/*
 * Copyright 2002-2007 the original author or authors.
 *
 * 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 org.springframework.ws.soap.addressing.messageid;

/*
 * RandomGUID from http://www.javaexchange.com/aboutRandomGUID.html
 * @version 1.2.1 11/05/02 @author Marc A. Mnich
 * 
 * From www.JavaExchange.com, Open Software licensing
 * 
 * 11/05/02 -- Performance enhancement from Mike Dubman. Moved InetAddr.getLocal to static block. Mike has measured a 10
 * fold improvement in run time. 01/29/02 -- Bug fix: Improper seeding of nonsecure Random object caused duplicate GUIDs
 * to be produced. Random object is now only created once per JVM. 01/19/02 -- Modified random seeding and added new
 * constructor to allow secure random feature. 01/14/02 -- Added random function seeding with JVM run time
 */

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

/**
 * Globally unique identifier generator.
 * <p/>
 * In the multitude of java GUID generators, I found none that guaranteed randomness. GUIDs are guaranteed to be
 * globally unique by using ethernet MACs, IP addresses, time elements, and sequential numbers. GUIDs are not expected
 * to be random and most often are easy/possible to guess given a sample from a given generator. SQL Server, for example
 * generates GUID that are unique but sequencial within a given instance.
 * <p/>
 * GUIDs can be used as security devices to hide things such as files within a filesystem where listings are unavailable
 * (e.g. files that are served up from a Web server with indexing turned off). This may be desirable in cases where
 * standard authentication is not appropriate. In this scenario, the RandomGuids are used as directories. Another
 * example is the use of GUIDs for primary keys in a database where you want to ensure that the keys are secret. Random
 * GUIDs can then be used in a URL to prevent hackers (or users) from accessing records by guessing or simply by
 * incrementing sequential numbers.
 * <p/>
 * There are many other possibilities of using GUIDs in the realm of security and encryption where the element of
 * randomness is important. This class was written for these purposes but can also be used as a general purpose GUID
 * generator as well.
 * <p/>
 * RandomGuid generates truly random GUIDs by using the system's IP address (name/IP), system time in milliseconds (as
 * an integer), and a very large random number joined together in a single String that is passed through an MD5 hash.
 * The IP address and system time make the MD5 seed globally unique and the random number guarantees that the generated
 * GUIDs will have no discernible pattern and cannot be guessed given any number of previously generated GUIDs. It is
 * generally not possible to access the seed information (IP, time, random number) from the resulting GUIDs as the MD5
 * hash algorithm provides one way encryption.
 * <p/>
 * <b>Security of RandomGuid</b>: RandomGuid can be called one of two ways -- with the basic java Random number
 * generator or a cryptographically strong random generator (SecureRandom). The choice is offered because the secure
 * random generator takes about 3.5 times longer to generate its random numbers and this performance hit may not be
 * worth the added security especially considering the basic generator is seeded with a cryptographically strong random
 * seed.
 * <p/>
 * Seeding the basic generator in this way effectively decouples the random numbers from the time component making it
 * virtually impossible to predict the random number component even if one had absolute knowledge of the System time.
 * Thanks to Ashutosh Narhari for the suggestion of using the static method to prime the basic random generator.
 * <p/>
 * Using the secure random option, this class complies with the statistical random number generator tests specified in
 * FIPS 140-2, Security Requirements for Cryptographic Modules, section 4.9.1.
 * <p/>
 * I converted all the pieces of the seed to a String before handing it over to the MD5 hash so that you could print it
 * out to make sure it contains the data you expect to see and to give a nice warm fuzzy. If you need better
 * performance, you may want to stick to byte[] arrays.
 * <p/>
 * I believe that it is important that the algorithm for generating random GUIDs be open for inspection and
 * modification. This class is free for all uses.
 *
 * @author Marc A. Mnich
 * @version 1.2.1 11/05/02
 */
public class RandomGuid {

    private static Random random;

    private static SecureRandom secureRandom;

    private static String id;

    private String guid;

    /*
      * Static block to take care of one time secureRandom seed. It takes a few seconds to initialize SecureRandom. You
      * might want to consider removing this static block or replacing it with a "time since first loaded" seed to reduce
      * this time. This block will run only once per JVM instance.
      */
    static {
        secureRandom = new SecureRandom();
        long secureInitializer = secureRandom.nextLong();
        random = new Random(secureInitializer);
        try {
            id = InetAddress.getLocalHost().toString();
        }
        catch (UnknownHostException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Default constructor. With no specification of security option, this constructor defaults to lower security, high
     * performance.
     */
    public RandomGuid() {
        getRandomGuid(false);
    }

    /**
     * Constructor with security option. Setting secure true enables each random number generated to be
     * cryptographically strong. Secure false defaults to the standard Random function seeded with a single
     * cryptographically strong random number.
     */
    public RandomGuid(boolean secure) {
        getRandomGuid(secure);
    }

    /** Method to generate the random GUID. */
    private void getRandomGuid(boolean secure) {
        MessageDigest md5;
        StringBuffer sbValueBeforeMD5 = new StringBuffer();

        try {
            md5 = MessageDigest.getInstance("MD5");
        }
        catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }

        long time = System.currentTimeMillis();
        long rand;

        if (secure) {
            rand = secureRandom.nextLong();
        }
        else {
            rand = random.nextLong();
        }

        // This StringBuffer can be as long as you need; the MD5
        // hash will always return 128 bits. You can change
        // the seed to include anything you want here.
        // You could even stream a file through the MD5 making
        // the odds of guessing it at least as great as that
        // of guessing the contents of the file!
        sbValueBeforeMD5.append(id);
        sbValueBeforeMD5.append(":");
        sbValueBeforeMD5.append(Long.toString(time));
        sbValueBeforeMD5.append(":");
        sbValueBeforeMD5.append(Long.toString(rand));

        String valueBeforeMD5 = sbValueBeforeMD5.toString();
        md5.update(valueBeforeMD5.getBytes());

        byte[] array = md5.digest();
        StringBuffer sb = new StringBuffer();
        for (int j = 0; j < array.length; ++j) {
            int b = array[j] & 0xFF;
            if (b < 0x10) {
                sb.append('0');
            }
            sb.append(Integer.toHexString(b));
        }
        guid = sb.toString();
    }

    /**
     * Convert to the standard format for GUID (Useful for SQL Server UniqueIdentifiers, etc). Example:
     * "C2FEEEAC-CFCD-11D1-8B05-00600806D9B6".
     */
    public String toString() {
        String raw = guid.toUpperCase();
        StringBuffer sb = new StringBuffer();
        sb.append(raw.substring(0, 8));
        sb.append("-");
        sb.append(raw.substring(8, 12));
        sb.append("-");
        sb.append(raw.substring(12, 16));
        sb.append("-");
        sb.append(raw.substring(16, 20));
        sb.append("-");
        sb.append(raw.substring(20));
        return sb.toString();
    }

}
