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.single;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Function;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  
  import java.util.Objects;
  
  /**
   * Maps the success value of the source to a Notification, then
   * maps it back to the corresponding signal type.
   * <p>History: 2.2.4 - experimental
   * @param <T> the element type of the source
   * @param <R> the element type of the Notification and result
   * @since 3.0.0
   */
  public final class SingleDematerialize<T, R> extends Maybe<R> {
  
      final Single<T> source;
  
      final Function<? super T, Notification<R>> selector;
  
      public SingleDematerialize(Single<T> source, Function<? super T, Notification<R>> selector) {
          this.source = source;
          this.selector = selector;
      }
  
      @Override
      protected void subscribeActual(MaybeObserver<? super R> observer) {
          source.subscribe(new DematerializeObserver<>(observer, selector));
      }
  
      static final class DematerializeObserver<T, R> implements SingleObserver<T>, Disposable {
  
          final MaybeObserver<? super R> downstream;
  
          final Function<? super T, Notification<R>> selector;
  
          Disposable upstream;
  
          DematerializeObserver(MaybeObserver<? super R> downstream,
                  Function<? super T, Notification<R>> selector) {
              this.downstream = downstream;
              this.selector = selector;
          }
  
          @Override
          public void dispose() {
              upstream.dispose();
          }
  
          @Override
          public boolean isDisposed() {
              return upstream.isDisposed();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(upstream, d)) {
                  upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onSuccess(T t) {
              Notification<R> notification;
  
              try {
                  notification = Objects.requireNonNull(selector.apply(t), "The selector returned a null Notification");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  downstream.onError(ex);
                  return;
              }
              if (notification.isOnNext()) {
                  downstream.onSuccess(notification.getValue());
              } else if (notification.isOnComplete()) {
                  downstream.onComplete();
              } else {
                  downstream.onError(notification.getError());
              }
          }
  
          @Override
          public void onError(Throwable e) {
              downstream.onError(e);
          }
      }
  }
  