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.flowable;
  
  import org.reactivestreams.Subscription;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.fuseable.FuseToFlowable;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class FlowableElementAtMaybe<T> extends Maybe<T> implements FuseToFlowable<T> {
      final Flowable<T> source;
  
      final long index;
  
      public FlowableElementAtMaybe(Flowable<T> source, long index) {
          this.source = source;
          this.index = index;
      }
  
      @Override
      protected void subscribeActual(MaybeObserver<? super T> observer) {
          source.subscribe(new ElementAtSubscriber<>(observer, index));
      }
  
      @Override
      public Flowable<T> fuseToFlowable() {
          return RxJavaPlugins.onAssembly(new FlowableElementAt<>(source, index, null, false));
      }
  
      static final class ElementAtSubscriber<T> implements FlowableSubscriber<T>, Disposable {
  
          final MaybeObserver<? super T> downstream;
  
          final long index;
  
          Subscription upstream;
  
          long count;
  
          boolean done;
  
          ElementAtSubscriber(MaybeObserver<? super T> actual, long index) {
              this.downstream = actual;
              this.index = index;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
                  downstream.onSubscribe(this);
                  s.request(index + 1);
              }
          }
  
          @Override
          public void onNext(T t) {
              if (done) {
                  return;
              }
              long c = count;
              if (c == index) {
                  done = true;
                  upstream.cancel();
                  upstream = SubscriptionHelper.CANCELLED;
                  downstream.onSuccess(t);
                  return;
              }
              count = c + 1;
          }
  
          @Override
          public void onError(Throwable t) {
              if (done) {
                  RxJavaPlugins.onError(t);
                  return;
              }
              done = true;
              upstream = SubscriptionHelper.CANCELLED;
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              upstream = SubscriptionHelper.CANCELLED;
              if (!done) {
                  done = true;
                  downstream.onComplete();
              }
          }
  
          @Override
          public void dispose() {
              upstream.cancel();
              upstream = SubscriptionHelper.CANCELLED;
          }
  
          @Override
          public boolean isDisposed() {
              return upstream == SubscriptionHelper.CANCELLED;
          }
  
      }
  }
  