package com.github.davidmoten.rx2;
   
   import com.github.davidmoten.guavamini.Optional;
   import com.github.davidmoten.rx2.flowable.CachedFlowable;
   import com.github.davidmoten.rx2.observable.CachedObservable;
   import com.github.davidmoten.rx2.observable.CloseableObservableWithReset;
   import io.reactivex.Flowable;
   import io.reactivex.Observable;
   import io.reactivex.Scheduler;
  import io.reactivex.disposables.Disposable;
  import io.reactivex.functions.Consumer;
  
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicReference;
  
  public final class Observables {
  
  
      private Observables() {
          // prevent instantiation
      }
  
      /**
       * Returns a cached {@link Flowable} like {@link Flowable#cache()}
       * except that the cache can be reset by calling
       * {@link CachedFlowable#reset()}.
       *
       * @param source
       *            the observable to be cached.
       * @param <T>
       *            the generic type of the source
       * @return a cached observable whose cache can be reset.
       */
      public static <T> CachedObservable<T> cache(Observable<T> source) {
          return new CachedObservable<T>(source);
      }
  
      /**
       * Returns a cached {@link Observable} like {@link Observable#cache()}
       * except that the cache can be reset by calling
       * {@link CachedObservable#reset()} and the cache will be automatically
       * reset an interval after first subscription (or first subscription after
       * reset). The interval is defined by {@code duration} and {@code unit} .
       *
       * @param source
       *            the source observable
       * @param duration
       *            duration till next reset
       * @param unit
       *            units corresponding to the duration
       * @param worker
       *            worker to use for scheduling reset. Don't forget to
       *            unsubscribe the worker when no longer required.
       * @param <T>
       *            the generic type of the source
       * @return cached observable that resets regularly on a time interval
       */
      public static <T> Observable<T> cache(final Observable<T> source, final long duration,
                                          final TimeUnit unit, final Scheduler.Worker worker) {
          final AtomicReference<CachedObservable<T>> cacheRef = new AtomicReference<CachedObservable<T>>();
          CachedObservable<T> cache = new CachedObservable<T>(source);
          cacheRef.set(cache);
          return cache.doOnSubscribe(new Consumer<Disposable>() {
              @Override
              public void accept(Disposable d) {
                  Runnable action = new Runnable() {
                      @Override
                      public void run() {
                          cacheRef.get().reset();
                      }
                  };
                  worker.schedule(action, duration, unit);
              }
          });
      }
  
      /**
       * Returns a cached {@link Observable} like {@link Observable#cache()}
       * except that the cache may be reset by the user calling
       * {@link CloseableObservableWithReset#reset}.
       *
       * @param source
       *            the source observable
       * @param duration
       *            duration till next reset
       * @param unit
       *            units corresponding to the duration
       * @param scheduler
       *            scheduler to use for scheduling reset.
       * @param <T>
       *            generic type of source observable
       * @return {@link CloseableObservableWithReset} that should be closed once
       *         finished to prevent worker memory leak.
       */
      public static <T> CloseableObservableWithReset<T> cache(final Observable<T> source,
                                                              final long duration, final TimeUnit unit, final Scheduler scheduler) {
          final AtomicReference<CachedObservable<T>> cacheRef = new AtomicReference<CachedObservable<T>>();
          final AtomicReference<Optional<Scheduler.Worker>> workerRef = new AtomicReference<Optional<Scheduler.Worker>>(
                  Optional.<Scheduler.Worker> absent());
         CachedObservable<T> cache = new CachedObservable<T>(source);
         cacheRef.set(cache);
         Runnable closeAction = new Runnable() {
             @Override
             public void run() {
                 while (true) {
                     Optional<Scheduler.Worker> w = workerRef.get();
                     if (w == null) {
                         // we are finished
                         break;
                     } else {
                         if (workerRef.compareAndSet(w, null)) {
                             if (w.isPresent()) {
                                 w.get().dispose();
                             }
                             // we are finished
                             workerRef.set(null);
                             break;
                         }
                     }
                     // if not finished then try again
                 }
             }
         };
         Runnable resetAction = new Runnable() {
 
             @Override
             public void run() {
                 startScheduledResetAgain(duration, unit, scheduler, cacheRef, workerRef);
             }
         };
         return new CloseableObservableWithReset<T>(cache, closeAction, resetAction);
     }
 
 
     private static <T> void startScheduledResetAgain(final long duration, final TimeUnit unit,
                                                      final Scheduler scheduler, final AtomicReference<CachedObservable<T>> cacheRef,
                                                      final AtomicReference<Optional<Scheduler.Worker>> workerRef) {
 
         Runnable action = new Runnable() {
             @Override
             public void run() {
                 cacheRef.get().reset();
             }
         };
         // CAS loop to cancel the current worker and create a new one
         while (true) {
             Optional<Scheduler.Worker> wOld = workerRef.get();
             if (wOld == null) {
                 // we are finished
                 return;
             }
             Optional<Scheduler.Worker> w = Optional.of(scheduler.createWorker());
             if (workerRef.compareAndSet(wOld, w)) {
                 if (wOld.isPresent())
                     wOld.get().dispose();
                 w.get().schedule(action, duration, unit);
                 break;
             }
         }
     }
 }