/*
    * Copyright 2019 LINE Corporation
    *
    * LINE Corporation 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:
    *
    *   https://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.linecorp.centraldogma.server.internal.storage;
  
  import static com.google.common.base.Preconditions.checkArgument;
  import static com.google.common.collect.ImmutableList.toImmutableList;
  import static com.linecorp.centraldogma.server.internal.ExecutorServiceUtil.terminate;
  import static java.util.Objects.requireNonNull;
  
  import java.time.Duration;
  import java.time.Instant;
  import java.util.List;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  import java.util.function.Predicate;
  
  import javax.annotation.Nullable;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.common.annotations.VisibleForTesting;
  import com.google.common.util.concurrent.FutureCallback;
  import com.google.common.util.concurrent.Futures;
  import com.google.common.util.concurrent.ListenableScheduledFuture;
  import com.google.common.util.concurrent.ListeningScheduledExecutorService;
  import com.google.common.util.concurrent.MoreExecutors;
  
  import com.linecorp.centraldogma.common.Author;
  import com.linecorp.centraldogma.server.command.Command;
  import com.linecorp.centraldogma.server.command.CommandExecutor;
  import com.linecorp.centraldogma.server.metadata.MetadataService;
  import com.linecorp.centraldogma.server.metadata.Token;
  import com.linecorp.centraldogma.server.metadata.Tokens;
  import com.linecorp.centraldogma.server.storage.project.ProjectManager;
  
  /**
   * A service class for purging projects and repositories that were removed before.
   */
  public class PurgeSchedulingService {
  
      private static final Logger logger = LoggerFactory.getLogger(PurgeSchedulingService.class);
  
      /**
       * How often to run the storage purge schedules. i.e. every minute.
       */
      private static final Duration TICK = Duration.ofMinutes(1);
  
      private final ProjectManager projectManager;
      private final ScheduledExecutorService purgeWorker;
      private final long maxRemovedRepositoryAgeMillis;
      private final StoragePurgingScheduler storagePurgingScheduler = new StoragePurgingScheduler();
  
      public PurgeSchedulingService(ProjectManager projectManager, ScheduledExecutorService purgeWorker,
                                    long maxRemovedRepositoryAgeMillis) {
          this.projectManager = requireNonNull(projectManager, "projectManager");
          this.purgeWorker = requireNonNull(purgeWorker, "purgeWorker");
          checkArgument(maxRemovedRepositoryAgeMillis >= 0,
                        "maxRemovedRepositoryAgeMillis: %s (expected: >= 0)", maxRemovedRepositoryAgeMillis);
          this.maxRemovedRepositoryAgeMillis = maxRemovedRepositoryAgeMillis;
      }
  
      public void start(CommandExecutor commandExecutor,
                        MetadataService metadataService) {
          if (isDisabled()) {
              return;
          }
          requireNonNull(commandExecutor, "commandExecutor");
          requireNonNull(metadataService, "metadataService");
          cleanPurgedFiles();
          storagePurgingScheduler.start(() -> {
              try {
                  purgeProjectAndRepository(commandExecutor, metadataService);
                  purgeToken(metadataService);
              } catch (Exception e) {
                  logger.warn("Unexpected purging service failure", e);
              }
          });
      }
  
      public boolean isStarted() {
          return storagePurgingScheduler.isStarted();
      }
  
      public void stop() {
         if (!isDisabled()) {
             storagePurgingScheduler.stop();
         }
     }
 
     private void cleanPurgedFiles() {
         projectManager.purgeMarked();
         projectManager.list().forEach((unused, project) -> project.repos().purgeMarked());
     }
 
     @VisibleForTesting
     void purgeProjectAndRepository(CommandExecutor commandExecutor,
                                    MetadataService metadataService) {
         final long minAllowedTimestamp = System.currentTimeMillis() - maxRemovedRepositoryAgeMillis;
         final Predicate<Instant> olderThanMinAllowed =
                 removedAt -> removedAt.toEpochMilli() < minAllowedTimestamp;
 
         purgeProject(commandExecutor, olderThanMinAllowed);
         purgeRepository(commandExecutor, metadataService, olderThanMinAllowed);
     }
 
     private void purgeProject(CommandExecutor commandExecutor,
                               Predicate<Instant> olderThanMinAllowed) {
         projectManager
                 .listRemoved()
                 .forEach((projectName, removal) -> {
                     if (olderThanMinAllowed.test(removal)) {
                         commandExecutor
                                 .execute(Command.purgeProject(Author.SYSTEM, projectName)).join();
                     }
                 });
     }
 
     private void purgeRepository(CommandExecutor commandExecutor,
                                  MetadataService metadataService,
                                  Predicate<Instant> olderThanMinAllowed) {
         projectManager
                 .list()
                 .forEach((unused, project) -> {
                     project.repos().listRemoved()
                            .forEach((repoName, removal) -> {
                                if (olderThanMinAllowed.test(removal)) {
                                    commandExecutor.execute(Command.purgeRepository(Author.SYSTEM,
                                                                                    project.name(),
                                                                                    repoName))
                                                   .join();
                                    metadataService.purgeRepo(Author.SYSTEM, project.name(), repoName).join();
                                }
                            });
                 });
     }
 
     private static void purgeToken(MetadataService metadataService) {
         final Tokens tokens = metadataService.getTokens();
         final List<String> purging = tokens.appIds().values()
                                            .stream()
                                            .filter(Token::isDeleted)
                                            .map(Token::appId)
                                            .collect(toImmutableList());
 
         if (!purging.isEmpty()) {
             logger.info("Purging {} tokens: {}", purging.size(), purging);
             purging.forEach(appId -> metadataService.purgeToken(Author.SYSTEM, appId));
         }
     }
 
     private boolean isDisabled() {
         return maxRemovedRepositoryAgeMillis == 0;
     }
 
     private final class StoragePurgingScheduler {
 
         @Nullable
         private volatile ListeningScheduledExecutorService scheduler;
 
         public boolean isStarted() {
             return scheduler != null;
         }
 
         public synchronized void start(Runnable task) {
             if (isStarted()) {
                 return;
             }
             requireNonNull(task, "task");
             final ListeningScheduledExecutorService scheduler = MoreExecutors.listeningDecorator(purgeWorker);
             this.scheduler = scheduler;
             @SuppressWarnings("UnstableApiUsage")
             final ListenableScheduledFuture<?> future = scheduler.scheduleWithFixedDelay(
                     task,
                     TICK.getSeconds(), TICK.getSeconds(), TimeUnit.SECONDS);
 
             Futures.addCallback(future, new FutureCallback<Object>() {
                 @Override
                 public void onSuccess(@Nullable Object result) {}
 
                 @Override
                 public void onFailure(Throwable cause) {
                     logger.error("Storage purge scheduler stopped due to an unexpected exception:", cause);
                 }
             }, purgeWorker);
         }
 
         public synchronized void stop() {
             final ExecutorService scheduler = this.scheduler;
 
             try {
                 final boolean interrupted = terminate(scheduler);
                 if (interrupted) {
                     Thread.currentThread().interrupt();
                 }
             } finally {
                 this.scheduler = null;
             }
         }
     }
 }