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package java.util;

import java.security.*;

/**

 * 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

 * {@code UUID}.  The bit layout described above is valid only for a {@code

 * UUID} 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 {@code

 * UUID}.  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 {@code UUID}s,

 * see <a href="http://www.ietf.org/rfc/rfc4122.txt"> <i>RFC&nbsp;4122: A

 * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2

 * "Algorithms for Creating a Time-Based UUID".

 *

 * @since   1.5

 */

public final class UUID implements java.io.Serializable, Comparable<UUID> {

    /**

     * 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;

    private static final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();

    /*

     * The random number generator used by this class to create random

     * based UUIDs. In a holder class to defer initialization until needed.

     */

    private static class Holder {

        static final SecureRandom numberGenerator = new SecureRandom();

    }

    // 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 : "data must be 16 bytes in length";

        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 {@code UUID} using the specified data.  {@code

     * mostSigBits} is used for the most significant 64 bits of the {@code

     * UUID} and {@code leastSigBits} becomes the least significant 64 bits of

     * the {@code UUID}.

     *

     * @param  mostSigBits

     *         The most significant bits of the {@code UUID}

     *

     * @param  leastSigBits

     *         The least significant bits of the {@code UUID}

     */

    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} is generated using a cryptographically strong pseudo

     * random number generator.

     *

     * @return  A randomly generated {@code UUID}

     */

    public static UUID randomUUID() {

        SecureRandom ng = Holder.numberGenerator;

        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  */

        return new UUID(randomBytes);

    }

    /**

     * Static factory to retrieve a type 3 (name based) {@code UUID} based on

     * the specified byte array.

     *

     * @param  name

     *         A byte array to be used to construct a {@code UUID}

     *

     * @return  A {@code UUID} 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", nsae);

        }

        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 {@code UUID} from the string standard representation as

     * described in the {@link #toString} method.

     *

     * @param  name

     *         A string that specifies a {@code UUID}

     *

     * @return  A {@code UUID} 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) {

        int len = name.length();

        if (len > 36) {

            throw new IllegalArgumentException("UUID string too large");

        }

        int dash1 = name.indexOf('-', 0);

        int dash2 = name.indexOf('-', dash1 + 1);

        int dash3 = name.indexOf('-', dash2 + 1);

        int dash4 = name.indexOf('-', dash3 + 1);

        int dash5 = name.indexOf('-', dash4 + 1);

        // For any valid input, dash1 through dash4 will be positive and dash5

        // negative, but it's enough to check dash4 and dash5:

        // - if dash1 is -1, dash4 will be -1

        // - if dash1 is positive but dash2 is -1, dash4 will be -1

        // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be

        //   positive, but so will dash5

        if (dash4 < 0 || dash5 >= 0) {

            throw new IllegalArgumentException("Invalid UUID string: " + name);

        }

        long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL;

        mostSigBits <<= 16;

        mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL;

        mostSigBits <<= 16;

        mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL;

        long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL;

        leastSigBits <<= 48;

        leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL;

        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 {@code UUID}.  The version

     * number describes how this {@code UUID} was generated.

     *

     * The version number has the following meaning:

     * <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 {@code UUID}

     */

    public int version() {

        // Version is bits masked by 0x000000000000F000 in MS long

        return (int)((mostSigBits >> 12) & 0x0f);

    }

    /**

     * The variant number associated with this {@code UUID}.  The variant

     * number describes the layout of the {@code UUID}.

     *

     * The variant number has the following meaning:

     * <ul>

     * <li>0    Reserved for NCS backward compatibility

     * <li>2    <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF&nbsp;RFC&nbsp;4122</a>

     * (Leach-Salz), used by this class

     * <li>6    Reserved, Microsoft Corporation backward compatibility

     * <li>7    Reserved for future definition

     * </ul>

     *

     * @return  The variant number of this {@code UUID}

     */

    public int variant() {

        // This field is composed of a varying number of bits.

        // 0    -    -    Reserved for NCS backward compatibility

        // 1    0    -    The IETF aka Leach-Salz variant (used by this class)

        // 1    1    0    Reserved, Microsoft backward compatibility

        // 1    1    1    Reserved for future definition.

        return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))

                      & (leastSigBits >> 63));

    }

    /**

     * 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 {@code UUID}.  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 {@code UUID} is not a time-based UUID then

     * this method throws UnsupportedOperationException.

     *

     * @throws UnsupportedOperationException

     *         If this UUID is not a version 1 UUID

     * @return The timestamp of this {@code UUID}.

     */

    public long timestamp() {

        if (version() != 1) {

            throw new UnsupportedOperationException("Not a time-based UUID");

        }

        return (mostSigBits & 0x0FFFL) << 48

             | ((mostSigBits >> 16) & 0x0FFFFL) << 32

             | mostSigBits >>> 32;

    }

    /**

     * 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 {@code 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 {@code UUID}

     *

     * @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");

        }

        return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);

    }

    /**

     * 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 {@code UUID}

     *

     * @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");

        }

        return leastSigBits & 0x0000FFFFFFFFFFFFL;

    }

    // Object Inherited Methods

    /**

     * Returns a {@code String} object representing this {@code UUID}.

     *

     * <p> The UUID string representation is as described by this BNF:

     * <blockquote><pre>

     * {@code

     * 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></blockquote>

     *

     * @return  A string representation of this {@code UUID}

     */

    public String toString() {

        return jla.fastUUID(leastSigBits, mostSigBits);

    }

    /**

     * Returns a hash code for this {@code UUID}.

     *

     * @return  A hash code value for this {@code UUID}

     */

    public int hashCode() {

        long hilo = mostSigBits ^ leastSigBits;

        return ((int)(hilo >> 32)) ^ (int) hilo;

    }

    /**

     * Compares this object to the specified object.  The result is {@code

     * true} if and only if the argument is not {@code null}, is a {@code UUID}

     * object, has the same variant, and contains the same value, bit for bit,

     * as this {@code UUID}.

     *

     * @param  obj

     *         The object to be compared

     *

     * @return  {@code true} if the objects are the same; {@code false}

     *          otherwise

     */

    public boolean equals(Object obj) {

        if ((null == obj) || (obj.getClass() != UUID.class))

            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 is greater than the second if the most

     * significant field in which the UUIDs differ is greater for the first

     * UUID.

     *

     * @param  val

     *         {@code UUID} to which this {@code UUID} is to be compared

     *

     * @return  -1, 0 or 1 as this {@code UUID} is less than, equal to, or

     *          greater than {@code val}

     *

     */

    public int compareTo(UUID val) {

        // The ordering is intentionally set up so that the UUIDs

        // can simply be numerically compared as two numbers

        return (this.mostSigBits < val.mostSigBits ? -1 :

                (this.mostSigBits > val.mostSigBits ? 1 :

                 (this.leastSigBits < val.leastSigBits ? -1 :

                  (this.leastSigBits > val.leastSigBits ? 1 :

                   0))));

    }

}