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/*
 * Copyright 2021 Google LLC
 *
 * 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
 *
 *     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.google.appengine.api.datastore;

import java.util.ConcurrentModificationException;
import java.util.concurrent.Future;

/**
 * Describes a logical unit of work to be performed against the datastore. Operations performed as
 * part of a single {@link Transaction} succeed or fail as a unit. Transactions can be committed and
 * rolled back synchronously and asynchronously.
 *
 */
public interface Transaction {

  /**
   * Commits the transaction. Whether this call succeeds or fails, all subsequent method invocations
   * on this object will throw {@link IllegalStateException}.
   *
   * @throws IllegalStateException If the transaction has already been committed, rolled back, a
   *     commit or a rollback is in progress (via an async call), or an attempt to commit or roll
   *     back has already failed. If there are any outstanding async datastore calls when this
   *     method is invoked, this method will block on the completion of those calls before
   *     proceeding. If any of those outstanding calls fails, the exception from the first failing
   *     call will be thrown.
   * @throws DatastoreFailureException If a datastore error occurs.
   * @throws ConcurrentModificationException If some other transaction modified the same entity
   *     groups concurrently.
   */
  void commit();

  /**
   * An asynchronous implementation of {@link #commit()}.
   *
   * @see #commit()
   * @return A Future associated with the call.
   */
  Future commitAsync();

  /**
   * Rolls back the transaction. Whether this call succeeds or fails, all subsequent method
   * invocations on this object will throw {@link IllegalStateException}.
   *
   * @throws IllegalStateException If the transaction has already been committed, rolled back, a
   *     commit or a rollback is in progress (via an async call), or an attempt to commit or roll
   *     back has already failed. If there are any outstanding async datastore calls when this
   *     method is invoked, this method will block on the completion of those calls before
   *     proceeding.
   * @throws DatastoreFailureException If a datastore error occurs.
   */
  void rollback();

  /**
   * An asynchronous implementation of {@link #rollback()}.
   *
   * @see #rollback()
   * @return A Future associated with the call.
   */
  Future rollbackAsync();

  /** @return The globally unique identifier for the {@code Transaction}. */
  String getId();

  /** @return The application id for the {@code Transaction}. */
  String getApp();

  /** @return {@code true} if the transaction is active, {@code false} otherwise. */
  boolean isActive();
}