/**
 * This application calculates the weekly pay for an employee given 
 * its pay rate and number of hours worked that week. The rule for 
 * calculating the pay is as follows: If the number of hours worked is 
 * no more than 40, pay should be the rate times the number of hours worked. 
 * If it's over 40 hours, overtime pay should be 1.5 the rate times the 
 * overtime hours.
 *
 * @author Hongyan Wang
 */ 

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

public class WageCalculatorGUI 
{
    //
    // main function
    //
    public static void main (String[] args)
    {
	// Create the panel that holds everything
	WageCalculatorPane	cal = new WageCalculatorPane ();
	
	// Create the window that holds the panel
	JFrame	win = new JFrame ();
	
	win.setSize (360, 180);
	win.setResizable (false);
	
	win.setLocation (300, 200);
	win.setTitle ("Weekly Pay Calculator");
	
	win.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
	
	win.setContentPane (cal);	// stick panel to the window
	
	win.setVisible (true);
    }
}

class WageCalculatorPane extends JPanel implements ActionListener
{
    //
    // private data members
    //
    private JLabel 		lbRate, lbHrs, lbWage;
    private JTextField	tfRate, tfHrs, tfWage;
    private JButton		btCal;
    
    
    public WageCalculatorPane ()
    {
	initComponents ();
    }
    
    public void actionPerformed (ActionEvent e)
    {
	Object	src = e.getSource ();
	
	if (src == tfRate)
	    {
		// just set focus to textfield for hours worked
		tfHrs.requestFocus ();
	    }
	else if (src == tfHrs || src == btCal)
	    {
		btCal.requestFocus ();
		
		// calculate and display the result
		calPay (); 
	    }
    }
    
    
    //
    // private methods
    //
    private void initComponents ()
    {
      	GridBagConstraints c;
	
	// Create the components
	lbRate = new JLabel("Pay Rate", JLabel.RIGHT);
        tfRate = new JTextField(10);
        tfRate.addActionListener (this);
        
        lbHrs = new JLabel ("Hours Worked", JLabel.RIGHT);
        tfHrs = new JTextField (10);
        tfHrs.addActionListener (this);
        
        btCal = new JButton("Calculate");
        btCal.addActionListener (this);
        
        lbWage = new JLabel("Weekly Pay", JLabel.RIGHT);
        tfWage = new JTextField(10);
        tfWage.setEditable (false);
        
        // Add components to frame
        setLayout(new GridBagLayout());
        
        // Add Pay Rate label
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 0;
        c.gridwidth = 2;
        c.fill = GridBagConstraints.BOTH;
        add(lbRate, c);
        
        
        // Add text field for pay rate        
        c = new GridBagConstraints();
        c.gridx = 3;
        c.gridy = 0;
        c.gridwidth = 3;
        c.fill = GridBagConstraints.HORIZONTAL;
        c.insets = new Insets(5, 21, 5, 0);
        add(tfRate, c);
        
        // Add label for hours worked
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 1;
        c.gridwidth = 2;
        c.fill = GridBagConstraints.BOTH;
        c.insets = new Insets(5, 0, 5, 0);
        add(lbHrs, c);
        
        // Add textfield for hours worked
        c = new GridBagConstraints();
        c.gridx = 3;
        c.gridy = 1;
        c.gridwidth = 3;
        c.fill = GridBagConstraints.HORIZONTAL;
        c.insets = new Insets(5, 21, 5, 0);
        add(tfHrs, c);	
        
        // Add button to calculate
        c = new GridBagConstraints();
        c.gridx = 6;
        c.gridy = 2;
        c.gridwidth = GridBagConstraints.REMAINDER;
        c.insets = new Insets (5, 21, 5, 0);
        add(btCal, c); 
        
        // Add label for wage
        c = new GridBagConstraints ();
        c.gridx = 1;
        c.gridy = 2;
        c.gridwidth = 2;
        c.insets = new Insets (5, 0, 5, 0);
        add (lbWage, c);
        
        // Add text field
        c = new GridBagConstraints ();
        c.gridx = 3;
        c.gridy = 2;
        c.gridwidth = 3;
        c.insets = new Insets (5, 21, 5, 0);
        add (tfWage, c);      
    }
    
	
    private void calPay ()
    {
	double rate, hrs, pay;
	
	try {
	    rate = Double.parseDouble (tfRate.getText ());
	} 
	catch (NumberFormatException nfe)
	    {
		JOptionPane.showMessageDialog (this, 
					       "Pay rate is not a properly formatted number");
		
		tfRate.requestFocus ();
		return;
	    }	
	
	try {
	    hrs = Double.parseDouble (tfHrs.getText ());
	} 
	catch (NumberFormatException nfe)
	    {
		JOptionPane.showMessageDialog (this, 
					       "Pay rate is not a properly formatted number");
		
		tfHrs.requestFocus ();
		return;
	    }
	
	
	if (rate < 0.0)
	    {
		JOptionPane.showMessageDialog (this, 
					       "Pay rate can't be negative");
		tfRate.requestFocus ();
		return;
	    }
	else if (hrs < 0.0)
	    {
		JOptionPane.showMessageDialog (this, 
					       "Hours worked can't be negative");
		tfHrs.requestFocus ();
		return;
	    }			
	
	if (hrs > 40.0)
	    pay = rate * 40.0 + rate * (hrs - 40.0) * 1.5;
	else
	    pay = rate * hrs;
	
	DecimalFormat	d2 = new DecimalFormat ("0.00");
	
	tfWage.setText (d2.format (pay));
    }
    
}