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.observable;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.disposables.SequentialDisposable;
  
  public final class ObservableSwitchIfEmpty<T> extends AbstractObservableWithUpstream<T, T> {
      final ObservableSource<? extends T> other;
      public ObservableSwitchIfEmpty(ObservableSource<T> source, ObservableSource<? extends T> other) {
          super(source);
          this.other = other;
      }
  
      @Override
      public void subscribeActual(Observer<? super T> t) {
          SwitchIfEmptyObserver<T> parent = new SwitchIfEmptyObserver<>(t, other);
          t.onSubscribe(parent.arbiter);
          source.subscribe(parent);
      }
  
      static final class SwitchIfEmptyObserver<T> implements Observer<T> {
          final Observer<? super T> downstream;
          final ObservableSource<? extends T> other;
          final SequentialDisposable arbiter;
  
          boolean empty;
  
          SwitchIfEmptyObserver(Observer<? super T> actual, ObservableSource<? extends T> other) {
              this.downstream = actual;
              this.other = other;
              this.empty = true;
              this.arbiter = new SequentialDisposable();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              arbiter.update(d);
          }
  
          @Override
          public void onNext(T t) {
              if (empty) {
                  empty = false;
              }
              downstream.onNext(t);
          }
  
          @Override
          public void onError(Throwable t) {
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              if (empty) {
                  empty = false;
                  other.subscribe(this);
              } else {
                  downstream.onComplete();
              }
          }
      }
  }
  