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 com.alibaba.metrics;
  
  import java.util.concurrent.TimeUnit;
  
  /**
   * A metric which calculates the distribution of a value.
   *
   * @see <a href="http://www.johndcook.com/standard_deviation.html">Accurately computing running
   *      variance</a>
   */
  public class HistogramImpl implements Histogram {
  
      private final Reservoir reservoir;
      private final BucketCounter count;
  
      /**
       * Creates a new {@link Histogram} with the given reservoir.
       *
       * @param type the reservoir type to create a histogram from
       */
      public HistogramImpl(ReservoirType type) {
          this(type, 60, 10, Clock.defaultClock());
      }
  
      public HistogramImpl(int interval, ReservoirType type) {
          this(type, interval, 10, Clock.defaultClock());
      }
  
      public HistogramImpl(int interval) {
          this(ReservoirType.EXPONENTIALLY_DECAYING, interval, 10, Clock.defaultClock());
      }
  
      /**
       * Creates a new {@link Histogram} with the given reservoir.
       *
       * @param type the reservoir type to create a histogram from
       * @param interval the interval to create bucket counter
       * @param numberOfBucket the number of bucket to create bucket counter
       * @param clock the clock the create bucket counter
       */
      public HistogramImpl(ReservoirType type, int interval, int numberOfBucket, Clock clock) {
          this.count = new BucketCounterImpl(interval, numberOfBucket, clock);
          switch (type) {
              case EXPONENTIALLY_DECAYING:
                  this.reservoir = new ExponentiallyDecayingReservoir(clock);
                  break;
              case SLIDING_TIME_WINDOW:
                  this.reservoir = new SlidingTimeWindowReservoir(interval, TimeUnit.SECONDS);
                  break;
              case SLIDING_WINDOW:
                  this.reservoir = new SlidingWindowReservoir(1024);
                  break;
              case UNIFORM:
                  this.reservoir = new UniformReservoir(1024);
                  break;
              case BUCKET:
                  this.reservoir = new BucketReservoir(interval, numberOfBucket, clock, count);
                  break;
              default:
                  this.reservoir = new ExponentiallyDecayingReservoir(clock);
          }
      }
  
      public HistogramImpl(Reservoir reservoir, int interval, int numberOfBucket, Clock clock) {
          this.reservoir = reservoir;
          this.count = new BucketCounterImpl(interval, numberOfBucket, clock);
      }
  
      /**
       * Adds a recorded value.
       *
       * @param value the length of the value
       */
      public void update(int value) {
          update((long) value);
      }
  
      /**
       * Adds a recorded value.
       *
       * @param value the length of the value
       */
      public void update(long value) {
          count.update();
          reservoir.update(value);
      }
  
      /**
       * Returns the number of values recorded.
       *
       * @return the number of values recorded
       */
      public long getCount() {
          return count.getCount();
      }
  
      public Snapshot getSnapshot() {
          return reservoir.getSnapshot();
      }
  
      @Override
      public long lastUpdateTime() {
          return count.lastUpdateTime();
      }
  }
  