package com.ruoyi.project.common;

public class IdGeneratorUtils {
    // 时间戳左移的位数（22位给计数器）
    private static final long TIMESTAMP_SHIFT = 22;
    private static final long COUNTER_BITS = 22L;
    private static final long MAX_COUNTER = (1L << COUNTER_BITS) - 1;

    private static long lastTimestamp = -1L;
    private static long counter = 0L;

    public synchronized static long nextId() {
        long timestamp = System.currentTimeMillis();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards");
        }

        if (timestamp == lastTimestamp) {
            counter = (counter + 1) & MAX_COUNTER;
            if (counter == 0) {
                // 同一毫秒内计数器用完，等待下一毫秒
                timestamp = waitNextMillis(lastTimestamp);
            }
        } else {
            counter = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp) << TIMESTAMP_SHIFT) | counter;
    }

    private static long waitNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <= lastTimestamp) {
            timestamp = System.currentTimeMillis();
        }
        return timestamp;
    }

}