/*
 * 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.math.stat.descriptive.rank;

import java.io.Serializable;

import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic;

/**
 * Returns the minimum of the available values.
 * <p>
 * <ul>
 * <li>The result is <code>NaN</code> iff all values are <code>NaN</code> 
 * (i.e. <code>NaN</code> values have no impact on the value of the statistic).</li>
 * <li>If any of the values equals <code>Double.NEGATIVE_INFINITY</code>, 
 * the result is <code>Double.NEGATIVE_INFINITY.</code></li>
 * </ul></p>
 * <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>
 * 
 * @version $Revision$ $Date$
 */
public class Min extends AbstractStorelessUnivariateStatistic implements Serializable {

    /** Serializable version identifier */
    private static final long serialVersionUID = -2941995784909003131L;  
      
    /**Number of values that have been added */
    private long n;
    
    /**Current value of the statistic */
    private double value;

    /**
     * Create a Min instance
     */
    public Min() {
        n = 0;
        value = Double.NaN;
    }
    
    /**
     * Copy constructor, creates a new {@code Min} identical
     * to the {@code original}
     * 
     * @param original the {@code Min} instance to copy
     */
    public Min(Min original) {
        copy(original, this);
    }
    
    /**
     * {@inheritDoc}
     */
    @Override
    public void increment(final double d) {
        if (d < value || Double.isNaN(value)) {
            value = d;
        }
        n++;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void clear() {
        value = Double.NaN;
        n = 0;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public double getResult() {
        return value;
    }

    /**
     * {@inheritDoc}
     */
    public long getN() {
        return n;
    }
    
    /**
     * Returns the minimum 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>IllegalArgumentException</code> if the array is null or
     * the array index parameters are not valid.</p>
     * <p>
     * <ul>
     * <li>The result is <code>NaN</code> iff all values are <code>NaN</code> 
     * (i.e. <code>NaN</code> values have no impact on the value of the statistic).</li>
     * <li>If any of the values equals <code>Double.NEGATIVE_INFINITY</code>, 
     * the result is <code>Double.NEGATIVE_INFINITY.</code></li>
     * </ul> </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 minimum of the values or Double.NaN if length = 0
     * @throws IllegalArgumentException 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) {
        double min = Double.NaN;
        if (test(values, begin, length)) {
            min = values[begin];
            for (int i = begin; i < begin + length; i++) {
                if (!Double.isNaN(values[i])) {
                    min = (min < values[i]) ? min : values[i];
                }
            }
        }
        return min;
    }
    
    /**
     * {@inheritDoc}
     */
    @Override
    public Min copy() {
        Min result = new Min();
        copy(this, result);
        return result;
    }
    
    /**
     * Copies source to dest.
     * <p>Neither source nor dest can be null.</p>
     * 
     * @param source Min to copy
     * @param dest Min to copy to
     * @throws NullPointerException if either source or dest is null
     */
    public static void copy(Min source, Min dest) {
        dest.n = source.n;
        dest.value = source.value;
    }
}
