content: // ===============================================================================
  // Authors: AFRL/RQQD
  // Organization: Air Force Research Laboratory, Aerospace Systems Directorate, Power and Control Division
  // 
  // Copyright (c) 2017 Government of the United State of America, as represented by
  // the Secretary of the Air Force.  No copyright is claimed in the United States under
  // Title 17, U.S. Code.  All Other Rights Reserved.
  // ===============================================================================
  
  /*
   * @(#)UUID.java    1.14 04/07/12
   *
   * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
   * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
   */
  package org.flexdock.util;
  
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.security.SecureRandom;
  
  /**
   *
   * A class that represents an immutable universally unique identifier (UUID).
   * A UUID represents a 128-bit value.
   *
   * <p>There exist different variants of these global identifiers. The methods
   * of this class are for manipulating the Leach-Salz variant, although the
   * constructors allow the creation of any variant of UUID (described below).
   *
   * <p>The layout of a variant 2 (Leach-Salz) UUID is as follows:
   *
   * The most significant long consists of the following unsigned fields:
   * <pre>
   * 0xFFFFFFFF00000000 time_low
   * 0x00000000FFFF0000 time_mid
   * 0x000000000000F000 version
   * 0x0000000000000FFF time_hi
   * </pre>
   * The least significant long consists of the following unsigned fields:
   * <pre>
   * 0xC000000000000000 variant
   * 0x3FFF000000000000 clock_seq
   * 0x0000FFFFFFFFFFFF node
   * </pre>
   *
   * <p>The variant field contains a value which identifies the layout of
   * the <tt>UUID</tt>. The bit layout described above is valid only for
   * a <tt>UUID</tt> with a variant value of 2, which indicates the
   * Leach-Salz variant.
   *
   * <p>The version field holds a value that describes the type of this
   * <tt>UUID</tt>. There are four different basic types of UUIDs: time-based,
   * DCE security, name-based, and randomly generated UUIDs. These types
   * have a version value of 1, 2, 3 and 4, respectively.
   *
   * <p>For more information including algorithms used to create <tt>UUID</tt>s,
   * see the Internet-Draft <a href="http://www.ietf.org/internet-drafts/draft-mealling-uuid-urn-03.txt">UUIDs and GUIDs</a>
   * or the standards body definition at
   * <a href="http://www.iso.ch/cate/d2229.html">ISO/IEC 11578:1996</a>.
   *
   * @version 1.14, 07/12/04
   * @since   1.5
   */
  public final class UUID implements java.io.Serializable, Comparable {
  
      /**
       * Explicit serialVersionUID for interoperability.
       */
      private static final long serialVersionUID = -4856846361193249489L;
  
      /*
       * The most significant 64 bits of this UUID.
       *
       * @serial
       */
      private final long mostSigBits;
  
      /*
       * The least significant 64 bits of this UUID.
       *
       * @serial
       */
      private final long leastSigBits;
  
      /*
       * The version number associated with this UUID. Computed on demand.
       */
      private transient int version = -1;
  
      /*
       * The variant number associated with this UUID. Computed on demand.
       */
      private transient int variant = -1;
  
      /*
       * The timestamp associated with this UUID. Computed on demand.
       */
      private transient volatile long timestamp = -1;
  
      /*
       * The clock sequence associated with this UUID. Computed on demand.
       */
      private transient int sequence = -1;
  
      /*
       * The node number associated with this UUID. Computed on demand.
       */
      private transient long node = -1;
  
      /*
       * The hashcode of this UUID. Computed on demand.
       */
      private transient int hashCode = -1;
  
      /*
       * The random number generator used by this class to create random
       * based UUIDs.
       */
      private static volatile SecureRandom numberGenerator = null;
  
      // Constructors and Factories
  
      /*
       * Private constructor which uses a byte array to construct the new UUID.
       */
      private UUID(byte[] data) {
          long msb = 0;
          long lsb = 0;
          //assert data.length == 16;
          for (int i=0; i<8; i++)
              msb = (msb << 8) | (data[i] & 0xff);
          for (int i=8; i<16; i++)
              lsb = (lsb << 8) | (data[i] & 0xff);
          this.mostSigBits = msb;
          this.leastSigBits = lsb;
      }
  
