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/*
 * Copyright (c) 2016-2023 VMware Inc. or its affiliates, All Rights Reserved.
 *
 * 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 reactor.core.publisher;

import java.util.Objects;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.function.Function;

import org.reactivestreams.Publisher;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import reactor.core.CoreSubscriber;
import reactor.core.Scannable;
import reactor.util.annotation.Nullable;
import reactor.util.context.Context;

/**
 * Signals a timeout (or switches to another sequence) in case a per-item
 * generated Publisher source fires an item or completes before the next item
 * arrives from the main source.
 *
 * @param  the main source type
 * @param  the value type for the timeout for the very first item
 * @param  the value type for the timeout for the subsequent items
 *
 * @see Reactive-Streams-Commons
 */
final class FluxTimeout extends InternalFluxOperator {

	final Publisher firstTimeout;

	final Function> itemTimeout;

	final Publisher other;

	final String timeoutDescription; //only useful when no `other`

	FluxTimeout(Flux source,
			Publisher firstTimeout,
			Function> itemTimeout,
			String timeoutDescription) {
		super(source);
		this.firstTimeout = Operators.toFluxOrMono(Objects.requireNonNull(firstTimeout,
				"firstTimeout"));
		this.itemTimeout = Objects.requireNonNull(itemTimeout, "itemTimeout");
		this.other = null;

		this.timeoutDescription = addNameToTimeoutDescription(source,
				Objects.requireNonNull(timeoutDescription, "timeoutDescription is needed when no fallback"));
	}

	FluxTimeout(Flux source,
			Publisher firstTimeout,
			Function> itemTimeout,
			Publisher other) {
		super(source);
		this.firstTimeout = Operators.toFluxOrMono(Objects.requireNonNull(firstTimeout, "firstTimeout"));
		this.itemTimeout = Objects.requireNonNull(itemTimeout, "itemTimeout");
		this.other = Operators.toFluxOrMono(Objects.requireNonNull(other, "other"));
		this.timeoutDescription = null;
	}

	@Override
	public CoreSubscriber subscribeOrReturn(CoreSubscriber actual) {
		return new TimeoutMainSubscriber<>(actual, firstTimeout, itemTimeout, other, timeoutDescription);
	}

	@Nullable
	static String addNameToTimeoutDescription(Publisher source,
			@Nullable  String timeoutDescription) {
		if (timeoutDescription == null) {
			return null;
		}

		Scannable s = Scannable.from(source);
		if (s.isScanAvailable()) {
			return timeoutDescription + " in '" + s.name() + "'";
		}
		else {
			return timeoutDescription;
		}
	}

	@Override
	public Object scanUnsafe(Attr key) {
		if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
		return super.scanUnsafe(key);
	}

	static final class TimeoutMainSubscriber
			extends Operators.MultiSubscriptionSubscriber {

		final Publisher firstTimeout;

		final Function> itemTimeout;

		final Publisher other;
		final String timeoutDescription; //only useful/non-null when no `other`

		Subscription s;

		volatile IndexedCancellable timeout;
		@SuppressWarnings("rawtypes")
		static final AtomicReferenceFieldUpdater
				TIMEOUT =
				AtomicReferenceFieldUpdater.newUpdater(TimeoutMainSubscriber.class,
						IndexedCancellable.class,
						"timeout");

		volatile long index;
		@SuppressWarnings("rawtypes")
		static final AtomicLongFieldUpdater INDEX =
				AtomicLongFieldUpdater.newUpdater(TimeoutMainSubscriber.class, "index");

		TimeoutMainSubscriber(
				CoreSubscriber actual,
				Publisher firstTimeout,
				Function> itemTimeout,
				@Nullable Publisher other,
				@Nullable String timeoutDescription
		) {
			super(Operators.serialize(actual));
			this.itemTimeout = itemTimeout;
			this.other = other;
			this.timeoutDescription = timeoutDescription;
			this.firstTimeout = firstTimeout;
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				this.s = s;

				set(s);

				TimeoutTimeoutSubscriber timeoutSubscriber = new TimeoutTimeoutSubscriber(this, 0L);
				this.timeout = timeoutSubscriber;

				actual.onSubscribe(this);
				firstTimeout.subscribe(timeoutSubscriber);
			}
		}

		@Override
		protected boolean shouldCancelCurrent() {
			return true;
		}

		@Override
		public void onNext(T t) {
			timeout.cancel();

			long idx = index;
			if (idx == Long.MIN_VALUE) {
				s.cancel();
				Operators.onNextDropped(t, actual.currentContext());
				return;
			}
			if (!INDEX.compareAndSet(this, idx, idx + 1)) {
				s.cancel();
				Operators.onNextDropped(t, actual.currentContext());
				return;
			}

			actual.onNext(t);

			producedOne();

