// Copyright 2017 The Nomulus Authors. All Rights Reserved.
//
// 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 google.registry.backup;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static google.registry.mapreduce.MapreduceRunner.PARAM_DRY_RUN;
import static google.registry.model.ofy.ObjectifyService.ofy;
import static google.registry.util.PipelineUtils.createJobPath;
import static java.lang.Boolean.FALSE;
import static java.lang.Boolean.TRUE;

import com.google.appengine.tools.mapreduce.Mapper;
import com.google.appengine.tools.mapreduce.Reducer;
import com.google.appengine.tools.mapreduce.ReducerInput;
import com.google.auto.value.AutoValue;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMultiset;
import com.google.common.flogger.FluentLogger;
import com.googlecode.objectify.Key;
import google.registry.config.RegistryConfig.Config;
import google.registry.mapreduce.MapreduceRunner;
import google.registry.mapreduce.inputs.CommitLogManifestInput;
import google.registry.mapreduce.inputs.EppResourceInputs;
import google.registry.model.EppResource;
import google.registry.model.ofy.CommitLogManifest;
import google.registry.model.ofy.CommitLogMutation;
import google.registry.model.translators.CommitLogRevisionsTranslatorFactory;
import google.registry.request.Action;
import google.registry.request.Parameter;
import google.registry.request.Response;
import google.registry.request.auth.Auth;
import google.registry.util.Clock;
import javax.inject.Inject;
import org.joda.time.DateTime;
import org.joda.time.Duration;

/**
 * Task that garbage collects old {@link CommitLogManifest} entities.
 *
 * <p>Once commit logs have been written to GCS, we don't really need them in Datastore anymore,
 * except to reconstruct point-in-time snapshots of the database. To make that possible, {@link
 * EppResource}s have a {@link EppResource#getRevisions} method that returns the commit logs for
 * older points in time. But that functionality is not useful after a certain amount of time, e.g.
 * thirty days, so unneeded revisions are deleted
 * (see {@link CommitLogRevisionsTranslatorFactory}). This leaves commit logs in the system that are
 * unneeded (have no revisions pointing to them). So this task runs periodically to delete the
 * "orphan" commit logs.
 *
 * <p>This action runs a mapreduce that goes over all existing {@link EppResource} and all {@link
 * CommitLogManifest} older than commitLogDatastreRetention, and erases the commit logs aren't in an
 * EppResource.
 *
 */
@Action(
  path = "/_dr/task/deleteOldCommitLogs",
  auth = Auth.AUTH_INTERNAL_ONLY
)
public final class DeleteOldCommitLogsAction implements Runnable {

  private static final int NUM_MAP_SHARDS = 20;
  private static final int NUM_REDUCE_SHARDS = 10;
  private static final FluentLogger logger = FluentLogger.forEnclosingClass();

  @Inject MapreduceRunner mrRunner;
  @Inject Response response;
  @Inject Clock clock;
  @Inject @Config("commitLogDatastoreRetention") Duration maxAge;
  @Inject @Parameter(PARAM_DRY_RUN) boolean isDryRun;
  @Inject DeleteOldCommitLogsAction() {}

  @Override
  public void run() {
    DateTime deletionThreshold = clock.nowUtc().minus(maxAge);
    logger.atInfo().log(
        "Processing asynchronous deletion of unreferenced CommitLogManifests older than %s",
        deletionThreshold);

    response.sendJavaScriptRedirect(createJobPath(mrRunner
          .setJobName("Delete old commit logs")
          .setModuleName("backend")
          .setDefaultMapShards(NUM_MAP_SHARDS)
          .setDefaultReduceShards(NUM_REDUCE_SHARDS)
          .runMapreduce(
              new DeleteOldCommitLogsMapper(deletionThreshold),
              new DeleteOldCommitLogsReducer(deletionThreshold, isDryRun),
              ImmutableList.of(
                  new CommitLogManifestInput(deletionThreshold),
                  EppResourceInputs.createKeyInput(EppResource.class)))));
  }

  /**
   * A mapper that iterates over all {@link EppResource} and {CommitLogManifest} entities.
   *
   * <p>It emits the target key and {@code false} for all revisions of each EppResources (meaning
   * "don't delete this"), and {@code true} for all CommitLogRevisions (meaning "delete this").
   *
   * <p>The reducer will then delete all CommitLogRevisions that only have {@code true}.
   */
  private static class DeleteOldCommitLogsMapper
      extends Mapper<Key<?>, Key<CommitLogManifest>, Boolean> {

    private static final long serialVersionUID = 8008689353479902948L;

    private static final String KIND_MANIFEST = Key.getKind(CommitLogManifest.class);

    private final DateTime threshold;

