src/main/java/org/apache/cassandra/sidecar/server/SidecarServerEvents.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.apache.cassandra.sidecar.server;

/**
 * Defines the {@link io.vertx.core.eventbus.EventBus} addresses where different notifications will be published
 * during Sidecar startup/shutdown, as well as CQL connection availability.
 *
 * <p>The messages can be published multiple times depending on whether Sidecar is started or stopped
 * during the lifetime of the application. Implementing consumers will need to deal with this expectation
 * internally.
 * <p>
 * The expectation is that:
 * <ul>
 * <li>{@link #ON_SERVER_START} will happen first
 * <li>{@link #ON_SERVER_STOP} can happen before {@link #ON_ALL_CASSANDRA_CQL_READY}
 * <li>{@link #ON_SERVER_START} can only happen for any subsequent calls only after a {@link #ON_SERVER_STOP} message
 * <li>{@link #ON_ALL_CASSANDRA_CQL_READY} might never happen
 * <li>{@link #ON_CASSANDRA_CQL_READY} can be called multiple times with different cassandraInstanceId values
 * <li>{@link #ON_CASSANDRA_CQL_DISCONNECTED} can be called multiple times with different cassandraInstanceId values
 * </ul>
 * <p>
 * However, implementers should choose to implement methods assuming no guarantees to the event sequence.
 */
public enum SidecarServerEvents
{
    /**
     * The {@link io.vertx.core.eventbus.EventBus} address where server start events will be published. Server start
     * will be published whenever Sidecar has successfully started and is ready listening for requests.
     */
    ON_SERVER_START,

    /**
     * The {@link io.vertx.core.eventbus.EventBus} address where server stop/shutdown events will be published.
     * Server stop events will be published whenever Sidecar is stopping or shutting down.
     */
    ON_SERVER_STOP,

    /**
     * The {@link io.vertx.core.eventbus.EventBus} address where events will be published when a CQL connection for
     * a given instance has been established. The instance identifier will be passed as part of the message.
     */
    ON_CASSANDRA_CQL_READY,

    /**
     * The {@link io.vertx.core.eventbus.EventBus} address where events will be published when a CQL connection for
     * a given instance has been disconnected. The instance identifier will be passed as part of the message.
     */
    ON_CASSANDRA_CQL_DISCONNECTED,

    /**
     * The {@link io.vertx.core.eventbus.EventBus} address where events will be published when all CQL connections
     * for the Sidecar-managed Cassandra instances are available.
     */
    ON_ALL_CASSANDRA_CQL_READY,

    /**
     * The {@link io.vertx.core.eventbus.EventBus} address where events will be published when a JMX connection for
     * a given instance has been established. The instance identifier will be passed as part of the message.
     */
    ON_CASSANDRA_JMX_READY,

    /**
     * The {@link io.vertx.core.eventbus.EventBus} address where events will be published when a JMX connection for
     * a given instance has been disconnected. The instance identifier will be passed as part of the message.
     */
    ON_CASSANDRA_JMX_DISCONNECTED,
    ;

    public String address()
    {
        return SidecarServerEvents.class.getName() + "." + name();
    }
}