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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.inlong.common.util;

public class SnowFlake {

    // start timestamp
    private static final long START_STMP = 1480166465631L;

    private static final long SEQUENCE_BIT = 9;
    private static final long MACHINE_BIT = 13;

    public static final long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private static final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    private static final long MACHINE_LEFT = SEQUENCE_BIT;
    private static final long TIMESTMP_LEFT = SEQUENCE_BIT + MACHINE_BIT;

    private long machineId;
    private long sequence = 0L;
    private long lastStmp = -1L;

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

    /**
     * generate nextId
     */
    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT
                | machineId << MACHINE_LEFT
                | sequence;
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

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

}