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.EmptyDisposable;
  import io.reactivex.rxjava3.internal.util.ExceptionHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class ObservableGenerate<T, S> extends Observable<T> {
      final Supplier<S> stateSupplier;
      final BiFunction<S, Emitter<T>, S> generator;
      final Consumer<? super S> disposeState;
  
      public ObservableGenerate(Supplier<S> stateSupplier, BiFunction<S, Emitter<T>, S> generator,
              Consumer<? super S> disposeState) {
          this.stateSupplier = stateSupplier;
          this.generator = generator;
          this.disposeState = disposeState;
      }
  
      @Override
      public void subscribeActual(Observer<? super T> observer) {
          S state;
  
          try {
              state = stateSupplier.get();
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              EmptyDisposable.error(e, observer);
              return;
          }
  
          GeneratorDisposable<T, S> gd = new GeneratorDisposable<>(observer, generator, disposeState, state);
          observer.onSubscribe(gd);
          gd.run();
      }
  
      static final class GeneratorDisposable<T, S>
      implements Emitter<T>, Disposable {
  
          final Observer<? super T> downstream;
          final BiFunction<S, ? super Emitter<T>, S> generator;
          final Consumer<? super S> disposeState;
  
          S state;
  
          volatile boolean cancelled;
  
          boolean terminate;
  
          boolean hasNext;
  
          GeneratorDisposable(Observer<? super T> actual,
                  BiFunction<S, ? super Emitter<T>, S> generator,
                  Consumer<? super S> disposeState, S initialState) {
              this.downstream = actual;
              this.generator = generator;
              this.disposeState = disposeState;
              this.state = initialState;
          }
  
          public void run() {
              S s = state;
  
              if (cancelled) {
                  state = null;
                  dispose(s);
                  return;
              }
  
              final BiFunction<S, ? super Emitter<T>, S> f = generator;
  
              for (;;) {
  
                  if (cancelled) {
                      state = null;
                      dispose(s);
                      return;
                  }
  
                  hasNext = false;
  
                  try {
                      s = f.apply(s, this);
                  } catch (Throwable ex) {
                      Exceptions.throwIfFatal(ex);
                      state = null;
                      cancelled = true;
                      onError(ex);
                      dispose(s);
                      return;
                  }
  
                  if (terminate) {
                      cancelled = true;
                      state = null;
                      dispose(s);
                      return;
                  }
              }
  
          }
  
          private void dispose(S s) {
              try {
                  disposeState.accept(s);
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  RxJavaPlugins.onError(ex);
              }
          }
  
          @Override
          public void dispose() {
              cancelled = true;
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          @Override
          public void onNext(T t) {
              if (!terminate) {
                  if (hasNext) {
                      onError(new IllegalStateException("onNext already called in this generate turn"));
                  } else {
                      if (t == null) {
                          onError(ExceptionHelper.createNullPointerException("onNext called with a null value."));
                      } else {
                          hasNext = true;
                          downstream.onNext(t);
                      }
                  }
              }
          }
  
          @Override
          public void onError(Throwable t) {
              if (terminate) {
                  RxJavaPlugins.onError(t);
              } else {
                  if (t == null) {
                      t = ExceptionHelper.createNullPointerException("onError called with a null Throwable.");
                  }
                  terminate = true;
                  downstream.onError(t);
              }
          }
  
          @Override
          public void onComplete() {
              if (!terminate) {
                  terminate = true;
                  downstream.onComplete();
              }
          }
      }
  }
  