content: /*
   * 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 com.datastax.oss.driver.internal.core.loadbalancing.helper;
  
  import com.datastax.oss.driver.api.core.loadbalancing.LoadBalancingPolicy;
  import com.datastax.oss.driver.api.core.metadata.Node;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import java.util.Map;
  import java.util.Optional;
  import java.util.UUID;
  import net.jcip.annotations.ThreadSafe;
  
  @FunctionalInterface
  @ThreadSafe
  public interface LocalDcHelper {
  
    /**
     * Returns the local datacenter, if it can be discovered, or returns {@link Optional#empty empty}
     * otherwise.
     *
     * <p>Implementors may choose to throw {@link IllegalStateException} instead of returning {@link
     * Optional#empty empty}, if they require a local datacenter to be defined in order to operate
     * properly.
     *
     * @param nodes All the nodes that were known to exist in the cluster (regardless of their state)
     *     when the load balancing policy was {@linkplain LoadBalancingPolicy#init(Map,
     *     LoadBalancingPolicy.DistanceReporter) initialized}. This argument is provided in case
     *     implementors need to inspect the cluster topology to discover the local datacenter.
     * @return The local datacenter, or {@link Optional#empty empty} if none found.
     * @throws IllegalStateException if the local datacenter could not be discovered, and this policy
     *     cannot operate without it.
     */
    @NonNull
    Optional<String> discoverLocalDc(@NonNull Map<UUID, Node> nodes);
  }
  