/*
 * Copyright DataStax, Inc.
 *
 * Licensed 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 static com.datastax.oss.driver.internal.core.time.Clock.LOG;

import com.datastax.oss.driver.api.core.config.DefaultDriverOption;
import com.datastax.oss.driver.api.core.config.DriverExecutionProfile;
import com.datastax.oss.driver.api.core.metadata.Node;
import com.datastax.oss.driver.internal.core.context.InternalDriverContext;
import com.datastax.oss.driver.internal.core.metadata.DefaultNode;
import edu.umd.cs.findbugs.annotations.NonNull;
import java.util.HashSet;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.UUID;
import net.jcip.annotations.ThreadSafe;

An implementation of LocalDcHelper that fetches the user-supplied datacenter, if any, from the programmatic configuration API, or else, from the driver configuration. If no local datacenter is explicitly defined, this implementation infers the local datacenter from the contact points: if all contact points share the same datacenter, that datacenter is returned. If the contact points are from different datacenters, or if no contact points reported any datacenter, an IllegalStateException is thrown. /**
 * An implementation of {@link LocalDcHelper} that fetches the user-supplied datacenter, if any,
 * from the programmatic configuration API, or else, from the driver configuration. If no local
 * datacenter is explicitly defined, this implementation infers the local datacenter from the
 * contact points: if all contact points share the same datacenter, that datacenter is returned. If
 * the contact points are from different datacenters, or if no contact points reported any
 * datacenter, an {@link IllegalStateException} is thrown.
 */
@ThreadSafe
public class InferringLocalDcHelper extends OptionalLocalDcHelper {

  public InferringLocalDcHelper(
      @NonNull InternalDriverContext context,
      @NonNull DriverExecutionProfile profile,
      @NonNull String logPrefix) {
    super(context, profile, logPrefix);
  }

  
Returns:
The local datacenter; always present./** @return The local datacenter; always present. */
  @NonNull
  @Override
  public Optional<String> discoverLocalDc(@NonNull Map<UUID, Node> nodes) {
    Optional<String> optionalLocalDc = super.discoverLocalDc(nodes);
    if (optionalLocalDc.isPresent()) {
      return optionalLocalDc;
    }
    Set<String> datacenters = new HashSet<>();
    Set<DefaultNode> contactPoints = context.getMetadataManager().getContactPoints();
    for (Node node : contactPoints) {
      String datacenter = node.getDatacenter();
      if (datacenter != null) {
        datacenters.add(datacenter);
      }
    }
    if (datacenters.size() == 1) {
      String localDc = datacenters.iterator().next();
      LOG.info("[{}] Inferred local DC from contact points: {}", logPrefix, localDc);
      return Optional.of(localDc);
    }
    if (datacenters.isEmpty()) {
      throw new IllegalStateException(
          "The local DC could not be inferred from contact points, please set it explicitly (see "
              + DefaultDriverOption.LOAD_BALANCING_LOCAL_DATACENTER.getPath()
              + " in the config, or set it programmatically with SessionBuilder.withLocalDatacenter)");
    }
    throw new IllegalStateException(
        String.format(
            "No local DC was provided, but the contact points are from different DCs: %s; "
                + "please set the local DC explicitly (see "
                + DefaultDriverOption.LOAD_BALANCING_LOCAL_DATACENTER.getPath()
                + " in the config, or set it programmatically with SessionBuilder.withLocalDatacenter)",
            formatNodesAndDcs(contactPoints)));
  }
}