Copyright (c) 2000, 2019 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
    Mickael Istria (Red Hat Inc.) - Bug 488938, 488937
/*******************************************************************************
 * Copyright (c) 2000, 2019 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Mickael Istria (Red Hat Inc.) - Bug 488938, 488937
 *******************************************************************************/
package org.eclipse.core.internal.utils;

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.GregorianCalendar;
import java.util.Random;

public class UniversalUniqueIdentifier implements java.io.Serializable {

	
All serializable objects should have a stable serialVersionUID
/**
	 * All serializable objects should have a stable serialVersionUID
	 */
	private static final long serialVersionUID = 1L;

	/* INSTANCE FIELDS =============================================== */

	private byte[] fBits = new byte[BYTES_SIZE];

	/* NON-FINAL PRIVATE STATIC FIELDS =============================== */

	private static BigInteger fgPreviousClockValue;
	private static int fgClockAdjustment = 0;
	private static int fgClockSequence = -1;
	private static byte[] nodeAddress;

	static {
		nodeAddress = computeNodeAddress();
	}

	/* PRIVATE STATIC FINAL FIELDS =================================== */

	private static Random fgRandomNumberGenerator = new Random();

	/* PUBLIC STATIC FINAL FIELDS ==================================== */

	public static final int BYTES_SIZE = 16;
	public static final byte[] UNDEFINED_UUID_BYTES = new byte[16];
	public static final int MAX_CLOCK_SEQUENCE = 0x4000;
	public static final int MAX_CLOCK_ADJUSTMENT = 0x7FFF;
	public static final int TIME_FIELD_START = 0;
	public static final int TIME_FIELD_STOP = 6;
	public static final int TIME_HIGH_AND_VERSION = 7;
	public static final int CLOCK_SEQUENCE_HIGH_AND_RESERVED = 8;
	public static final int CLOCK_SEQUENCE_LOW = 9;
	public static final int NODE_ADDRESS_START = 10;
	public static final int NODE_ADDRESS_BYTE_SIZE = 6;

	public static final int BYTE_MASK = 0xFF;

	public static final int HIGH_NIBBLE_MASK = 0xF0;

	public static final int LOW_NIBBLE_MASK = 0x0F;

	public static final int SHIFT_NIBBLE = 4;

	public static final int ShiftByte = 8;

	
UniversalUniqueIdentifier default constructor returns a
new instance that has been initialized to a unique value.
/**
	 UniversalUniqueIdentifier default constructor returns a
	 new instance that has been initialized to a unique value.
	 */
	public UniversalUniqueIdentifier() {
		this.setVersion(1);
		this.setVariant(1);
		this.setTimeValues();
		this.setNode(getNodeAddress());
	}

	
Constructor that accepts the bytes to use for the instance.   The format
of the byte array is compatible with the toBytes() method.
The constructor returns the undefined uuid if the byte array is invalid.
See Also:
toBytes()
BYTES_SIZE/**
	 Constructor that accepts the bytes to use for the instance.   The format
	 of the byte array is compatible with the <code>toBytes()</code> method.
	
	 <p>The constructor returns the undefined uuid if the byte array is invalid.
	
	 @see #toBytes()
	 @see #BYTES_SIZE
	 */
	public UniversalUniqueIdentifier(byte[] byteValue) {
		fBits = new byte[BYTES_SIZE];
		if (byteValue.length >= BYTES_SIZE)
			System.arraycopy(byteValue, 0, fBits, 0, BYTES_SIZE);
	}

	private void appendByteString(StringBuilder buffer, byte value) {
		String hexString;

		if (value < 0)
			hexString = Integer.toHexString(256 + value);
		else
			hexString = Integer.toHexString(value);
		if (hexString.length() == 1)
			buffer.append("0"); //$NON-NLS-1$
		buffer.append(hexString);
	}

	private static BigInteger clockValueNow() {
		GregorianCalendar now = new GregorianCalendar();
		BigInteger nowMillis = BigInteger.valueOf(now.getTime().getTime());
		BigInteger baseMillis = BigInteger.valueOf(now.getGregorianChange().getTime());

		return (nowMillis.subtract(baseMillis).multiply(BigInteger.valueOf(10000L)));
	}

	public static int compareTime(byte[] fBits1, byte[] fBits2) {
		for (int i = TIME_FIELD_STOP; i >= 0; i--)
			if (fBits1[i] != fBits2[i])
				return (0xFF & fBits1[i]) - (0xFF & fBits2[i]);
		return 0;
	}

	
Answers the node address attempting to mask the IP
address of this machine.
Returns:
byte[] the node address/**
	 * Answers the node address attempting to mask the IP
	 * address of this machine.
	 *
	 * @return byte[] the node address
	 */
	private static byte[] computeNodeAddress() {

		byte[] address = new byte[NODE_ADDRESS_BYTE_SIZE];
		SecureRandom randomizer = new SecureRandom();
		randomizer.nextBytes(address);

