/*
 * Copyright (c) MuleSoft, Inc.  All rights reserved.  http://www.mulesoft.com
 * The software in this package is published under the terms of the CPAL v1.0
 * license, a copy of which has been included with this distribution in the
 * LICENSE.txt file.
 */
package org.mule.runtime.core.processor;

import static java.util.Collections.singletonList;
import static org.mule.runtime.core.api.context.notification.EnrichedNotificationInfo.createInfo;
import static org.mule.runtime.core.api.processor.MessageProcessors.processToApply;
import static org.mule.runtime.core.api.rx.Exceptions.UNEXPECTED_EXCEPTION_PREDICATE;
import static org.mule.runtime.core.api.rx.Exceptions.checkedConsumer;
import static org.mule.runtime.core.config.i18n.CoreMessages.asyncDoesNotSupportTransactions;
import static org.mule.runtime.core.config.i18n.CoreMessages.objectIsNull;
import static org.mule.runtime.core.context.notification.AsyncMessageNotification.PROCESS_ASYNC_COMPLETE;
import static org.mule.runtime.core.context.notification.AsyncMessageNotification.PROCESS_ASYNC_SCHEDULED;
import static org.mule.runtime.core.transaction.TransactionCoordination.isTransactionActive;
import static reactor.core.publisher.Flux.from;
import static reactor.core.publisher.Flux.just;
import static reactor.core.scheduler.Schedulers.fromExecutorService;

import org.mule.runtime.api.exception.MuleException;
import org.mule.runtime.api.lifecycle.Initialisable;
import org.mule.runtime.api.lifecycle.InitialisationException;
import org.mule.runtime.api.lifecycle.Startable;
import org.mule.runtime.api.lifecycle.Stoppable;
import org.mule.runtime.api.scheduler.Scheduler;
import org.mule.runtime.core.DefaultEventContext;
import org.mule.runtime.core.api.Event;
import org.mule.runtime.core.api.construct.FlowConstruct;
import org.mule.runtime.core.api.exception.MessagingExceptionHandler;
import org.mule.runtime.core.api.exception.MessagingExceptionHandlerAware;
import org.mule.runtime.core.api.processor.MessageProcessorChain;
import org.mule.runtime.core.api.processor.Processor;
import org.mule.runtime.core.api.processor.strategy.ProcessingStrategy;
import org.mule.runtime.core.api.routing.RoutingException;
import org.mule.runtime.core.api.scheduler.SchedulerService;
import org.mule.runtime.core.context.notification.AsyncMessageNotification;
import org.mule.runtime.core.exception.MessagingException;
import org.mule.runtime.core.session.DefaultMuleSession;

import java.util.List;
import java.util.function.Consumer;

import javax.inject.Inject;

import org.reactivestreams.Publisher;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Processes {@link Event}'s asynchronously using a {@link ProcessingStrategy} to schedule asynchronous processing of
 * MessageProcessor delegate configured the next {@link Processor}. The next {@link Processor} is therefore be executed in a
 * different thread regardless of the exchange-pattern configured on the inbound endpoint. If a transaction is present then an
 * exception is thrown.
 */
public class AsyncDelegateMessageProcessor extends AbstractMessageProcessorOwner
    implements Processor, Initialisable, Startable, Stoppable, MessagingExceptionHandlerAware {

  @Inject
  private SchedulerService schedulerService;

  protected Logger logger = LoggerFactory.getLogger(getClass());

  protected MessageProcessorChain delegate;

  private Scheduler scheduler;
  protected String name;
  private MessagingExceptionHandler messagingExceptionHandler;

  public AsyncDelegateMessageProcessor(MessageProcessorChain delegate) {
    this.delegate = delegate;
  }

  public AsyncDelegateMessageProcessor(MessageProcessorChain delegate, String name) {
    this.delegate = delegate;
    this.name = name;
  }

  @Override
  public void initialise() throws InitialisationException {
    if (delegate == null) {
      throw new InitialisationException(objectIsNull("delegate message processor"), this);
    }
    super.initialise();
  }

  @Override
  public void start() throws MuleException {
    scheduler = schedulerService.cpuLightScheduler(muleContext.getSchedulerBaseConfig().withName(name));
    super.start();
  }

  @Override
  public void stop() throws MuleException {
    scheduler.stop();
    scheduler = null;
    super.stop();
  }

  @Override
  public Event process(Event event) throws MuleException {
    return processToApply(event, this);
  }

  private void assertNotTransactional(Event event) throws RoutingException {
    if (isTransactionActive()) {
      throw new RoutingException(asyncDoesNotSupportTransactions(), delegate);
    }
  }

  @Override
  public Publisher<Event> apply(Publisher<Event> publisher) {
    return from(publisher)
        .doOnNext(checkedConsumer(event -> assertNotTransactional(event)))
        .doOnNext(request -> just(request)
            .map(event -> asyncEvent(request))
            .transform(innerPublisher -> from(innerPublisher)
                .doOnNext(fireAsyncScheduledNotification(flowConstruct))
                .doOnNext(asyncRequest -> just(asyncRequest)
                    .publishOn(fromExecutorService(scheduler))
                    .transform(delegate)
                    .doOnNext(event -> fireAsyncCompleteNotification(event, flowConstruct, null))
                    .doOnError(MessagingException.class, e -> fireAsyncCompleteNotification(e.getEvent(), flowConstruct, e))
                    .onErrorResume(MessagingException.class, messagingExceptionHandler)
                    .doOnError(UNEXPECTED_EXCEPTION_PREDICATE,
                               exception -> logger.error("Unhandled exception in async processing.",
                                                         exception))
                    // Even though no response is ever used with this processor, complete the EventContext anyway, so
                    // parent context completes when async processing is complete.
                    .doOnNext(event -> asyncRequest.getContext().success(event))
                    .doOnError(throwable -> asyncRequest.getContext().error(throwable))
                    .subscribe()))
            .onErrorResume(MessagingException.class, messagingExceptionHandler)
            .doOnError(UNEXPECTED_EXCEPTION_PREDICATE,
                       exception -> logger.error("Unhandled exception in async processing.", exception))
            .subscribe());
  }

  private Event asyncEvent(Event event) {
    // Clone event, make it async and remove ReplyToHandler
    return Event.builder(DefaultEventContext.child(event.getContext()), event)
        .replyToHandler(null)
        .session(new DefaultMuleSession(event.getSession())).build();
  }

  private Consumer<Event> fireAsyncScheduledNotification(FlowConstruct flowConstruct) {
    return event -> muleContext.getNotificationManager()
        .fireNotification(new AsyncMessageNotification(createInfo(event, null, this), flowConstruct,
                                                       PROCESS_ASYNC_SCHEDULED));
  }

  private void fireAsyncCompleteNotification(Event event, FlowConstruct flowConstruct, MessagingException exception) {
    muleContext.getNotificationManager()
        .fireNotification(new AsyncMessageNotification(createInfo(event, exception, this), flowConstruct,
                                                       PROCESS_ASYNC_COMPLETE));
  }

  @Override
  protected List<Processor> getOwnedMessageProcessors() {
    return singletonList(delegate);
  }

  @Override
  public void setMessagingExceptionHandler(MessagingExceptionHandler messagingExceptionHandler) {
    this.messagingExceptionHandler = messagingExceptionHandler;
    delegate.setMessagingExceptionHandler(messagingExceptionHandler);
  }
}