/* Copyright (c) 2011-2013 GoPivotal, Inc. All Rights Reserved. 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 com.yiboshi.science.utils;

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 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 (ClassNotFoundException e) {
		}

		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 String 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).toString().replaceAll("-", "");
	}

	/**
	 * Create a new time-based UUID.
	 *
	 * @return the new UUID
	 */
	public static String 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).toString().replaceAll("-", "");
	}

	public static void main(String[] args) {
		String uuid = String.valueOf(UUID.randomUUID());
		System.out.println (uuid);
	}

}