001/**
002 * Copyright (c) 2008-2009 Apple Inc. All rights reserved.
003 * Copyright (C) 2012 FuseSource, Inc.
004 * http://fusesource.com
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License");
007 * you may not use this file except in compliance with the License.
008 * You may obtain a copy of the License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.fusesource.hawtdispatch;
020
021/**
022 * <p>
023 * The EventAggregator interface is used by the {@link CustomDispatchSource} objects to handle
024 * coalescing data before passing it to the application.  Implementations of this class should
025 * be stateless to remain thread-safe.  You can also use one of several built in implementations:
026 * </p>
027 *
028 * <ul>
029 * <li>{@link EventAggregators#INTEGER_ADD}</li>
030 * <li>{@link EventAggregators#INTEGER_OR}</li>
031 * <li>{@link EventAggregators#LONG_ADD}</li>
032 * <li>{@link EventAggregators#LONG_OR}</li> 
033 * </ul>
034 *
035 * @author <a href="http://hiramchirino.com">Hiram Chirino</a>
036 */
037public interface EventAggregator<Event, MergedEvent> {
038
039    /**
040     * <p>
041     * Merge the given event with the previous event values.
042     * </p>
043     *
044     * @param previous may be null
045     * @param event the value that should be merged
046     * @return a newly merged result
047     */
048    public MergedEvent mergeEvent(MergedEvent previous, Event event);
049
050    /**
051     * <p>
052     * Merge the given events with the previous event values.
053     * </p>
054     *
055     * @param previous the value of previous merges
056     * @param events the value of more merges
057     * @return a newly merged result
058     */
059    public MergedEvent mergeEvents(MergedEvent previous, MergedEvent events);
060
061}