Easter Egg Timer

EasterEggTimer.java

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

import rx.Observable;
import rx.subjects.PublishSubject;

public class KonamiTimer {
  private final PublishSubject<Integer> input;
  private final int triggerCount;

  public KonamiTimer(int triggerCount) {
    this.triggerCount = triggerCount;
    this.input = PublishSubject.create();
  }

  public void onInput() {
    input.onNext(1);
  }

  /** Emits when unlocked */
  public Observable<Void> completed() {
    return input
        .buffer(5, TimeUnit.SECONDS)
        .map(List::size)
        .filter(x -> x >= triggerCount)
        .map(x -> null);
  }
}