/*
 * 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 maximum 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.POSITIVE_INFINITY</code>, the
 * result is <code>Double.POSITIVE_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 Max extends AbstractStorelessUnivariateStatistic implements Serializable {

	/** Serializable version identifier */
	private static final long serialVersionUID = -5593383832225844641L;

	/** Number of values that have been added */
	private long n;

	/** Current value of the statistic */
	private double value;

	/**
	 * Create a Max instance
	 */
	public Max() {
		n = 0;
		value = Double.NaN;
	}

	/**
	 * Copy constructor, creates a new {@code Max} identical to the
	 * {@code original}
	 * 
	 * @param original
	 *            the {@code Max} instance to copy
	 */
	public Max(Max 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 maximum 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.POSITIVE_INFINITY</code>,
	 * the result is <code>Double.POSITIVE_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 maximum 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 max = Double.NaN;
		if (test(values, begin, length)) {
			max = values[begin];
			for (int i = begin; i < begin + length; i++) {
				if (!Double.isNaN(values[i])) {
					max = (max > values[i]) ? max : values[i];
				}
			}
		}
		return max;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public Max copy() {
		Max result = new Max();
		copy(this, result);
		return result;
	}

	/**
	 * Copies source to dest.
	 * <p>
	 * Neither source nor dest can be null.
	 * </p>
	 * 
	 * @param source
	 *            Max to copy
	 * @param dest
	 *            Max to copy to
	 * @throws NullPointerException
	 *             if either source or dest is null
	 */
	public static void copy(Max source, Max dest) {
		dest.n = source.n;
		dest.value = source.value;
	}
}
