package org.apache.fulcrum.yaafi.service.shutdown;
   
   /*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  
  import java.io.File;
  import java.io.IOException;
  import java.io.InputStream;
  import java.security.MessageDigest;
  import java.util.Arrays;
  
  import org.apache.avalon.framework.logger.Logger;
  import org.apache.commons.io.IOUtils;
  import org.apache.fulcrum.yaafi.framework.util.InputStreamLocator;
  
  /**
   * Monitors a resource and checks if it has changed
   *
   * @author <a href="mailto:siegfried.goeschl@it20one.at">Siegfried Goeschl</a>
   */
  
  public class ShutdownEntry {
  
  	/** the location to monitor for changes */
  	private String location;
  
  	/** the last message digest of the location */
  	private byte[] digest;
  
  	/** the locator to load the monitored resource */
  	private InputStreamLocator locator;
  
  	/** keep a notice for the very first invocation */
  	private boolean isFirstInvocation;
  
  	/** the logger to be used */
  	private Logger logger;
  
  	/** use System.exit() to shutdown the JVM */
  	private boolean useSystemExit;
  
  	/**
  	 * Constructor
  	 *
  	 * @param logger         the logger to use
  	 * @param applicationDir the home directory of the application
  	 * @param location       the location to monitor for changes
  	 * @param useSystemExit  use System.exit() on shutdown
  	 */
  	public ShutdownEntry(Logger logger, File applicationDir, String location, boolean useSystemExit) {
  		this.isFirstInvocation = true;
  		this.useSystemExit = useSystemExit;
  		this.location = location;
  		this.locator = new InputStreamLocator(applicationDir);
  		this.logger = logger;
  	}
  
  	/**
  	 * @return has the monitored location changed
  	 */
  	public boolean hasChanged() {
  		boolean result = false;
  		InputStream is = null;
  		byte[] currDigest = null;
  
  		try {
  			// get a grip on our resource
  
  			is = this.locate();
  
  			if (is == null) {
  				String msg = "Unable to find the following resource : " + this.getLocation();
  				this.logger.warn(msg);
  			} else {
  				// calculate a SHA-1 digest
  
  				currDigest = this.getDigest(is);
  				is.close();
  				is = null;
  
  				if (this.isFirstInvocation() == true) {
  					isFirstInvocation = false;
  					this.logger.debug("Storing SHA-1 digest of " + this.getLocation());
 					this.setDigest(currDigest);
 				} else {
 					if (equals(this.digest, currDigest) == false) {
 						this.logger.debug("The following resource has changed : " + this.getLocation());
 						this.setDigest(currDigest);
 						result = true;
 					}
 				}
 			}
 
 			return result;
 		} catch (Exception e) {
 			String msg = "The ShutdownService encountered an internal error";
 			this.logger.error(msg, e);
 			return false;
 		} finally {
 			if (is != null) {
 				try {
 					is.close();
 				} catch (Exception e) {
 					String msg = "Can't close the InputStream during error recovery";
 					this.logger.error(msg, e);
 				}
 			}
 		}
 
 	}
 
 	/**
 	 * @return Returns the useSystemExit.
 	 */
 	public boolean isUseSystemExit() {
 		return useSystemExit;
 	}
 
 	/**
 	 * @return Returns the isFirstInvocation.
 	 */
 	private boolean isFirstInvocation() {
 		return isFirstInvocation;
 	}
 
 	/**
 	 * @return Returns the location.
 	 */
 	private String getLocation() {
 		return location;
 	}
 
 	/**
 	 * Creates an InputStream
 	 * 
 	 * @return InputStream of the location
 	 * @throws IOException if unable to open the stream
 	 */
 	public InputStream locate() throws IOException {
 		return this.locator.locate(this.getLocation());
 	}
 
 	/**
 	 * Creates a message digest
 	 * 
 	 * @param is Input stream
 	 * @return byte array of the input stream
 	 */
 	private byte[] getDigest(InputStream is) throws Exception {
 		byte[] result = null;
 		byte[] content = null;
 
 		// convert to byte array
 		content = IOUtils.toByteArray(is);
 
 		MessageDigest sha1 = MessageDigest.getInstance("SHA1");
 		sha1.update(content);
 		result = sha1.digest();
 
 		return result;
 	}
 
 	/**
 	 * @param digest The digest to set.
 	 */
 	private void setDigest(byte[] digest) {
 		this.digest = digest;
 	}
 
 	/**
 	 * Compares two byte[] for equality
 	 */
 	private static boolean equals(byte[] lhs, byte[] rhs) {
 		// JDK provided method
 		return Arrays.equals(lhs, rhs);
 	}
 
 }