event-sourcing/event-sourcing-core/src/main/scala/org/apache/james/eventsourcing/EventBus.scala

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package org.apache.james.eventsourcing

import javax.inject.Inject
import org.apache.james.eventsourcing.eventstore.{EventStore, EventStoreFailedException}
import org.reactivestreams.Publisher
import org.slf4j.LoggerFactory
import reactor.core.scala.publisher.{SFlux, SMono}

object EventBus {
  private val LOGGER = LoggerFactory.getLogger(classOf[EventBus])
}

class EventBus @Inject() (eventStore: EventStore, subscribers: Set[Subscriber]) {
  @throws[EventStoreFailedException]
  def publish(events: Iterable[Event]): SMono[Void] =
    SMono(eventStore.appendAll(events))
        .`then`(runHandlers(events, subscribers))

  def runHandlers(events: Iterable[Event], subscribers: Set[Subscriber]): SMono[Void] =
    SFlux.fromIterable(events.flatMap((event: Event) => subscribers.map(subscriber => (event, subscriber))))
      .concatMap(infos => runHandler(infos._1, infos._2))
      .`then`()
      .`then`(SMono.empty)

  def runHandler(event: Event, subscriber: Subscriber): Publisher[Void] =
    SMono(ReactiveSubscriber.asReactiveSubscriber(subscriber).handleReactive(event))
      .onErrorResume(e => {
        EventBus.LOGGER.error("Error while calling {} for {}", subscriber, event, e)
        SMono.empty
      })
}