/*
 * 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;

import org.apache.commons.math.MathRuntimeException;

/**
 * Abstract base class for all implementations of the
 * {@link UnivariateStatistic} interface.
 * <p>
 * Provides a default implementation of <code>evaluate(double[]),</code>
 * delegating to <code>evaluate(double[], int, int)</code> in the natural way.
 * </p>
 * <p>
 * Also includes a <code>test</code> method that performs generic parameter
 * validation for the <code>evaluate</code> methods.
 * </p>
 * 
 * @version $Revision$ $Date$
 */
public abstract class AbstractUnivariateStatistic implements UnivariateStatistic {

	/**
	 * {@inheritDoc}
	 */
	public double evaluate(final double[] values) {
		test(values, 0, 0);
		return evaluate(values, 0, values.length);
	}

	/**
	 * {@inheritDoc}
	 */
	public abstract double evaluate(final double[] values, final int begin, final int length);

	/**
	 * {@inheritDoc}
	 */
	public abstract UnivariateStatistic copy();

	/**
	 * This method is used by <code>evaluate(double[], int, int)</code> methods
	 * to verify that the input parameters designate a subarray of positive
	 * length.
	 * <p>
	 * <ul>
	 * <li>returns <code>true</code> iff the parameters designate a subarray of
	 * positive length</li>
	 * <li>throws <code>IllegalArgumentException</code> if the array is null or
	 * or the indices are invalid</li>
	 * <li>returns <code>false</li> if the array is non-null, but 
	 * <code>length</code> is 0.
	 * </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 true if the parameters are valid and designate a subarray of
	 *         positive length
	 * @throws IllegalArgumentException
	 *             if the indices are invalid or the array is null
	 */
	protected boolean test(final double[] values, final int begin, final int length) {

		if (values == null) {
			throw MathRuntimeException.createIllegalArgumentException("input values array is null");
		}

		if (begin < 0) {
			throw MathRuntimeException.createIllegalArgumentException("start position cannot be negative ({0})", begin);
		}

		if (length < 0) {
			throw MathRuntimeException.createIllegalArgumentException("length cannot be negative ({0})", length);
		}

		if (begin + length > values.length) {
			throw MathRuntimeException.createIllegalArgumentException("subarray ends after array end");
		}

		if (length == 0) {
			return false;
		}

		return true;

	}
}