export class SnowflakeIdGenerator {
  private readonly startTimeStamp = 1609459200000; // 起始时间戳，这里设置为 2021-01-01 00:00:00
  private readonly workerIdBits = 5;
  private readonly dataCenterIdBits = 5;
  private readonly sequenceBits = 12;

  private readonly maxWorkerId = -1 ^ (-1 << this.workerIdBits);
  private readonly maxDataCenterId = -1 ^ (-1 << this.dataCenterIdBits);

  private readonly workerIdShift = this.sequenceBits;
  private readonly dataCenterIdShift = this.sequenceBits + this.workerIdBits;
  private readonly timestampLeftShift = this.sequenceBits + this.workerIdBits + this.dataCenterIdBits;
  private readonly sequenceMask = -1 ^ (-1 << this.sequenceBits);

  private workerId: number;
  private dataCenterId: number;
  private sequence = 0;
  private lastTimestamp = -1;

  constructor(workerId: number, dataCenterId: number) {
    if (workerId > this.maxWorkerId || workerId < 0) {
      throw new Error(`Worker ID 必须在 0 到 ${this.maxWorkerId} 之间`);
    }
    if (dataCenterId > this.maxDataCenterId || dataCenterId < 0) {
      throw new Error(`数据中心 ID 必须在 0 到 ${this.maxDataCenterId} 之间`);
    }
    this.workerId = workerId;
    this.dataCenterId = dataCenterId;
  }

  private waitNextMillis(lastTimestamp: number): number {
    let timestamp = this.getCurrentTimestamp();
    while (timestamp <= lastTimestamp) {
      timestamp = this.getCurrentTimestamp();
    }
    return timestamp;
  }

  private getCurrentTimestamp(): number {
    return Date.now();
  }

  nextId(): number {
    let timestamp = this.getCurrentTimestamp();

    if (timestamp < this.lastTimestamp) {
      throw new Error('时钟回拨，拒绝生成 ID 达 ' + (this.lastTimestamp - timestamp) + ' 毫秒');
    }

    if (timestamp === this.lastTimestamp) {
      this.sequence = (this.sequence + 1) & this.sequenceMask;
      if (this.sequence === 0) {
        timestamp = this.waitNextMillis(this.lastTimestamp);
      }
    } else {
      this.sequence = 0;
    }

    this.lastTimestamp = timestamp;

    return (
      ((timestamp - this.startTimeStamp) << this.timestampLeftShift) |
      (this.dataCenterId << this.dataCenterIdShift) |
      (this.workerId << this.workerIdShift) |
      this.sequence
    );
  }
}