/*
 * Copyright (c) 2011-2018 Pivotal Software Inc, 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
 *
 *       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 reactor.core.publisher;

import java.time.Duration;
import java.util.Objects;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.function.Function;
import java.util.stream.Stream;

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;

retries a source when a companion sequence signals
an item in response to the main's error signal

If the companion sequence signals when the main source is active, the repeat
attempt is suppressed and any terminal signal will terminate the main source with the same signal immediately.
Type parameters:
<T> – the source value type
See Also:
Reactive-Streams-Commons/**
 * retries a source when a companion sequence signals
 * an item in response to the main's error signal
 * <p>
 * <p>If the companion sequence signals when the main source is active, the repeat
 * attempt is suppressed and any terminal signal will terminate the main source with the same signal immediately.
 *
 * @param <T> the source value type
 * @see <a href="https://github.com/reactor/reactive-streams-commons">Reactive-Streams-Commons</a>
 */
final class FluxRetryWhen<T> extends FluxOperator<T, T> {

	static final Duration MAX_BACKOFF = Duration.ofMillis(Long.MAX_VALUE);

	final Function<? super Flux<Throwable>, ? extends Publisher<?>> whenSourceFactory;

	FluxRetryWhen(Flux<? extends T> source,
							  Function<? super Flux<Throwable>, ? extends Publisher<?>> whenSourceFactory) {
		super(source);
		this.whenSourceFactory = Objects.requireNonNull(whenSourceFactory, "whenSourceFactory");
	}

	static <T> void subscribe(CoreSubscriber<? super T> s, Function<? super
			Flux<Throwable>, ?
			extends Publisher<?>> whenSourceFactory, Publisher<? extends T> source) {
		RetryWhenOtherSubscriber other = new RetryWhenOtherSubscriber();
		Subscriber<Throwable> signaller = Operators.serialize(other.completionSignal);

		signaller.onSubscribe(Operators.emptySubscription());

		CoreSubscriber<T> serial = Operators.serialize(s);

		RetryWhenMainSubscriber<T> main =
				new RetryWhenMainSubscriber<>(serial, signaller, source);
		other.main = main;

		serial.onSubscribe(main);

		Publisher<?> p;

		try {
			p = Objects.requireNonNull(whenSourceFactory.apply(other),
			"The whenSourceFactory returned a null Publisher");
		}
		catch (Throwable e) {
			s.onError(Operators.onOperatorError(e, s.currentContext()));
			return;
		}

		p.subscribe(other);

		if (!main.cancelled) {
			source.subscribe(main);
		}
	}

	@Override
	public void subscribe(CoreSubscriber<? super T> actual) {
		subscribe(actual, whenSourceFactory, source);
	}

	static final class RetryWhenMainSubscriber<T> extends
	                                              Operators.MultiSubscriptionSubscriber<T, T> {

		final Operators.DeferredSubscription otherArbiter;

		final Subscriber<Throwable> signaller;

		final Publisher<? extends T> source;

		Context context;

		volatile int wip;
		static final AtomicIntegerFieldUpdater<RetryWhenMainSubscriber> WIP =
		  AtomicIntegerFieldUpdater.newUpdater(RetryWhenMainSubscriber.class, "wip");

		long produced;
		
		RetryWhenMainSubscriber(CoreSubscriber<? super T> actual, Subscriber<Throwable> signaller,
												Publisher<? extends T> source) {
			super(actual);
			this.signaller = signaller;
			this.source = source;
			this.otherArbiter = new Operators.DeferredSubscription();
			this.context = actual.currentContext();
		}

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

		@Override
		public Stream<? extends Scannable> inners() {
			return Stream.of(Scannable.from(signaller), otherArbiter);
		}

		@Override
		public void cancel() {
			if (!cancelled) {
				otherArbiter.cancel();
				super.cancel();
			}