      /**
       * Constructs a new <tt>UUID</tt> using the specified data.
       * <tt>mostSigBits</tt> is used for the most significant 64 bits
       * of the <tt>UUID</tt> and <tt>leastSigBits</tt> becomes the
       * least significant 64 bits of the <tt>UUID</tt>.
       *
       * @param  mostSigBits
       * @param  leastSigBits
       */
      public UUID(long mostSigBits, long leastSigBits) {
          this.mostSigBits = mostSigBits;
          this.leastSigBits = leastSigBits;
      }
  
      /**
       * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
       *
       * The <code>UUID</code> is generated using a cryptographically strong
       * pseudo random number generator.
       *
       * @return  a randomly generated <tt>UUID</tt>.
       */
      public static UUID randomUUID() {
          SecureRandom ng = numberGenerator;
          if (ng == null) {
              numberGenerator = ng = new SecureRandom();
          }
  
          byte[] randomBytes = new byte[16];
          ng.nextBytes(randomBytes);
          randomBytes[6]  &= 0x0f;  /* clear version        */
          randomBytes[6]  |= 0x40;  /* set to version 4     */
          randomBytes[8]  &= 0x3f;  /* clear variant        */
          randomBytes[8]  |= 0x80;  /* set to IETF variant  */
          UUID result = new UUID(randomBytes);
          return new UUID(randomBytes);
      }
  
      /**
       * Static factory to retrieve a type 3 (name based) <tt>UUID</tt> based on
       * the specified byte array.
       *
       * @param  name a byte array to be used to construct a <tt>UUID</tt>.
       * @return  a <tt>UUID</tt> generated from the specified array.
       */
      public static UUID nameUUIDFromBytes(byte[] name) {
          MessageDigest md;
          try {
              md = MessageDigest.getInstance("MD5");
          } catch (NoSuchAlgorithmException nsae) {
              throw new InternalError("MD5 not supported");
          }
          byte[] md5Bytes = md.digest(name);
          md5Bytes[6]  &= 0x0f;  /* clear version        */
          md5Bytes[6]  |= 0x30;  /* set to version 3     */
          md5Bytes[8]  &= 0x3f;  /* clear variant        */
          md5Bytes[8]  |= 0x80;  /* set to IETF variant  */
          return new UUID(md5Bytes);
      }
  
      /**
       * Creates a <tt>UUID</tt> from the string standard representation as
       * described in the {@link #toString} method.
       *
       * @param  name a string that specifies a <tt>UUID</tt>.
       * @return  a <tt>UUID</tt> with the specified value.
       * @throws IllegalArgumentException if name does not conform to the
       *         string representation as described in {@link #toString}.
       */
      public static UUID fromString(String name) {
          String[] components = name.split("-");
          if (components.length != 5)
              throw new IllegalArgumentException("Invalid UUID string: "+name);
          for (int i=0; i<5; i++)
              components[i] = "0x"+components[i];
  
          long mostSigBits = Long.decode(components[0]).longValue();
          mostSigBits <<= 16;
          mostSigBits |= Long.decode(components[1]).longValue();
          mostSigBits <<= 16;
          mostSigBits |= Long.decode(components[2]).longValue();
  
          long leastSigBits = Long.decode(components[3]).longValue();
          leastSigBits <<= 48;
          leastSigBits |= Long.decode(components[4]).longValue();
  
          return new UUID(mostSigBits, leastSigBits);
      }
  
      // Field Accessor Methods
  
      /**
       * Returns the least significant 64 bits of this UUID's 128 bit value.
       *
       * @return the least significant 64 bits of this UUID's 128 bit value.
       */
      public long getLeastSignificantBits() {
          return leastSigBits;
      }
  
      /**
       * Returns the most significant 64 bits of this UUID's 128 bit value.
       *
       * @return the most significant 64 bits of this UUID's 128 bit value.
       */
      public long getMostSignificantBits() {
          return mostSigBits;
      }
  
