package mvc;

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.io.File;
import java.io.FilenameFilter;

import javax.swing.*;

/**
 * A directory watcher periodially checks for modification of a directory
 * and fires a property change event when it notices a change. 
 * @author kjg
 * @version 1.0
 *
 */
public class DirectoryWatcher implements ActionListener {
	PropertyChangeSupport pcs;  // to manage listeners and firing events
	File dir;  // the directory being watched
	long lastModified;  // to remember the previously seen modification time
	Timer timer;  // for periodic examination of the modification time
	
	/**
	 * Creates a directory watcher for the given directory
	 * @param dir the directory to be watched for modification
	 */
	public DirectoryWatcher(File dir) {
		pcs = new PropertyChangeSupport(this);
		timer = new Timer(500, this);  // check for modification every 1/2 second
		setDirectory(dir);
	}
	
	/**
	 * Changes the directory to be watched.  Will cause a property change event to be
	 * fired initially, and then each time the watcher notices modification of the directory.
	 * @param dir the directory to watch, or null if no directory is to be watched
	 * @throws IllegalArgumentException the parameter is not a directory
	 */
	public void setDirectory(File dir) {
		if (dir == null)
			timer.stop();
		else if (!dir.isDirectory()) {
			timer.stop();
			throw new IllegalArgumentException(dir + " is not a directory.");
		} else {
			this.dir = dir;
			lastModified = 0;
			timer.start();
		}
	}
	
	/**
	 * Gets the directory being watched
	 * @return the currently watched directory
	 */
	public File getDirectory() {
		return dir;
	}

	/**
	 * On each "tick" of the timer, check to see if the watched directory has been modified
	 * since the last time it was checked.
	 */
	public void actionPerformed(ActionEvent ae) {
		if (dir.lastModified() > lastModified) {
			lastModified = dir.lastModified();  // remember the new modification time
			pcs.firePropertyChange("directory modified", null, null);
		}
	}
	/**
	 * Adds a property change listener to be notified whenever the directory is modified, or
	 * when a different directory is being watched.
	 * @param listener  
	 */
	public void addPropertyChangeListener(PropertyChangeListener listener) {
		pcs.addPropertyChangeListener(listener);
	}

	public void removePropertyChangeListener(PropertyChangeListener listener) {
		pcs.removePropertyChangeListener(listener);
	}
	
	// This test program uses the DirectoryWatcher.  It creates a JList that is
	// updated whenever the contents of the selected directory changes.
	public static void main(String[] args) {
		final JFrame f = new JFrame();
		f.setLayout(new BorderLayout());
		
		// Create the JList and directory watcher.
		final JList list = new JList();
		final DirectoryWatcher dw = new DirectoryWatcher(new File("."));
		
		// Add a listener to the directory watcher to update the list when the directory
		// is modified.
		dw.addPropertyChangeListener(new PropertyChangeListener() {
			public void propertyChange(PropertyChangeEvent arg0) {
				list.setListData(dw.dir.list(new FilenameFilter(){
					// as a filtering example, include only directories and java files in the list
					public boolean accept(File directory, String name) {
						return new File(directory,name).isDirectory() || name.contains(".java");
					}
				}));
			}
		});
		
		//Create a browse button and an action listener to bring up a file chooser for
		//changing directories.
		JButton b = new JButton("browse...");
		b.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent arg0) {
				JFileChooser chooser = new JFileChooser(dw.getDirectory());
				chooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
			    int userResponse = chooser.showOpenDialog(f);
			    if (userResponse == JFileChooser.APPROVE_OPTION) {
			    	dw.setDirectory(chooser.getSelectedFile());
			    }
			}
		});
		
		// Put the list (within a scroll pane) and the browse button into the frame
		f.add(new JScrollPane(list));
		f.add(b, BorderLayout.SOUTH);
		f.pack();
		f.setVisible(true);
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
}