package org.djutils.stats.summarizers;
   
   import org.djutils.exceptions.Throw;
   
   /**
    * The WeightedTally class defines a statistical tally. A WeightedTally is a time-weighted tally. The WeightedTally used to
    * extend the Tally, but because the calculation method and method signatures are different, the WeightedTally has been made
    * self-contained.
    * <p>
   * Copyright (c) 2002-2022 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights reserved. See
   * for project information <a href="https://simulation.tudelft.nl/" target="_blank"> https://simulation.tudelft.nl</a>. The DSOL
   * project is distributed under a three-clause BSD-style license, which can be found at
   * <a href="https://simulation.tudelft.nl/dsol/3.0/license.html" target="_blank">
   * https://simulation.tudelft.nl/dsol/3.0/license.html</a>. <br>
   * @author <a href="https://www.tudelft.nl/averbraeck" target="_blank"> Alexander Verbraeck</a>
   * @author <a href="https://www.tudelft.nl/staff/p.knoppers/">Peter Knoppers</a>
   */
  public class WeightedTally implements WeightedTallyInterface
  {
      /** */
      private static final long serialVersionUID = 20200228L;
  
      /** The sum of the weights of this WeightedTally. */
      private double sumOfWeights = 0;
  
      /** The mean of this WeightedTally. */
      private double weightedMean = 0;
  
      /** The sum of this WeightedTally. */
      private double weightedSum = 0;
  
      /** The total ingested weight times the variance of this WeightedTally. */
      private double weightTimesVariance = 0;
  
      /** The minimum observed value of this WeightedTally. */
      private double min = Double.NaN;
  
      /** The maximum observed value of this WeightedTally. */
      private double max = Double.NaN;
  
      /** The number of non-zero weight measurements of this WeightedTally. */
      private long n = 0;
  
      /** The description of this WeightedTally. */
      private final String description;
  
      /** The synchronization lock. */
      @SuppressWarnings("checkstyle:visibilitymodifier")
      protected Object semaphore = new Object();
  
      /**
       * Construct a new WeightedTally with a description.
       * @param description String; the description of this WeightedTally
       */
      public WeightedTally(final String description)
      {
          this.description = description;
          initialize();
      }
  
      /** {@inheritDoc} */
      @Override
      public final String getDescription()
      {
          return this.description;
      }
  
      /** {@inheritDoc} */
      @Override
      public final double getMax()
      {
          return this.max;
      }
  
      /** {@inheritDoc} */
      @Override
      public final double getMin()
      {
          return this.min;
      }
  
      /** {@inheritDoc} */
      @Override
      public final long getN()
      {
          return this.n;
      }
  
      /** {@inheritDoc} */
      @Override
      public final double getWeightedSampleMean()
      {
          synchronized (this.semaphore)
          {
              if (this.n > 0)
              {
                  return this.weightedMean;
              }
              return Double.NaN;
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final double getWeightedSampleStDev()
     {
         synchronized (this.semaphore)
         {
             if (this.n > 1)
             {
                 return Math.sqrt(getWeightedSampleVariance());
             }
             return Double.NaN;
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final double getWeightedPopulationStDev()
     {
         synchronized (this.semaphore)
         {
             return Math.sqrt(getWeightedPopulationVariance());
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final double getWeightedSampleVariance()
     {
         synchronized (this.semaphore)
         {
             if (this.n > 1)
             {
                 return getWeightedPopulationVariance() * this.n / (this.n - 1);
             }
             return Double.NaN;
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final double getWeightedPopulationVariance()
     {
         synchronized (this.semaphore)
         {
             return this.weightTimesVariance / this.sumOfWeights;
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final double getWeightedSum()
     {
         return this.weightedSum;
     }
 
     /** {@inheritDoc} */
     @Override
     public void initialize()
     {
         synchronized (this.semaphore)
         {
             this.min = Double.NaN;
             this.max = Double.NaN;
             this.n = 0;
             this.sumOfWeights = 0.0;
             this.weightedMean = 0.0;
             this.weightTimesVariance = 0.0;
             this.weightedSum = 0.0;
         }
     }
 
     /**
      * Process one observed weighted value.
      * @param weight double; the weight of the value to process
      * @param value double; the value to process
      * @return double; the value
      */
     public double register(final double weight, final double value)
     {
         Throw.when(Double.isNaN(weight), IllegalArgumentException.class, "weight may not be NaN");
         Throw.when(weight < 0, IllegalArgumentException.class, "weight may not be negative");
         Throw.when(Double.isNaN(value), IllegalArgumentException.class, "value may not be NaN");
         if (0.0 == weight)
         {
             return value;
         }
         synchronized (this.semaphore)
         {
             if (this.n == 0)
             {
                 this.min = value;
                 this.max = value;
             }
             this.n++;
             // Eq 47 in https://fanf2.user.srcf.net/hermes/doc/antiforgery/stats.pdf
             this.sumOfWeights += weight;
             double prevWeightedMean = this.weightedMean;
             // Eq 53 in https://fanf2.user.srcf.net/hermes/doc/antiforgery/stats.pdf
             this.weightedMean += weight / this.sumOfWeights * (value - prevWeightedMean);
             // Eq 68 in https://fanf2.user.srcf.net/hermes/doc/antiforgery/stats.pdf
             this.weightTimesVariance += weight * (value - prevWeightedMean) * (value - this.weightedMean);
             this.weightedSum += weight * value;
             if (value < this.min)
             {
                 this.min = value;
             }
             if (value > this.max)
             {
                 this.max = value;
             }
         }
         return value;
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings("checkstyle:designforextension")
     public String toString()
     {
         return "WeightedTally [sumOfWeights=" + this.sumOfWeights + ", weightedMean=" + this.weightedMean + ", weightedSum="
                 + this.weightedSum + ", weightTimesVariance=" + this.weightTimesVariance + ", min=" + this.min + ", max="
                 + this.max + ", n=" + this.n + ", description=" + this.description + "]";
     }
 
 }