import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import java.util.Locale;

import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;


public class TipPanel extends JPanel {

	private final double PERCENTAGE = .2;
	
	JLabel prompt;
	JTextField data;
	JButton button;
	JTextField result;
	
	public TipPanel() {
		prompt = new JLabel("Enter Total of Bill:");
		
		data = new JTextField();
		data.setColumns(15);
		
		button = new JButton("Calculate Tip");
		button.addActionListener(new ButtonListener());
		
		result = new JTextField();
		result.setColumns(20);
		result.setEditable(false);
		
		this.setLayout(new BorderLayout());
		
		JPanel nsubpanel = new JPanel();
		nsubpanel.setLayout(new GridLayout(1, 3));
		nsubpanel.add(prompt);
		nsubpanel.add(data);
		nsubpanel.add(button);
		
		this.add(nsubpanel, BorderLayout.NORTH);
		this.add(result, BorderLayout.SOUTH);
		this.setPreferredSize(new Dimension(400, 100));
		
	}
	
	private class ButtonListener implements ActionListener {
		
		public void actionPerformed(ActionEvent event) {
			double amount;
			try {
				amount = Double.parseDouble(data.getText());
			} catch(NumberFormatException nfe) {
				result.setText("Invalid bill total");
				data.setText("");
				return;
			}
			double tip = (amount*PERCENTAGE);
			
			NumberFormat numberFormat = NumberFormat.getNumberInstance(Locale.getDefault() );
			numberFormat.setMaximumFractionDigits(2);
			numberFormat.setMinimumFractionDigits(2);
			
			result.setText("Tip amount: " + numberFormat.format(tip));
			
			data.setText("");
		}
	}
}