      /**
       * The version number associated with this <tt>UUID</tt>. The version
       * number describes how this <tt>UUID</tt> was generated.
       *
       * The version number has the following meaning:<p>
       * <ul>
       * <li>1    Time-based UUID
       * <li>2    DCE security UUID
       * <li>3    Name-based UUID
       * <li>4    Randomly generated UUID
       * </ul>
       *
       * @return  the version number of this <tt>UUID</tt>.
       */
      public int version() {
          if (version < 0) {
              // Version is bits masked by 0x000000000000F000 in MS long
              version = (int)((mostSigBits >> 12) & 0x0f);
          }
          return version;
      }
  
      /**
       * The variant number associated with this <tt>UUID</tt>. The variant
       * number describes the layout of the <tt>UUID</tt>.
       *
       * The variant number has the following meaning:<p>
       * <ul>
       * <li>0    Reserved for NCS backward compatibility
       * <li>2    The Leach-Salz variant (used by this class)
       * <li>6    Reserved, Microsoft Corporation backward compatibility
       * <li>7    Reserved for future definition
       * </ul>
       *
       * @return  the variant number of this <tt>UUID</tt>.
       */
      public int variant() {
          if (variant < 0) {
              // This field is composed of a varying number of bits
              if ((leastSigBits >>> 63) == 0) {
                  variant = 0;
              } else if ((leastSigBits >>> 62) == 2) {
                  variant = 2;
              } else {
                  variant = (int)(leastSigBits >>> 61);
              }
          }
          return variant;
      }
  
      /**
       * The timestamp value associated with this UUID.
       *
       * <p>The 60 bit timestamp value is constructed from the time_low,
       * time_mid, and time_hi fields of this <tt>UUID</tt>. The resulting
       * timestamp is measured in 100-nanosecond units since midnight,
       * October 15, 1582 UTC.<p>
       *
       * The timestamp value is only meaningful in a time-based UUID, which
       * has version type 1. If this <tt>UUID</tt> is not a time-based UUID then
       * this method throws UnsupportedOperationException.
       *
       * @throws UnsupportedOperationException if this UUID is not a
       *         version 1 UUID.
       */
      public long timestamp() {
          if (version() != 1) {
              throw new UnsupportedOperationException("Not a time-based UUID");
          }
          long result = timestamp;
          if (result < 0) {
              result = (mostSigBits & 0x0000000000000FFFL) << 48;
              result |= ((mostSigBits >> 16) & 0xFFFFL) << 32;
              result |= mostSigBits >>> 32;
              timestamp = result;
          }
          return result;
      }
  
      /**
       * The clock sequence value associated with this UUID.
       *
       * <p>The 14 bit clock sequence value is constructed from the clock
       * sequence field of this UUID. The clock sequence field is used to
       * guarantee temporal uniqueness in a time-based UUID.<p>
       *
       * The  clockSequence value is only meaningful in a time-based UUID, which
       * has version type 1. If this UUID is not a time-based UUID then
       * this method throws UnsupportedOperationException.
       *
       * @return  the clock sequence of this <tt>UUID</tt>.
       * @throws UnsupportedOperationException if this UUID is not a
       *         version 1 UUID.
       */
      public int clockSequence() {
          if (version() != 1) {
              throw new UnsupportedOperationException("Not a time-based UUID");
          }
          if (sequence < 0) {
              sequence = (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
          }
          return sequence;
      }
  
      /**
       * The node value associated with this UUID.
       *
       * <p>The 48 bit node value is constructed from the node field of
       * this UUID. This field is intended to hold the IEEE 802 address
       * of the machine that generated this UUID to guarantee spatial
       * uniqueness.<p>
       *
       * The node value is only meaningful in a time-based UUID, which
       * has version type 1. If this UUID is not a time-based UUID then
       * this method throws UnsupportedOperationException.
       *
       * @return  the node value of this <tt>UUID</tt>.
       * @throws UnsupportedOperationException if this UUID is not a
       *         version 1 UUID.
       */
      public long node() {
          if (version() != 1) {
              throw new UnsupportedOperationException("Not a time-based UUID");
          }
          if (node < 0) {
              node = leastSigBits & 0x0000FFFFFFFFFFFFL;
          }
          return node;
      }
  
