@Slf4j
@Service
public class IdGenerateService {
    private final SnowFlakeIdGenerator snowFlakeIdGenerator;
    private static final int DATA_CENTER_ID = 0;
    public IdGenerateService(ServerInfoService serverInfoService) {
        long id = serverInfoService.fetchServiceInfo().getId();
        snowFlakeIdGenerator = new SnowFlakeIdGenerator(DATA_CENTER_ID, id);
        log.info("[IdGenerateService] initialize IdGenerateService successfully, ID:{}", id);
    }
    /**
     * 分配分布式唯一ID
     * @return 分布式唯一ID
     */
    public long allocate() {
        return snowFlakeIdGenerator.nextId();
    }
}

public interface ServerInfoService {
    /**
     * fetch current server info
     * @return ServerInfo
     */
    ServerInfo fetchServiceInfo();
}

@Slf4j
@Service
public class ServerInfoServiceImpl implements ServerInfoService {
    private final ServerInfo serverInfo;
    private final ServerInfoRepository serverInfoRepository;
    private static final long MAX_SERVER_CLUSTER_SIZE = 10000;
    private static final String SERVER_INIT_LOCK = "server_init_lock";
    private static final int SERVER_INIT_LOCK_MAX_TIME = 15000;
    @Autowired
    public ServerInfoServiceImpl(LockService lockService, ServerInfoRepository serverInfoRepository) {
        this.serverInfo = new ServerInfo();
        String ip = NetUtils.getLocalHost();
        serverInfo.setIp(ip);
        serverInfo.setBornTime(System.currentTimeMillis());
        this.serverInfoRepository = serverInfoRepository;
        Stopwatch sw = Stopwatch.createStarted();
        while (!lockService.tryLock(SERVER_INIT_LOCK, SERVER_INIT_LOCK_MAX_TIME)) {
            log.info("[ServerInfoService] waiting for lock: {}", SERVER_INIT_LOCK);
            CommonUtils.easySleep(100);
        }
        try {
            // register server then get server_id
            ServerInfoDO server = serverInfoRepository.findByIp(ip);
            if (server == null) {
                ServerInfoDO newServerInfo = new ServerInfoDO(ip);
                server = serverInfoRepository.saveAndFlush(newServerInfo);
            } else {
                serverInfoRepository.updateGmtModifiedByIp(ip, new Date());
            }
            if (server.getId() < MAX_SERVER_CLUSTER_SIZE) {
                serverInfo.setId(server.getId());
            } else {
                long retryServerId = retryServerId();
                serverInfo.setId(retryServerId);
                serverInfoRepository.updateIdByIp(retryServerId, ip);
            }
        } catch (Exception e) {
            log.error("[ServerInfoService] init server failed", e);
            throw e;
        } finally {
            lockService.unlock(SERVER_INIT_LOCK);
        }
        log.info("[ServerInfoService] ip:{}, id:{}, cost:{}", ip, serverInfo.getId(), sw);
    }
    @Scheduled(fixedRate = 15000, initialDelay = 15000)
    public void heartbeat() {
        serverInfoRepository.updateGmtModifiedByIp(serverInfo.getIp(), new Date());
    }
    private long retryServerId() {
        List<ServerInfoDO> serverInfoList = serverInfoRepository.findAll();
        log.info("[ServerInfoService] current server record num in database: {}", serverInfoList.size());
        // clean inactive server record first
        if (serverInfoList.size() > MAX_SERVER_CLUSTER_SIZE) {
            // use a large time interval to prevent valid records from being deleted when the local time is inaccurate
            Date oneDayAgo = DateUtils.addDays(new Date(), -1);
            int delNum =serverInfoRepository.deleteByGmtModifiedBefore(oneDayAgo);
            log.warn("[ServerInfoService] delete invalid {} server info record before {}", delNum, oneDayAgo);
            serverInfoList = serverInfoRepository.findAll();
        }
        if (serverInfoList.size() > MAX_SERVER_CLUSTER_SIZE) {
            throw new PowerJobException(String.format("The powerjob-server cluster cannot accommodate %d machines, please rebuild another cluster", serverInfoList.size()));
        }
        Set<Long> uedServerIds = serverInfoList.stream().map(ServerInfoDO::getId).collect(Collectors.toSet());
        for (long i = 1; i <= MAX_SERVER_CLUSTER_SIZE; i++) {
            if (uedServerIds.contains(i)) {
                continue;
            }
            log.info("[ServerInfoService] ID[{}] is not used yet, try as new server id", i);
            return i;
        }
        throw new PowerJobException("impossible");
    }
    @Autowired(required = false)
    public void setBuildProperties(BuildProperties buildProperties) {
        if (buildProperties == null) {
            return;
        }
        String pomVersion = buildProperties.getVersion();
        if (StringUtils.isNotBlank(pomVersion)) {
            serverInfo.setVersion(pomVersion);
        }
    }
    @Override
    public ServerInfo fetchServiceInfo() {
        return serverInfo;
    }
}