			Publisher p;

			try {
				p = Objects.requireNonNull(itemTimeout.apply(t),
						"The itemTimeout returned a null Publisher");
			}
			catch (Throwable e) {
				actual.onError(Operators.onOperatorError(this, e, t,
						actual.currentContext()));
				return;
			}

			TimeoutTimeoutSubscriber ts = new TimeoutTimeoutSubscriber(this, idx + 1);

			if (!setTimeout(ts)) {
				return;
			}

			Operators.toFluxOrMono(p).subscribe(ts);
		}

		@Override
		public void onError(Throwable t) {
			long idx = index;
			if (idx == Long.MIN_VALUE) {
				Operators.onErrorDropped(t, actual.currentContext());
				return;
			}
			if (!INDEX.compareAndSet(this, idx, Long.MIN_VALUE)) {
				Operators.onErrorDropped(t, actual.currentContext());
				return;
			}

			cancelTimeout();

			actual.onError(t);
		}

		@Override
		public void onComplete() {
			long idx = index;
			if (idx == Long.MIN_VALUE) {
				return;
			}
			if (!INDEX.compareAndSet(this, idx, Long.MIN_VALUE)) {
				return;
			}

			cancelTimeout();

			actual.onComplete();
		}

		void cancelTimeout() {
			IndexedCancellable s = timeout;
			if (s != CancelledIndexedCancellable.INSTANCE) {
				s = TIMEOUT.getAndSet(this, CancelledIndexedCancellable.INSTANCE);
				if (s != null && s != CancelledIndexedCancellable.INSTANCE) {
					s.cancel();
				}
			}
		}

		@Override
		public void cancel() {
			index = Long.MIN_VALUE;
			cancelTimeout();
			super.cancel();
		}

		boolean setTimeout(IndexedCancellable newTimeout) {

			for (; ; ) {
				IndexedCancellable currentTimeout = timeout;

				if (currentTimeout == CancelledIndexedCancellable.INSTANCE) {
					newTimeout.cancel();
					return false;
				}

				if (currentTimeout != null && currentTimeout.index() >= newTimeout.index()) {
					newTimeout.cancel();
					return false;
				}

				if (TIMEOUT.compareAndSet(this, currentTimeout, newTimeout)) {
					if (currentTimeout != null) {
						currentTimeout.cancel();
					}
					return true;
				}
			}
		}

		void doTimeout(long i) {
			if (index == i && INDEX.compareAndSet(this, i, Long.MIN_VALUE)) {
				handleTimeout();
			}
		}

		void doError(long i, Throwable e) {
			if (index == i && INDEX.compareAndSet(this, i, Long.MIN_VALUE)) {
				super.cancel();

				actual.onError(e);
			}
		}

		void handleTimeout() {
			if (other == null) {
				super.cancel();
				actual.onError(new TimeoutException("Did not observe any item or terminal signal within "
						+ timeoutDescription + " (and no fallback has been configured)"));
			}
			else {
				set(Operators.emptySubscription());

				other.subscribe(new TimeoutOtherSubscriber<>(actual, this));
			}
		}

		@Override
		public Object scanUnsafe(Attr key) {
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
			return super.scanUnsafe(key);
		}
	}

	static final class TimeoutOtherSubscriber implements InnerConsumer {

		final CoreSubscriber actual;

		final Operators.MultiSubscriptionSubscriber arbiter;

		TimeoutOtherSubscriber(CoreSubscriber actual,
				Operators.MultiSubscriptionSubscriber arbiter) {
			this.actual = actual;
			this.arbiter = arbiter;
		}

		@Override
		public Context currentContext() {
			return actual.currentContext();
		}

		@Override
		public void onSubscribe(Subscription s) {
			arbiter.set(s);
		}

		@Override
		public void onNext(T t) {
			actual.onNext(t);
		}

		@Override
		public void onError(Throwable t) {
			actual.onError(t);
		}

		@Override
		public void onComplete() {
			actual.onComplete();
		}

		@Override
		public Object scanUnsafe(Attr key) {
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
			return null;
		}
	}

	interface IndexedCancellable {

		long index();

		void cancel();
	}

	enum CancelledIndexedCancellable implements IndexedCancellable {
		INSTANCE;

		@Override
		public long index() {
			return Long.MAX_VALUE;
		}

		@Override
		public void cancel() {

		}

	}

	static final class TimeoutTimeoutSubscriber
			implements InnerConsumer