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.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.disposables.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  import java.util.Objects;
  
  public final class ObservableCollect<T, U> extends AbstractObservableWithUpstream<T, U> {
      final Supplier<? extends U> initialSupplier;
      final BiConsumer<? super U, ? super T> collector;
  
      public ObservableCollect(ObservableSource<T> source,
              Supplier<? extends U> initialSupplier, BiConsumer<? super U, ? super T> collector) {
          super(source);
          this.initialSupplier = initialSupplier;
          this.collector = collector;
      }
  
      @Override
      protected void subscribeActual(Observer<? super U> t) {
          U u;
          try {
              u = Objects.requireNonNull(initialSupplier.get(), "The initialSupplier returned a null value");
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              EmptyDisposable.error(e, t);
              return;
          }
  
          source.subscribe(new CollectObserver<>(t, u, collector));
  
      }
  
      static final class CollectObserver<T, U> implements Observer<T>, Disposable {
          final Observer<? super U> downstream;
          final BiConsumer<? super U, ? super T> collector;
          final U u;
  
          Disposable upstream;
  
          boolean done;
  
          CollectObserver(Observer<? super U> actual, U u, BiConsumer<? super U, ? super T> collector) {
              this.downstream = actual;
              this.collector = collector;
              this.u = u;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void dispose() {
              upstream.dispose();
          }
  
          @Override
          public boolean isDisposed() {
              return upstream.isDisposed();
          }
  
          @Override
          public void onNext(T t) {
              if (done) {
                  return;
              }
              try {
                  collector.accept(u, t);
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  upstream.dispose();
                  onError(e);
              }
          }
  
          @Override
          public void onError(Throwable t) {
              if (done) {
                  RxJavaPlugins.onError(t);
                  return;
              }
              done = true;
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              if (done) {
                  return;
              }
              done = true;
              downstream.onNext(u);
              downstream.onComplete();
          }
      }
  }
  