content: /*
   * Copyright [2021-present] [ahoo wang <ahoowang@qq.com> (https://github.com/Ahoo-Wang)].
   * Licensed 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 me.ahoo.cosid.snowflake;
  
  import me.ahoo.cosid.snowflake.exception.ClockBackwardsException;
  import me.ahoo.cosid.snowflake.exception.TimestampOverflowException;
  
  import com.google.common.base.Strings;
  
  /**
   * Abstract SnowflakeId.
   *
   * @author ahoo wang
   */
  public abstract class AbstractSnowflakeId implements SnowflakeId {
  
      protected final long epoch;
      protected final int timestampBit;
      protected final int machineBit;
      protected final int sequenceBit;
  
      protected final long maxTimestamp;
      protected final long maxSequence;
      protected final int maxMachineId;
  
      protected final long machineLeft;
      protected final long timestampLeft;
      /**
       * WARN:machineLeft greater than 30 will cause overflow, so machineId should be long when calculating.
       */
      protected final long machineId;
      private final long sequenceResetThreshold;
      protected long sequence = 0L;
      protected long lastTimestamp = -1L;
  
      public AbstractSnowflakeId(long epoch,
                                 int timestampBit,
                                 int machineBit,
                                 int sequenceBit,
                                 int machineId,
                                 long sequenceResetThreshold) {
          if ((timestampBit + machineBit + sequenceBit) > TOTAL_BIT) {
              throw new IllegalArgumentException("total bit can't be greater than TOTAL_BIT[63] .");
          }
          this.epoch = epoch;
          this.timestampBit = timestampBit;
          this.machineBit = machineBit;
          this.sequenceBit = sequenceBit;
          this.maxTimestamp = ~(-1L << timestampBit);
          this.maxSequence = ~(-1L << sequenceBit);
          this.maxMachineId = ~(-1 << machineBit);
          this.machineLeft = sequenceBit;
          this.timestampLeft = this.machineLeft + machineBit;
          if (machineId > this.maxMachineId || machineId < 0) {
              throw new IllegalArgumentException(Strings.lenientFormat("machineId[%s] can't be greater than maxMachineId[%s] or less than 0 .", machineId, maxMachineId));
          }
          this.machineId = machineId;
          this.sequenceResetThreshold = sequenceResetThreshold;
      }
  
      protected long nextTime() {
          long time = getCurrentTime();
          while (time <= lastTimestamp) {
              time = getCurrentTime();
          }
          return time;
      }
  
      /**
       * get current timestamp.
       *
       * @return current timestamp
       */
      protected abstract long getCurrentTime();
  
      @Override
      public synchronized long generate() {
          long currentTimestamp = getCurrentTime();
          if (currentTimestamp < lastTimestamp) {
              throw new ClockBackwardsException(lastTimestamp, currentTimestamp);
          }
  
          //region Reset sequence based on sequence reset threshold,Optimize the problem of uneven sharding.
  
          if (currentTimestamp > lastTimestamp
                  && sequence >= sequenceResetThreshold) {
              sequence = 0L;
          }
  
          sequence = (sequence + 1) & maxSequence;
  
          if (sequence == 0L) {
              currentTimestamp = nextTime();
          }
  
          //endregion
          lastTimestamp = currentTimestamp;
          long diffTimestamp = (currentTimestamp - epoch);
          if (diffTimestamp > maxTimestamp) {
              throw new TimestampOverflowException(epoch, diffTimestamp, maxTimestamp);
          }
          return diffTimestamp << timestampLeft
                  | machineId << machineLeft
                  | sequence;
      }
  
      @Override
      public long getEpoch() {
          return epoch;
      }
  
      @Override
      public int getTimestampBit() {
          return timestampBit;
      }
  
      @Override
      public int getMachineBit() {
          return machineBit;
      }
  
      @Override
      public int getSequenceBit() {
          return sequenceBit;
      }
  
      @Override
      public long getMaxTimestamp() {
          return maxTimestamp;
      }
  
      @Override
      public int getMaxMachineId() {
          return maxMachineId;
      }
  
      @Override
      public long getMaxSequence() {
          return maxSequence;
      }
  
      @Override
      public long getLastTimestamp() {
          return lastTimestamp;
      }
  
      @Override
      public int getMachineId() {
          return (int) machineId;
      }
  
  }
  