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.mixed;
  
  import java.util.Objects;
  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.Function;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.util.AtomicThrowable;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Maps the upstream items into {@link SingleSource}s and switches (subscribes) to the newer ones
   * while disposing the older ones and emits the latest success value if available, optionally delaying
   * errors from the main source or the inner sources.
   * <p>History: 2.1.11 - experimental
   * @param <T> the upstream value type
   * @param <R> the downstream value type
   * @since 2.2
   */
  public final class ObservableSwitchMapSingle<T, R> extends Observable<R> {
  
      final Observable<T> source;
  
      final Function<? super T, ? extends SingleSource<? extends R>> mapper;
  
      final boolean delayErrors;
  
      public ObservableSwitchMapSingle(Observable<T> source,
              Function<? super T, ? extends SingleSource<? extends R>> mapper,
              boolean delayErrors) {
          this.source = source;
          this.mapper = mapper;
          this.delayErrors = delayErrors;
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          if (!ScalarXMapZHelper.tryAsSingle(source, mapper, observer)) {
              source.subscribe(new SwitchMapSingleMainObserver<>(observer, mapper, delayErrors));
          }
      }
  
      static final class SwitchMapSingleMainObserver<T, R> extends AtomicInteger
      implements Observer<T>, Disposable {
  
          private static final long serialVersionUID = -5402190102429853762L;
  
          final Observer<? super R> downstream;
  
          final Function<? super T, ? extends SingleSource<? extends R>> mapper;
  
          final boolean delayErrors;
  
          final AtomicThrowable errors;
  
          final AtomicReference<SwitchMapSingleObserver<R>> inner;
  
          static final SwitchMapSingleObserver<Object> INNER_DISPOSED =
                  new SwitchMapSingleObserver<>(null);
  
          Disposable upstream;
  
          volatile boolean done;
  
          volatile boolean cancelled;
  
          SwitchMapSingleMainObserver(Observer<? super R> downstream,
                  Function<? super T, ? extends SingleSource<? extends R>> mapper,
                  boolean delayErrors) {
              this.downstream = downstream;
              this.mapper = mapper;
              this.delayErrors = delayErrors;
              this.errors = new AtomicThrowable();
              this.inner = new AtomicReference<>();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(upstream, d)) {
                  upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          @SuppressWarnings({ "unchecked", "rawtypes" })
          public void onNext(T t) {
              SwitchMapSingleObserver<R> current = inner.get();
              if (current != null) {
                  current.dispose();
              }
  
              SingleSource<? extends R> ss;
  
              try {
                  ss = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null SingleSource");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  upstream.dispose();
                  inner.getAndSet((SwitchMapSingleObserver)INNER_DISPOSED);
                  onError(ex);
                  return;
              }
  
              SwitchMapSingleObserver<R> observer = new SwitchMapSingleObserver<>(this);
  
              for (;;) {
                  current = inner.get();
                  if (current == INNER_DISPOSED) {
                      break;
                  }
                  if (inner.compareAndSet(current, observer)) {
                      ss.subscribe(observer);
                      break;
                  }
              }
          }
  
          @Override
          public void onError(Throwable t) {
              if (errors.tryAddThrowableOrReport(t)) {
                  if (!delayErrors) {
                      disposeInner();
                  }
                  done = true;
                  drain();
              }
          }
  
          @Override
          public void onComplete() {
              done = true;
              drain();
          }
  
          @SuppressWarnings({ "unchecked", "rawtypes" })
          void disposeInner() {
              SwitchMapSingleObserver<R> current = inner.getAndSet((SwitchMapSingleObserver)INNER_DISPOSED);
              if (current != null && current != INNER_DISPOSED) {
                  current.dispose();
              }
          }
  
          @Override
          public void dispose() {
              cancelled = true;
              upstream.dispose();
              disposeInner();
              errors.tryTerminateAndReport();
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          void innerError(SwitchMapSingleObserver<R> sender, Throwable ex) {
              if (inner.compareAndSet(sender, null)) {
                  if (errors.tryAddThrowableOrReport(ex)) {
                      if (!delayErrors) {
                          upstream.dispose();
                          disposeInner();
                      }
                      drain();
                  }
              } else {
                  RxJavaPlugins.onError(ex);
              }
          }
  
          void drain() {
              if (getAndIncrement() != 0) {
                  return;
              }
  
              int missed = 1;
              Observer<? super R> downstream = this.downstream;
              AtomicThrowable errors = this.errors;
              AtomicReference<SwitchMapSingleObserver<R>> inner = this.inner;
  
              for (;;) {
  
                  for (;;) {
                      if (cancelled) {
                          return;
                      }
  
                      if (errors.get() != null) {
                          if (!delayErrors) {
                              errors.tryTerminateConsumer(downstream);
                              return;
                          }
                      }
  
                      boolean d = done;
                      SwitchMapSingleObserver<R> current = inner.get();
                      boolean empty = current == null;
  
                      if (d && empty) {
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
  
                      if (empty || current.item == null) {
                          break;
                      }
  
                      inner.compareAndSet(current, null);
  
                      downstream.onNext(current.item);
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          static final class SwitchMapSingleObserver<R>
          extends AtomicReference<Disposable> implements SingleObserver<R> {
  
              private static final long serialVersionUID = 8042919737683345351L;
  
              final SwitchMapSingleMainObserver<?, R> parent;
  
              volatile R item;
  
              SwitchMapSingleObserver(SwitchMapSingleMainObserver<?, R> parent) {
                  this.parent = parent;
              }
  
              @Override
              public void onSubscribe(Disposable d) {
                  DisposableHelper.setOnce(this, d);
              }
  
              @Override
              public void onSuccess(R t) {
                  item = t;
                  parent.drain();
              }
  
              @Override
              public void onError(Throwable e) {
                  parent.innerError(this, e);
              }
  
              void dispose() {
                  DisposableHelper.dispose(this);
              }
          }
      }
  }
  