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Camel Zookeeper Master Support

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/*
 * 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.camel.component.zookeepermaster.group;

import java.io.Closeable;
import java.io.IOException;
import java.util.List;
import java.util.Map;

public interface Group extends Closeable {

    /**
     * Are we connected with the cluster?
     */
    boolean isConnected();

    /**
     * Start this member
     */
    void start();

    /**
     * A member should be closed to release acquired resources used to monitor the group membership.
     *
     * When the member is closed, any memberships registered via this Group will be removed from the group.
     */
    @Override
    void close() throws IOException;

    /**
     * Registers a listener which will be called when the cluster membership changes or the group is connected or
     * disconnected.
     */
    void add(GroupListener listener);

    /**
     * Removes a previously added listener.
     */
    void remove(GroupListener listener);

    /**
     * Update the state of this group member. If the state is null, the member will leave the group.
     *
     * This method can be called even if the group is not started, in which case the state will be stored and updated
     * when the group becomes started.
     *
     * @param state the new state of this group member
     */
    void update(T state);

    /**
     * Get the list of members connected to this group.
     */
    Map members();

    /**
     * Check if we are the master.
     */
    boolean isMaster();

    /**
     * Retrieve the master node.
     */
    T master();

    /**
     * Retrieve the list of slaves.
     */
    List slaves();

    /**
     * Gets the last state.
     * 
     * This can be used by clients to access that last state, such as when the clients is being added as a
     * {@link #add(GroupListener) listener} but wants to retrieve the last state to be up to date when the client is
     * added.
     *
     * @return the state, or null if no last state yet.
     */
    T getLastState();

}