/*

 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: 

 * < Sequence [2], ProcessID [2], Time [4], IP Addr [4] >,

 * 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.

  *

  *

  */