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// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.vespa.zookeeper;

import com.google.inject.Inject;
import com.yahoo.cloud.config.ZookeeperServerConfig;
import com.yahoo.component.AbstractComponent;
import com.yahoo.net.HostName;
import com.yahoo.yolean.Exceptions;

import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.stream.Collectors;

/**
 * Starts zookeeper server and supports reconfiguring zookeeper cluster. Created as a component
 * without any config injected, to make sure that it is not recreated when config changes.
 *
 * @author hmusum
 */
public class Reconfigurer extends AbstractComponent {

    private static final Logger log = java.util.logging.Logger.getLogger(Reconfigurer.class.getName());

    private static final Duration MIN_TIMEOUT = Duration.ofMinutes(3);
    private static final Duration NODE_TIMEOUT = Duration.ofMinutes(1);

    private final ExponentialBackoff backoff = new ExponentialBackoff(Duration.ofSeconds(1), Duration.ofSeconds(10));
    private final VespaZooKeeperAdmin vespaZooKeeperAdmin;
    private final Sleeper sleeper;

    private ZooKeeperRunner zooKeeperRunner;
    private ZookeeperServerConfig activeConfig;

    @Inject
    public Reconfigurer(VespaZooKeeperAdmin vespaZooKeeperAdmin) {
        this(vespaZooKeeperAdmin, new Sleeper());
    }

    Reconfigurer(VespaZooKeeperAdmin vespaZooKeeperAdmin, Sleeper sleeper) {
        this.vespaZooKeeperAdmin = Objects.requireNonNull(vespaZooKeeperAdmin);
        this.sleeper = Objects.requireNonNull(sleeper);
        log.log(Level.FINE, "Created ZooKeeperReconfigurer");
    }

    void startOrReconfigure(ZookeeperServerConfig newConfig, VespaZooKeeperServer server) {
        if (zooKeeperRunner == null)
            zooKeeperRunner = startServer(newConfig, server);

        if (shouldReconfigure(newConfig))
            reconfigure(newConfig);
    }

    ZookeeperServerConfig activeConfig() {
        return activeConfig;
    }

    void shutdown() {
        if (zooKeeperRunner != null) {
            zooKeeperRunner.shutdown();
        }
    }

    private boolean shouldReconfigure(ZookeeperServerConfig newConfig) {
        if (!newConfig.dynamicReconfiguration()) return false;
        if (activeConfig == null) return false;
        return !newConfig.equals(activeConfig());
    }

    private ZooKeeperRunner startServer(ZookeeperServerConfig zookeeperServerConfig, VespaZooKeeperServer server) {
        ZooKeeperRunner runner = new ZooKeeperRunner(zookeeperServerConfig, server);
        activeConfig = zookeeperServerConfig;
        return runner;
    }

    private void reconfigure(ZookeeperServerConfig newConfig) {
        Instant reconfigTriggered = Instant.now();
        List newServers = difference(servers(newConfig), servers(activeConfig));
        String leavingServers = String.join(",", difference(serverIds(activeConfig), serverIds(newConfig)));
        String joiningServers = String.join(",", newServers);
        leavingServers = leavingServers.isEmpty() ? null : leavingServers;
        joiningServers = joiningServers.isEmpty() ? null : joiningServers;
        log.log(Level.INFO, "Will reconfigure ZooKeeper cluster. Joining servers: " + joiningServers +
                            ", leaving servers: " + leavingServers);
        String connectionSpec = localConnectionSpec(activeConfig);
        Instant now = Instant.now();
        Instant end = now.plus(reconfigTimeout(newServers.size()));
        // Loop reconfiguring since we might need to wait until another reconfiguration is finished before we can succeed
        for (int attempt = 1; now.isBefore(end); attempt++) {
            try {
                Instant reconfigStarted = Instant.now();
                vespaZooKeeperAdmin.reconfigure(connectionSpec, joiningServers, leavingServers);
                Instant reconfigEnded = Instant.now();
                log.log(Level.INFO, "Reconfiguration completed in " +
                                    Duration.between(reconfigTriggered, reconfigEnded) +
                                    ", after " + attempt + " attempt(s). ZooKeeper reconfig call took " +
                                    Duration.between(reconfigStarted, reconfigEnded));
                activeConfig = newConfig;
                return;
            } catch (ReconfigException e) {
                Duration delay = backoff.delay(attempt);
                log.log(Level.WARNING, "Reconfiguration attempt " + attempt + " failed. Retrying in " + delay +
                                       ", time left " + Duration.between(now, end) + ": " +
                                       Exceptions.toMessageString(e));
                sleeper.sleep(delay);
            } finally {
                now = Instant.now();
            }
        }
    }

    /** Returns the timeout to use for the given joining server count */
    private static Duration reconfigTimeout(int joiningServers) {
        // For reconfig to succeed, the current ensemble must have a majority. When an ensemble grows and the joining
        // servers outnumber the existing ones, we have to wait for enough of them to start to have a majority.
        return Duration.ofMillis(Math.max(joiningServers * NODE_TIMEOUT.toMillis(), MIN_TIMEOUT.toMillis()));
    }

    private static String localConnectionSpec(ZookeeperServerConfig config) {
        return HostName.getLocalhost() + ":" + config.clientPort();
    }

    private static List serverIds(ZookeeperServerConfig config) {
        return config.server().stream()
                     .map(ZookeeperServerConfig.Server::id)
                     .map(String::valueOf)
                     .collect(Collectors.toList());
    }

    private static List servers(ZookeeperServerConfig config) {
        // See https://zookeeper.apache.org/doc/r3.5.8/zookeeperReconfig.html#sc_reconfig_clientport for format
        return config.server().stream()
                     .map(server -> server.id() + "=" + server.hostname() + ":" + server.quorumPort() + ":" +
                                    server.electionPort() + ";" + config.clientPort())
                     .collect(Collectors.toList());
    }

    private static  List difference(List list1, List list2) {
        List copy = new ArrayList<>(list1);
        copy.removeAll(list2);
        return copy;
    }

}