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.observers;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.core.Observer;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.*;
  import io.reactivex.rxjava3.internal.disposables.*;
  import io.reactivex.rxjava3.internal.util.ExceptionHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Wraps another {@link Observer} and ensures all {@code onXXX} methods conform the protocol
   * (except the requirement for serialized access).
   *
   * @param <T> the value type
   */
  public final class SafeObserver<T> implements Observer<T>, Disposable {
      /** The actual Subscriber. */
      final Observer<? super T> downstream;
      /** The subscription. */
      Disposable upstream;
      /** Indicates a terminal state. */
      boolean done;
  
      /**
       * Constructs a {@code SafeObserver} by wrapping the given actual {@link Observer}.
       * @param downstream the actual {@code Observer} to wrap, not {@code null} (not validated)
       */
      public SafeObserver(@NonNull Observer<? super T> downstream) {
          this.downstream = downstream;
      }
  
      @Override
      public void onSubscribe(@NonNull Disposable d) {
          if (DisposableHelper.validate(this.upstream, d)) {
              this.upstream = d;
              try {
                  downstream.onSubscribe(this);
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  done = true;
                  // can't call onError because the actual's state may be corrupt at this point
                  try {
                      d.dispose();
                  } catch (Throwable e1) {
                      Exceptions.throwIfFatal(e1);
                      RxJavaPlugins.onError(new CompositeException(e, e1));
                      return;
                  }
                  RxJavaPlugins.onError(e);
              }
          }
      }
  
      @Override
      public void dispose() {
          upstream.dispose();
      }
  
      @Override
      public boolean isDisposed() {
          return upstream.isDisposed();
      }
  
      @Override
      public void onNext(@NonNull T t) {
          if (done) {
              return;
          }
          if (upstream == null) {
              onNextNoSubscription();
              return;
          }
  
          if (t == null) {
              Throwable ex = ExceptionHelper.createNullPointerException("onNext called with a null value.");
              try {
                  upstream.dispose();
              } catch (Throwable e1) {
                  Exceptions.throwIfFatal(e1);
                  onError(new CompositeException(ex, e1));
                  return;
              }
              onError(ex);
              return;
          }
  
          try {
              downstream.onNext(t);
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              try {
                  upstream.dispose();
              } catch (Throwable e1) {
                  Exceptions.throwIfFatal(e1);
                  onError(new CompositeException(e, e1));
                  return;
              }
              onError(e);
          }
      }
  
      void onNextNoSubscription() {
          done = true;
  
          Throwable ex = new NullPointerException("Subscription not set!");
  
          try {
              downstream.onSubscribe(EmptyDisposable.INSTANCE);
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              // can't call onError because the actual's state may be corrupt at this point
              RxJavaPlugins.onError(new CompositeException(ex, e));
              return;
          }
          try {
              downstream.onError(ex);
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              // if onError failed, all that's left is to report the error to plugins
              RxJavaPlugins.onError(new CompositeException(ex, e));
          }
      }
  
      @Override
      public void onError(@NonNull Throwable t) {
          if (done) {
              RxJavaPlugins.onError(t);
              return;
          }
          done = true;
  
          if (upstream == null) {
              Throwable npe = new NullPointerException("Subscription not set!");
  
              try {
                  downstream.onSubscribe(EmptyDisposable.INSTANCE);
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  // can't call onError because the actual's state may be corrupt at this point
                  RxJavaPlugins.onError(new CompositeException(t, npe, e));
                  return;
              }
              try {
                  downstream.onError(new CompositeException(t, npe));
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  // if onError failed, all that's left is to report the error to plugins
                  RxJavaPlugins.onError(new CompositeException(t, npe, e));
              }
              return;
          }
  
          if (t == null) {
              t = ExceptionHelper.createNullPointerException("onError called with a null Throwable.");
          }
  
          try {
              downstream.onError(t);
          } catch (Throwable ex) {
              Exceptions.throwIfFatal(ex);
  
              RxJavaPlugins.onError(new CompositeException(t, ex));
          }
      }
  
      @Override
      public void onComplete() {
          if (done) {
              return;
          }
  
          done = true;
  
          if (upstream == null) {
              onCompleteNoSubscription();
              return;
          }
  
          try {
              downstream.onComplete();
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              RxJavaPlugins.onError(e);
          }
      }
  
      void onCompleteNoSubscription() {
  
          Throwable ex = new NullPointerException("Subscription not set!");
  
          try {
              downstream.onSubscribe(EmptyDisposable.INSTANCE);
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              // can't call onError because the actual's state may be corrupt at this point
              RxJavaPlugins.onError(new CompositeException(ex, e));
              return;
          }
          try {
              downstream.onError(ex);
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              // if onError failed, all that's left is to report the error to plugins
              RxJavaPlugins.onError(new CompositeException(ex, e));
          }
      }
  
  }
  