/**
 * Copyright (c) 2013-Now http://jeesite.com All rights reserved.
 */
package com.jeesite.common.idgen;

import java.util.Random;

/**
 * 来自于twitter项目snowflake的id产生方案，全局唯一，时间有序。
 * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
 * https://github.com/twitter/snowflake/blob/scala_28/src/main/
 * 		scala/com/twitter/service/snowflake/IdWorker.scala
 */
public class IdWorker {
	
	private final static long twepoch = 1288834974657L;
	// 机器标识位数
	private final static long workerIdBits = 5L;
	// 数据中心标识位数
	private final static long datacenterIdBits = 5L;
	// 机器ID最大值
	private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
	// 数据中心ID最大值
	private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	// 毫秒内自增位
	private final static long sequenceBits = 12L;
	// 机器ID偏左移12位
	private final static long workerIdShift = sequenceBits;
	// 数据中心ID左移17位
	private final static long datacenterIdShift = sequenceBits + workerIdBits;
	// 时间毫秒左移22位
	private final static long timestampLeftShift = sequenceBits + workerIdBits
			+ datacenterIdBits;

	private final static long sequenceMask = -1L ^ (-1L << sequenceBits);

	private static long lastTimestamp = -1L;

	private long sequence = 0L;
	private final long workerId;
	private final long datacenterId;

	public IdWorker(long workerId, long datacenterId) {
		if (workerId > maxWorkerId || workerId < 0) {
			if (workerId == -1){
				this.workerId = new Random().nextInt((int)maxWorkerId);
			}else{
				throw new IllegalArgumentException(
						"worker Id can't be greater than %d or less than 0");
			}
		}else{
			this.workerId = workerId;
		}
		if (datacenterId > maxDatacenterId || datacenterId < 0) {
			if (datacenterId == -1){
				this.datacenterId = new Random().nextInt((int)maxDatacenterId);
			}else{
				throw new IllegalArgumentException(
						"datacenter Id can't be greater than %d or less than 0");
			}
		}else{
			this.datacenterId = datacenterId;
		}
	}

	public synchronized long nextId() {
		long timestamp = timeGen();
		if (timestamp < lastTimestamp) {
			try {
				throw new Exception(
						"Clock moved backwards.  Refusing to generate id for "
								+ (lastTimestamp - timestamp) + " milliseconds");
			} catch (Exception e) {
				e.printStackTrace();
			}
		}

		if (lastTimestamp == timestamp) {
			// 当前毫秒内，则+1
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				// 当前毫秒内计数满了，则等待下一秒
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0;
		}
		lastTimestamp = timestamp;
		// ID偏移组合生成最终的ID，并返回ID
		long nextId = ((timestamp - twepoch) << timestampLeftShift)
				| (datacenterId << datacenterIdShift)
				| (workerId << workerIdShift) | sequence;

		return nextId;
	}

	private long tilNextMillis(final long lastTimestamp) {
		long timestamp = this.timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = this.timeGen();
		}
		return timestamp;
	}

	private long timeGen() {
		return System.currentTimeMillis();
	}
	
//	////////////  test  ////////////
//	
//	public static void main(String[] args) throws Exception {
//		final Set<Long> set = SetUtils.newHashSet();
//
//		final IdWorker w1 = new IdWorker(-1, -1);
//		final IdWorker w2 = new IdWorker(-1, -1);
//		final CyclicBarrier cdl = new CyclicBarrier(100);
//
//		for (int i = 0; i < 1000; i++) {
//			new Thread(new Runnable() {
//				@Override
//				public void run() {
//					try {
//						cdl.await();
//					} catch (InterruptedException e) {
//						e.printStackTrace();
//					} catch (BrokenBarrierException e) {
//						e.printStackTrace();
//					}
//					
//					// id
//					Long id = w1.nextId();
//					if (set.contains(id)){
//						System.out.println(id + " exists");
//					}
//					set.add(id);
//					System.out.println(id);
//					
//					// id2
//					Long id2 = w2.nextId();
//					if (set.contains(id2)){
//						System.out.println(id2 + " exists");
//					}
//					set.add(id2);
//					System.out.println(id2);
//				}
//			}).start();
//		}
//		try {
//			TimeUnit.SECONDS.sleep(5);
//		} catch (InterruptedException e) {
//			e.printStackTrace();
//		}
//	}
	
}