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Support for topology discovery of instances.
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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.sling.discovery;

import java.util.Set;

import aQute.bnd.annotation.ProviderType;

/**
 * A topology view is a cross-cluster list of instances and clusters
 * that have announced themselves with the DiscoveryService.
 * 
 * All instances in a topology must and do have a unique sling.id.
 * @see InstanceDescription#getSlingId()
 */
@ProviderType
public interface TopologyView {

    /**
     * Checks if this TopologyView is currently valid - or if the
     * service knows of a topology change just going on (or another
     * uncertainty about the topology such as IOException etc)
     * @return true if this TopologyView is currently valid, false
     * if the service knows of a topology change just going on (or
     * another issue with discovery like IOException etc)
     */
    boolean isCurrent();

    /**
     * Provides the InstanceDescription belonging to this instance.
     * @return the InstanceDescription belonging to this instance
     */
    InstanceDescription getLocalInstance();

    /**
     * Provides the set of InstanceDescriptions in the entire topology,
     * without any particular order
     * @return the set of InstanceDescriptions in the entire topology,
     * without any particular order
     */
    Set getInstances();

    /**
     * Searches through this topology and picks those accepted by the provided
     * InstanceFilter - and returns them without any particular order
     * @param filter the filter to use
     * @return the set of InstanceDescriptions which were accepted by the InstanceFilter,
     * without any particular order
     */
    Set findInstances(InstanceFilter filter);

    /**
     * Provides the collection of ClusterViews.
     * 
     * Note that all InstanceDescriptions belong to exactly one ClusterView -
     * including InstanceDescriptions that form "a cluster of 1"
     * @return the set of ClusterViews, without any particular order
     */
    Set getClusterViews();
}