/src/main/java/com/fasterxml/uuid/impl/TimeBasedGenerator.java

package com.fasterxml.uuid.impl;

import java.util.UUID;

import com.fasterxml.uuid.*;

/**
 * Implementation of UUID generator that uses time/location based generation
 * method (variant 1).
 *<p>
 * As all JUG provided implementations, this generator is fully thread-safe.
 * Additionally it can also be made externally synchronized with other
 * instances (even ones running on other JVMs); to do this,
 * use {@link com.fasterxml.uuid.ext.FileBasedTimestampSynchronizer}
 * (or equivalent).
 *
 * @since 3.0
 */
public class TimeBasedGenerator extends NoArgGenerator
{
    /*
    /**********************************************************************
    /* Configuration
    /**********************************************************************
     */

    protected final EthernetAddress _ethernetAddress;

    /**
     * Object used for synchronizing access to timestamps, to guarantee
     * that timestamps produced by this generator are unique and monotonically increasings.
     * Some implementations offer even stronger guarantees, for example that
     * same guarantee holds between instances running on different JVMs (or
     * with native code).
     */
    protected final UUIDTimer _timer;

    /**
     * Base values for the second long (last 8 bytes) of UUID to construct
     */
    protected final long _uuidL2;
    
    /*
    /**********************************************************************
    /* Construction
    /**********************************************************************
     */

    /**
     * @param ethAddr Hardware address (802.1) to use for generating
     *   spatially unique part of UUID. If system has more than one NIC,
     */
    
    public TimeBasedGenerator(EthernetAddress ethAddr, UUIDTimer timer)
    {
        byte[] uuidBytes = new byte[16];
        if (ethAddr == null) {
            ethAddr = EthernetAddress.constructMulticastAddress();
        }
        // initialize baseline with MAC address info
        _ethernetAddress = ethAddr;
        _ethernetAddress.toByteArray(uuidBytes, 10);
        // and add clock sequence
        int clockSeq = timer.getClockSequence();
        uuidBytes[UUIDUtil.BYTE_OFFSET_CLOCK_SEQUENCE] = (byte) (clockSeq >> 8);
        uuidBytes[UUIDUtil.BYTE_OFFSET_CLOCK_SEQUENCE+1] = (byte) clockSeq;
        long l2 = UUIDUtil.gatherLong(uuidBytes, 8);
        _uuidL2 = UUIDUtil.initUUIDSecondLong(l2);
        _timer = timer;
    }
    
    /*
    /**********************************************************************
    /* Access to config
    /**********************************************************************
     */

    @Override
    public UUIDType getType() { return UUIDType.TIME_BASED; }

    public EthernetAddress getEthernetAddress() { return _ethernetAddress; }
    
    /*
    /**********************************************************************
    /* UUID generation
    /**********************************************************************
     */
    
    /* As timer is not synchronized (nor _uuidBytes), need to sync; but most
     * importantly, synchronize on timer which may also be shared between
     * multiple instances
     */
    @Override
    public UUID generate()
    {
        final long rawTimestamp = _timer.getTimestamp();
        // Time field components are kind of shuffled, need to slice:
        int clockHi = (int) (rawTimestamp >>> 32);
        int clockLo = (int) rawTimestamp;
        // and dice
        int midhi = (clockHi << 16) | (clockHi >>> 16);
        // need to squeeze in type (4 MSBs in byte 6, clock hi)
        midhi &= ~0xF000; // remove high nibble of 6th byte
        midhi |= 0x1000; // type 1
        long midhiL = (long) midhi;
        midhiL = ((midhiL << 32) >>> 32); // to get rid of sign extension
        // and reconstruct
        long l1 = (((long) clockLo) << 32) | midhiL;
        // last detail: must force 2 MSB to be '10'
        return new UUID(l1, _uuidL2);
    }
}