/**
 * Copyright (c) 2011-2020, hubin (jobob@qq.com).
 *
 * 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.foc.util;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

/**
 * <p>
 * 分布式高效有序ID生产黑科技(sequence)
 * <br>
 * 优化开源项目：http://git.oschina.net/yu120/sequence
 * </p>
 * 
 * @author hubin
 * @date 2016-08-18
 */
public class Sequence {
    /* 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 long twepoch = 1288834974657L;
    private final long workerIdBits = 5L;/* 机器标识位数 */
    private final long datacenterIdBits = 5L;
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private final long sequenceBits = 12L;/* 毫秒内自增位 */
    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    /* 时间戳左移动位 */
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long workerId;
    
    /* 数据标识id部分 */
    private long datacenterId;
    private long sequence = 0L;/* 0，并发控制 */
    private long lastTimestamp = -1L;/* 上次生产id时间戳 */
    
    public Sequence() {
        /*
         * 数据标识id部分
         */
        this.datacenterId = getDatacenterId() % (maxDatacenterId + 1);

        /*
         * MAC + PID 的 hashcode 获取16个低位
         */
        long macPidHashCode = (datacenterId + "" + getJvmPid()).hashCode() & 0xffff;
        this.workerId = macPidHashCode % (maxWorkerId + 1);
    }

    /**
     * @param workerId
     *            工作机器ID
     * @param datacenterId
     *            序列号
     */
    public Sequence(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) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift) | sequence;
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return SystemClock.now();
    }
    
    /**
     * <p>
     * 获取 PID
     * </p>
     */
    private static String getJvmPid() {
        String name = ManagementFactory.getRuntimeMXBean().getName();
        // get pid
        if (name != null) {
            return name.split("@")[0];
        }
        return null;
    }

    /**
     * <p>
     * 数据标识id部分
     * </p>
     */
    protected static long getDatacenterId() {
        try {
            InetAddress ip = InetAddress.getLocalHost();
            NetworkInterface network = NetworkInterface.getByInetAddress(ip);
            long id;
            if (network == null) {
                id = 1;
            } else {
                byte[] mac = network.getHardwareAddress();
                id = ((0x000000FF & (long) mac[mac.length - 1])
                        | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
            }
            return id;
        } catch (Exception e) {
            e.printStackTrace();
//            throw new IllegalArgumentException(e);
        }
        return System.currentTimeMillis();
    }

}