    DeleteOldCommitLogsMapper(DateTime threshold) {
      this.threshold = threshold;
    }

    @Override
    public void map(final Key<?> key) {
      // key is either a Key<CommitLogManifest> or a Key<? extends EppResource>.
      //
      // If it's a CommitLogManifest we just emit it as is (no need to load it).
      if (key.getKind().equals(KIND_MANIFEST)) {
        getContext().incrementCounter("old commit log manifests found");
        // safe because we checked getKind
        @SuppressWarnings("unchecked")
        Key<CommitLogManifest> manifestKey = (Key<CommitLogManifest>) key;
        emit(manifestKey, true);
        return;
      }

      // If it isn't a Key<CommitLogManifest> then it should be an EppResource, which we need to
      // load to emit the revisions.
      //
      Object object = ofy().load().key(key).now();
      checkNotNull(object, "Received a key to a missing object. key: %s", key);
      checkState(
          object instanceof EppResource,
          "Received a key to an object that isn't EppResource nor CommitLogManifest."
          + " Key: %s object type: %s",
          key,
          object.getClass().getName());

      getContext().incrementCounter("EPP resources found");
      EppResource eppResource = (EppResource) object;
      if (eppResource.getCreationTime().isAfter(threshold)) {
        getContext().incrementCounter("EPP resources newer than threshold");
      }
      for (Key<CommitLogManifest> manifestKey : eppResource.getRevisions().values()) {
        emit(manifestKey, false);
      }
      getContext()
          .incrementCounter("EPP resource revisions found", eppResource.getRevisions().size());
      checkAndLogRevisionCoverageError(eppResource);
    }

    /**
     * Check if given eppResource has the required revisions.
     *
     * <p>Revisions are used to recreate the state of the resource at a given day in the past
     * "commitLogDatastoreRenention". To do that, we need at least one revision that's older than
     * this duration (is dated before "threshold"), or at least one revision within a day of the
     * resource's creation if it was created after the threshold.
     *
     * <p>Here we check that the given eppResource has the revisions it needs.
     *
     * <p>It's just a sanity check - since we're relying on the revisions to be correct for the
     * deletion to work. We want to alert any problems we find in the revisions.
     *
     * <p>This really checks {@link CommitLogRevisionsTranslatorFactory#transformBeforeSave}.
     * There's nothing we can do at this point to prevent the damage - we only report on it.
     */
    private void checkAndLogRevisionCoverageError(EppResource eppResource) {
      // First - check if there even are revisions
      if (eppResource.getRevisions().isEmpty()) {
        getContext().incrementCounter("EPP resources missing all revisions (SEE LOGS)");
        logger.atSevere().log("EPP resource missing all revisions: %s", Key.create(eppResource));
        return;
      }
      // Next, check if there's a revision that's older than "CommitLogDatastoreRetention". There
      // should have been at least one at the time this resource was saved.
      //
      // Alternatively, if the resource is newer than the threshold - there should be at least one
      // revision within a day of the creation time.
      DateTime oldestRevisionDate = eppResource.getRevisions().firstKey();
      if (oldestRevisionDate.isBefore(threshold)
          || oldestRevisionDate.isBefore(eppResource.getCreationTime().plusDays(1))) {
        // We're OK!
        return;
      }
      // The oldest revision date is newer than the threshold! This shouldn't happen.
      getContext().incrementCounter("EPP resources missing pre-threshold revision (SEE LOGS)");
      logger.atSevere().log(
          "EPP resource missing old enough revision: "
              + "%s (created on %s) has %d revisions between %s and %s, while threshold is %s",
          Key.create(eppResource),
          eppResource.getCreationTime(),
          eppResource.getRevisions().size(),
          eppResource.getRevisions().firstKey(),
          eppResource.getRevisions().lastKey(),
          threshold);
      // We want to see how bad it is though: if the difference is less than a day then this might
      // still be OK (we only need logs for the end of the day). But if it's more than a day, then
      // we are 100% sure we can't recreate all the history we need from the revisions.
      Duration interval = new Duration(threshold, oldestRevisionDate);
      if (interval.isLongerThan(Duration.standardDays(1))) {
        getContext()
            .incrementCounter("EPP resources missing pre-(threshold+1d) revision (SEE LOGS)");
      }
    }
  }

