import greenfoot.*;

/**
 * A proton wave that expands and destroys asteroids in its path.
 * 
 * @author Michael Kölling
 * @version 0.1
 */
public class ProtonWave extends Actor
{
    /** The damage this wave will deal */
    private static final int DAMAGE = 30;
    
    /** How many images should be used in the animation of the wave */
    private static final int NUMBER_IMAGES= 30;
    
    /** 
     * The images of the wave. 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 proton wave.
     */
    public ProtonWave() 
    {
        initializeImages();
        setImage(images[0]);
        Greenfoot.playSound("proton.wav");
    }
    
    /** 
     * Create the images for expanding the wave.
     */
    public static void initializeImages() 
    {
        if(images == null) 
        {
            GreenfootImage baseImage = new GreenfootImage("wave.png");
            images = new GreenfootImage[NUMBER_IMAGES];
            int i = 0;
            while (i < NUMBER_IMAGES) 
            {
                int size = (i+1) * ( baseImage.getWidth() / NUMBER_IMAGES );
                images[i] = new GreenfootImage(baseImage);
                images[i].scale(size, size);
                i++;
            }
        }
    }
    
    /**
     * Act for the proton wave is: grow and check whether we hit anything.
     */
    public void act()
    {   
        checkAsteroidHit();
        
        setImage(images[imageNo]);
        
        imageNo += increment;
        if(imageNo >= NUMBER_IMAGES) 
        {
            increment = -increment;
            imageNo += increment;
        }
        
        if(imageNo < 0) 
        {
            getWorld().removeObject(this);
        }       
    }
    
    private void checkAsteroidHit()
    {
        Asteroid asteroid = (Asteroid) getOneIntersectingObject(Asteroid.class);
        if (asteroid != null)
        {
            getWorld().removeObject(this);
            asteroid.hit(DAMAGE);
        }
    }
}