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The Java operations layer for the MongoDB Java Driver. Third parties can ' + 'wrap this layer to provide custom higher-level APIs

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/*
 * Copyright 2008-present MongoDB, 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.mongodb.internal.connection;

import com.mongodb.MongoException;
import com.mongodb.ServerAddress;
import com.mongodb.connection.ClusterId;
import com.mongodb.connection.ClusterSettings;
import com.mongodb.connection.ClusterType;
import com.mongodb.lang.Nullable;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;

import static com.mongodb.assertions.Assertions.assertNotNull;

/**
 * This class is not part of the public API and may be removed or changed at any time
 */
public final class DnsMultiServerCluster extends AbstractMultiServerCluster {
    private final DnsSrvRecordMonitor dnsSrvRecordMonitor;
    private volatile MongoException srvResolutionException;


    public DnsMultiServerCluster(final ClusterId clusterId, final ClusterSettings settings, final ClusterableServerFactory serverFactory,
                                 final DnsSrvRecordMonitorFactory dnsSrvRecordMonitorFactory) {
        super(clusterId, settings, serverFactory);
        dnsSrvRecordMonitor = dnsSrvRecordMonitorFactory.create(assertNotNull(settings.getSrvHost()), settings.getSrvServiceName(),
                new DnsSrvRecordInitializer() {
            private volatile boolean initialized;

            @Override
            public void initialize(final Collection hosts) {
                srvResolutionException = null;
                if (!initialized) {
                    initialized = true;
                    DnsMultiServerCluster.this.initialize(applySrvMaxHosts(hosts));
                } else {
                    DnsMultiServerCluster.this.onChange(applySrvMaxHosts(hosts));
                }
            }

            private Collection applySrvMaxHosts(final Collection hosts) {
                Collection newHosts = hosts;
                Integer srvMaxHosts = getSettings().getSrvMaxHosts();
                if (srvMaxHosts != null && srvMaxHosts > 0) {
                    if (srvMaxHosts < hosts.size()) {
                        List newHostsList = new ArrayList<>(hosts);
                        Collections.shuffle(newHostsList, ThreadLocalRandom.current());
                        newHosts = newHostsList.subList(0, srvMaxHosts);
                    }
                }
                return newHosts;
            }

            @Override
            public void initialize(final MongoException initializationException) {
                if (!initialized) {
                    srvResolutionException = initializationException;
                    DnsMultiServerCluster.this.initialize(Collections.emptyList());
                }
            }

            @Override
            public ClusterType getClusterType() {
                return DnsMultiServerCluster.this.getClusterType();
            }
        });
        dnsSrvRecordMonitor.start();
    }

    @Nullable
    @Override
    protected MongoException getSrvResolutionException() {
        return srvResolutionException;
    }

    @Override
    public void close() {
        if (dnsSrvRecordMonitor != null) {
            dnsSrvRecordMonitor.close();
        }
        super.close();
    }
}