/*
 * Copyright (C) 2009-2021 Lightbend Inc. <https://www.lightbend.com>
 */

package akka.persistence.journal.japi;

import java.util.Optional;

import scala.concurrent.Future;

import akka.persistence.*;

interface AsyncWritePlugin {
  // #async-write-plugin-api
  /**
   * Java API, Plugin API: asynchronously writes a batch (`Iterable`) of persistent messages to the
   * journal.
   *
   * <p>The batch is only for performance reasons, i.e. all messages don't have to be written
   * atomically. Higher throughput can typically be achieved by using batch inserts of many records
   * compared to inserting records one-by-one, but this aspect depends on the underlying data store
   * and a journal implementation can implement it as efficient as possible. Journals should aim to
   * persist events in-order for a given `persistenceId` as otherwise in case of a failure, the
   * persistent state may be end up being inconsistent.
   *
   * <p>Each `AtomicWrite` message contains the single `PersistentRepr` that corresponds to the
   * event that was passed to the `persist` method of the `PersistentActor`, or it contains several
   * `PersistentRepr` that corresponds to the events that were passed to the `persistAll` method of
   * the `PersistentActor`. All `PersistentRepr` of the `AtomicWrite` must be written to the data
   * store atomically, i.e. all or none must be stored. If the journal (data store) cannot support
   * atomic writes of multiple events it should reject such writes with an `Optional` with an
   * `UnsupportedOperationException` describing the issue. This limitation should also be documented
   * by the journal plugin.
   *
   * <p>If there are failures when storing any of the messages in the batch the returned `Future`
   * must be completed with failure. The `Future` must only be completed with success when all
   * messages in the batch have been confirmed to be stored successfully, i.e. they will be
   * readable, and visible, in a subsequent replay. If there is uncertainty about if the messages
   * were stored or not the `Future` must be completed with failure.
   *
   * <p>Data store connection problems must be signaled by completing the `Future` with failure.
   *
   * <p>The journal can also signal that it rejects individual messages (`AtomicWrite`) by the
   * returned `Iterable&lt;Optional&lt;Exception&gt;&gt;`. The returned `Iterable` must have as many
   * elements as the input `messages` `Iterable`. Each `Optional` element signals if the
   * corresponding `AtomicWrite` is rejected or not, with an exception describing the problem.
   * Rejecting a message means it was not stored, i.e. it must not be included in a later replay.
   * Rejecting a message is typically done before attempting to store it, e.g. because of
   * serialization error.
   *
   * <p>Data store connection problems must not be signaled as rejections.
   *
   * <p>Note that it is possible to reduce number of allocations by caching some result `Iterable`
   * for the happy path, i.e. when no messages are rejected.
   *
   * <p>Calls to this method are serialized by the enclosing journal actor. If you spawn work in
   * asynchronous tasks it is alright that they complete the futures in any order, but the actual
   * writes for a specific persistenceId should be serialized to avoid issues such as events of a
   * later write are visible to consumers (query side, or replay) before the events of an earlier
   * write are visible. This can also be done with consistent hashing if it is too fine grained to
   * do it on the persistenceId level. Normally a `PersistentActor` will only have one outstanding
   * write request to the journal but it may emit several write requests when `persistAsync` is used
   * and the max batch size is reached.
   *
   * <p>This call is protected with a circuit-breaker.
   */
  Future<Iterable<Optional<Exception>>> doAsyncWriteMessages(Iterable<AtomicWrite> messages);

  /**
   * Java API, Plugin API: synchronously deletes all persistent messages up to `toSequenceNr`.
   *
   * <p>This call is protected with a circuit-breaker.
   *
   * @see AsyncRecoveryPlugin
   */
  Future<Void> doAsyncDeleteMessagesTo(String persistenceId, long toSequenceNr);
  // #async-write-plugin-api
}
