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 java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  
  /**
   * Subscribes to the other source if the main source is empty.
   *
   * @param <T> the value type
   */
  public final class MaybeSwitchIfEmpty<T> extends AbstractMaybeWithUpstream<T, T> {
  
      final MaybeSource<? extends T> other;
  
      public MaybeSwitchIfEmpty(MaybeSource<T> source, MaybeSource<? extends T> other) {
          super(source);
          this.other = other;
      }
  
      @Override
      protected void subscribeActual(MaybeObserver<? super T> observer) {
          source.subscribe(new SwitchIfEmptyMaybeObserver<>(observer, other));
      }
  
      static final class SwitchIfEmptyMaybeObserver<T>
      extends AtomicReference<Disposable>
      implements MaybeObserver<T>, Disposable {
  
          private static final long serialVersionUID = -2223459372976438024L;
  
          final MaybeObserver<? super T> downstream;
  
          final MaybeSource<? extends T> other;
  
          SwitchIfEmptyMaybeObserver(MaybeObserver<? super T> actual, MaybeSource<? extends T> other) {
              this.downstream = actual;
              this.other = other;
          }
  
          @Override
          public void dispose() {
              DisposableHelper.dispose(this);
          }
  
          @Override
          public boolean isDisposed() {
              return DisposableHelper.isDisposed(get());
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.setOnce(this, d)) {
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onSuccess(T value) {
              downstream.onSuccess(value);
          }
  
          @Override
          public void onError(Throwable e) {
              downstream.onError(e);
          }
  
          @Override
          public void onComplete() {
              Disposable d = get();
              if (d != DisposableHelper.DISPOSED) {
                  if (compareAndSet(d, null)) {
                      other.subscribe(new OtherMaybeObserver<T>(downstream, this));
                  }
              }
          }
  
          static final class OtherMaybeObserver<T> implements MaybeObserver<T> {
  
              final MaybeObserver<? super T> downstream;
  
              final AtomicReference<Disposable> parent;
              OtherMaybeObserver(MaybeObserver<? super T> actual, AtomicReference<Disposable> parent) {
                  this.downstream = actual;
                  this.parent = parent;
              }
  
              @Override
              public void onSubscribe(Disposable d) {
                  DisposableHelper.setOnce(parent, d);
              }
  
              @Override
              public void onSuccess(T value) {
                  downstream.onSuccess(value);
              }
  
              @Override
              public void onError(Throwable e) {
                  downstream.onError(e);
              }
  
              @Override
              public void onComplete() {
                  downstream.onComplete();
              }
          }
  
      }
  }
  