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/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch 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.elasticsearch.action.support;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.ClusterStateObserver;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.unit.TimeValue;
import org.elasticsearch.node.NodeClosedException;
import org.elasticsearch.threadpool.ThreadPool;

import java.util.Arrays;
import java.util.function.Consumer;
import java.util.function.Predicate;

/**
 * This class provides primitives for waiting for a configured number of shards
 * to become active before sending a response on an {@link ActionListener}.
 */
public class ActiveShardsObserver {

    private static final Logger logger = LogManager.getLogger(ActiveShardsObserver.class);

    private final ClusterService clusterService;
    private final ThreadPool threadPool;

    public ActiveShardsObserver(final ClusterService clusterService, final ThreadPool threadPool) {
        this.clusterService = clusterService;
        this.threadPool = threadPool;
    }

    /**
     * Waits on the specified number of active shards to be started before executing the
     *
     * @param indexNames the indices to wait for active shards on
     * @param activeShardCount the number of active shards to wait on before returning
     * @param timeout the timeout value
     * @param onResult a function that is executed in response to the requisite shards becoming active or a timeout (whichever comes first)
     * @param onFailure a function that is executed in response to an error occurring during waiting for the active shards
     */
    public void waitForActiveShards(final String[] indexNames,
                                    final ActiveShardCount activeShardCount,
                                    final TimeValue timeout,
                                    final Consumer onResult,
                                    final Consumer onFailure) {

        // wait for the configured number of active shards to be allocated before executing the result consumer
        if (activeShardCount == ActiveShardCount.NONE) {
            // not waiting, so just run whatever we were to run when the waiting is
            onResult.accept(true);
            return;
        }

        final ClusterState state = clusterService.state();
        final ClusterStateObserver observer = new ClusterStateObserver(state, clusterService, null, logger, threadPool.getThreadContext());
        if (activeShardCount.enoughShardsActive(state, indexNames)) {
            onResult.accept(true);
        } else {
            final Predicate shardsAllocatedPredicate = newState -> activeShardCount.enoughShardsActive(newState, indexNames);

            final ClusterStateObserver.Listener observerListener = new ClusterStateObserver.Listener() {
                @Override
                public void onNewClusterState(ClusterState state) {
                    onResult.accept(true);
                }

                @Override
                public void onClusterServiceClose() {
                    logger.debug("[{}] cluster service closed while waiting for enough shards to be started.", Arrays.toString(indexNames));
                    onFailure.accept(new NodeClosedException(clusterService.localNode()));
                }

                @Override
                public void onTimeout(TimeValue timeout) {
                    onResult.accept(false);
                }
            };

            observer.waitForNextChange(observerListener, shardsAllocatedPredicate, timeout);
        }
    }

}