      // Object Inherited Methods
  
      /**
       * Returns a <code>String</code> object representing this
       * <code>UUID</code>.
       *
       * <p>The UUID string representation is as described by this BNF :
       * <pre>
       *  UUID                   = <time_low> "-" <time_mid> "-"
       *                           <time_high_and_version> "-"
       *                           <variant_and_sequence> "-"
       *                           <node>
       *  time_low               = 4*<hexOctet>
       *  time_mid               = 2*<hexOctet>
       *  time_high_and_version  = 2*<hexOctet>
       *  variant_and_sequence   = 2*<hexOctet>
       *  node                   = 6*<hexOctet>
       *  hexOctet               = <hexDigit><hexDigit>
       *  hexDigit               =
       *        "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
       *        | "a" | "b" | "c" | "d" | "e" | "f"
       *        | "A" | "B" | "C" | "D" | "E" | "F"
       * </pre>
       *
       * @return  a string representation of this <tt>UUID</tt>.
       */
      public String toString() {
          return (digits(mostSigBits >> 32, 8) + "-" +
                  digits(mostSigBits >> 16, 4) + "-" +
                  digits(mostSigBits, 4) + "-" +
                  digits(leastSigBits >> 48, 4) + "-" +
                  digits(leastSigBits, 12));
      }
  
      /** Returns val represented by the specified number of hex digits. */
      private static String digits(long val, int digits) {
          long hi = 1L << (digits * 4);
          return Long.toHexString(hi | (val & (hi - 1))).substring(1);
      }
  
      /**
       * Returns a hash code for this <code>UUID</code>.
       *
       * @return  a hash code value for this <tt>UUID</tt>.
       */
      public int hashCode() {
          if (hashCode == -1) {
              hashCode = (int)((mostSigBits >> 32) ^
                               mostSigBits ^
                               (leastSigBits >> 32) ^
                               leastSigBits);
          }
          return hashCode;
      }
  
      /**
       * Compares this object to the specified object.  The result is
       * <tt>true</tt> if and only if the argument is not
       * <tt>null</tt>, is a <tt>UUID</tt> object, has the same variant,
       * and contains the same value, bit for bit, as this <tt>UUID</tt>.
       *
       * @param   obj   the object to compare with.
       * @return  <code>true</code> if the objects are the same;
       *          <code>false</code> otherwise.
       */
      public boolean equals(Object obj) {
          if (!(obj instanceof UUID))
              return false;
          if (((UUID)obj).variant() != this.variant())
              return false;
          UUID id = (UUID)obj;
          return (mostSigBits == id.mostSigBits &&
                  leastSigBits == id.leastSigBits);
      }
  
      // Comparison Operations
  
      /**
       * Compares this UUID with the specified UUID.
       *
       * <p>The first of two UUIDs follows the second if the most significant
       * field in which the UUIDs differ is greater for the first UUID.
       *
       * @param  val <tt>UUID</tt> to which this <tt>UUID</tt> is to be compared.
       * @return -1, 0 or 1 as this <tt>UUID</tt> is less than, equal
       *         to, or greater than <tt>val</tt>.
       */
      public int compareTo(Object val) {
          UUID uuid = (UUID) val;
          // The ordering is intentionally set up so that the UUIDs
          // can simply be numerically compared as two numbers
          return (this.mostSigBits < uuid.mostSigBits ? -1 :
                  (this.mostSigBits > uuid.mostSigBits ? 1 :
                   (this.leastSigBits < uuid.leastSigBits ? -1 :
                    (this.leastSigBits > uuid.leastSigBits ? 1 :
                     0))));
      }
  
      /**
       * Reconstitute the <tt>UUID</tt> instance from a stream (that is,
       * deserialize it). This is necessary to set the transient fields
       * to their correct uninitialized value so they will be recomputed
       * on demand.
       */
      private void readObject(java.io.ObjectInputStream in)
      throws java.io.IOException, ClassNotFoundException {
  
          in.defaultReadObject();
  
          // Set "cached computation" fields to their initial values
          version = -1;
          variant = -1;
          timestamp = -1;
          sequence = -1;
          node = -1;
          hashCode = -1;
      }
  }
  