/*
 *
 * Copyright (c) 2006 The Apache Software Foundation
 *
 * 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 org.apache.qpid.server.queue;

import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 * Distributes messages among a list of subsscription managers, using their
 * weighting.
 *
 */
class NestedSubscriptionManager implements SubscriptionManager
{
    private final List<WeightedSubscriptionManager> _subscribers = new CopyOnWriteArrayList<WeightedSubscriptionManager>();
    private int _iterations;
    private int _index;

    void addSubscription(WeightedSubscriptionManager s)
    {
        _subscribers.add(s);
    }

    void removeSubscription(WeightedSubscriptionManager s)
    {
        _subscribers.remove(s);
    }

    public boolean hasActiveSubscribers()
    {
        for(WeightedSubscriptionManager s : _subscribers)
        {
            if(s.hasActiveSubscribers())
            {
                return true;
            }
        }
        return false;
    }

    public Subscription nextSubscriber(AMQMessage msg)
    {
        WeightedSubscriptionManager start = current();
        for(WeightedSubscriptionManager s = start; s != null; s = next(start))
        {
            if(hasMore(s))
            {
                return nextSubscriber(s);
            }
        }
        return null;
    }

    private Subscription nextSubscriber(WeightedSubscriptionManager s)
    {
        _iterations++;
        return s.nextSubscriber(null);
    }

    private WeightedSubscriptionManager current()
    {
        return _subscribers.isEmpty() ? null : _subscribers.get(_index);
    }

    private boolean hasMore(WeightedSubscriptionManager s)
    {
        return _iterations < s.getWeight();
    }

    private WeightedSubscriptionManager next(WeightedSubscriptionManager start)
    {
        WeightedSubscriptionManager s = next();
        return s == start && !hasMore(s) ? null : s;
    }

    private WeightedSubscriptionManager next()
    {
        _iterations = 0;
        if(++_index >= _subscribers.size())
        {
            _index = 0;
        }
        return _subscribers.get(_index);
    }
}