		// set the MSB of the first octet to 1 to distinguish from IEEE node addresses
		address[0] = (byte) (address[0] | (byte) 0x80);

		return address;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (!(obj instanceof UniversalUniqueIdentifier))
			return false;

		byte[] other = ((UniversalUniqueIdentifier) obj).fBits;
		if (fBits == other)
			return true;
		if (fBits.length != other.length)
			return false;
		for (int i = 0; i < fBits.length; i++) {
			if (fBits[i] != other[i])
				return false;
		}
		return true;
	}

	private static byte[] getNodeAddress() {
		return nodeAddress;
	}

	@Override
	public int hashCode() {
		return fBits[0] + fBits[3] + fBits[7] + fBits[11] + fBits[15];
	}

	private static int nextClockSequence() {

		if (fgClockSequence == -1)
			fgClockSequence = (int) (fgRandomNumberGenerator.nextDouble() * MAX_CLOCK_SEQUENCE);

		fgClockSequence = (fgClockSequence + 1) % MAX_CLOCK_SEQUENCE;

		return fgClockSequence;
	}

	private static BigInteger nextTimestamp() {

		BigInteger timestamp = clockValueNow();
		int timestampComparison;

		timestampComparison = timestamp.compareTo(fgPreviousClockValue);

		if (timestampComparison == 0) {
			if (fgClockAdjustment == MAX_CLOCK_ADJUSTMENT) {
				while (timestamp.compareTo(fgPreviousClockValue) == 0)
					timestamp = clockValueNow();
				timestamp = nextTimestamp();
			} else
				fgClockAdjustment++;
		} else {
			fgClockAdjustment = 0;

			if (timestampComparison < 0)
				nextClockSequence();
		}

		return timestamp;
	}

	private void setClockSequence(int clockSeq) {
		int clockSeqHigh = (clockSeq >>> ShiftByte) & LOW_NIBBLE_MASK;
		int reserved = fBits[CLOCK_SEQUENCE_HIGH_AND_RESERVED] & HIGH_NIBBLE_MASK;

		fBits[CLOCK_SEQUENCE_HIGH_AND_RESERVED] = (byte) (reserved | clockSeqHigh);
		fBits[CLOCK_SEQUENCE_LOW] = (byte) (clockSeq & BYTE_MASK);
	}

	protected void setNode(byte[] bytes) {

		System.arraycopy(bytes, 0, fBits, NODE_ADDRESS_START, NODE_ADDRESS_BYTE_SIZE);
	}

	private void setTimestamp(BigInteger timestamp) {
		BigInteger value = timestamp;
		BigInteger bigByte = BigInteger.valueOf(256L);
		BigInteger[] results;
		int version;
		int timeHigh;

		for (int index = TIME_FIELD_START; index < TIME_FIELD_STOP; index++) {
			results = value.divideAndRemainder(bigByte);
			value = results[0];
			fBits[index] = (byte) results[1].intValue();
		}
		version = fBits[TIME_HIGH_AND_VERSION] & HIGH_NIBBLE_MASK;
		timeHigh = value.intValue() & LOW_NIBBLE_MASK;
		fBits[TIME_HIGH_AND_VERSION] = (byte) (timeHigh | version);
	}

	protected synchronized void setTimeValues() {
		this.setTimestamp(timestamp());
		this.setClockSequence(fgClockSequence);
	}

	protected int setVariant(int variantIdentifier) {
		int clockSeqHigh = fBits[CLOCK_SEQUENCE_HIGH_AND_RESERVED] & LOW_NIBBLE_MASK;
		int variant = variantIdentifier & LOW_NIBBLE_MASK;

		fBits[CLOCK_SEQUENCE_HIGH_AND_RESERVED] = (byte) ((variant << SHIFT_NIBBLE) | clockSeqHigh);
		return (variant);
	}

	protected void setVersion(int versionIdentifier) {
		int timeHigh = fBits[TIME_HIGH_AND_VERSION] & LOW_NIBBLE_MASK;
		int version = versionIdentifier & LOW_NIBBLE_MASK;

		fBits[TIME_HIGH_AND_VERSION] = (byte) (timeHigh | (version << SHIFT_NIBBLE));
	}

	private static BigInteger timestamp() {
		BigInteger timestamp;

		if (fgPreviousClockValue == null) {
			fgClockAdjustment = 0;
			nextClockSequence();
			timestamp = clockValueNow();
		} else
			timestamp = nextTimestamp();

		fgPreviousClockValue = timestamp;
		return fgClockAdjustment == 0 ? timestamp : timestamp.add(BigInteger.valueOf(fgClockAdjustment));
	}

	
This representation is compatible with the (byte[]) constructor.
See Also:
UniversalUniqueIdentifier(byte[])/**
	 This representation is compatible with the (byte[]) constructor.
	
	 @see #UniversalUniqueIdentifier(byte[])
	 */
	public byte[] toBytes() {
		byte[] result = new byte[fBits.length];

		System.arraycopy(fBits, 0, result, 0, fBits.length);
		return result;
	}

	@Override
	public String toString() {
		StringBuilder buffer = new StringBuilder();
		for (byte bit : fBits)
			appendByteString(buffer, bit);
		return buffer.toString();
	}

	public String toStringAsBytes() {
		StringBuilder result = new StringBuilder("{"); //$NON-NLS-1$

		for (int i = 0; i < fBits.length; i++) {
			result.append(fBits[i]);
			if (i < fBits.length + 1)
				result.append(',');
		}
		result.append('}');
		return result.toString();
	}
}