event-sourcing/event-store-cassandra/src/main/scala/org/apache/james/eventsourcing/eventstore/cassandra/CassandraEventStore.scala

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package org.apache.james.eventsourcing.eventstore.cassandra

import com.google.common.base.Preconditions
import javax.inject.Inject
import org.apache.james.eventsourcing.eventstore.{EventStore, EventStoreFailedException, History}
import org.apache.james.eventsourcing.{AggregateId, Event, EventId}
import org.reactivestreams.Publisher
import reactor.core.scala.publisher.SMono

class CassandraEventStore @Inject() (eventStoreDao: EventStoreDao) extends EventStore {
  override def appendAll(events: Iterable[Event]): Publisher[Void] =
    if (events.nonEmpty) {
      doAppendAll(events)
    } else {
      SMono.empty
    }

  private def doAppendAll(events: Iterable[Event]): SMono[Void] = {
    Preconditions.checkArgument(Event.belongsToSameAggregate(events))
    val snapshotId = events.filter(_.isASnapshot).map(_.eventId).headOption
    eventStoreDao.appendAll(events, snapshotId)
      .filter(success => success)
      .single()
      .onErrorMap({
        case _: NoSuchElementException => EventStoreFailedException("Concurrent update to the EventStore detected")
        case e => e
      })
      .`then`(SMono.empty)
  }

  override def getEventsOfAggregate(aggregateId: AggregateId): SMono[History] =
    eventStoreDao.getSnapshot(aggregateId)
      .flatMap(snapshotId => eventStoreDao.getEventsOfAggregate(aggregateId, snapshotId))
      .switchIfEmpty(eventStoreDao.getEventsOfAggregate(aggregateId))

  override def remove(aggregateId: AggregateId): Publisher[Void] = eventStoreDao.delete(aggregateId)
}