public class SnowFlakeIdGenerator {
    /**
     * 起始的時間戳(a special day for me)
     */
    private final static long START_STAMP = 1555776000000L;
    /**
     * 序列號占用的位數(shù)
     */
    private final static long SEQUENCE_BIT = 6;
    /**
     * 機器標識占用的位數(shù)
     */
    private final static long MACHINE_BIT = 14;
    /**
     * 數(shù)據(jù)中心占用的位數(shù)
     */
    private final static long DATA_CENTER_BIT = 2;
    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATA_CENTER_NUM = ~(-1L << DATA_CENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;
    /**
     * 數(shù)據(jù)中心
     */
    private final long dataCenterId;
    /**
     * 機器標識
     */
    private final long machineId;
    /**
     * 序列號
     */
    private long sequence = 0L;
    /**
     * 上一次時間戳
     */
    private long lastTimestamp = -1L;

    public SnowFlakeIdGenerator(long dataCenterId, long machineId) {
        if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {
            throw new IllegalArgumentException("dataCenterId can't be greater than MAX_DATA_CENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.dataCenterId = dataCenterId;
        this.machineId = machineId;
    }

    /**
     * 產(chǎn)生下一個ID
     */
    public synchronized long nextId() {
        long currStamp = getNewStamp();
        if (currStamp < lastTimestamp) {
            return futureId();
        }

        if (currStamp == lastTimestamp) {
            //相同毫秒內(nèi)，序列號自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列數(shù)已經(jīng)達到最大
            if (sequence == 0L) {
                currStamp = getNextMill();
            }
        } else {
            //不同毫秒內(nèi)，序列號置為0
            sequence = 0L;
        }

        lastTimestamp = currStamp;

        return (currStamp - START_STAMP) << TIMESTAMP_LEFT //時間戳部分
                | dataCenterId << DATA_CENTER_LEFT       //數(shù)據(jù)中心部分
                | machineId << MACHINE_LEFT             //機器標識部分
                | sequence;                             //序列號部分
    }

    /**
     * 發(fā)生時鐘回撥時借用未來時間生成Id，避免運行過程中任務(wù)調(diào)度和工作流直接進入不可用狀態(tài)
     * 注：該方式不可解決原算法中停服狀態(tài)下時鐘回撥導(dǎo)致的重復(fù)id問題
     */
    private long futureId() {
        sequence = (sequence + 1) & MAX_SEQUENCE;
        if (sequence == 0L) {
            lastTimestamp = lastTimestamp + 1;
        }

        return (lastTimestamp - START_STAMP) << TIMESTAMP_LEFT //時間戳部分
                | dataCenterId << DATA_CENTER_LEFT       //數(shù)據(jù)中心部分
                | machineId << MACHINE_LEFT             //機器標識部分
                | sequence;                             //序列號部分
    }

    private long getNextMill() {
        long mill = getNewStamp();
        while (mill <= lastTimestamp) {
            mill = getNewStamp();
        }
        return mill;
    }

    private long getNewStamp() {
        return System.currentTimeMillis();
    }
}