/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2011, 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.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);
  
  }