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CQL implementation for Achilles using Datastax Java driver
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/*
 * Copyright (C) 2012-2014 DuyHai DOAN
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package info.archinnov.achilles.internal.utils;

import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Random;
import java.util.Set;
import java.util.UUID;


/**
 * The goods are here: www.ietf.org/rfc/rfc4122.txt.
 */
public class UUIDGen
{
    // A grand day! millis at 00:00:00.000 15 Oct 1582.
    private static final long START_EPOCH = -12219292800000L;
    private static final long clockSeqAndNode = makeClockSeqAndNode();

    // placement of this singleton is important.  It needs to be instantiated *AFTER* the other statics.
    private static final UUIDGen instance = new UUIDGen();

    private long lastNanos;

    private UUIDGen()
    {
        // make sure someone didn't whack the clockSeqAndNode by changing the order of instantiation.
        if (clockSeqAndNode == 0) throw new RuntimeException("singleton instantiation is misplaced.");
    }

    /**
     * Creates a type 1 UUID (time-based UUID).
     *
     * @return a UUID instance
     */
    public static UUID getTimeUUID()
    {
        return new UUID(instance.createTimeSafe(), clockSeqAndNode);
    }


    /**
     * @param uuid
     * @return microseconds since Unix epoch
     */
    public static long microsTimestamp(UUID uuid)
    {
        final long timestamp = uuid.timestamp();
        long remainder = timestamp%1000;
        return (timestamp / 10) + START_EPOCH * 1000 + remainder;
    }

    public static long increasingMicroTimestamp() {
        final UUID timeUUID = getTimeUUID();
        return microsTimestamp(timeUUID);
    }


    private static long makeClockSeqAndNode()
    {
        long clock = new Random(System.currentTimeMillis()).nextLong();

        long lsb = 0;
        lsb |= 0x8000000000000000L;                 // variant (2 bits)
        lsb |= (clock & 0x0000000000003FFFL) << 48; // clock sequence (14 bits)
        lsb |= makeNode();                          // 6 bytes
        return lsb;
    }

    // needs to return two different values for the same when.
    // we can generate at most 10k UUIDs per ms.
    private synchronized long createTimeSafe()
    {
        long nanosSince = (System.currentTimeMillis() - START_EPOCH) * 10000;
        if (nanosSince > lastNanos)
            lastNanos = nanosSince;
        else
            nanosSince = ++lastNanos;

        return createTime(nanosSince);
    }


    private static long createTime(long nanosSince)
    {
        long msb = 0L;
        msb |= (0x00000000ffffffffL & nanosSince) << 32;
        msb |= (0x0000ffff00000000L & nanosSince) >>> 16;
        msb |= (0xffff000000000000L & nanosSince) >>> 48;
        msb |= 0x0000000000001000L; // sets the version to 1.
        return msb;
    }

    private static long makeNode()
    {
       /*
        * We don't have access to the MAC address but need to generate a node part
        * that identify this host as uniquely as possible.
        * The spec says that one option is to take as many source that identify
        * this node as possible and hash them together. That's what we do here by
        * gathering all the ip of this host.
        * Note that FBUtilities.getBroadcastAddress() should be enough to uniquely
        * identify the node *in the cluster* but it triggers DatabaseDescriptor
        * instanciation and the UUID generator is used in Stress for instance,
        * where we don't want to require the yaml.
        */
        Collection localAddresses = getAllLocalAddresses();
        if (localAddresses.isEmpty())
            throw new RuntimeException("Cannot generate the node component of the UUID because cannot retrieve any IP addresses.");

        // ideally, we'd use the MAC address, but java doesn't expose that.
        byte[] hash = hash(localAddresses);
        long node = 0;
        for (int i = 0; i < Math.min(6, hash.length); i++)
            node |= (0x00000000000000ff & (long)hash[i]) << (5-i)*8;
        assert (0xff00000000000000L & node) == 0;

        // Since we don't use the mac address, the spec says that multicast
        // bit (least significant bit of the first octet of the node ID) must be 1.
        return node | 0x0000010000000000L;
    }

    private static byte[] hash(Collection data)
    {
        try
        {
            MessageDigest messageDigest = MessageDigest.getInstance("MD5");
            for(InetAddress addr : data)
                messageDigest.update(addr.getAddress());

            return messageDigest.digest();
        }
        catch (NoSuchAlgorithmException nsae)
        {
            throw new RuntimeException("MD5 digest algorithm is not available", nsae);
        }
    }

    private static Collection getAllLocalAddresses()
    {
        Set localAddresses = new HashSet();
        try
        {
            Enumeration nets = NetworkInterface.getNetworkInterfaces();
            if (nets != null)
            {
                while (nets.hasMoreElements())
                    localAddresses.addAll(Collections.list(nets.nextElement().getInetAddresses()));
            }
        }
        catch (SocketException e)
        {
            throw new AssertionError(e);
        }
        return localAddresses;
    }
}

// for the curious, here is how I generated START_EPOCH
//        Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT-0"));
//        c.set(Calendar.YEAR, 1582);
//        c.set(Calendar.MONTH, Calendar.OCTOBER);
//        c.set(Calendar.DAY_OF_MONTH, 15);
//        c.set(Calendar.HOUR_OF_DAY, 0);
//        c.set(Calendar.MINUTE, 0);
//        c.set(Calendar.SECOND, 0);
//        c.set(Calendar.MILLISECOND, 0);
//        long START_EPOCH = c.getTimeInMillis();