import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;


interface Oracle {
	String ask(Oracle asker, String query) throws Exception;
}


interface Actor extends Oracle { }


interface UseCaseController extends Oracle {
   String execute(Oracle caller, String cmmd) throws Exception;
}

class GetDiscount implements UseCaseController {

	private Actor dbase;
	private double amt;

	public void setDbase(Actor a) { dbase = a; }

	public String ask(Oracle asker, String query) throws Exception {
		if (query.equals("amount?")) {
			return "" + amt;
		} else {
			return null;
		}
	}

	public String execute(Oracle a, String cmmd) throws Exception {
		String response = a.ask(this, "amount?");
		amt = new Double(response);
		if (amt < 0) {
			throw new Exception();
		}
		response = dbase.ask(this, "rate?");
		double rate = new Double(response);
		return "" + rate * amt;
	}
}

// adapters:

class MockUI implements Actor {
	private UseCaseController port;
	public void setPort(UseCaseController c) {
		port = c;
	}

	public void initiate() throws Exception {
		for(int i = 0; i < 10; i++) {
			String result = port.execute(this, null);
			System.out.println(result);
		}
	}

	public String ask(Oracle asker, String query) throws Exception {
		if (query.equals("amount?")) {
			return "$" + 1000 * Math.random();
		} else {
			return null;
		}
	}
}

class CUI implements Actor {
	private UseCaseController port;
	private Scanner kbd = new Scanner(System.in);
	public void setPort(UseCaseController c) {
		port = c;
	}

	public void initiate() throws Exception {
		while(true) {
			System.out.print("-> ");
			String cmmd = kbd.next();
			if (cmmd.equals("quit")) break;
			String result = port.execute(this, cmmd);
			System.out.println(result);
		}
		System.out.println("bye");
	}

	public String ask(Oracle asker, String query) throws Exception {
		System.out.print(query);
		return kbd.next();
	}
}

class GUI extends JPanel implements Actor, ActionListener {
	private UseCaseController port;
	private JButton discountButton = new JButton("get discount");
	private JLabel resultLabel = new JLabel("    0    ");
	public void setPort(UseCaseController c) {
		port = c;
	}

	public GUI() {
		add(discountButton);
		discountButton.addActionListener(this);
		add(new JLabel("discount = $"));
		add(resultLabel);

	}

	public void actionPerformed(ActionEvent ae) {
		try {
			String result = port.execute(this, "");
			resultLabel.setText(result);
			repaint();
		} catch(Exception e) {
			JOptionPane.showMessageDialog(this, "invalid amount");
		}
	}

	public void initiate() throws Exception {
		JFrame frame = new JFrame();
		frame.setTitle("Discount Calculator");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.add(this);
		frame.pack();
		frame.setVisible(true);
	}


	public String ask(Oracle asker, String query) throws Exception {
		return JOptionPane.showInputDialog("amount?");
	}
}



class MockDbase implements Actor {
	public String ask(Oracle asker, String query) throws Exception {
		if (query.equals("rate?")) {
			String amt = asker.ask(this, "amount?");
			double a = new Double(amt);
			if (a > 500) {
				return "" + .08;
			} else {
				return "" + .04;
			}
		} else {
			return null;
		}
	}
}


public class TestGetDiscount {
	public static void main(String[] args) {
		try {
			GetDiscount c = new GetDiscount();
			c.setDbase(new MockDbase());
			//MockUI ui = new MockUser();
			//CUI ui = new CUI();
			GUI ui = new GUI();
			ui.setPort(c);
			ui.initiate();
		} catch(Exception e) {
			System.out.println(e);
		}
	}
}