// Copyright 2016 Google Inc. 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 com.google.domain.registry.model;

import com.google.domain.registry.model.EppResource.SharedFields;

import javax.xml.bind.annotation.XmlTransient;

/**
 * Base class for entities that are the root of a Registry 2.0 entity group that gets enrolled in
 * commit logs for backup purposes.
 *
 * <p>The commit log system needs to preserve the ordering of closely timed mutations to entities
 * in a single entity group. We require an {@link UpdateAutoTimestamp} field on the root of a group
 * so that we can enforce strictly increasing timestamps.
 */
public abstract class BackupGroupRoot extends ImmutableObject {
  /**
   * An automatically managed timestamp of when this object was last written to datastore.
   *
   * <p>Note that this is distinct from the EPP-specified {@link SharedFields#lastUpdateTime} on
   * {@link EppResource} objects, in that it is updated on every save, rather than just in response
   * to an {@code <update>} command.
   */
  @XmlTransient
  UpdateAutoTimestamp updateTimestamp = UpdateAutoTimestamp.create(null);

  /** Get the {@link UpdateAutoTimestamp} for this entity. */
  public final UpdateAutoTimestamp getUpdateAutoTimestamp() {
    return updateTimestamp;
  }
}