/*
 * 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
 *
 *    https://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 autodispose2;

import io.reactivex.rxjava3.annotations.NonNull;
import io.reactivex.rxjava3.core.Observer;
import io.reactivex.rxjava3.plugins.RxJavaPlugins;
import java.util.concurrent.atomic.AtomicInteger;
import org.reactivestreams.Subscriber;

/**
 * Utility methods to perform half-serialization: a form of serialization
 * where onNext is guaranteed to be called from a single thread but
 * onError or onComplete may be called from any threads.
 * <p>
 * The onNext methods have been modified to return a boolean indicating whether or not the delegate
 * observer was sent a terminal event.
 */
final class HalfSerializer {
  /** Utility class. */
  private HalfSerializer() {
    throw new IllegalStateException("No instances!");
  }

  /**
   * Emits the given value if possible and terminates if there was an onComplete or onError
   * while emitting, drops the value otherwise.
   *
   * @param <T> the value type
   * @param subscriber the target Subscriber to emit to
   * @param value the value to emit
   * @param wip the serialization work-in-progress counter/indicator
   * @param error the holder of Throwables
   * @return true if a terminal event was emitted to {@code observer}, false if not
   */
  public static <@NonNull T> boolean onNext(Subscriber<? super T> subscriber,
      T value,
      AtomicInteger wip,
      AtomicThrowable error) {
    if (wip.get() == 0 && wip.compareAndSet(0, 1)) {
      subscriber.onNext(value);
      if (wip.decrementAndGet() != 0) {
        Throwable ex = error.terminate();
        if (ex != null) {
          subscriber.onError(ex);
        } else {
          subscriber.onComplete();
        }
        return true;
      }
    }
    return false;
  }

  /**
   * Emits the given exception if possible or adds it to the given error container to
   * be emitted by a concurrent onNext if one is running.
   * Undeliverable exceptions are sent to the RxJavaPlugins.onError.
   *
   * @param subscriber the target Subscriber to emit to
   * @param ex the Throwable to emit
   * @param wip the serialization work-in-progress counter/indicator
   * @param error the holder of Throwables
   */
  public static void onError(Subscriber<?> subscriber, Throwable ex, AtomicInteger wip, AtomicThrowable error) {
    if (error.addThrowable(ex)) {
      if (wip.getAndIncrement() == 0) {
        subscriber.onError(error.terminate());
      }
    } else {
      RxJavaPlugins.onError(ex);
    }
  }

  /**
   * Emits an onComplete signal or an onError signal with the given error or indicates
   * the concurrently running onNext should do that.
   *
   * @param subscriber the target Subscriber to emit to
   * @param wip the serialization work-in-progress counter/indicator
   * @param error the holder of Throwables
   */
  public static void onComplete(Subscriber<?> subscriber, AtomicInteger wip, AtomicThrowable error) {
    if (wip.getAndIncrement() == 0) {
      Throwable ex = error.terminate();
      if (ex != null) {
        subscriber.onError(ex);
      } else {
        subscriber.onComplete();
      }
    }
  }

  /**
   * Emits the given value if possible and terminates if there was an onComplete or onError
   * while emitting, drops the value otherwise.
   *
   * @param <T> the value type
   * @param observer the target Observer to emit to
   * @param value the value to emit
   * @param wip the serialization work-in-progress counter/indicator
   * @param error the holder of Throwables
   * @return true if a terminal event was emitted to {@code observer}, false if not
   */
  public static <@NonNull T> boolean onNext(Observer<? super T> observer, T value, AtomicInteger wip, AtomicThrowable error) {
    if (wip.get() == 0 && wip.compareAndSet(0, 1)) {
      observer.onNext(value);
      if (wip.decrementAndGet() != 0) {
        Throwable ex = error.terminate();
        if (ex != null) {
          observer.onError(ex);
        } else {
          observer.onComplete();
        }
        return true;
      }
    }
    return false;
  }

  /**
   * Emits the given exception if possible or adds it to the given error container to
   * be emitted by a concurrent onNext if one is running.
   * Undeliverable exceptions are sent to the RxJavaPlugins.onError.
   *
   * @param observer the target Subscriber to emit to
   * @param ex the Throwable to emit
   * @param wip the serialization work-in-progress counter/indicator
   * @param error the holder of Throwables
   */
  public static void onError(Observer<?> observer, Throwable ex, AtomicInteger wip, AtomicThrowable error) {
    if (error.addThrowable(ex)) {
      if (wip.getAndIncrement() == 0) {
        observer.onError(error.terminate());
      }
    } else {
      RxJavaPlugins.onError(ex);
    }
  }

  /**
   * Emits an onComplete signal or an onError signal with the given error or indicates
   * the concurrently running onNext should do that.
   *
   * @param observer the target Subscriber to emit to
   * @param wip the serialization work-in-progress counter/indicator
   * @param error the holder of Throwables
   */
  public static void onComplete(Observer<?> observer, AtomicInteger wip, AtomicThrowable error) {
    if (wip.getAndIncrement() == 0) {
      Throwable ex = error.terminate();
      if (ex != null) {
        observer.onError(ex);
      } else {
        observer.onComplete();
      }
    }
  }
}
