/*
 * Copyright (c) 2011-2014 Pivotal Software, Inc.
 *
 *  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 reactor.core.support;

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Helper for creating random and Type 1 (time-based) UUIDs.
 *
 * @author Jon Brisbin
 */
public abstract class UUIDUtils {

	private static boolean IS_THREADLOCALRANDOM_AVAILABLE = false;
	private static       Random random;
	private static final long   leastSigBits;
	private static final ReentrantLock lock = new ReentrantLock();
	private static long lastTime;

	static {
		try {
			IS_THREADLOCALRANDOM_AVAILABLE = null != UUIDUtils.class.getClassLoader().loadClass(
					"java.util.concurrent.ThreadLocalRandom"
			);
		} catch(Throwable t) {
		}

		byte[] seed = new SecureRandom().generateSeed(8);
		leastSigBits = new BigInteger(seed).longValue();
		if(!IS_THREADLOCALRANDOM_AVAILABLE) {
			random = new Random(leastSigBits);
		}
	}

	private UUIDUtils() {
	}

	/**
	 * Create a new random UUID.
	 *
	 * @return the new UUID
	 */
	public static UUID random() {
		byte[] randomBytes = new byte[16];
		if(IS_THREADLOCALRANDOM_AVAILABLE) {
			java.util.concurrent.ThreadLocalRandom.current().nextBytes(randomBytes);
		} else {
			random.nextBytes(randomBytes);
		}

		long mostSigBits = 0;
		for(int i = 0; i < 8; i++) {
			mostSigBits = (mostSigBits << 8) | (randomBytes[i] & 0xff);
		}
		long leastSigBits = 0;
		for(int i = 8; i < 16; i++) {
			leastSigBits = (leastSigBits << 8) | (randomBytes[i] & 0xff);
		}

		return new UUID(mostSigBits, leastSigBits);
	}

	/**
	 * Create a new time-based UUID.
	 *
	 * @return the new UUID
	 */
	public static UUID create() {
		long timeMillis = (System.currentTimeMillis() * 10000) + 0x01B21DD213814000L;

		lock.lock();
		try {
			if(timeMillis > lastTime) {
				lastTime = timeMillis;
			} else {
				timeMillis = ++lastTime;
			}
		} finally {
			lock.unlock();
		}

		// time low
		long mostSigBits = timeMillis << 32;

		// time mid
		mostSigBits |= (timeMillis & 0xFFFF00000000L) >> 16;

		// time hi and version
		mostSigBits |= 0x1000 | ((timeMillis >> 48) & 0x0FFF); // version 1

		return new UUID(mostSigBits, leastSigBits);
	}

}
