/*
 * Copyright (c) 2011-2017 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
 *
 *       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.Callable;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.function.Consumer;
import java.util.function.Function;

import org.reactivestreams.Subscription;

import reactor.core.CoreSubscriber;
import reactor.core.Exceptions;
import reactor.core.Fuseable;
import reactor.util.annotation.Nullable;
import reactor.util.context.Context;

Uses a resource, generated by a supplier for each individual Subscriber,
while streaming the values from a
Publisher derived from the same resource and makes sure the resource is released
if the sequence terminates or the Subscriber cancels.


Eager resource cleanup happens just before the source termination and exceptions
raised by the cleanup Consumer may override the terminal event. Non-eager
cleanup will drop any exception.
Type parameters:
<T> – the value type streamed
<S> – the resource type
See Also:
Reactive-Streams-Commons/**
 * Uses a resource, generated by a supplier for each individual Subscriber,
 * while streaming the values from a
 * Publisher derived from the same resource and makes sure the resource is released
 * if the sequence terminates or the Subscriber cancels.
 * <p>
 * <p>
 * Eager resource cleanup happens just before the source termination and exceptions
 * raised by the cleanup Consumer may override the terminal event. Non-eager
 * cleanup will drop any exception.
 *
 * @param <T> the value type streamed
 * @param <S> the resource type
 *
 * @see <a href="https://github.com/reactor/reactive-streams-commons">Reactive-Streams-Commons</a>
 */
final class MonoUsing<T, S> extends Mono<T> implements Fuseable, SourceProducer<T>  {

	final Callable<S> resourceSupplier;

	final Function<? super S, ? extends Mono<? extends T>> sourceFactory;

	final Consumer<? super S> resourceCleanup;

	final boolean eager;

	MonoUsing(Callable<S> resourceSupplier,
			Function<? super S, ? extends Mono<? extends T>> sourceFactory,
			Consumer<? super S> resourceCleanup,
			boolean eager) {
		this.resourceSupplier =
				Objects.requireNonNull(resourceSupplier, "resourceSupplier");
		this.sourceFactory = Objects.requireNonNull(sourceFactory, "sourceFactory");
		this.resourceCleanup = Objects.requireNonNull(resourceCleanup, "resourceCleanup");
		this.eager = eager;
	}

	@Override
	public void subscribe(CoreSubscriber<? super T> actual) {
		S resource;

		try {
			resource = resourceSupplier.call();
		}
		catch (Throwable e) {
			Operators.error(actual, Operators.onOperatorError(e, actual.currentContext()));
			return;
		}

		Mono<? extends T> p;

		try {
			p = Objects.requireNonNull(sourceFactory.apply(resource),
					"The sourceFactory returned a null value");
		}
		catch (Throwable e) {

			try {
				resourceCleanup.accept(resource);
			}
			catch (Throwable ex) {
				e = Exceptions.addSuppressed(ex, Operators.onOperatorError(e, actual.currentContext()));
			}

			Operators.error(actual, Operators.onOperatorError(e, actual.currentContext()));
			return;
		}

		if (p instanceof Fuseable) {
			p.subscribe(new MonoUsingSubscriber<>(actual,
					resourceCleanup,
					resource,
					eager,
					true));
		}
		else {
			p.subscribe(new MonoUsingSubscriber<>(actual,
					resourceCleanup,
					resource,
					eager,
					false));
		}
	}

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

	static final class MonoUsingSubscriber<T, S>
			implements InnerOperator<T, T>, QueueSubscription<T> {

		final CoreSubscriber<? super T> actual;

		final Consumer<? super S> resourceCleanup;

		final S resource;

		final boolean eager;
		final boolean allowFusion;

		Subscription         s;
		@Nullable
		QueueSubscription<T> qs;

		volatile int wip;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater<MonoUsingSubscriber> WIP =
				AtomicIntegerFieldUpdater.newUpdater(MonoUsingSubscriber.class, "wip");

		int mode;
		boolean valued;

		MonoUsingSubscriber(CoreSubscriber<? super T> actual,
				Consumer<? super S> resourceCleanup,
				S resource,
				boolean eager,
				boolean allowFusion) {
			this.actual = actual;
			this.resourceCleanup = resourceCleanup;
			this.resource = resource;
			this.eager = eager;
			this.allowFusion = allowFusion;
		}

