/*
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.
 *
 *
 */