code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.internal.operators.maybe;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.fuseable.HasUpstreamMaybeSource;
  import io.reactivex.rxjava3.internal.observers.DeferredScalarDisposable;
  
  /**
   * Wraps a MaybeSource and exposes it as an Observable, relaying signals in a backpressure-aware manner
   * and composes cancellation through.
   *
   * @param <T> the value type
   */
  public final class MaybeToObservable<T> extends Observable<T> implements HasUpstreamMaybeSource<T> {
  
      final MaybeSource<T> source;
  
      public MaybeToObservable(MaybeSource<T> source) {
          this.source = source;
      }
  
      @Override
      public MaybeSource<T> source() {
          return source;
      }
  
      @Override
      protected void subscribeActual(Observer<? super T> observer) {
          source.subscribe(create(observer));
      }
  
      /**
       * Creates a {@link MaybeObserver} wrapper around a {@link Observer}.
       * <p>History: 2.1.11 - experimental
       * @param <T> the value type
       * @param downstream the downstream {@code Observer} to talk to
       * @return the new MaybeObserver instance
       * @since 2.2
       */
      public static <T> MaybeObserver<T> create(Observer<? super T> downstream) {
          return new MaybeToObservableObserver<>(downstream);
      }
  
      static final class MaybeToObservableObserver<T> extends DeferredScalarDisposable<T>
      implements MaybeObserver<T> {
  
          private static final long serialVersionUID = 7603343402964826922L;
  
          Disposable upstream;
  
          MaybeToObservableObserver(Observer<? super T> downstream) {
              super(downstream);
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onSuccess(T value) {
              complete(value);
          }
  
          @Override
          public void onError(Throwable e) {
              error(e);
          }
  
          @Override
          public void onComplete() {
              complete();
          }
  
          @Override
          public void dispose() {
              super.dispose();
              upstream.dispose();
          }
      }
  }
  