/*
 * 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
 *
 *       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.util.Objects;
import java.util.concurrent.Callable;
import java.util.function.Consumer;
import java.util.function.Function;

import reactor.core.CoreSubscriber;
import reactor.core.Exceptions;
import reactor.core.Fuseable;

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 even. 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 even. 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
	@SuppressWarnings("unchecked")
	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 FluxUsing.UsingFuseableSubscriber<>(actual,
					resourceCleanup,
					resource,
					eager));
		}
		else if (actual instanceof ConditionalSubscriber) {
			p.subscribe(new FluxUsing.UsingConditionalSubscriber<>((ConditionalSubscriber<? super
					T>) actual,
					resourceCleanup,
					resource,
					eager));
		}
		else {
			p.subscribe(new FluxUsing.UsingSubscriber<>(actual,
					resourceCleanup,
					resource,
					eager));
		}
	}

	@Override
	public Object scanUnsafe(Attr key) {
		return null; //no particular key to be represented, still useful in hooks
	}
}