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 *
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 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
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 */

package org.glassfish.grizzly.http2;

import java.util.LinkedList;

/**
 * The queue of element bundles.
 * Each bundle in the queue may be empty or have some elements.
 */
final class BundleQueue {
    private final LinkedList> internalQueue = new LinkedList<>();
    private int lastElementAbsoluteDistance;

    /**
     * Add the element to the specified bundle.
     * The bundle is represented by its order in the queue. It is not possible to
     * add the element to a bundle, which already exists and is not the last
     * bundle in the queue.
     * 
     * @param bundle
     * @param element 
     */
    public void add(final int bundle, final E element) {
        if (lastElementAbsoluteDistance > bundle) {
            throw new IllegalStateException("New element must have greater" + " absolute distance than the last element in the queue");
        }
        internalQueue.addLast(new Record<>(element, bundle - lastElementAbsoluteDistance));
        lastElementAbsoluteDistance = bundle;
    }

    /**
     * Returns true if there is available element in the current bundle.
     */
    public boolean hasNext() {
        return !internalQueue.isEmpty() && internalQueue.getFirst().distance == 0;
    }

    /**
     * Returns next available element in the current bundle.
     */
    public E next() {
        if (!hasNext()) {
            throw new IllegalStateException("There is no next element available");
        }
        return internalQueue.removeFirst().value;
    }

    /**
     * Switches to the next bundle in the queue, all the unread elements from
     * the previously active bundle will be removed.
     * @return true if next bundle exists and is not empty
     */
    public boolean nextBundle() {
        if (internalQueue.isEmpty()) {
            return false;
        }
        // skip old records
        while (internalQueue.getFirst().distance == 0) {
            internalQueue.removeFirst();
            if (internalQueue.isEmpty()) {
                return false;
            }
        }
        lastElementAbsoluteDistance--;
        return --internalQueue.getFirst().distance == 0;
    }

    private static final class Record {

        private final E value;
        private int distance;

        public Record(final E value, final int distance) {
            this.value = value;
            this.distance = distance;
        }
    }
    
}