		}

		public void setWhen(Subscription w) {
			otherArbiter.set(w);
		}

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

			produced++;
		}

		@Override
		public void onError(Throwable t) {
			long p = produced;
			if (p != 0L) {
				produced = 0;
				produced(p);
			}

			otherArbiter.request(1);

			signaller.onNext(t);
		}

		@Override
		public void onComplete() {
			otherArbiter.cancel();

			actual.onComplete();
		}

		void resubscribe(Object trigger) {
			if (WIP.getAndIncrement(this) == 0) {
				do {
					if (cancelled) {
						return;
					}

					//flow that emit a Context as a trigger for the re-subscription are
					//used to REPLACE the currentContext()
					if (trigger instanceof Context) {
						this.context = (Context) trigger;
					}

					source.subscribe(this);

				} while (WIP.decrementAndGet(this) != 0);
			}
		}

		void whenError(Throwable e) {
			super.cancel();

			actual.onError(e);
		}

		void whenComplete() {
			super.cancel();

			actual.onComplete();
		}
	}

	static final class RetryWhenOtherSubscriber extends Flux<Throwable>
	implements InnerConsumer<Object> {
		RetryWhenMainSubscriber<?> main;

		final DirectProcessor<Throwable> completionSignal = new DirectProcessor<>();

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

		@Override
		@Nullable
		public Object scanUnsafe(Attr key) {
			if (key == Attr.PARENT) return main.otherArbiter;
			if (key == Attr.ACTUAL) return main;

			return null;
		}

		@Override
		public void onSubscribe(Subscription s) {
			main.setWhen(s);
		}

		@Override
		public void onNext(Object t) {
			main.resubscribe(t);
		}

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

		@Override
		public void onComplete() {
			main.whenComplete();
		}

		@Override
		public void subscribe(CoreSubscriber<? super Throwable> actual) {
			completionSignal.subscribe(actual);
		}
	}

	static Function<Flux<Throwable>, Publisher<Long>> randomExponentialBackoffFunction(
			long numRetries, Duration firstBackoff, Duration maxBackoff,
			double jitterFactor) {
		if (jitterFactor < 0 || jitterFactor > 1) throw new IllegalArgumentException("jitterFactor must be between 0 and 1 (default 0.5)");
		Objects.requireNonNull(firstBackoff, "firstBackoff is required");
		Objects.requireNonNull(maxBackoff, "maxBackoff is required");

		return t -> t.index()
		             .flatMap(t2 -> {
			             long iteration = t2.getT1();

			             if (iteration >= numRetries) {
				             return Mono.<Long>error(new IllegalStateException("Retries exhausted: " + iteration + "/" + numRetries, t2.getT2()));
			             }

			             Duration nextBackoff;
			             try {
				             nextBackoff = firstBackoff.multipliedBy((long) Math.pow(2, iteration));
				             if (nextBackoff.compareTo(maxBackoff) > 0) {
					             nextBackoff = maxBackoff;
				             }
			             }
			             catch (ArithmeticException overflow) {
				             nextBackoff = maxBackoff;
			             }

			             //short-circuit delay == 0 case
			             if (nextBackoff.isZero()) {
				             return Mono.just(iteration);
			             }

			             ThreadLocalRandom random = ThreadLocalRandom.current();

			             long jitterOffset;
			             try {
				             jitterOffset = nextBackoff.multipliedBy((long) (100 * jitterFactor))
				                                       .dividedBy(100)
				                                       .toMillis();
			             }
			             catch (ArithmeticException ae) {
				             jitterOffset = Math.round(Long.MAX_VALUE * jitterFactor);
			             }
			             long lowBound = Math.max(firstBackoff.minus(nextBackoff)
			                                                  .toMillis(), -jitterOffset);
			             long highBound = Math.min(maxBackoff.minus(nextBackoff)
			                                                 .toMillis(), jitterOffset);

			             long jitter;
			             if (highBound == lowBound) {
				             if (highBound == 0) jitter = 0;
				             else jitter = random.nextLong(highBound);
			             }
			             else {
				             jitter = random.nextLong(lowBound, highBound);
			             }
			             Duration effectiveBackoff = nextBackoff.plusMillis(jitter);
			             return Mono.delay(effectiveBackoff);
		             });
	}
}