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.jdk8;
  
  import java.util.*;
  
  import io.reactivex.rxjava3.core.Observable;
  import io.reactivex.rxjava3.core.Observer;
  import io.reactivex.rxjava3.functions.Function;
  import io.reactivex.rxjava3.internal.observers.BasicFuseableObserver;
  
  /**
   * Map the upstream values into an Optional and emit its value if any.
   * @param <T> the upstream element type
   * @param <R> the output element type
   * @since 3.0.0
   */
  public final class ObservableMapOptional<T, R> extends Observable<R> {
  
      final Observable<T> source;
  
      final Function<? super T, Optional<? extends R>> mapper;
  
      public ObservableMapOptional(Observable<T> source, Function<? super T, Optional<? extends R>> mapper) {
          this.source = source;
          this.mapper = mapper;
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          source.subscribe(new MapOptionalObserver<>(observer, mapper));
      }
  
      static final class MapOptionalObserver<T, R> extends BasicFuseableObserver<T, R> {
  
          final Function<? super T, Optional<? extends R>> mapper;
  
          MapOptionalObserver(Observer<? super R> downstream, Function<? super T, Optional<? extends R>> mapper) {
              super(downstream);
              this.mapper = mapper;
          }
  
          @Override
          public void onNext(T t) {
              if (done) {
                  return;
              }
  
              if (sourceMode != NONE) {
                  downstream.onNext(null);
                  return;
              }
  
              Optional<? extends R> result;
              try {
                  result = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null Optional");
              } catch (Throwable ex) {
                  fail(ex);
                  return;
              }
  
              if (result.isPresent()) {
                  downstream.onNext(result.get());
              }
          }
  
          @Override
          public int requestFusion(int mode) {
              return transitiveBoundaryFusion(mode);
          }
  
          @Override
          public R poll() throws Throwable {
              for (;;) {
                  T item = qd.poll();
                  if (item == null) {
                      return null;
                  }
                  Optional<? extends R> result = Objects.requireNonNull(mapper.apply(item), "The mapper returned a null Optional");
                  if (result.isPresent()) {
                      return result.get();
                  }
              }
          }
      }
  }
  