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/*
 * Licensed 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 com.gh.bmd.jrt.core;

import java.util.Collection;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

/**
 * Interface defining a queue with the possibility to add nested queues with additional elements.
 * 
 * This interface is used to abstract the handling of placeholders for asynchronously available
 * data, in order to support forced input and output ordering.
 * 

 * Created by davide on 9/30/14.
 *
 * @param  the element type.
 */
interface NestedQueue {

    /**
     * Adds the specified element to the queue.
     * 

     * Note that the element can be null.
     *
     * @param element the element to add.
     * @throws java.lang.IllegalStateException if the queue has been already closed.
     */
    void add(@Nullable E element);

    /**
     * Adds all the elements returned by the specified iterable.
     * 
     * Note that the any of the returned element can be null.
     *
     * @param elements the element iterable.
     * @throws java.lang.IllegalStateException if the queue has been already closed.
     */
    void addAll(@Nonnull Iterable elements);

    /**
     * Adds a nested queue to this one.
     *
     * @return the newly added nested queue.
     * @throws java.lang.IllegalStateException if the queue has been already closed.
     */
    @Nonnull
    NestedQueue addNested();

    /**
     * Clears the queue.
     */
    void clear();

    /**
     * Closes this queue.

     * After the method returns no further additions can be made to this queue. Though, elements can
     * be safely removed.
     */
    void close();

    /**
     * Check if the queue does not contain any element.
     *
     * @return whether the queue is empty.
     */
    boolean isEmpty();

    /**
     * Moves all the elements to the specified collection.
     *
     * @param collection the collection to fill.
     */
    void moveTo(@Nonnull final Collection collection);

    /**
     * Removes the first element added into the queue.
     *
     * @return the element.
     * @throws java.util.NoSuchElementException if the queue is empty.
     */
    @Nullable
    E removeFirst();
}