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.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.BiPredicate;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Compares two MaybeSources to see if they are both empty or emit the same value compared
   * via a BiPredicate.
   *
   * @param <T> the common base type of the sources
   */
  public final class MaybeEqualSingle<T> extends Single<Boolean> {
      final MaybeSource<? extends T> source1;
  
      final MaybeSource<? extends T> source2;
  
      final BiPredicate<? super T, ? super T> isEqual;
  
      public MaybeEqualSingle(MaybeSource<? extends T> source1, MaybeSource<? extends T> source2,
              BiPredicate<? super T, ? super T> isEqual) {
          this.source1 = source1;
          this.source2 = source2;
          this.isEqual = isEqual;
      }
  
      @Override
      protected void subscribeActual(SingleObserver<? super Boolean> observer) {
          EqualCoordinator<T> parent = new EqualCoordinator<>(observer, isEqual);
          observer.onSubscribe(parent);
          parent.subscribe(source1, source2);
      }
  
      @SuppressWarnings("serial")
      static final class EqualCoordinator<T>
      extends AtomicInteger
      implements Disposable {
          final SingleObserver<? super Boolean> downstream;
  
          final EqualObserver<T> observer1;
  
          final EqualObserver<T> observer2;
  
          final BiPredicate<? super T, ? super T> isEqual;
  
          EqualCoordinator(SingleObserver<? super Boolean> actual, BiPredicate<? super T, ? super T> isEqual) {
              super(2);
              this.downstream = actual;
              this.isEqual = isEqual;
              this.observer1 = new EqualObserver<>(this);
              this.observer2 = new EqualObserver<>(this);
          }
  
          void subscribe(MaybeSource<? extends T> source1, MaybeSource<? extends T> source2) {
              source1.subscribe(observer1);
              source2.subscribe(observer2);
          }
  
          @Override
          public void dispose() {
              observer1.dispose();
              observer2.dispose();
          }
  
          @Override
          public boolean isDisposed() {
              return DisposableHelper.isDisposed(observer1.get());
          }
  
          @SuppressWarnings("unchecked")
          void done() {
              if (decrementAndGet() == 0) {
                  Object o1 = observer1.value;
                  Object o2 = observer2.value;
  
                  if (o1 != null && o2 != null) {
                      boolean b;
  
                      try {
                          b = isEqual.test((T)o1, (T)o2);
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          downstream.onError(ex);
                          return;
                      }
  
                      downstream.onSuccess(b);
                  } else {
                      downstream.onSuccess(o1 == null && o2 == null);
                  }
              }
          }
  
          void error(EqualObserver<T> sender, Throwable ex) {
              if (getAndSet(0) > 0) {
                  if (sender == observer1) {
                      observer2.dispose();
                  } else {
                      observer1.dispose();
                  }
                  downstream.onError(ex);
              } else {
                  RxJavaPlugins.onError(ex);
              }
          }
      }
  
      static final class EqualObserver<T>
      extends AtomicReference<Disposable>
      implements MaybeObserver<T> {
  
          private static final long serialVersionUID = -3031974433025990931L;
  
          final EqualCoordinator<T> parent;
  
          Object value;
  
          EqualObserver(EqualCoordinator<T> parent) {
              this.parent = parent;
          }
  
          public void dispose() {
              DisposableHelper.dispose(this);
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              DisposableHelper.setOnce(this, d);
          }
  
          @Override
          public void onSuccess(T value) {
              this.value = value;
              parent.done();
          }
  
          @Override
          public void onError(Throwable e) {
              parent.error(this, e);
          }
  
          @Override
          public void onComplete() {
              parent.done();
          }
  
      }
  }
  