		@Override
		@Nullable
		public Object scanUnsafe(Attr key) {
			if (key == Attr.TERMINATED || key == Attr.CANCELLED)
				return wip == 1;
			if (key == Attr.PARENT) return s;
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public CoreSubscriber<? super T> actual() {
			return actual;
		}

		@Override
		public void request(long n) {
			s.request(n);
		}

		@Override
		public void cancel() {
			if (WIP.compareAndSet(this, 0, 1)) {
				s.cancel();

				cleanup();
			}
		}

		void cleanup() {
			try {
				resourceCleanup.accept(resource);
			}
			catch (Throwable e) {
				Operators.onErrorDropped(e, actual.currentContext());
			}
		}

		@SuppressWarnings("unchecked")
		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				this.s = s;
				if (s instanceof QueueSubscription) {
					this.qs = (QueueSubscription<T>) s;
				}

				actual.onSubscribe(this);
			}
		}

		@Override
		public void onNext(T t) {
			if (mode == ASYNC) {
				actual.onNext(null);
				return;
			}
			this.valued = true;

			if (eager && WIP.compareAndSet(this, 0, 1)) {
				try {
					resourceCleanup.accept(resource);
				}
				catch (Throwable e) {
					Context ctx = actual.currentContext();
					actual.onError(Operators.onOperatorError(e, ctx));
					Operators.onDiscard(t, ctx);
					return;
				}
			}

			actual.onNext(t);
			actual.onComplete();

			if (!eager && WIP.compareAndSet(this, 0, 1)) {
				try {
					resourceCleanup.accept(resource);
				}
				catch (Throwable e) {
					Operators.onErrorDropped(e, actual.currentContext());
				}
			}
		}

		@Override
		public void onError(Throwable t) {
			if (valued && mode != ASYNC) {
				Operators.onErrorDropped(t, actual.currentContext());
				return;
			}
			if (eager && WIP.compareAndSet(this, 0, 1)) {
				try {
					resourceCleanup.accept(resource);
				}
				catch (Throwable e) {
					Throwable _e = Operators.onOperatorError(e, actual.currentContext());
					t = Exceptions.addSuppressed(_e, t);
				}
			}

			actual.onError(t);

			if (!eager && WIP.compareAndSet(this, 0, 1)) {
				cleanup();
			}
		}

		@Override
		public void onComplete() {
			if (valued && mode != ASYNC) {
				return;
			}
			//this should only happen in the empty case
			if (eager && WIP.compareAndSet(this, 0, 1)) {
				try {
					resourceCleanup.accept(resource);
				}
				catch (Throwable e) {
					actual.onError(Operators.onOperatorError(e, actual.currentContext()));
					return;
				}
			}

			actual.onComplete();

			if (!eager && WIP.compareAndSet(this, 0, 1)) {
				try {
					resourceCleanup.accept(resource);
				}
				catch (Throwable e) {
					Operators.onErrorDropped(e, actual.currentContext());
				}
			}
		}

		@Override
		public void clear() {
			if (qs != null) {
				qs.clear();
			}
		}

		@Override
		public boolean isEmpty() {
			return qs == null || qs.isEmpty();
		}

		@Override
		@Nullable
		public T poll() {
			if (mode == NONE || qs == null) {
				return null;
			}

			T v = qs.poll();

			if (v != null) {
				valued = true;
				if (eager && WIP.compareAndSet(this, 0, 1)) {
					try {
						resourceCleanup.accept(resource); //throws upwards
					}
					catch (Throwable t) {
						Operators.onDiscard(v, actual.currentContext());
						throw t;
					}
				}
			}
			else if (mode == SYNC) {
				if (!eager && WIP.compareAndSet(this, 0, 1)) {
					try {
						resourceCleanup.accept(resource);
					}
					catch (Throwable t) {
						if (!valued) throw t;
						else Operators.onErrorDropped(t, actual.currentContext());
						//returns null, ie onComplete, in the second case
					}
				}
			}
			return v;
		}

		@Override
		public int requestFusion(int requestedMode) {
			if (qs == null) {
				mode = NONE;
				return NONE;
			}
			int m = qs.requestFusion(requestedMode);
			mode = m;
			return m;
		}

		@Override
		public int size() {
			if (qs == null) {
				return 0;
			}
			return qs.size();
		}
	}
}