RiddleCarousel.java

package com.vanniktech.rxriddles.operators.withscheduler;

import java.time.Duration;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;

import io.reactivex.rxjava3.core.Completable;
import io.reactivex.rxjava3.core.Flowable;
import io.reactivex.rxjava3.core.Observable;
import io.reactivex.rxjava3.core.Scheduler;
import io.reactivex.rxjava3.core.Single;

public class RiddleCarousel {
	/**
	 * After each fetchInterval, fetch the current acquirer List.
	 * From the fetched acquirer List, emit the next item after carouselInterval.
	 * Repeat the same acquirer List, until the next time the acquirerList is fetched.
	 * Then use the new acquirer List.
	 * <p>
	 * Use Case: You want to show the available acquirers from an external resource and show each of them for carouselInterval in the UI.
	 */
	public static Observable<String> solve(Callable<List<String>> acquirerCallable, Duration fetchInterval, Duration carouselInterval, Scheduler scheduler) {
		Flowable<Long> carouselIntervalFlowable = Flowable.interval(carouselInterval.toMillis(), TimeUnit.MILLISECONDS, scheduler)
														  .startWithItem(1L)
														  .publish()
														  .autoConnect();
		return Single.fromCallable(acquirerCallable)
					 .subscribeOn(scheduler)
					 .repeatWhen(objectFlowable -> objectFlowable.delay(fetchInterval.toMillis(), TimeUnit.MILLISECONDS, scheduler))
					 .flatMap(strings -> Flowable.zip(Flowable.fromIterable(strings).take(strings.size()), carouselIntervalFlowable, (s, aLong) -> s)
												 .repeat()
												 .takeUntil(Completable.complete()
																	   .delay(fetchInterval.toMillis(), TimeUnit.MILLISECONDS, scheduler)
																	   .toFlowable()))
					 .toObservable();
	}
}