/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 2002-2003 The Apache Software Foundation.  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. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Axis" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 APACHE SOFTWARE FOUNDATION OR
 * ITS 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.axis.utils;

import org.apache.axis.components.logger.LogFactory;
import org.apache.commons.logging.Log;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;

/**
 * Code borrowed from AuthenticatorBase.java for generating a secure id's.
 */
public class SessionUtils
{

   /**
    * Field log
    */
   private static Log log = LogFactory.getLog(SessionUtils.class.getName());

   /**
    * The default message digest algorithm to use if we cannot use
    * the requested one.
    */
   protected static final String DEFAULT_ALGORITHM = "MD5";

   /**
    * The number of random bytes to include when generating a
    * session identifier.
    */
   protected static final int SESSION_ID_BYTES = 16;

   /**
    * The message digest algorithm to be used when generating session
    * identifiers.  This must be an algorithm supported by the
    * <code>java.security.MessageDigest</code> class on your platform.
    */
   protected static String algorithm = DEFAULT_ALGORITHM;

   /**
    * Return the MessageDigest implementation to be used when
    * creating session identifiers.
    */
   protected static MessageDigest digest = null;

   /**
    * A random number generator to use when generating session identifiers.
    */
   protected static Random random = null;

   /**
    * The Java class name of the random number generator class to be used
    * when generating session identifiers.
    */
   protected static String randomClass = "java.security.SecureRandom";

   /**
    * Host name/ip.
    */
   private static String thisHost = null;

   /**
    * Generate and return a new session identifier.
    *
    * @return a new session id
    */
   public static synchronized String generateSessionId()
   {
      // Generate a byte array containing a session identifier
      byte bytes[] = new byte[SESSION_ID_BYTES];

      getRandom().nextBytes(bytes);
      bytes = getDigest().digest(bytes);

      // Render the result as a String of hexadecimal digits
      StringBuffer result = new StringBuffer();

      for (int i = 0; i < bytes.length; i++)
      {
         byte b1 = (byte)((bytes[i] & 0xf0) >> 4);
         byte b2 = (byte)(bytes[i] & 0x0f);

         if (b1 < 10)
         {
            result.append((char)('0' + b1));
         }
         else
         {
            result.append((char)('A' + (b1 - 10)));
         }
         if (b2 < 10)
         {
            result.append((char)('0' + b2));
         }
         else
         {
            result.append((char)('A' + (b2 - 10)));
         }
      }
      return (result.toString());
   }

   /**
    * Generate and return a new session identifier.
    *
    * @return a new session.
    */
   public static synchronized Long generateSession()
   {
      return new Long(getRandom().nextLong());
   }

   /**
    * Return the MessageDigest object to be used for calculating
    * session identifiers.  If none has been created yet, initialize
    * one the first time this method is called.
    *
    * @return Message Digest
    */
   private static synchronized MessageDigest getDigest()
   {
      if (digest == null)
      {
         try
         {
            digest = MessageDigest.getInstance(algorithm);
         }
         catch (NoSuchAlgorithmException e)
         {
            try
            {
               digest = MessageDigest.getInstance(DEFAULT_ALGORITHM);
            }
            catch (NoSuchAlgorithmException f)
            {
               digest = null;
            }
         }
      }
      return (digest);
   }

   /**
    * Return the random number generator instance we should use for
    * generating session identifiers.  If there is no such generator
    * currently defined, construct and seed a new one.
    *
    * @return Random object
    */
   private static synchronized Random getRandom()
   {
      if (random == null)
      {
         try
         {
            Class clazz = Class.forName(randomClass);

            random = (Random)clazz.newInstance();
            long seed = System.currentTimeMillis();
            char entropy[] = getEntropy().toCharArray();

            for (int i = 0; i < entropy.length; i++)
            {
               long update = ((byte)entropy[i]) << ((i % 8) * 8);

               seed ^= update;
            }
            random.setSeed(seed);
         }
         catch (Exception e)
         {
            random = new java.util.Random();
         }
      }
      return (random);
   }

   /**
    * Method getEntropy
    *
    * @return a unique string
    */
   private static String getEntropy()
   {
      if (null == thisHost)
      {
         try
         {
            thisHost = java.net.InetAddress.getLocalHost().getHostName();
         }
         catch (java.net.UnknownHostException e)
         {
            log.error(Messages.getMessage("javaNetUnknownHostException00"),
                    e);
            thisHost = "localhost";
         }
      }
      StringBuffer s = new StringBuffer();

      // Unique string
      s.append(s.hashCode()).append('.').append(System.currentTimeMillis())
              .append(".AXIS@").append(thisHost);
      return s.toString();
   }
}
