/*
 * Copyright (c) 2003, 2014, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.util;

import java.security.*;

import jdk.internal.misc.JavaLangAccess;
import jdk.internal.misc.SharedSecrets;

/**
 * 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
 * &quot;Algorithms for Creating a Time-Based UUID&quot;.
 *
 * @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))));
 }
}