import com.google.auto.value.AutoValue;
import io.vavr.collection.List;

import static io.vavr.API.*;
import static io.vavr.Predicates.instanceOf;

interface Recommendation {

    String id();
}

@AutoValue
abstract class EventRecommendation implements Recommendation {

    public abstract String id();

    public abstract int numberOfEpisodeTitles();

    public static EventRecommendation create(String id, int numberOfEpisodeTitles) {
        return new AutoValue_EventRecommendation(id, numberOfEpisodeTitles);
    }

}

@AutoValue
abstract class ContentRecommendation implements Recommendation {

    public abstract String id();

    public static ContentRecommendation create(String id) {
        return new AutoValue_ContentRecommendation(id);
    }
}

public final class Test {

    public static void main(String[] args) {
        List<Recommendation> recommendations = List.of(
                EventRecommendation.create("event-111", 2),
                EventRecommendation.create("event-222", 3),
                EventRecommendation.create("event-333", 1),
                ContentRecommendation.create("content-111"),
                ContentRecommendation.create("content-222"),
                ContentRecommendation.create("content-333"));
        int sum = recommendations.toStream()
                .map(recommendation -> Match(recommendation).of(
                        Case($(instanceOf(EventRecommendation.class)), EventRecommendation::numberOfEpisodeTitles),
                        Case($(), 0)))
                .sum()
                .intValue();
        System.out.println(sum); // should be 6
    }
}