/*
 * Copyright (C) 2007 The Guava Authors
 * Copyright 2020-2022 Equinix, Inc
 * Copyright 2014-2022 The Billing Project, LLC
 *
 * The Billing Project licenses this file to you 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.killbill.commons.eventbus;

import org.killbill.commons.utils.Preconditions;

/**
 * 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
 */
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(final Object source, final Object event) {
        this.source = Preconditions.checkNotNull(source);
        this.event = Preconditions.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;
    }

    @Override
    public String toString() {
        return "DeadEvent {" +
               "source=" + source +
               ", event=" + event +
               '}';
    }
}