  /**
   * Reducer that deletes unreferenced {@link CommitLogManifest} + child {@link CommitLogMutation}.
   *
   * <p>It receives the manifestKey to possibly delete, and a list of boolean 'verdicts' from
   * various sources (the "old manifests" source and the "still referenced" source) on whether it's
   * OK to delete this manifestKey. If even one source returns "false" (meaning "it's not OK to
   * delete this manifest") then it won't be deleted.
   */
  static class DeleteOldCommitLogsReducer
      extends Reducer<Key<CommitLogManifest>, Boolean, Void> {

    private static final long serialVersionUID = -4918760187627937268L;

    private final DateTime deletionThreshold;
    private final boolean isDryRun;

    @AutoValue
    abstract static class DeletionResult {
      enum Status {
        ALREADY_DELETED,
        AFTER_THRESHOLD,
        SUCCESS;
      }

      public abstract Status status();
      public abstract int numDeleted();

      static DeletionResult create(Status status, int numDeleted) {
        return
            new AutoValue_DeleteOldCommitLogsAction_DeleteOldCommitLogsReducer_DeletionResult(
                status, numDeleted);
      }
    }

    DeleteOldCommitLogsReducer(DateTime deletionThreshold, boolean isDryRun) {
      this.deletionThreshold = deletionThreshold;
      this.isDryRun = isDryRun;
    }

    @Override
    public void reduce(
        final Key<CommitLogManifest> manifestKey,
        ReducerInput<Boolean> canDeleteVerdicts) {
      ImmutableMultiset<Boolean> canDeleteMultiset = ImmutableMultiset.copyOf(canDeleteVerdicts);
      if (canDeleteMultiset.count(TRUE) > 1) {
        getContext().incrementCounter("commit log manifests incorrectly mapped multiple times");
      }
      if (canDeleteMultiset.count(FALSE) > 1) {
        getContext().incrementCounter("commit log manifests referenced multiple times");
      }
      if (canDeleteMultiset.contains(FALSE)) {
        getContext().incrementCounter(
            canDeleteMultiset.contains(TRUE)
            ? "old commit log manifests still referenced"
            : "new (or nonexistent) commit log manifests referenced");
        getContext().incrementCounter(
            "EPP resource revisions handled",
            canDeleteMultiset.count(FALSE));
        return;
      }

      DeletionResult deletionResult = ofy().transactNew(() -> {
        CommitLogManifest manifest = ofy().load().key(manifestKey).now();
        // It is possible that the same manifestKey was run twice, if a shard had to be restarted
        // or some weird failure. If this happens, we want to exit immediately.
        // Note that this can never happen in dryRun.
        if (manifest == null) {
          return DeletionResult.create(DeletionResult.Status.ALREADY_DELETED, 0);
        }
        // Doing a sanity check on the date. This is the only place we use the CommitLogManifest,
        // so maybe removing this test will improve performance. However, unless it's proven that
        // the performance boost is significant (and we've tested this enough to be sure it never
        // happens)- the safty of "let's not delete stuff we need from prod" is more important.
        if (manifest.getCommitTime().isAfter(deletionThreshold)) {
          return DeletionResult.create(DeletionResult.Status.AFTER_THRESHOLD, 0);
        }
        Iterable<Key<CommitLogMutation>> commitLogMutationKeys = ofy().load()
            .type(CommitLogMutation.class)
            .ancestor(manifestKey)
            .keys()
            .iterable();
        ImmutableList<Key<?>> keysToDelete = ImmutableList.<Key<?>>builder()
            .addAll(commitLogMutationKeys)
            .add(manifestKey)
            .build();
        // Normally in a dry run we would log the entities that would be deleted, but those can
        // number in the millions so we skip the logging.
        if (!isDryRun) {
          ofy().deleteWithoutBackup().keys(keysToDelete);
        }
        return DeletionResult.create(DeletionResult.Status.SUCCESS, keysToDelete.size());
      });

      switch (deletionResult.status()) {
        case SUCCESS:
          getContext().incrementCounter("old commit log manifests deleted");
          getContext().incrementCounter("total entities deleted", deletionResult.numDeleted());
          break;
        case ALREADY_DELETED:
          getContext().incrementCounter("attempts to delete an already deleted manifest");
          break;
        case AFTER_THRESHOLD:
          logger.atSevere().log(
              "Won't delete CommitLogManifest %s that is too recent.", manifestKey);
          getContext().incrementCounter("manifests incorrectly assigned for deletion (SEE LOGS)");
          break;
      }
    }
  }
}