import javax.swing.event.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.BorderLayout;
import java.net.URL;

/**
 * Simple illustration of GUI construction for a rudimentary
 * web-browser.
 * <P>
 * Illustrates Layouts, Buttons, Menus, and simple GUI construction.
 * Exercises for the reader include making the buttons functional,
 * adding a Home button, and more. Thhis can be done via extensionn
 * or by modifying the existing class.
 *
 * <P>
 * When creating a browser, client code should set the size of
 * of the frame (note that Browser extends JFrame).
 * <P>
 * <PRE>
 *   Browser b = new Browser();
 *   b.setSize(400,400);
 *   b.setVisible(true);
 * </PRE>
 *
 * @author Owen Astrachan
 */

public class Browser extends JFrame
{
    private JEditorPane myEditor;          // displays web page
    private JLabel      myNextURL;         // if link clicked, go here
    private JTextField  myURLDisplay;      // user-entered url
    private JButton     myBackButton;      // generates call of doBack()
    private JButton     myNextButton;      // generates call of doNext()

    /**
     * Construct the web browser, calling code should set size of frame.
     */
    public Browser()
    {
	myEditor = new JEditorPane();
	myEditor.setEditable(false);   // allows links to be followed
	initGui();
    }

    private void makeMenu()
    {
	JMenu fileMenu = new JMenu("File");
	JMenuBar menubar = new JMenuBar();
	menubar.add(fileMenu);

	fileMenu.add(new AbstractAction("Quit")
	    {
		public void actionPerformed(ActionEvent e) {
		    System.exit(0);
		}
	    });
	setJMenuBar(menubar);
    }

    
    private JPanel makeButtons()
    {
	myBackButton = new JButton("Back");
	myNextButton = new JButton("Next");

	// add listener so backButton calls doBack()
	myBackButton.addActionListener(new ActionListener(){
		public void actionPerformed(ActionEvent e) {
		    doBack();
		}
	    });

	// add listener so nextButton calls doNext()
	myNextButton.addActionListener(new ActionListener(){
		public void actionPerformed(ActionEvent e) {
		    doNext();
		}
	    });	

	// create panel with back at left, next at right, return it
	JPanel panel = new JPanel(new BorderLayout());	
	panel.add(myBackButton, BorderLayout.WEST);
	panel.add(myNextButton, BorderLayout.EAST);
	return panel;
    }

    /**
     * called when back button pressed
     */
    protected void doBack()
    {
        JOptionPane.showMessageDialog(null,"you pressed the back button");
    }

    /**
     * called when next button pressed
     */
    protected void doNext()
    {
        JOptionPane.showMessageDialog(null,"you pressed the next button");
    }

    /**
     * Make user-entered URL/text field and back/next buttons
     */
    private JPanel makeTopPanel()
    {
	myURLDisplay = new JTextField(35);
	JLabel     topLabel = new JLabel("url/address ");
	JPanel urlPanel = new JPanel(new BorderLayout());
	urlPanel.add(topLabel,      BorderLayout.WEST);
	urlPanel.add(myURLDisplay,  BorderLayout.CENTER);
	urlPanel.add(makeButtons(), BorderLayout.NORTH);	

	// if user presses return, load/show the URL
	myURLDisplay.addActionListener(new ActionListener() {
		public void actionPerformed(ActionEvent e) {
		    showPage(e.getActionCommand());
		}
	    });
	
	return urlPanel;
    }

    /**
     * Make the panel where "would-be" clicked URL is displayed
     */
    private JPanel makeBottomPanel()
    {
	// bottomLabel is a hack. Because the myNextURL label
	// is initially empty it doesn't show up, the bottomLabel does
	
	myNextURL = new JLabel();
	JLabel bottomLabel = new JLabel(" ");
	JPanel bottomPanel = new JPanel(new BorderLayout());
	bottomPanel.add(bottomLabel, BorderLayout.WEST);
	bottomPanel.add(myNextURL,   BorderLayout.CENTER);
	return bottomPanel;
    }
    
    private void initGui()
    {
	JPanel topPanel = makeTopPanel();
	JPanel bottomPanel = makeBottomPanel();
	
	// make editor respond to link-clicks/mouse-overs, make it scroll
	myEditor.addHyperlinkListener(new LinkFollower());
	JScrollPane scroller = new JScrollPane(myEditor);

	// add components to frame, make it exit when closed
	// default for contentPane is BorderLayout, use this
	
	this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	this.getContentPane().add(topPanel,    BorderLayout.NORTH);
	this.getContentPane().add(scroller,    BorderLayout.CENTER);
	this.getContentPane().add(bottomPanel, BorderLayout.SOUTH);

	makeMenu();
	setTitle("Duke/108 Wowser-Browser");
    }

    /**
     * displays the url the user enters and echo
     * the url in the textfield (even if it came from there!)
     * the echo makes it so link-clicking shows the URL
     */
    private void showPage(String url)
    {
	try {
	    myEditor.setPage(url);
	    myURLDisplay.setText(url);	    
	}
	catch (Exception e) {
	    myEditor.setContentType("text/html");
	    myEditor.setText("<html>Could not load "+url+"</html>");
	}
    }

    /**
     * Show where link would take us if clicked
     */
    
    private void showNextURL(String s)
    {
	myNextURL.setText(s);
    }

    /**
     * Inner class to deal with link-clicks and mouse-overs
     */
     
    private  class LinkFollower implements HyperlinkListener
    {
	public void hyperlinkUpdate(HyperlinkEvent evt)
	{	    
	    if (evt.getEventType() == HyperlinkEvent.EventType.ACTIVATED) {
	    // user clicked a link, load it and show it
		try {
		    showPage(evt.getURL().toString());
		}
		catch (Exception e) {
		    String s = evt.getURL().toString();
		    JOptionPane.showMessageDialog(
			Browser.this,
                        "loading problem for "+s+" "+e,
                        "Load Problem",
                        JOptionPane.ERROR_MESSAGE);

		} 
	    }
	    else if (evt.getEventType() == HyperlinkEvent.EventType.ENTERED) {
		// user moused-into a link, show what would load
		
		try {
		    showNextURL(evt.getURL().toString());
		}
		catch (Exception e) {
		    // nothing to do, if URL fails, don't pre-announce
		} 		
	    }
	    else if (evt.getEventType() == HyperlinkEvent.EventType.EXITED) {
		// user moused-out of a link, erase what was shown
		
		showNextURL("");
	    }
	}
    }

    public static void main(String args[])
    {
	Browser b = new Browser();
	b.setSize(600,600);
	b.setLocation(10,20);
	b.setVisible(true);
    }
}