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/*
 * 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;
import com.google.common.base.MoreObjects;

/**
 * Wraps an event that was posted, but which had no subscribers and thus could
 * not be delivered.
 *
 * 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 (not 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;
  }

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(this)
      .add("source", source)
      .add("event", event)
      .toString();
  }
}