/*
    * Copyright 2021 TiKV Project Authors.
    *
    * 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 org.tikv.common.util;
  
  import java.util.concurrent.ThreadLocalRandom;
  
  public class BackOffFunction {
    private final int base;
    private final int cap;
    private final BackOffer.BackOffStrategy strategy;
    private long lastSleep;
    private int attempts;
  
    private BackOffFunction(int base, int cap, BackOffer.BackOffStrategy strategy) {
      this.base = base;
      this.cap = cap;
      this.strategy = strategy;
      lastSleep = base;
    }
  
    public static BackOffFunction create(int base, int cap, BackOffer.BackOffStrategy strategy) {
      return new BackOffFunction(base, cap, strategy);
    }
  
    /**
     * Do back off in exponential with optional jitters according to different back off strategies.
     * See http://www.awsarchitectureblog.com/2015/03/backoff.html
     */
    long getSleepMs(long maxSleepMs) {
      long sleep = 0;
      long v = expo(base, cap, attempts);
      switch (strategy) {
        case NoJitter:
          sleep = v;
          break;
        case FullJitter:
          sleep = ThreadLocalRandom.current().nextLong(v);
          break;
        case EqualJitter:
          sleep = v / 2 + ThreadLocalRandom.current().nextLong(v / 2);
          break;
        case DecorrJitter:
          sleep = Math.min(cap, base + ThreadLocalRandom.current().nextLong(lastSleep * 3 - base));
          break;
      }
  
      if (maxSleepMs > 0 && sleep > maxSleepMs) {
        sleep = maxSleepMs;
      }
  
      attempts++;
      lastSleep = sleep;
      return lastSleep;
    }
  
    private int expo(int base, int cap, int n) {
      return (int) Math.min(cap, base * Math.pow(2.0d, n));
    }
  
    public enum BackOffFuncType {
      BoTiKVRPC,
      BoTxnLock,
      BoTxnLockFast,
      BoPDRPC,
      BoRegionMiss,
      BoUpdateLeader,
      BoServerBusy,
      BoTxnNotFound,
      BoCheckTimeout,
      BoCheckHealth,
      BoTsoBatchUsedUp
    }
  }