/*
   Wotonomy: OpenStep design patterns for pure Java applications.
   Copyright (C) 2001 Intersect Software Corporation
   
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.
   
  This library 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.
  
  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, see http://www.gnu.org
  */
  
  package net.wotonomy.control;
  
  import java.net.InetAddress;
  
  /***
  * EOTemporaryGlobalID is a network-wide unique key.
  * This is used by EOEditingContext to construct temporary
  * ids when new objects are created.  <br><br>
  *
  * The specified format of the key is a byte array: 
  * &lt; Sequence [2], ProcessID [2], Time [4], IP Addr [4] &gt;,
  * but because java does not allow access to the process id,
  * the timestamp of when this class is first loaded is used
  * to simulate a process id.
  * 
  *
  * @author michael@mpowers.net
  * @author $Author: cgruber $
  * @version $Revision: 893 $
  */
  public class EOTemporaryGlobalID 
      extends EOGlobalID 
  {
      /***
      * Holds the length in bytes of the key that is generated.
      */
      public static final int UniqueBinaryKeyLength = 12;
      
      private static int sequence;
      private static byte[] processid; // 2 bytes
      private static byte[] ipaddr; // 4 bytes
      
      static // static initializer
      {
          // init sequence
          sequence = 0;
          
          // init processid
          processid = new byte[2];
          long time = System.currentTimeMillis();
          processid[1] = (byte) time;
          time = time >> 8;
          processid[0] = (byte) time;
  
          // init ipaddr
          ipaddr = new byte[4];
          try
          {
              ipaddr = InetAddress.getLocalHost().getAddress();
          }
          catch ( Exception exc )
          {
              // could not obtain ip address - use pid twice
              ipaddr[0] = processid[0];
              ipaddr[1] = processid[1];
              ipaddr[2] = processid[0];
              ipaddr[3] = processid[1];
          }
      }
      
      private byte[] key;
      private int hashCode;
  
      /***
      * Generates a new id with a unique key.
      */    
      public EOTemporaryGlobalID()
      {
          key = new byte[UniqueBinaryKeyLength];
          
          // init sequence (important byte first)
          key[0] = (byte) ( sequence ); 
          key[1] = (byte) ( sequence >> 8 );
          sequence++;
          
          // populate pid (important byte first)
          key[2] = processid[1];
          key[3] = processid[0];
          
          // init time (important byte first)
          long time = System.currentTimeMillis();
         key[4] = (byte) time;
         time = time >> 8;
         key[5] = (byte) time;
         time = time >> 8;
         key[6] = (byte) time;
         time = time >> 8;
         key[7] = (byte) time;
         
         // populate ipaddr
         key[8]  = ipaddr[0];
         key[9]  = ipaddr[1];
         key[10] = ipaddr[2];
         key[11] = ipaddr[3];
 
         // use string's hash code
         hashCode = new String( key ).hashCode();
     }
     
     /***
     * Private constructor for cloning.
     */
     private EOTemporaryGlobalID( byte[] aKey )
     {
 //        key = aKey; // this might be faster
 
         // make copy of key - might be safer
         key = new byte[ UniqueBinaryKeyLength ];
         for ( int i = 0; i < UniqueBinaryKeyLength; i++ )
         {
             key[i] = aKey[i];
         }
         
         // use string's hash code
         hashCode = new String( aKey ).hashCode();
     }
     
     /***
     * Returns true.
     */
     public boolean isTemporary()
     {
         return true;   
     }
     
     /***
     * Returns whether the keys are equal.
     */
     public boolean equals( Object anObject )
     {
         if ( ! ( anObject instanceof EOTemporaryGlobalID ) ) 
             return false;   
         
         byte[] otherKey = ((EOTemporaryGlobalID)anObject).key;
         
         for ( int i = 0; i < UniqueBinaryKeyLength; i++ )
         {
             if ( key[i] != otherKey[i] ) return false;
         }
         return true;
     }
     
     /***
     * Returns a copy of this object.
     */
     public Object clone()
     {
         // faster than super.clone()
         return new EOTemporaryGlobalID( key );
     }
     
     public int hashCode()
     {
         return hashCode;           
     }
     
     /***
     * Returns a string representation of this key.
     * This is a 24-character string with each pair
     * of characters holding a hexadecimal value that
     * is 128 more than the value of the corresponding 
     * byte (to account for two's complement).
     */
     public String toString()
     {
         String hex;
         StringBuffer buffer = new StringBuffer();
         for ( int i = 0; i < key.length; i++ )
         {
             // get string: adjust for two's complement
             hex = Integer.toHexString( key[i]+128 );
             // pad with zero so we take two characters
             if ( hex.length() == 1 ) hex = "0" + hex;
             // append hex code
             buffer.append( hex );
         }
         return buffer.toString();
     }
 }
 
 /*
  * $Log$
  * Revision 1.1  2006/02/16 13:19:57  cgruber
  * Check in all sources in eclipse-friendly maven-enabled packages.
  *
  * Revision 1.4  2001/04/29 22:02:45  mpowers
  * Work on id transposing between editing contexts.
  *
  * Revision 1.3  2001/02/15 21:13:30  mpowers
  * First draft implementation is complete.  Now on to debugging.
  *
  * Revision 1.2  2001/02/14 23:03:02  mpowers
  * A near-complete first draft of EOEditingContext.
  *
  * Revision 1.1  2001/02/13 23:24:29  mpowers
  * Implementing more of editing context.
  *
  *
  */