/*
 * ToroDB
 * Copyright © 2014 8Kdata Technology (www.8kdata.com)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

package com.torodb.mongodb.repl.topology;

import com.eightkdata.mongowp.OpTime;
import com.eightkdata.mongowp.server.api.tools.Empty;
import com.google.common.net.HostAndPort;
import com.torodb.core.services.IdleTorodbService;
import com.torodb.mongodb.commands.pojos.ReplicaSetConfig;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import java.time.Clock;
import java.time.Instant;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionException;
import java.util.concurrent.ThreadFactory;

import javax.inject.Inject;
import javax.inject.Singleton;

/**
 *
 */
@Singleton
public class TopologyService extends IdleTorodbService {

  private static final Logger LOGGER = LogManager.getLogger(TopologyService.class);

  private final TopologyHeartbeatHandler heartbeatHandler;
  private final TopologyExecutor executor;
  private final Clock clock;

  @Inject
  public TopologyService(TopologyHeartbeatHandler heartbeatHandler,
      ThreadFactory threadFactory, TopologyExecutor executor,
      Clock clock) {
    super(threadFactory);
    this.heartbeatHandler = heartbeatHandler;
    this.executor = executor;
    this.clock = clock;
  }

  public CompletableFuture<Empty> initiate(ReplicaSetConfig rsConfig) {
    return executor.onAnyVersion().mapAsync(coord -> {
      coord.updateConfig(rsConfig, clock.instant());
      return Empty.getInstance();
    });
  }

  public CompletableFuture<Optional<HostAndPort>> getLastUsedSyncSource() {
    return executor.onAnyVersion()
        .mapAsync(TopologyCoordinator::getSyncSourceAddress);
  }

  public CompletableFuture<Optional<HostAndPort>> chooseNewSyncSource(
      Optional<OpTime> lastFetchedOpTime) {
    return executor.onAnyVersion()
        .mapAsync(coord -> {
          Instant now = clock.instant();
          HostAndPort currentSyncSource = coord.getSyncSourceAddress()
              .orElse(null);
          boolean shouldChange = currentSyncSource == null || coord.shouldChangeSyncSource(
              currentSyncSource, now);
          if (shouldChange) {
            return coord.chooseNewSyncSource(
                clock.instant(),
                lastFetchedOpTime
            );
          } else {
            return coord.getSyncSourceAddress();
          }
        });
  }

  CompletableFuture<Boolean> shouldChangeSyncSource() {
    return executor.onAnyVersion()
        .mapAsync(coord -> {
          Instant now = clock.instant();
          HostAndPort currentSyncSource = coord.getSyncSourceAddress()
              .orElse(null);
          return currentSyncSource == null || coord.shouldChangeSyncSource(currentSyncSource, now);
        });
  }

  @Override
  protected void startUp() throws Exception {
    LOGGER.debug("Starting topology service");

    heartbeatHandler.startAsync();
    heartbeatHandler.awaitRunning();

    boolean topologyReady;
    int attempts = 0;
    do {
      topologyReady = calculateTopologyReady();
      if (!topologyReady) {
        LOGGER.debug("Waiting until topology is ready");
        Thread.sleep(1000);
      }
      attempts++;
    }
    while (!topologyReady && attempts < 30);
    if (!topologyReady) {
      throw new RuntimeException("Topology was not able to be ready "
          + "after " + attempts + " attempts");
    }

    LOGGER.info("Topology service started");
  }

  @Override
  protected void shutDown() throws Exception {
    LOGGER.info("Topology service shutted down");

    heartbeatHandler.stopAsync();
    heartbeatHandler.awaitTerminated();
  }

  private boolean isTopologyReady(TopologyCoordinator coord) {
    return coord.chooseNewSyncSource(clock.instant(), Optional.empty()).isPresent();
  }

  private boolean calculateTopologyReady() {
    try {
      return executor.onAnyVersion()
          .mapAsync(this::isTopologyReady)
          .join();
    } catch (CompletionException ex) {
      Throwable cause = ex.getCause() != null ? ex.getCause() : ex;
      throw new RuntimeException("Topology startup failed before it "
          + "was ready to accept requests", cause);
    }
  }

}