/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
    *
    * This program and the accompanying materials are dual-licensed under
    * either the terms of the Eclipse Public License v1.0 as published by
    * the Eclipse Foundation
    *
    *   or (per the licensee's choosing)
   *
   * under the terms of the GNU Lesser General Public License version 2.1
   * as published by the Free Software Foundation.
   */
  package ch.qos.logback.access.common.filter;
  
  abstract public class PeriodicStats {
  
      private long nextPeriodBegins = 0;
      private long lastTotal = 0;
      private long lastCount = 0;
  
      private double average;
      private int n;
  
      PeriodicStats() {
          this(System.currentTimeMillis());
      }
  
      PeriodicStats(long now) {
          nextPeriodBegins = computeStartOfNextPeriod(now);
      }
  
      void update(long now, long total) {
          if (now > nextPeriodBegins) {
              lastCount = total - lastTotal;
              lastTotal = total;
              average = (average * n + lastCount) / (++n);
              nextPeriodBegins = computeStartOfNextPeriod(now);
          }
      }
  
      public double getAverage() {
          return average;
      }
  
      public long getLastCount() {
          return lastCount;
      }
  
      void reset(long now) {
          nextPeriodBegins = computeStartOfNextPeriod(now);
          lastTotal = 0;
          lastCount = 0;
          average = 0.0;
          n = 0;
      }
  
      void reset() {
          reset(System.currentTimeMillis());
      }
  
      abstract long computeStartOfNextPeriod(long now);
  
  }