/*
    * Copyright (C) 2007 The Guava Authors
    *
    * 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.google.common.eventbus;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.Beta;
  
  /**
   * Wraps an event that was posted, but which had no subscribers and thus could
   * not be delivered.
   *
   * <p>Registering a DeadEvent subscriber is useful for debugging or logging, as
   * it can detect misconfigurations in a system's event distribution.
   *
   * @author Cliff Biffle
   * @since 10.0
   */
  @Beta
  public class DeadEvent {
  
    private final Object source;
    private final Object event;
  
    /**
     * Creates a new DeadEvent.
     *
     * @param source  object broadcasting the DeadEvent (generally the
     *                {@link EventBus}).
     * @param event   the event that could not be delivered.
     */
    public DeadEvent(Object source, Object event) {
      this.source = checkNotNull(source);
      this.event = checkNotNull(event);
    }
  
    /**
     * Returns the object that originated this event (<em>not</em> the object that
     * originated the wrapped event).  This is generally an {@link EventBus}.
     *
     * @return the source of this event.
     */
    public Object getSource() {
      return source;
    }
  
    /**
     * Returns the wrapped, 'dead' event, which the system was unable to deliver
     * to any registered subscriber.
     *
     * @return the 'dead' event that could not be delivered.
     */
    public Object getEvent() {
      return event;
    }
  
  }