Snowflake.hpp

#pragma once
#include <chrono>
#include <concord/time_utils.hpp>

namespace bolt {
class SnowflakeWorker {
  public:
  SnowflakeWorker(const uint8_t datacenterId, const uint8_t workerId)
    : datacenterId_(datacenterId), workerId_(workerId) {}

  virtual ~SnowflakeWorker() {}

  uint64_t nextId() {
    sequence_ = (sequence_ + 1) & sequenceMask;

    uint64_t time = timeNowMilli();
    // when the sequence wraps back to 0 (at 4096), we have to guarantee that
    // the last key is greater than this key
    if(sequence_ == 0) {
      while(time <= lastTimestamp_) {
        time = timeNowMilli();
      }
    }
    lastTimestamp_ = time;

    return (lastTimestamp_ << (sequenceBits + workerBits + datacenterBits))
           | ((datacenterId_ & 0b11111) << (sequenceBits + workerBits))
           | ((workerBits & 0b11111) << sequenceBits) | sequence_;
  }

  private:
  const uint8_t sequenceBits = 12;
  const uint8_t workerBits = 5;
  const uint8_t datacenterBits = 5;
  const uint8_t timestampBits = 64 - datacenterBits - workerBits - sequenceBits;
  const uint64_t sequenceMask = -1 ^ (-1 << sequenceBits);
  uint16_t sequence_{0};
  uint64_t lastTimestamp_{0};
  uint8_t datacenterId_;
  uint8_t workerId_;
};
}