package org.newdawn.spaceinvaders;

/**
 * An entity which represents one of our space invader aliens.
 * 
 * @author Kevin Glass
 */
public class AlienEntity extends Entity {
	/** The speed at which the alient moves horizontally */
	private double moveSpeed = 75;
	/** The game in which the entity exists */
	private Game game;
	/** The animation frames */
	private Sprite[] frames = new Sprite[4];
	/** The time since the last frame change took place */
	private long lastFrameChange;
	/** The frame duration in milliseconds, i.e. how long any given frame of animation lasts */
	private long frameDuration = 250;
	/** The current frame of animation being displayed */
	private int frameNumber;
	
	/**
	 * Create a new alien entity
	 * 
	 * @param game The game in which this entity is being created
	 * @param x The intial x location of this alien
	 * @param y The intial y location of this alient
	 */
	public AlienEntity(Game game,int x,int y) {
		super("sprites/alien.gif",x,y);
		
		// setup the animatin frames

		frames[0] = sprite;
		frames[1] = SpriteStore.get().getSprite("sprites/alien2.gif");
		frames[2] = sprite;
		frames[3] = SpriteStore.get().getSprite("sprites/alien3.gif");
		
		this.game = game;
		dx = -moveSpeed;
	}

	/**
	 * Request that this alien moved based on time elapsed
	 * 
	 * @param delta The time that has elapsed since last move
	 */
	public void move(long delta) {
		// since the move tells us how much time has passed

		// by we can use it to drive the animation, however

		// its the not the prettiest solution

		lastFrameChange += delta;
		
		// if we need to change the frame, update the frame number

		// and flip over the sprite in use

		if (lastFrameChange > frameDuration) {
			// reset our frame change time counter

			lastFrameChange = 0;
			
			// update the frame

			frameNumber++;
			if (frameNumber >= frames.length) {
				frameNumber = 0;
			}
			
			sprite = frames[frameNumber];
		}
		
		// if we have reached the left hand side of the screen and

		// are moving left then request a logic update 

		if ((dx < 0) && (x < 10)) {
			game.updateLogic();
		}
		// and vice vesa, if we have reached the right hand side of 

		// the screen and are moving right, request a logic update

		if ((dx > 0) && (x > 750)) {
			game.updateLogic();
		}
		
		// proceed with normal move

		super.move(delta);
	}
	
	/**
	 * Update the game logic related to aliens
	 */
	public void doLogic() {
		// swap over horizontal movement and move down the

		// screen a bit

		dx = -dx;
		y += 10;
		
		// if we've reached the bottom of the screen then the player

		// dies

		if (y > 570) {
			game.notifyDeath();
		}
	}
	
	/**
	 * Notification that this alien has collided with another entity
	 * 
	 * @param other The other entity
	 */
	public void collidedWith(Entity other) {
		// collisions with aliens are handled elsewhere

	}
}