/*
    * 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 org.apache.commons.math4.legacy.stat.descriptive.summary;
  
  import org.apache.commons.math4.legacy.exception.MathIllegalArgumentException;
  import org.apache.commons.math4.legacy.exception.NullArgumentException;
  import org.apache.commons.math4.legacy.stat.descriptive.AbstractStorelessUnivariateStatistic;
  import org.apache.commons.math4.core.jdkmath.JdkMath;
  import org.apache.commons.math4.legacy.core.MathArrays;
  
  /**
   * Returns the sum of the natural logs for this collection of values.
   * <p>
   * Uses {@link org.apache.commons.math4.core.jdkmath.JdkMath#log(double)} to compute the logs.
   * Therefore,
   * <ul>
   * <li>If any of values are &lt; 0, the result is <code>NaN.</code></li>
   * <li>If all values are non-negative and less than
   * <code>Double.POSITIVE_INFINITY</code>,  but at least one value is 0, the
   * result is <code>Double.NEGATIVE_INFINITY.</code></li>
   * <li>If both <code>Double.POSITIVE_INFINITY</code> and
   * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
   * <code>NaN.</code></li>
   * </ul>
   * <p>
   * <strong>Note that this implementation is not synchronized.</strong> If
   * multiple threads access an instance of this class concurrently, and at least
   * one of the threads invokes the <code>increment()</code> or
   * <code>clear()</code> method, it must be synchronized externally.</p>
   */
  public class SumOfLogs extends AbstractStorelessUnivariateStatistic {
      /** Number of values that have been added. */
      private int n;
  
      /**
       * The currently running value.
       */
      private double value;
  
      /**
       * Create a SumOfLogs instance.
       */
      public SumOfLogs() {
         value = 0d;
         n = 0;
      }
  
      /**
       * Copy constructor, creates a new {@code SumOfLogs} identical
       * to the {@code original}.
       *
       * @param original the {@code SumOfLogs} instance to copy
       * @throws NullArgumentException if original is null
       */
      public SumOfLogs(SumOfLogs original) throws NullArgumentException {
          copy(original, this);
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void increment(final double d) {
          value += JdkMath.log(d);
          n++;
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public double getResult() {
          return value;
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public long getN() {
          return n;
      }
  
      /**
       * {@inheritDoc}
      */
     @Override
     public void clear() {
         value = 0d;
         n = 0;
     }
 
     /**
      * Returns the sum of the natural logs of the entries in the specified portion of
      * the input array, or <code>Double.NaN</code> if the designated subarray
      * is empty.
      * <p>
      * Throws <code>MathIllegalArgumentException</code> if the array is null.</p>
      * <p>
      * See {@link SumOfLogs}.</p>
      *
      * @param values the input array
      * @param begin index of the first array element to include
      * @param length the number of elements to include
      * @return the sum of the natural logs of the values or 0 if
      * length = 0
      * @throws MathIllegalArgumentException if the array is null or the array index
      *  parameters are not valid
      */
     @Override
     public double evaluate(final double[] values, final int begin, final int length)
         throws MathIllegalArgumentException {
 
         double sumLog = Double.NaN;
         if (MathArrays.verifyValues(values, begin, length, true)) {
             sumLog = 0.0;
             for (int i = begin; i < begin + length; i++) {
                 sumLog += JdkMath.log(values[i]);
             }
         }
         return sumLog;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public SumOfLogs copy() {
         SumOfLogs result = new SumOfLogs();
         // No try-catch or advertised exception here because args are valid
         copy(this, result);
         return result;
     }
 
     /**
      * Copies source to dest.
      * <p>Neither source nor dest can be null.</p>
      *
      * @param source SumOfLogs to copy
      * @param dest SumOfLogs to copy to
      * @throws NullArgumentException if either source or dest is null
      */
     public static void copy(SumOfLogs source, SumOfLogs dest)
         throws NullArgumentException {
         NullArgumentException.check(source);
         NullArgumentException.check(dest);
         dest.n = source.n;
         dest.value = source.value;
     }
 }