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/*
 * Copyright (c) 2016-2021 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 org.reactivestreams.Subscriber;

import reactor.core.CoreSubscriber;

/**
 * Hook into the {@link org.reactivestreams.Publisher#subscribe(Subscriber)} of a
 * {@link Mono} and execute a provided callback before calling
 * {@link org.reactivestreams.Publisher#subscribe(Subscriber)} directly with the
 * {@link CoreSubscriber}.
 *
 * 
 * Note that any exception thrown by the hook short circuit the subscription process and
 * are forwarded to the {@link Subscriber}'s {@link Subscriber#onError(Throwable)} method.
 *
 * @param  the value type
 * @author Simon Baslé
 */
final class MonoDoFirst extends InternalMonoOperator {

	final Runnable onFirst;

	MonoDoFirst(Mono source, Runnable onFirst) {
		super(source);
		this.onFirst = onFirst;
	}

	@Override
	public CoreSubscriber subscribeOrReturn(CoreSubscriber actual) {
		onFirst.run();

		return actual;
	}

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