content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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.apache.kafka.server.quota;
  
  import org.apache.kafka.common.MetricName;
  import org.apache.kafka.common.metrics.KafkaMetric;
  import org.apache.kafka.common.metrics.Measurable;
  import org.apache.kafka.common.metrics.QuotaViolationException;
  import org.apache.kafka.common.metrics.stats.Rate;
  
  /**
   * Helper functions related to quotas
   */
  public class QuotaUtils {
  
      /**
       * This calculates the amount of time needed to bring the observed rate within quota
       * assuming that no new metrics are recorded.
       * <br/>
       * If O is the observed rate and T is the target rate over a window of W, to bring O down to T,
       * we need to add a delay of X to W such that O * W / (W + X) = T.
       * Solving for X, we get X = (O - T)/T * W.
       *
       * @param timeMs current time in milliseconds
       * @return Delay in milliseconds
       */
      public static long throttleTime(QuotaViolationException e, long timeMs) {
          double difference = e.value() - e.bound();
          // Use the precise window used by the rate calculation
          double throttleTimeMs = difference / e.bound() * windowSize(e.metric(), timeMs);
          return Math.round(throttleTimeMs);
      }
  
      /**
       * Calculates the amount of time needed to bring the observed rate within quota using the same algorithm as
       * throttleTime() utility method but the returned value is capped to given maxThrottleTime
       */
      public static long boundedThrottleTime(QuotaViolationException e, long maxThrottleTime, long timeMs) {
          return Math.min(throttleTime(e, timeMs), maxThrottleTime);
      }
  
      /**
       * Returns window size of the given metric
       *
       * @param metric metric with measurable of type Rate
       * @param timeMs current time in milliseconds
       * @throws IllegalArgumentException if given measurable is not Rate
       */
      private static long windowSize(KafkaMetric metric, long timeMs) {
          return measurableAsRate(metric.metricName(), metric.measurable()).windowSize(metric.config(), timeMs);
      }
  
      /**
       * Casts provided Measurable to Rate
       * @throws IllegalArgumentException if given measurable is not Rate
       */
      private static Rate measurableAsRate(MetricName name, Measurable measurable) {
          if (measurable instanceof Rate) {
              return (Rate) measurable;
          } else {
              throw new IllegalArgumentException("Metric " + name + " is not a Rate metric, value " + measurable);
          }
      }
  
  }
  