package com.xinyartech.erp.core.util;

import java.lang.management.ManagementFactory;

import java.net.InetAddress;

import java.net.NetworkInterface;

import java.util.HashSet;

import java.util.Set;

/**

 * <p>名称：IdWorker.java</p>

 * <p>描述：分布式自增长ID</p>

 * <pre>

 *     Twitter的 Snowflake　JAVA实现方案

 * </pre>

 * 核心代码为其IdWorker这个类实现，其原理结构如下，我分别用一个0表示一位，用—分割开部分的作用：

 * 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000

 * 在上面的字符串中，第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，

 * 然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识），

 * 然后12位该毫秒内的当前毫秒内的计数，加起来刚好64位，为一个Long型。

 * 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），

 * 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。

 * <p>

 * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))

 *

 * @author Lynch

 */

public class IdWorker {

     // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）

    private final static long twepoch = 1563954651588L;

    // 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);

    /* 上次生产id时间戳 */

    private static long lastTimestamp = -1L;

    // 0，并发控制

    private long sequence = 0L;

    private final long workerId;

    // 数据标识id部分

    private final long datacenterId;

    public IdWorker(){

        this.datacenterId = getDatacenterId(maxDatacenterId);

        this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);

    }

    /**

     * @param workerId

     *            工作机器ID

     * @param datacenterId

     *            序列号

     */

    public IdWorker(long workerId, long datacenterId) {

        if (workerId > maxWorkerId || workerId < 0) {

            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));

        }

        if (datacenterId > maxDatacenterId || datacenterId < 0) {

            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));

        }

        this.workerId = workerId;

        this.datacenterId = datacenterId;

    }

    /**

     * 获取下一个ID

     *

     * @return

     */

    public synchronized long nextId() {

        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {

            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));

        }

        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 = 0L;

        }

        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();

    }

    /**

     * <p>

     * 获取 maxWorkerId

     * </p>

     */

    protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {

        StringBuffer mpid = new StringBuffer();

        mpid.append(datacenterId);

        String name = ManagementFactory.getRuntimeMXBean().getName();

        if (!name.isEmpty()) {

         /*

          * GET jvmPid

          */

            mpid.append(name.split("@")[0]);

        }

      /*

       * MAC + PID 的 hashcode 获取16个低位

       */

        return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);

    }

    /**

     * <p>

     * 数据标识id部分

     * </p>

     */

    protected static long getDatacenterId(long maxDatacenterId) {

        long id = 0L;

        try {

            InetAddress ip = InetAddress.getLocalHost();

            NetworkInterface network = NetworkInterface.getByInetAddress(ip);

            if (network == null) {

                id = 1L;

            } else {

                byte[] mac = network.getHardwareAddress();

                id = ((0x000000FF & (long) mac[mac.length - 1])

                        | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;

                id = id % (maxDatacenterId + 1);

            }

        } catch (Exception e) {

            System.out.println(" getDatacenterId: " + e.getMessage());

        }

        return id;

    }

    public static void main(String[] args) {

        long start = System.currentTimeMillis();

        IdWorker idWorker=new IdWorker(0,0);

        Set<Long> idSet = new HashSet<Long>();

        for(int i=0;i<1000000;i++){

            long nextId = idWorker.nextId();

            idSet.add(nextId);

            //System.out.println(nextId);

        }

        System.out.println(System.currentTimeMillis() - start);

        System.out.println(idSet.size());

    }

}