import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.math.BigInteger;

public class Goldbachia extends Applet implements Runnable {
	static BigInteger zero = new BigInteger("0");
	static BigInteger one = new BigInteger("1");
	static BigInteger two = new BigInteger("2");

	private Thread kicker;
	Controls controls;
	Algorithm algorithm;
	private String input2;
	private String output2;

	public void init() {
		controls = new Controls();
		setLayout(new BorderLayout());
		add("Center", controls);
		controls.setEnabled(true);
	}

	public void run() {
		try {
			if (algorithm == null) {
				algorithm = new Algorithm();
			}
			output2 = "Calculating, please wait...";
			controls.ta.setText(output2);

			algorithm.init();

			input2 = controls.tf.getText();

			algorithm.input(input2);
			algorithm.calculate();
			output2 = algorithm.output();
			controls.ta.setText(output2);
			do {
				BigInteger n = new BigInteger(input2);
				BigInteger nplusone = new BigInteger("0");
				nplusone = n.add(one);
				input2 = nplusone.toString();

				algorithm.input(input2);
				algorithm.calculate();
				output2 = output2 + '\n' + algorithm.output();
				controls.ta.setText(output2);
			} while (true);
		}
		catch (Exception e) {
		}
	}

	public synchronized void stop() {
		if (kicker != null) {
			try {
				kicker.stop();
			}
			catch (IllegalThreadStateException e) {
			}
			kicker = null;
		}
		if (algorithm != null) {
			try {
				algorithm.stop();
			}
			catch (IllegalThreadStateException e) {
			}
		}
	}

	synchronized void startCalculation() {
		if (kicker == null || !kicker.isAlive()) {
			kicker = new Thread(this);
			kicker.start();
		}
	}

	class Controls extends Panel implements ActionListener {
		TextField tf = new TextField(40);
		Button b = new Button("Calculate");
		TextArea ta = new TextArea("", 10, 60, TextArea.SCROLLBARS_VERTICAL_ONLY);

		public Controls() {
			tf.setText("Enter a positive integer, n, here");
			add(tf);

			b.addActionListener(this);
			add(b);

			ta.setText("Tests whether n! is a counterexample to Goldbach's Conjecture");
			add(ta);
		}

		public void actionPerformed(ActionEvent ae) {
			String label = ae.getActionCommand();

			if (label.equals("Calculate")) {
				startCalculation();
			}
		}
	}
	
	class Algorithm {
	private String input;
	private String output;
	protected boolean stopRequested = false;
	BigInteger bestyet = new BigInteger("0");

	public void init() {
		stopRequested = false;
	}

	public void stop() {
		stopRequested = true;
	}

	public void input(String strInput) {
		input = strInput;
	}

	public String output() {
		return output;
	}

	public void calculate() {
		BigInteger n = new BigInteger(input);

		boolean found = false;

		BigInteger test = new BigInteger("0");
		test = factorial(n);

		BigInteger halftest = new BigInteger("0");
		halftest = test.divide(two);

		BigInteger p = new BigInteger("0");
		p = n;
		while ((p.compareTo(halftest) <= 0) && (found == false)) {
			if (isprime(p)) {
				BigInteger q = new BigInteger("0");
				q = test.subtract(p);
				if (isprime(q)) {
					if (p.divide(n).compareTo(bestyet) > 0) bestyet = p.divide(n);
					output = p.toString() + " + ? = " + n.toString() + "!" + '\t' + bestyet.toString();
					found = true;
				}
			}
			p = p.add(one);
			controls.ta.setText(output2 + '\n' + p.toString());
			if (stopRequested) {
				return;
			}
		}

		if (found == false) {
			output = n.toString() + "! is a COUNTEREXAMPLE!";
		}
	}

	private BigInteger factorial(BigInteger in) {
		BigInteger i = new BigInteger("1");
		BigInteger out = new BigInteger("1");

		while (i.compareTo(in) <= 0) {
			out = out.multiply(i);
			i = i.add(one);
		}

		return out;
	}

	private boolean isprime(BigInteger n) {
		return n.isProbablePrime(100);
	}
	}
}