import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import java.awt.Graphics2D; // Used for anti-aliasing
import java.awt.RenderingHints; // Used for anti-aliasing

import javax.swing.JFrame;
import javax.swing.Timer;
import javax.swing.ImageIcon;

public class GraphicsMoveAndCollideWithKeyboardAndJFrame extends JFrame implements ActionListener, KeyListener
{
	private Timer timer;
	Font font = new Font("Helvetica", Font.BOLD, 14);
	FontMetrics metrics = this.getFontMetrics(font);

	// The benefit of using the 'ImageIcon' class over the 'Toolkit' class
	//  is that unlike the 'Toolkit' class, which doesn't actually load the
	//  image until it is displayed, the 'ImageIcon' class fully loads the
	//  image when the object is created, making it possible to immediately
	//  determine and use the dimensions of the image
	private Image apple = new ImageIcon("data_files/apple.png").getImage();
	private Image alien = new ImageIcon("data_files/alien.png").getImage();

	private int width = 400, height = 250;
	private boolean collision, pressedLeft, pressedRight, pressedUp, pressedDown;
	private int appleX, appleY, alienX, alienY;

	public static void main(String[] args)
	{
		// Create an instance of the 'GraphicsMoveAndCollideWithKeyboardAndJFrame' class
		new GraphicsMoveAndCollideWithKeyboardAndJFrame();
	}

	// Constructor
	public GraphicsMoveAndCollideWithKeyboardAndJFrame()
	{
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setSize(width, height);
		setTitle("Collision Detection on a JFrame");
		setLocationRelativeTo(null);
		setResizable(false);
		setVisible(true);
		setFocusable(true);

		addKeyListener(this);

		collision = false;
		appleX = 100;
		appleY = 120;
		alienX = width;
		alienY = 80;

		// Set and start a new Swing timer to fire every 10 milliseconds
		//  (after an initial delay of 500 milliseconds); this timer,
		//  along with the distance (number of pixels) that the apple and
		//  alien move with each cycle, controls how fast the objects move
		//  on the frame
		timer = new Timer(10, this);
		timer.setInitialDelay(500);
		timer.start();
	}

	// This method will be called whenever the user presses a key, as well
	//  as automatically by the timer (necessary for the alien to move
	//  across the frame)
	public void actionPerformed(ActionEvent e)
	{
		if (pressedLeft && appleX > 4)
			appleX -= 2;
		if (pressedRight && appleX < width - 14)
			appleX += 2;
		if (pressedUp && appleY > 24)
			appleY -= 2;
		if (pressedDown && appleY < height - 14)
			appleY += 2;

		if (alienX < 0)
			alienX = width;
		alienX -= 1;

		repaint();
		checkCollisions();
	}

	// Create a rectangle around the apple, and another rectangle around
	//  the alien; then check to see if the two rectangles have collided
	public void checkCollisions()
	{
		Rectangle rApple = new Rectangle(appleX, appleY, apple.getWidth(null), apple.getHeight(null));
		Rectangle rAlien = new Rectangle(alienX, alienY, alien.getWidth(null), alien.getHeight(null));

		if (rApple.intersects(rAlien))
			collision = true;
	}

	// Check to see if the user has PRESSED an arrow key
	public void keyPressed(KeyEvent e)
	{
		int key = e.getKeyCode();

		if (key == KeyEvent.VK_LEFT)
			pressedLeft = true;
		if (key == KeyEvent.VK_RIGHT)
			pressedRight = true;
		if (key == KeyEvent.VK_UP)
			pressedUp = true;
		if (key == KeyEvent.VK_DOWN)
			pressedDown = true;
	}

	// Check to see if the user has RELEASED an arrow key
	public void keyReleased(KeyEvent e)
	{
		int key = e.getKeyCode();

		if (key == KeyEvent.VK_LEFT)
			pressedLeft = false;
		if (key == KeyEvent.VK_RIGHT)
			pressedRight = false;
		if (key == KeyEvent.VK_UP)
			pressedUp = false;
		if (key == KeyEvent.VK_DOWN)
			pressedDown = false;
	}

	// This empty method is needed to avoid an Eclipse error message above
	public void keyTyped(KeyEvent e)
	{
	}

	public void update(Graphics g)
	{
		paint(g);
	}

	public void paint(Graphics g)
	{
		// This line causes graphics and text to be rendered with anti-aliasing
		//  turned on, making the overall display look smoother and cleaner
		((Graphics2D) g).setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

		if (!collision)
		{
			// Draw/Redraw the frame background so that previous instances of
			//  the graphics are not left behind and visible on the frame
			g.setColor(Color.BLACK);
			g.fillRect(0, 0, width, height);

			// Draw/Redraw the apple and the alien
			g.drawImage(apple, appleX, appleY, this);
			g.drawImage(alien, alienX, alienY, this);
		}
		else
		{
			// A collision has occurred, so finish the program
			timer.stop();
			String message = "Collision Detected!";

			// Center the "collision" message in the frame 
			g.setColor(Color.white);
			g.setFont(font);
			g.drawString(message, (getWidth() - metrics.stringWidth(message)) / 2, getHeight() / 2);
		}

		// This line synchronizes the graphics state by flushing buffers containing
		//  graphics events and forcing the frame drawing to happen now; otherwise,
		//  it can sometimes take a few extra milliseconds for the drawing to take
		//  place, which can result in jerky graphics movement; this line ensures
		//  that the display is up-to-date; it is useful for animation, since it
		//  reduces or eliminates flickering
		Toolkit.getDefaultToolkit().sync();
	}
}