/*
    * EL4J, the Extension Library for the J2EE, adds incremental enhancements to
    * the spring framework, http://el4j.sf.net
    * Copyright (C) 2005 by ELCA Informatique SA, Av. de la Harpe 22-24,
    * 1000 Lausanne, Switzerland, http://www.elca.ch
    *
    * EL4J is published under the GNU Lesser General Public License (LGPL)
    * Version 2.1. See http://www.gnu.org/licenses/
    *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
   * GNU Lesser General Public License for more details.
   *
   * For alternative licensing, please contact info@elca.ch
   */
  package ch.elca.el4j.services.persistence.generic.primarykey;
  
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  import java.security.SecureRandom;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import ch.elca.el4j.util.codingsupport.annotations.FindBugsSuppressWarnings;
  
  /**
   * This key generator generates UUIDs as described in "EJB Design Patterns", F.
   * Marinescu, pages 112-116. It is a simplified version of the algorithm
   * presented in
   * http://www1.ics.uci.edu/~ejw/authoring/uuid-guid/draft-leach-uuids-guids-01.txt
   *
   * The returned UUID is a hex-encoded 32-digit number.
   *
   * @svnLink $Revision: 4010 $;$Date: 2009-12-01 10:59:54 +0100 (Di, 01. Dez 2009) $;$Author: jonasha $;$URL: https://el4j.svn.sourceforge.net/svnroot/el4j/branches/el4j_3_1/el4j/framework/modules/core/src/main/java/ch/elca/el4j/services/persistence/generic/primarykey/UuidPrimaryKeyGenerator.java $
   *
   * @author Martin Zeltner (MZE)
   */
  public class UuidPrimaryKeyGenerator implements PrimaryKeyGenerator {
  	/**
  	 * Private logger of this class.
  	 */
  	private static Logger s_logger
  		= LoggerFactory.getLogger(UuidPrimaryKeyGenerator.class);
  
  	/**
  	 * Middle value.
  	 */
  	private String m_midValue;
  	
  	/**
  	 * Seeder.
  	 */
  	private SecureRandom m_seeder;
  	
  	/**
  	 * String aaray with zeros.
  	 */
  	private String[] m_zeros;
  
  	/**
  	 * Default constructor.
  	 */
  	public UuidPrimaryKeyGenerator() {
  		init();
  	}
  
  	/**
  	 * {@inheritDoc}
  	 */
  	@FindBugsSuppressWarnings(value = "INT_VACUOUS_BIT_OPERATION", 
  							justification = "Ensures that no rounding takes place")
  	public String getPrimaryKey() {
  		long time = System.currentTimeMillis();
  		int timeLow = (int) time & 0xFFFFFFFF;
  		int value = m_seeder.nextInt();
  		String keyString = toHexString(timeLow) + m_midValue
  			+ toHexString(value);
  		return keyString;
  	}
  
  	// Checkstyle: MagicNumber off
  	/**
  	 * Initalize the primary key generator.
  	 */
  	private void init() {
  		// Fill the m_zeros table
  		final int ZERO_ARRAY_LENGTH = 8;
  		m_zeros = new String[ZERO_ARRAY_LENGTH];
  		m_zeros[0] = "";
  		for (int i = 1; i < ZERO_ARRAY_LENGTH; i++) {
  			m_zeros[i] = m_zeros[i - 1] + "0";
  		}
  
  		// Get the IP address as an hex string
  		byte[] bytes = null;
  		try {
  			InetAddress inetAddress = InetAddress.getLocalHost();
 			bytes = inetAddress.getAddress();
 		} catch (UnknownHostException npe) {
 			s_logger.debug("Host ip could not be found. Following "
 				+ "will be used: 127.0.0.1");
 			bytes = new byte[] {1, 0, 0, 127};
 		}
 		int intAddress = 0;
 		for (int i = 0; i < bytes.length; i++) {
 			int unsignedByte = bytes[i] & 0xFF;
 			intAddress = (intAddress + unsignedByte) << 8;
 		}
 		String hexInetAddress = toHexString(intAddress);
 
 		String thisHashCode = toHexString(System.identityHashCode(this));
 
 		m_midValue = hexInetAddress + thisHashCode;
 
 		m_seeder = new SecureRandom();
 	}
 
 	/**
 	 * Method to convert from decimal to hexadecimal.
 	 *
 	 * @param i Is the given decimal number.
 	 * @return Returns the hexadecimal value of given decimal number.
 	 */
 	private String toHexString(int i) {
 		String hex = Integer.toHexString(i);
 		int hexLength = hex.length();
 		return m_zeros[8 - hexLength] + hex;
 	}
 	// Checkstyle: MagicNumber on
 }