// Copyright 2016 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.model.smd;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.Iterables.isEmpty;
import static google.registry.model.common.EntityGroupRoot.getCrossTldKey;
import static google.registry.model.ofy.ObjectifyService.allocateId;
import static google.registry.model.ofy.ObjectifyService.ofy;
import static google.registry.util.CacheUtils.memoizeWithShortExpiration;
import static google.registry.util.DateTimeUtils.START_OF_TIME;
import static google.registry.util.DateTimeUtils.isBeforeOrAt;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Function;
import com.google.common.base.Supplier;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;
import com.googlecode.objectify.Key;
import com.googlecode.objectify.VoidWork;
import com.googlecode.objectify.Work;
import com.googlecode.objectify.annotation.EmbedMap;
import com.googlecode.objectify.annotation.Entity;
import com.googlecode.objectify.annotation.Id;
import com.googlecode.objectify.annotation.Ignore;
import com.googlecode.objectify.annotation.OnSave;
import com.googlecode.objectify.annotation.Parent;
import google.registry.model.ImmutableObject;
import google.registry.model.annotations.NotBackedUp;
import google.registry.model.annotations.NotBackedUp.Reason;
import google.registry.model.common.EntityGroupRoot;
import google.registry.util.CollectionUtils;
import java.util.Map;
import org.joda.time.DateTime;

/**
 * Signed Mark Data Revocation List (SMDRL).
 *
 * <p>Represents a SMDRL file downloaded from the TMCH MarksDB each day. The list holds the ids of
 * all the {@link SignedMark SignedMarks} that have been revoked. A new list is created for each new
 * file that's created, depending on the timestamp.
 *
 * <p>We'll be putting the entire table into a single entity for the sake of performance. But in
 * order to avoid exceeding the one megabyte max entity size limit, we'll also be sharding that
 * entity into multiple entities, each entity containing {@value #SHARD_SIZE} rows.
 *
 * @see google.registry.tmch.SmdrlCsvParser
 * @see "http://tools.ietf.org/html/draft-lozano-tmch-func-spec-08#section-6.2"
 */
@Entity
@NotBackedUp(reason = Reason.EXTERNALLY_SOURCED)
public class SignedMarkRevocationList extends ImmutableObject {

  @VisibleForTesting
  static final int SHARD_SIZE = 10000;

  /** Common ancestor for queries. */
  @Parent
  Key<EntityGroupRoot> parent = getCrossTldKey();

  /** ID for the sharded entity. */
  @Id
  long id;

  /** Time when this list was last updated, as specified in the first line of the CSV file. */
  DateTime creationTime;

  /** A map from SMD IDs to revocation time. */
  @EmbedMap
  Map</*@MatchesPattern("[0-9]+-[0-9]+")*/ String, DateTime> revokes;

  /** Indicates that this is a shard rather than a "full" list. */
  @Ignore
  boolean isShard;

  /**
   * A cached supplier that fetches the SMDRL shards from the datastore and recombines them into a
   * single {@link SignedMarkRevocationList} object.
   */
  private static final Supplier<SignedMarkRevocationList> CACHE =
      memoizeWithShortExpiration(new Supplier<SignedMarkRevocationList>() {
        @Override
        public SignedMarkRevocationList get() {
          // Open a new transactional read even if we are in a transaction currently.
          return ofy().transactNewReadOnly(new Work<SignedMarkRevocationList>() {
            @Override
            public SignedMarkRevocationList run() {
              Iterable<SignedMarkRevocationList> shards = ofy()
                  .load()
                  .type(SignedMarkRevocationList.class)
                  .ancestor(getCrossTldKey());
              DateTime creationTime =
                  isEmpty(shards)
                      ? START_OF_TIME
                      : checkNotNull(Iterables.get(shards, 0).creationTime, "creationTime");
              ImmutableMap.Builder<String, DateTime> revokes = new ImmutableMap.Builder<>();
              for (SignedMarkRevocationList shard : shards) {
                revokes.putAll(shard.revokes);
                checkState(
                    creationTime.equals(shard.creationTime),
                    "Inconsistent creation times: %s vs. %s", creationTime, shard.creationTime);
              }
              return create(creationTime, revokes.build());
            }});
        }});

  /** Return a single logical instance that combines all the datastore shards. */
  public static SignedMarkRevocationList get() {
    return CACHE.get();
  }

  /** Create a new {@link SignedMarkRevocationList} without saving it. */
  public static SignedMarkRevocationList create(
      DateTime creationTime, ImmutableMap<String, DateTime> revokes) {
    SignedMarkRevocationList instance = new SignedMarkRevocationList();
    instance.creationTime = checkNotNull(creationTime, "creationTime");
    instance.revokes = checkNotNull(revokes, "revokes");
    return instance;
  }

  /** Returns {@code true} if the SMD ID has been revoked at the given point in time. */
  public boolean isSmdRevoked(String smdId, DateTime now) {
    DateTime revoked = revokes.get(checkNotNull(smdId, "smdId"));
    if (revoked == null) {
      return false;
    }
    return isBeforeOrAt(revoked, now);
  }

  /** Returns the creation timestamp specified at the top of the SMDRL CSV file. */
  public DateTime getCreationTime() {
    return creationTime;
  }

  /** Returns the number of revocations. */
  public int size() {
    return revokes.size();
  }

  /** Save this list to the datastore in sharded form. Returns {@code this}. */
  public SignedMarkRevocationList save() {
    ofy().transact(new VoidWork() {
      @Override
      public void vrun() {
        ofy().deleteWithoutBackup().keys(ofy()
            .load()
            .type(SignedMarkRevocationList.class)
            .ancestor(getCrossTldKey())
            .keys());
        ofy().saveWithoutBackup().entities(FluentIterable
            .from(CollectionUtils.partitionMap(revokes, SHARD_SIZE))
            .transform(new Function<ImmutableMap<String, DateTime>, SignedMarkRevocationList>() {
              @Override
              public SignedMarkRevocationList apply(ImmutableMap<String, DateTime> shardRevokes) {
                SignedMarkRevocationList shard = create(creationTime, shardRevokes);
                shard.id = allocateId();
                shard.isShard = true;  // Avoid the exception in disallowUnshardedSaves().
                return shard;
              }}));
      }});
    return this;
  }

  /** As a safety mechanism, fail if someone tries to save this class directly. */
  @OnSave
  void disallowUnshardedSaves() {
    if (!isShard) {
      throw new UnshardedSaveException();
    }
  }

  /** Exception when trying to directly save a {@link SignedMarkRevocationList} without sharding. */
  public static class UnshardedSaveException extends RuntimeException {}
}