/**
 * Copyright (c) 2013, Redsolution LTD. All rights reserved.
 *
 * This file is part of Xabber project; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License, Version 3.
 *
 * Xabber is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License,
 * along with this program. If not, see http://www.gnu.org/licenses/.
 */
package com.xabber.android.data.connection;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

/**
 * Address pool.
 *
 * @author alexander.ivanov
 */
public abstract class AbstractPool<Item, Source> {

    protected final Queue<Item> pool;
    protected final Queue<Item> used;

    public AbstractPool() {
        this.pool = new LinkedList<Item>();
        this.used = new LinkedList<Item>();
    }

    /**
     * Updates pool with specified values.
     *
     * @param values <code>null</code> if no changes in the pool should be made.
     */
    synchronized public void update(Source[] values) {
        if (values == null)
            return;
        List<Item> items = new ArrayList<Item>();
        for (Source value : values) {
            Item item = convert(value);
            if (item != null)
                items.add(item);
        }
        update(items);
    }

    /**
     * @param value
     * @return Converted value or <code>null</code> if value shouldn't be used.
     */
    abstract Item convert(Source value);

    /**
     * Checks and updates pool with items.
     *
     * @param items
     */
    abstract void update(List<Item> items);

    /**
     * Returns first value from the pool. Make it as used. Reset pool if it is
     * empty.
     *
     * @return <code>null</code> if pool was empty.
     */
    synchronized public Item getNext() {
        if (pool.isEmpty()) {
            pool.addAll(used);
            used.clear();
            return null;
        }
        Item address = pool.remove();
        used.add(address);
        return address;
    }

}
