package org.gcube.smartgears.handlers.application.lifecycle;

import static org.gcube.common.events.Observes.Kind.resilient;
import static org.gcube.smartgears.Constants.profile_management;
import static org.gcube.smartgears.handlers.ProfileEvents.addToContext;
import static org.gcube.smartgears.handlers.ProfileEvents.changed;
import static org.gcube.smartgears.handlers.ProfileEvents.removeFromContext;
import static org.gcube.smartgears.lifecycle.application.ApplicationLifecycle.activation;
import static org.gcube.smartgears.lifecycle.application.ApplicationLifecycle.failure;
import static org.gcube.smartgears.lifecycle.application.ApplicationLifecycle.stop;

import java.util.Collections;
import java.util.List;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

import org.gcube.common.events.Observes;
import org.gcube.common.events.Observes.Kind;
import org.gcube.smartgears.Constants;
import org.gcube.smartgears.configuration.Mode;
import org.gcube.smartgears.context.Property;
import org.gcube.smartgears.context.application.ApplicationContext;
import org.gcube.smartgears.handlers.application.ApplicationLifecycleEvent;
import org.gcube.smartgears.handlers.application.ApplicationLifecycleHandler;
import org.gcube.smartgears.lifecycle.application.ApplicationLifecycle;
import org.gcube.smartgears.lifecycle.application.ApplicationState;
import org.gcube.smartgears.lifecycle.container.ContainerLifecycle;
import org.gcube.smartgears.provider.ProviderFactory;
import org.gcube.smartgears.publishing.Publisher;
import org.gcube.smartgears.utils.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 
 * Manages the resource profile of the application.
 * <p>
 * 
 * The manager:
 * 
 * <ul>
 * <li>creates the profile when the application starts for the first time;
 * <li>loads the profile when the application restarts;
 * <li>publishes the profile when the application becomes active, and at any
 * lifecycle change thereafter;
 * <li>stores the profile locally after each publication;
 * </ul>
 * 
 * @author Fabio Simeoni
 */
public class ApplicationProfileManager extends ApplicationLifecycleHandler {

	Logger log = LoggerFactory.getLogger(ApplicationProfileManager.class);

	private ApplicationContext context;
	private ScheduledFuture<?> periodicUpdates;
	private static final String PUBLISHED_PROP = "published";
	private List<Publisher> publishers = ProviderFactory.provider().publishers();


	@Override
	public void onStart(ApplicationLifecycleEvent.Start e) {

		context = e.context();

		activated();

		// note we don't fire profile events, but wait for the final startup
		// outcome which
		// will result in a state change. only then we publish and store the
		// profile
		// this avoids the redundancy and performance penalty of storing and
		// publishing multiple
		// times in rapid succession (which would be correct). Revise if proves
		// problematic in corner
		// cases.

	}


	private void activated(){

		publishers = context.container().configuration().mode()!=Mode.offline? 
				ProviderFactory.provider().publishers():
					Collections.emptyList();
		
		registerObservers();
		schedulePeriodicUpdates();
	}

	// helpers
	private void registerObservers() {

		context.events().subscribe(new Object() {

			@Observes({ activation, stop, failure })
			void onChanged(ApplicationLifecycle lc) {

				log.debug("moving app {} to {}",context.name(), lc.state().remoteForm());

				// since we do not know the observers, they will deal with
				// failures and their consequences
				// any that comes back will be logged in this event thread
				context.events().fire(context, changed);
			}

			/*
			@Observes(value = published)
			void shareAfterPublish(GCoreEndpoint profile) {

				share(profile); // publish may produce a new profile instance

			}*/

			@Observes(value = changed, kind = Kind.safe)
			void publishAfterChange(ApplicationContext context) {


				//if we've failed before first publication do not try to publish
				//(we may well have failed there)
				if (!context.properties().contains(PUBLISHED_PROP)) {
					log.info("publishing application for the first time");
					context.properties().add(new Property(PUBLISHED_PROP, true));
					if (context.lifecycle().state() != ApplicationState.failed) {
						publishers.forEach(p -> { 
							try {
								p.create(context, 
										context.container().authorizationProvider().getContexts());
							}catch (Exception e) {
								log.error("cannot publish {} for first time with publisher type {} (see details)",context.name(), p.getClass().getCanonicalName(), e);
							}
						});
					}
				}
				else 
					publishers.forEach(p -> { 
						try {
							p.update(context);
						}catch (Exception e) {
							log.error("cannot publish {} with publisher type {} (see details)",context.name(), p.getClass().getCanonicalName(), e);
						}
					});

			}
		});

		//registering ContextObserver in container HUB
		context.container().events().subscribe(new Object() {

			@Observes(value = addToContext)
			void addTo(String scope) {
				log.info("add_to_context event arrived in app {}", context.name());
				for (Publisher publisher: publishers)
					try {
						log.debug("publishing application in context {}", scope);
						publisher.create(context, 
								Collections.singleton(scope));

					}catch (Exception e) {

						log.error("cannot add context {} with publisher type {} (see details)",scope, publisher.getClass().getCanonicalName(), e);

						// since we've failed no published event is fired and profile
						// will not be stored.
						// we do it manually to ensure we leave some local trace of the
						// changed profile.
						//TODO: CHECK --- store(profile);
					}

			}

			@Observes(value = removeFromContext)
			void removeFrom(String scope) {
				log.info("remove_from_context event arrived in app {}", context.name());
				for (Publisher publisher: publishers)
					try {
						log.debug("unpublishing application from scope {}", scope);
						publisher.remove(context, 
								Collections.singleton(scope));
					}catch (Exception e) {

						log.error("cannot remove scope {} with publisher type {} (see details)",scope, publisher.getClass().getCanonicalName(), e);

						// since we've failed no published event is fired and profile
						// will not be stored.
						// we do it manually to ensure we leave some local trace of the
						// changed profile.
						//TODO: CHECK --- store(profile);
					}

			}
		});

	}

	private void schedulePeriodicUpdates() {

		// register to cancel updates
		context.events().subscribe(

				new Object() {

					// we register it in response to lifecycle events so that we can stop and resume along with application
					@Observes(value = { activation }, kind = resilient)
					synchronized void restartPeriodicUpdates(ApplicationLifecycle lc) {

						//already running
						if (periodicUpdates!=null)
							return;

						if (lc.state()==ApplicationState.active)
							log.info("scheduling periodic updates of application {} profile", context.name());

						else
							log.info("resuming periodic updates of application {} profile", context.name());

						final Runnable updateTask = new Runnable() {
							public void run() {
								//if handling of event generates failures these will be reported
								//for resilience we do not fail the application
								log.trace("firing change event on application {} ", context.name());
								context.events().fire(context,changed);
							}
						};

						periodicUpdates = Utils.scheduledServicePool.scheduleAtFixedRate(updateTask, 
								Constants.application_republish_frequency_in_minutes, 
								Constants.application_republish_frequency_in_minutes , TimeUnit.MINUTES);

					}

					@Observes(value = { stop, failure }, kind = resilient)
					synchronized void cancelPeriodicUpdates(ContainerLifecycle ignore) {

						if (periodicUpdates != null){
							log.trace("stopping periodic updates of application {} profile", context.name());

							try {
								periodicUpdates.cancel(true);
								periodicUpdates=null;
							}
							catch(Exception e) {
								log.warn("could not stop periodic updates of application {}", context.name(),e);
							}
						}
					}

				});

	}


	@Override
	public String toString() {
		return profile_management;
	}

}