/*

  * Licensed under the MIT License

  * 

  * Copyright 2010 (c) Flávio Silva, http://flsilva.com

  *

  * Permission is hereby granted, free of charge, to any person

  * obtaining a copy of this software and associated documentation

  * files (the "Software"), to deal in the Software without

  * restriction, including without limitation the rights to use,

  * copy, modify, merge, publish, distribute, sublicense, and/or sell

  * copies of the Software, and to permit persons to whom the

  * Software is furnished to do so, subject to the following

  * conditions:

  *

  * The above copyright notice and this permission notice shall be

  * included in all copies or substantial portions of the Software.

  *

  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES

  * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND

  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT

  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,

  * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR

  * OTHER DEALINGS IN THE SOFTWARE.

  * 

  * http://www.opensource.org/licenses/mit-license.php

  */

 package org.as3collections

 {

         import org.as3collections.ICollection;

         /**

          * A collection designed for holding elements prior to processing.

          * Besides basic <code>ICollection</code> operations, queues provide additional insertion, extraction, and inspection operations.

          * Each of these methods exists in two forms: one throws an error if the operation fails, the other returns a special value (either <code>null</code> or <code>false</code>, depending on the operation).

          * <p>

          * <table class="innertable">

          * <tr>

          * <th></th>

          * <th><em>Throws error</em></th>

          * <th><em>Returns special value</em></th>

          * </tr>

          * <tr>

          * <td><b>Insert</b></td>

          * <td><code>add</code></td>

          * <td><code>offer</code></td>

          * </tr>

          * <tr>

          * <td><b>Remove</b></td>

          * <td><code>dequeue</code></td>

          * <td><code>poll</code></td>

          * </tr>

          * <tr>

          * <td><b>Examine</b></td>

          * <td><code>element</code></td>

          * <td><code>peek</code></td>

          * </tr>

          * </table>

          * </p>

          * <p>Queues typically, but do not necessarily, order elements in a FIFO (first-in-first-out) manner.

          * Among the exceptions are priority queues, which order elements according to a supplied comparator, or the elements' natural ordering, and LIFO queues (or stacks) which order the elements LIFO (last-in-first-out).

          * Whatever the ordering used, the head of the queue is that element which would be removed by a call to <code>dequeue</code> or <code>poll</code>.

          * In a FIFO queue, all new elements are inserted at the <em>tail</em> of the queue.

          * Other kinds of queues may use different placement rules.

          * Every <code>IQueue</code> implementation must specify its ordering properties.</p>

          * <p>The <code>offer</code> method inserts an element if possible, otherwise returning <code>false</code>.

          * This differs from the <code>add</code> method, which can fail to add an element only by throwing an error.

          * The <code>offer</code> method is designed for use when failure is a normal, rather than exceptional occurrence.</p>

          * <p>The <code>dequeue</code> and <code>poll</code> methods remove and return the head of the queue.

          * Exactly which element is removed from the queue is a function of the queue's ordering policy, which differs from implementation to implementation.

          * The <code>dequeue</code> and <code>poll</code> methods differ only in their behavior when the queue is empty: the <code>dequeue</code> method throws an error, while the <code>poll</code> method returns <code>null</code>.</p> 

          * <p>The <code>element</code> and <code>peek</code> methods return, but do not remove, the head of the queue.

          * The <code>element</code> and <code>peek</code> methods differ only in their behavior when the queue is empty: the <code>element</code> method throws an error, while the <code>peek</code> method returns null.</p>

          * <p><code>IQueue</code> implementations generally do not allow insertion of <code>null</code> elements</p>

          * 

          * @author Flávio Silva

          */

         public interface IQueue extends ICollection

         {

                 /**

                  * Retrieves and removes the head of this queue.

                  * 

                  * @throws         org.as3collections.errors.NoSuchElementError         if this queue is empty.

                  * @return         the head of this queue.

                   */

                 function dequeue(): *;

                 /**

                  * Retrieves, but does not remove, the head of this queue.

                  * This method differs from <code>peek</code> only in that it throws an error if this queue is empty. 

                  * 

                  * @throws         org.as3collections.errors.NoSuchElementError         if this queue is empty.

                  * @return         the head of this queue.

                   */

                 function element(): *;

                 /**

                  * Inserts the specified element into this queue if it is possible to do so immediately without violating restrictions.

                  * When using a restricted queue (like <code>TypedQueue</code> and <code>UniqueQueue</code>), this method is generally preferable to <code>add</code>, which can fail to insert an element only by throwing an error. 

                  * 

                  * @param          element         the element to add.

                  * @return         <code>true</code> if the element was added to this queue, else <code>false</code>. 

                  */

                 function offer(element:*): Boolean;

                 /**

                  * Retrieves, but does not remove, the head of this queue, or returns <code>null</code> if this queue is empty. 

                  * 

                  * @return         the head of this queue, or <code>null</code> if this queue is empty.

                   */

                 function peek(): *;

                 /**

                  * Retrieves and removes the head of this queue, or returns <code>null</code> if this queue is empty. 

                  * 

                  * @return         the head of this queue, or <code>null</code> if this queue is empty.

                   */

                 function poll(): *;

         }

 }