/*
 * Copyright (c) 2003, 2004 Rafael Steil
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, 
 * with or without modification, are permitted provided 
 * that the following conditions are met:
 * 
 * 1) Redistributions of source code must retain the above 
 * copyright notice, this list of conditions and the 
 * following  disclaimer.
 * 2)  Redistributions in binary form must reproduce the 
 * above copyright notice, this list of conditions and 
 * the following disclaimer in the documentation and/or 
 * other materials provided with the distribution.
 * 3) Neither the name of "Rafael Steil" nor 
 * the names of its contributors may be used to endorse 
 * or promote products derived from this software without 
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT 
 * HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, 
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 
 * THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE 
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, 
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER 
 * IN CONTRACT, STRICT LIABILITY, OR TORT 
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE
 * 
 * Created on 02/06/2004 23:29:51
 * The JForum Project
 * http://www.jforum.net
 */
package net.jforum.util;

import java.io.File;
import java.util.HashMap;
import java.util.Map;
import java.util.Timer;
import java.util.TimerTask;

import org.apache.log4j.Logger;

/**
 * Monitor class for file changes.
 * 
 * @author Rafael Steil
 * @version $Id: FileMonitor.java,v 1.9 2007/04/12 02:11:53 rafaelsteil Exp $
 */
public class FileMonitor
{
	private static Logger logger = Logger.getLogger(FileMonitor.class);
	private static final FileMonitor instance = new FileMonitor();
	private Timer timer;
	private Map timerEntries;
	
	private FileMonitor() {
		this.timerEntries = new HashMap();
		this.timer = new Timer(true);
	}
	
	public static FileMonitor getInstance() {
		return instance;
	}
	
	/**
	 * Add a file to the monitor
	 * 
	 * @param listener The file listener
	 * @param filename The filename to watch
	 * @param period The watch interval.
	 */
	public void addFileChangeListener(FileChangeListener listener, 
		String filename, long period) {
		this.removeFileChangeListener(filename);
		
		logger.info("Watching " + filename);
		
		FileMonitorTask task = new FileMonitorTask(listener, filename);
		
		this.timerEntries.put(filename, task);
		this.timer.schedule(task, period, period);
	}
	
	/**
	 * Stop watching a file
	 * 
	 * @param listener The file listener
	 * @param filename The filename to keep watch
	 */
	public void removeFileChangeListener(String filename) {
		FileMonitorTask task = (FileMonitorTask)this.timerEntries.remove(filename);
		
		if (task != null) {
			task.cancel();
		}
	}
	
	private static class FileMonitorTask extends TimerTask {
		private FileChangeListener listener;
		private String filename;
		private File monitoredFile;
		private long lastModified;
		
		public FileMonitorTask(FileChangeListener listener, String filename) {
			this.listener = listener;
			this.filename = filename;
			
			this.monitoredFile = new File(filename);
			if (!this.monitoredFile.exists()) {
				return;
			}
			
			this.lastModified = this.monitoredFile.lastModified();
		}
		
		public void run() {
			long latestChange = this.monitoredFile.lastModified();
			if (this.lastModified != latestChange) {
				this.lastModified = latestChange;
				
				this.listener.fileChanged(this.filename);
			}
		}
	}
}