michael@0: /**
michael@0:  * Copyright (c) 2012, Ben Fortuna
michael@0:  * All rights reserved.
michael@0:  *
michael@0:  * Redistribution and use in source and binary forms, with or without
michael@0:  * modification, are permitted provided that the following conditions
michael@0:  * are met:
michael@0:  *
michael@0:  *  o Redistributions of source code must retain the above copyright
michael@0:  * notice, this list of conditions and the following disclaimer.
michael@0:  *
michael@0:  *  o Redistributions in binary form must reproduce the above copyright
michael@0:  * notice, this list of conditions and the following disclaimer in the
michael@0:  * documentation and/or other materials provided with the distribution.
michael@0:  *
michael@0:  *  o Neither the name of Ben Fortuna nor the names of any other contributors
michael@0:  * may be used to endorse or promote products derived from this software
michael@0:  * without specific prior written permission.
michael@0:  *
michael@0:  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
michael@0:  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
michael@0:  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
michael@0:  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
michael@0:  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
michael@0:  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
michael@0:  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
michael@0:  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
michael@0:  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
michael@0:  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
michael@0:  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
michael@0:  */
michael@0: package net.fortuna.ical4j.util;
michael@0: 
michael@0: import java.net.SocketException;
michael@0: 
michael@0: import net.fortuna.ical4j.model.DateTime;
michael@0: import net.fortuna.ical4j.model.property.Uid;
michael@0: 
michael@0: /**
michael@0:  * $Id$
michael@0:  *
michael@0:  * Created on 11/03/2007
michael@0:  *
michael@0:  * Generates {@link Uid} properties in a similar fashion to that recommended in section 4.8.4.7 of the specification.
michael@0:  * @author Ben Fortuna
michael@0:  */
michael@0: public class UidGenerator {
michael@0: 
michael@0:     private final String pid;
michael@0: 
michael@0:     private final HostInfo hostInfo;
michael@0: 
michael@0:     private static long lastMillis;
michael@0: 
michael@0:     /**
michael@0:      * @param pid a unique process identifier for the host machine
michael@0:      * @throws SocketException where host information cannot be retrieved
michael@0:      */
michael@0:     public UidGenerator(String pid) throws SocketException {
michael@0:         this(new InetAddressHostInfo(), pid);
michael@0:     }
michael@0: 
michael@0:     /**
michael@0:      * @param hostInfo custom host information
michael@0:      * @param pid a unique process identifier for the host machine
michael@0:      */
michael@0:     public UidGenerator(HostInfo hostInfo, String pid) {
michael@0:         this.hostInfo = hostInfo;
michael@0:         this.pid = pid;
michael@0:     }
michael@0: 
michael@0:     /**
michael@0:      * @return a unique component identifier
michael@0:      */
michael@0:     public Uid generateUid() {
michael@0:         final StringBuffer b = new StringBuffer();
michael@0:         b.append(uniqueTimestamp());
michael@0:         b.append('-');
michael@0:         b.append(pid);
michael@0:         if (hostInfo != null) {
michael@0:             b.append('@');
michael@0:             b.append(hostInfo.getHostName());
michael@0:         }
michael@0:         return new Uid(b.toString());
michael@0:     }
michael@0: 
michael@0:     /**
michael@0:      * Generates a timestamp guaranteed to be unique for the current JVM instance.
michael@0:      * @return a {@link DateTime} instance representing a unique timestamp
michael@0:      */
michael@0:     private static DateTime uniqueTimestamp() {
michael@0:         long currentMillis;
michael@0:         synchronized (UidGenerator.class) {
michael@0:             currentMillis = System.currentTimeMillis();
michael@0:             // guarantee uniqueness by ensuring timestamp is always greater
michael@0:             // than the previous..
michael@0:             if (currentMillis < lastMillis) {
michael@0:                 currentMillis = lastMillis;
michael@0:             }
michael@0:             if (currentMillis - lastMillis < Dates.MILLIS_PER_SECOND) {
michael@0:                 currentMillis += Dates.MILLIS_PER_SECOND;
michael@0:             }
michael@0:             lastMillis = currentMillis;
michael@0:         }
michael@0:         final DateTime timestamp = new DateTime(currentMillis);
michael@0:         timestamp.setUtc(true);
michael@0:         return timestamp;
michael@0:     }
michael@0: }