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/**
 *  Copyright 2005-2014 Red Hat, Inc.
 *
 *  Red Hat 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 io.fabric8.groups;

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.
     */
    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();

}