package net.xnzn.utils;

import com.google.common.base.Preconditions;

import java.time.LocalDateTime;
import java.time.ZoneId;

public class Id {
   private static final long EPOCH = LocalDateTime.of(2021, 12, 29, 9, 2).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
   private static final long SEQUENCE_BITS = 12L;
   private static final long WORKER_ID_BITS = 10L;
   static final long WORKER_ID_MAX_VALUE = 1024L;
   private static final long SEQUENCE_MASK = 4095L;
   private static final long WORKER_ID_LEFT_SHIFT_BITS = 12L;
   private static final long TIMESTAMP_LEFT_SHIFT_BITS = 22L;
   static Long WORKER_ID;
   private static long SEQUENCE;
   private static long LAST_TIME;

   public Id(Long workerId) {
      WORKER_ID = workerId;
   }

   public static long next() {
      return nextKey();
   }

   public static String nextString() {
      return String.valueOf(next());
   }

   private static synchronized long nextKey() {
      long currentMillis = System.currentTimeMillis();
      Preconditions.checkState(LAST_TIME <= currentMillis, "Clock is moving backwards, last time is %d milliseconds, current time is %d milliseconds", LAST_TIME, currentMillis);
      if (LAST_TIME == currentMillis) {
         if (0L == (SEQUENCE = SEQUENCE + 1L & 4095L)) {
            currentMillis = waitUntilNextTime(currentMillis);
         }
      } else {
         SEQUENCE = 0L;
      }

      LAST_TIME = currentMillis;
      return currentMillis - EPOCH << 22 | WORKER_ID << 12 | SEQUENCE;
   }

   private static long waitUntilNextTime(final long lastTime) {
      long time;
      for(time = System.currentTimeMillis(); time <= lastTime; time = System.currentTimeMillis()) {
      }

      return time;
   }
}