/*
 * Created on june 12th, 2003
 * Copyright (C) 2003, 2004, 2005, 2006 Aelitis, All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * AELITIS, SAS au capital de 46,603.30 euros
 * 8 Allee Lenotre, La Grille Royale, 78600 Le Mesnil le Roi, France.
 *
 */
package org.gudy.azureus2.core3.util;

/**
 * 
 * This class is used to compute average (mostly for speed transfer).
 *
 * @author Olivier
 * 
 */
public class Average {
  /**
  * It uses a simple array of longs to store values in a cycling way.
  * The array has 2 more elements than really needed to compute the average.
  * One is the next one to be filled, and its value is always 0,
  * and the other one is the one currently filled,
  * which value is not taken into account for the average.
  */

  //The refresh rate of the average (ms)
  private int refreshRate;

  //the period (in ms)
  private int period;

  //The number of elements in the average
  private int nbElements;

  //The time the average was last updated (divided by the refreshRate).
  private long lastUpdate;

  //The values
  private long values[];

  /**
   * Private constructor for an Average
   * @param _refreshRate the refresh rate in ms
   * @param _period the period in s
   */
  protected Average(int _refreshRate, int _period) {
    this.refreshRate = _refreshRate;
    this.period = _period;

    this.nbElements = (_period * 1000) / _refreshRate + 2;
    this.lastUpdate = getEffectiveTime() / _refreshRate;
    //this.values = new long[this.nbElements];
  }

  /**
   * The way to get a new Average Object, it does some parameter checking.
   * refreshRate must be greater than 100,
   * and period*1000 must be greater than refreshRate
   * @param refreshRate in ms
   * @param period in s
   * @return the newlly created Average, or null if parameters are wrong
   */
  public static Average getInstance(int refreshRate, int period) {
    if (refreshRate < 100)
      return null;
    if ((period * 1000) < refreshRate)
      return null;
    return new Average(refreshRate, period);
  }

  /**
   * This method is used to update the buffer tha stores the values,
   * in fact it mostly does clean-up over this buffer,
   * erasing all values that have not been updated.
   * @param timeFactor which is the currentTime divided by the refresh Rate
   */
  private synchronized void update(long timeFactor) {
	    //If we have a really OLD lastUpdate, we could erase the buffer a 
	    //huge number of time, so if it's really old, we change it so we'll only
	    //erase the buffer once.
	  
	    if (lastUpdate < timeFactor - nbElements)
		      lastUpdate = timeFactor - nbElements - 1;
	    
	  if(values != null)
	  {
		    //For all values between lastUpdate + 1 (next value than last updated)
		    //and timeFactor (which is the new value insertion position) 
		    for (long i = lastUpdate + 1; i <= timeFactor; i++) {
		      //We set the value to 0.
		      values[(int) (i % nbElements)] = 0;
		    }
		    //We also clear the next value to be inserted (so on next time change...)
		    values[(int) ((timeFactor + 1) % nbElements)] = 0;
	  }

    //And we update lastUpdate.
    lastUpdate = timeFactor;
  }

  /**
   * Public method to add a value to the average,
   * the time it is added is the time this method is called.
   * @param value the value to be added to the Average
   */
  public void addValue(long value) {
    if(values == null && value != 0)
    	values = new long[nbElements];
    if(values != null)
    {
        //We get the current time factor.
        long timeFactor = getEffectiveTime() / refreshRate;
        //We first update the buffer.
        update(timeFactor);
        //And then we add our value to current element
    	values[(int) (timeFactor % nbElements)] += value;
    }
    	
  }

  /**
   * This method can be called to get the current average value.
   * @return the current Average computed.
   */
  public long getAverage() {
	  return( getSum() / period );
  }
  
  public double getDoubleAverage() {
	  return( (double)getSum() / period );
  }
  
  public String getDoubleAverageAsString( int precision ) {
	  return( DisplayFormatters.formatDecimal( getDoubleAverage(), precision ));
  }
  
  public long getAverage(int average_period )
  {
	  int	slots = average_period<=0?(nbElements - 2):(average_period / refreshRate);
	  
	  if ( slots <= 0 ){
		  
		  slots = 1;
		  
	  }else if ( slots > nbElements - 2 ){
		  
		  slots = nbElements - 2;
	  }
	 
	  if ( slots == 1 ){
		 
		  return( getPointValue());
	  }
	  
	  long res = getSum(slots) / ( period * slots / ( nbElements - 2 ));
	  
	  return( res );
  }
  
  public long
  getPointValue()
  {
	  long timeFactor = getEffectiveTime() / refreshRate;
	  //We first update the buffer
	  update(timeFactor);

	  return(values != null ? values[(int)((timeFactor-1)% nbElements)] : 0);
  }
  
  protected final long getSum() {
    //The sum of all elements used for the average.
    long sum = 0;
    
    if(values != null)
    {
        //We get the current timeFactor
        long timeFactor = getEffectiveTime() / refreshRate;
        //We first update the buffer
        update(timeFactor);
        //Starting on oldest one (the one after the next one)
        //Ending on last one fully updated (the one previous current one)
        for (long i = timeFactor + 2; i < timeFactor + nbElements; i++) {
          //Simple addition
          sum += values[(int) (i % nbElements)];
        }
    }


    //We return the sum divided by the period
    return(sum);
  }
  
  protected final long getSum(int slots) {
	    //We get the current timeFactor
	    long timeFactor = getEffectiveTime() / refreshRate;
	    //We first update the buffer
	    update(timeFactor);

	    //The sum of all elements used for the average.
	    long sum = 0;
	    
	    if ( slots < 1 ){
	    	
	    	slots = 1;
	    	
	    }else if ( slots > nbElements-2 ){
	    	
	    	slots = nbElements-2;
	    }
	    
	    //Starting on oldest one (the one after the next one)
	    //Ending on last one fully updated (the one previous current one)
	    
	    long end_slot 	= timeFactor + nbElements;
	    long start_slot = end_slot - slots;
	    
	    if (values != null)
			for (long i = start_slot; i < end_slot; i++)
			{
				sum += values[(int) (i % nbElements)];
			}

	    //We return the sum divided by the period
	    return(sum);
	  }
  
  protected long
  getEffectiveTime()
  {
	  return( SystemTime.getMonotonousTime());
  }
}
