/*
 * 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.math3.util;

/**
 * Provides a standard interface for double arrays. Allows different array implementations to
 * support various storage mechanisms such as automatic expansion, contraction, and array "rolling".
 */
public interface DoubleArray {

    /**
     * Returns the number of elements currently in the array. Please note that this may be different
     * from the length of the internal storage array.
     *
     * @return number of elements
     */
    int getNumElements();

    /**
     * Returns the element at the specified index. Note that if an out of bounds index is supplied a
     * ArrayIndexOutOfBoundsException will be thrown.
     *
     * @param index index to fetch a value from
     * @return value stored at the specified index
     * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than zero or is greater
     *     than <code>getNumElements() - 1</code>.
     */
    double getElement(int index);

    /**
     * Sets the element at the specified index. If the specified index is greater than <code>
     * getNumElements() - 1</code>, the <code>numElements</code> property is increased to <code>
     * index +1</code> and additional storage is allocated (if necessary) for the new element and
     * all (uninitialized) elements between the new element and the previous end of the array).
     *
     * @param index index to store a value in
     * @param value value to store at the specified index
     * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than zero.
     */
    void setElement(int index, double value);

    /**
     * Adds an element to the end of this expandable array
     *
     * @param value to be added to end of array
     */
    void addElement(double value);

    /**
     * Adds elements to the end of this expandable array
     *
     * @param values to be added to end of array
     */
    void addElements(double[] values);

    /**
     * Adds an element to the end of the array and removes the first element in the array. Returns
     * the discarded first element. The effect is similar to a push operation in a FIFO queue.
     *
     * <p>Example: If the array contains the elements 1, 2, 3, 4 (in that order) and
     * addElementRolling(5) is invoked, the result is an array containing the entries 2, 3, 4, 5 and
     * the value returned is 1.
     *
     * @param value the value to be added to the array
     * @return the value which has been discarded or "pushed" out of the array by this rolling
     *     insert
     */
    double addElementRolling(double value);

    /**
     * Returns a double[] array containing the elements of this <code>DoubleArray</code>. If the
     * underlying implementation is array-based, this method should always return a copy, rather
     * than a reference to the underlying array so that changes made to the returned array have no
     * effect on the <code>DoubleArray.</code>
     *
     * @return all elements added to the array
     */
    double[] getElements();

    /** Clear the double array */
    void clear();
}