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package org.glassfish.jersey.examples.rx.agent;

import java.util.Collections;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.container.AsyncResponse;
import javax.ws.rs.container.Suspended;
import javax.ws.rs.core.GenericType;

import javax.inject.Singleton;

import org.glassfish.jersey.client.rx.RxWebTarget;
import org.glassfish.jersey.client.rx.rxjava.RxObservable;
import org.glassfish.jersey.client.rx.rxjava.RxObservableInvoker;
import org.glassfish.jersey.examples.rx.domain.AgentResponse;
import org.glassfish.jersey.examples.rx.domain.Calculation;
import org.glassfish.jersey.examples.rx.domain.Destination;
import org.glassfish.jersey.examples.rx.domain.Forecast;
import org.glassfish.jersey.examples.rx.domain.Recommendation;
import org.glassfish.jersey.server.Uri;

import rx.Observable;
import rx.schedulers.Schedulers;

/**
 * Obtain information about visited (destination) and recommended (destination, forecast, price) places for "RxJava" user. Uses
 * RxJava Observable and Jersey Client to obtain the data.
 *
 * @author Michal Gajdos (michal.gajdos at oracle.com)
 */
@Singleton
@Path("agent/observable")
@Produces("application/json")
public class ObservableAgentResource {

    @Uri("remote/destination")
    private WebTarget destination;

    @Uri("remote/calculation/from/{from}/to/{to}")
    private WebTarget calculation;

    @Uri("remote/forecast/{destination}")
    private WebTarget forecast;

    @GET
    public void observable(@Suspended final AsyncResponse async) {
        final long time = System.nanoTime();
        final Queue<String> errors = new ConcurrentLinkedQueue<>();

        Observable.just(new AgentResponse())
                // Obtain visited destinations.
                .zipWith(visited(errors), (response, visited) -> {
                    response.setVisited(visited);
                    return response;
                })
                // Obtain recommended destinations. (does not depend on visited ones)
                .zipWith(recommended(errors), (response, recommendations) -> {
                    response.setRecommended(recommendations);
                    return response;
                })
                // Observe on another thread than the one processing visited or recommended destinations.
                .observeOn(Schedulers.io())
                // Subscribe.
                .subscribe(response -> {
                    // Do something with errors.

                    response.setProcessingTime((System.nanoTime() - time) / 1000000);
                    async.resume(response);
                }, async::resume);
    }

    private Observable<List<Destination>> visited(final Queue<String> errors) {
        return RxObservable.from(destination).path("visited").request()
                // Identify the user.
                .header("Rx-User", "RxJava")
                // Reactive invoker.
                .rx()
                // Return a list of destinations.
                .get(new GenericType<List<Destination>>() {})
                // Handle Errors.
                .onErrorReturn(throwable -> {
                    errors.offer("Visited: " + throwable.getMessage());
                    return Collections.emptyList();
                });
    }

    private Observable<List<Recommendation>> recommended(final Queue<String> errors) {
        // Recommended places.
        final Observable<Destination> recommended = RxObservable.from(destination).path("recommended").request()
                // Identify the user.
                .header("Rx-User", "RxJava")
                // Reactive invoker.
                .rx()
                // Return a list of destinations.
                .get(new GenericType<List<Destination>>() {})
                // Handle Errors.
                .onErrorReturn(throwable -> {
                    errors.offer("Recommended: " + throwable.getMessage());
                    return Collections.emptyList();
                })
                // Emit destinations one-by-one.
                .flatMap(Observable::from)
                // Remember emitted items for dependant requests.
                .cache();

        // Forecasts. (depend on recommended destinations)
        final RxWebTarget<RxObservableInvoker> rxForecast = RxObservable.from(forecast);
        final Observable<Forecast> forecasts = recommended.flatMap(destination ->
                rxForecast
                        .resolveTemplate("destination", destination.getDestination()).request().rx().get(Forecast.class)
                        .onErrorReturn(throwable -> {
                            errors.offer("Forecast: " + throwable.getMessage());
                            return new Forecast(destination.getDestination(), "N/A");
                        }));

        // Calculations. (depend on recommended destinations)
        final RxWebTarget<RxObservableInvoker> rxCalculation = RxObservable.from(calculation);
        final Observable<Calculation> calculations = recommended.flatMap(destination ->
                rxCalculation.resolveTemplate("from", "Moon").resolveTemplate("to", destination.getDestination())
                        .request().rx().get(Calculation.class)
                        .onErrorReturn(throwable -> {
                            errors.offer("Calculation: " + throwable.getMessage());
                            return new Calculation("Moon", destination.getDestination(), -1);
                        }));

        return Observable.zip(recommended, forecasts, calculations, Recommendation::new).toList();
    }
}
