/* 
 * DirectoryMonitor.java
 * 
 * Created 26.05.2007.
 *
 * eaio: NativeCall - calling operating system methods from Java
 * Copyright (c) 2004-2007 Johann Burkard (<mailto:jb@eaio.com>)
 * <http://eaio.com>
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
 * NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 * USE OR OTHER DEALINGS IN THE SOFTWARE.
 * 
 */
package com.eaio.nativecall.monitor;

import java.io.File;
import java.io.IOException;
import java.util.Arrays;

import sun.misc.ServiceConfigurationError;

import com.eaio.nativecall.Holder;
import com.eaio.nativecall.IntCall;
import com.eaio.nativecall.NativeCall;

/**
 * Monitors a directory for changes. Does not rely on polling.
 * 
 * @author <a href="mailto:jb@eaio.com">Johann Burkard</a>
 * @version $Id: DirectoryMonitor.java 138 2008-02-21 22:45:48Z Johann $
 * @see <a
 *      href="http://johannburkard.de/blablog/programming/java/2007/05/25/Call-native-methods-in-a-DLL-from-Java-without-JNI.html">Call
 *      native methods in a DLL from Java without JNI</a>
 * @see <a href="http://johannburkard.de/software/nativecall/" target="_top">NativeCall &#8211; call native methods from Java without <acronym title="Java Native Interface">JNI</acronym></a>
 */
public class DirectoryMonitor {

	private static final Integer DESIRED_ACCESS = new Integer(0x80000000); // GENERIC_READ

	private static final Integer SHARE_MODE = new Integer(0x01 | 0x02 | 0x04); // READ, WRITE, DELETE

	private static final Integer CREATION_DISPOSITION = new Integer(3); // OPEN_EXISTING

	private static final Integer FLAGS_AND_ATTRIBUTES = new Integer(0x2000000); // BACKUP_SEMANTICS

	private static final Integer NOTIFY_FILTER = new Integer(0x01 | 0x02); // CHANGE_FILE_NAME, CHANGE_DIR_NAME

	protected final File directory;

	/**
	 * Constructor for DirectoryMonitor.
	 * 
	 * @param dir
	 *            the directory to monitor. The directory must exist.
	 * @throws ServiceConfigurationError
	 * @throws IOException
	 * @throws UnsupportedOperationException
	 * @throws UnsatisfiedLinkError
	 * @throws SecurityException
	 * @throws IllegalArgumentException
	 *             if the directory does not exist or is not a directory
	 */
	public DirectoryMonitor(File dir) throws SecurityException,
			UnsatisfiedLinkError, UnsupportedOperationException, IOException,
			ServiceConfigurationError {
		if (!dir.exists()) {
			throw new IllegalArgumentException(dir + " does not exist");
		}
		if (!dir.isDirectory()) {
			throw new IllegalArgumentException(dir + " is not a directory");
		}
		this.directory = dir;
		NativeCall.init();
	}

	/**
	 * Starts watching the directory and returns once it's contents have
	 * changed.
	 * 
	 * @throws IOException
	 */
	public void monitor() throws IOException {
		IntCall createFile = null;
		IntCall closeHandle = null;
		IntCall readDirectoryChanges = null;

		int dirHandle = 0;
		try {
			createFile = new IntCall("CreateFileA");
			closeHandle = new IntCall("CloseHandle");
			readDirectoryChanges = new IntCall("ReadDirectoryChangesW");

			dirHandle = createFile.executeCall(new Object[] {
					directory.getCanonicalPath(), DESIRED_ACCESS, SHARE_MODE,
					null, CREATION_DISPOSITION, FLAGS_AND_ATTRIBUTES, null });

			Holder returnedBufferLength = new Holder(new Integer(0));
	
			byte[] buffer = new byte[1024];
			Arrays.fill(buffer, (byte) 0xff);
			Holder fileNotifyInformation = new Holder(buffer);

			readDirectoryChanges.executeBooleanCall(new Object[] {
					new Integer(dirHandle), fileNotifyInformation,
					new Integer(buffer.length), Boolean.FALSE, NOTIFY_FILTER,
					returnedBufferLength, null, null });

		}
		finally {
			if (closeHandle != null) {
				if (dirHandle != 0) {
					closeHandle.executeBooleanCall(new Integer(dirHandle));
				}
				closeHandle.destroy();
			}
			if (readDirectoryChanges != null) {
				readDirectoryChanges.destroy();
			}
			if (createFile != null) {
				createFile.destroy();
			}
		}
	}

}