setImage(images);
        Greenfoot.playSound("MetalExplosion.wav");
    }    
    
    /** 
     * Create the images for explosion.
     */
    public synchronized static void initializeImages() 
    {
        if(images == null) {
            GreenfootImage baseImage = new GreenfootImage("explosion-big.png");
            images = new GreenfootImage();
            for (int i = 0; i < IMAGE_COUNT; i++)
            {
                int size = (i+1) * ( baseImage.getWidth() / IMAGE_COUNT );
                images = new GreenfootImage(baseImage);
                images.scale(size, size);
            }
        }
    }
    
    /**
     * Explode!
     */
    public void act()
    { 
        setImage(images);

        imageNo += increment;
        if(imageNo >= IMAGE_COUNT) {
            increment = -increment;
            imageNo += increment;
        }
        
        if(imageNo < 0) {
            getWorld().removeObject(this);
        }
    }
}