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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.flink.runtime.io.network;

import org.apache.flink.runtime.event.TaskEvent;
import org.apache.flink.runtime.io.network.api.TaskEventHandler;
import org.apache.flink.runtime.io.network.partition.ResultPartitionID;
import org.apache.flink.runtime.io.network.partition.consumer.LocalInputChannel;
import org.apache.flink.runtime.io.network.partition.consumer.RemoteInputChannel;
import org.apache.flink.runtime.util.event.EventListener;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.HashMap;
import java.util.Map;

import static org.apache.flink.util.Preconditions.checkNotNull;

/**
 * The task event dispatcher dispatches events flowing backwards from a consuming task to the task
 * producing the consumed result.
 *
 * Backwards events only work for tasks, which produce pipelined results, where both the
 * producing and consuming task are running at the same time.
 */
public class TaskEventDispatcher implements TaskEventPublisher {
	private static final Logger LOG = LoggerFactory.getLogger(TaskEventDispatcher.class);

	private final Map registeredHandlers = new HashMap<>();

	/**
	 * Registers the given partition for incoming task events allowing calls to {@link
	 * #subscribeToEvent(ResultPartitionID, EventListener, Class)}.
	 *
	 * @param partitionId
	 * 		the partition ID
	 */
	public void registerPartition(ResultPartitionID partitionId) {
		checkNotNull(partitionId);

		synchronized (registeredHandlers) {
			LOG.debug("registering {}", partitionId);
			if (registeredHandlers.put(partitionId, new TaskEventHandler()) != null) {
				throw new IllegalStateException(
					"Partition " + partitionId + " already registered at task event dispatcher.");
			}
		}
	}

	/**
	 * Removes the given partition from listening to incoming task events, thus forbidding calls to
	 * {@link #subscribeToEvent(ResultPartitionID, EventListener, Class)}.
	 *
	 * @param partitionId
	 * 		the partition ID
	 */
	public void unregisterPartition(ResultPartitionID partitionId) {
		checkNotNull(partitionId);

		synchronized (registeredHandlers) {
			LOG.debug("unregistering {}", partitionId);
			// NOTE: tolerate un-registration of non-registered task (unregister is always called
			//       in the cleanup phase of a task even if it never came to the registration - see
			//       Task.java)
			registeredHandlers.remove(partitionId);
		}
	}

	/**
	 * Subscribes a listener to this dispatcher for events on a partition.
	 *
	 * @param partitionId
	 * 		ID of the partition to subscribe for (must be registered via {@link
	 * 		#registerPartition(ResultPartitionID)} first!)
	 * @param eventListener
	 * 		the event listener to subscribe
	 * @param eventType
	 * 		event type to subscribe to
	 */
	public void subscribeToEvent(
			ResultPartitionID partitionId,
			EventListener eventListener,
			Class eventType) {
		checkNotNull(partitionId);
		checkNotNull(eventListener);
		checkNotNull(eventType);

		TaskEventHandler taskEventHandler;
		synchronized (registeredHandlers) {
			taskEventHandler = registeredHandlers.get(partitionId);
		}
		if (taskEventHandler == null) {
			throw new IllegalStateException(
				"Partition " + partitionId + " not registered at task event dispatcher.");
		}
		taskEventHandler.subscribe(eventListener, eventType);
	}

	/**
	 * Publishes the event to the registered {@link EventListener} instances.
	 *
	 * This method is either called directly from a {@link LocalInputChannel} or the network I/O
	 * thread on behalf of a {@link RemoteInputChannel}.
	 *
	 * @return whether the event was published to a registered event handler (initiated via {@link
	 * #registerPartition(ResultPartitionID)}) or not
	 */
	@Override
	public boolean publish(ResultPartitionID partitionId, TaskEvent event) {
		checkNotNull(partitionId);
		checkNotNull(event);

		TaskEventHandler taskEventHandler;
		synchronized (registeredHandlers) {
			taskEventHandler = registeredHandlers.get(partitionId);
		}

		if (taskEventHandler != null) {
			taskEventHandler.publish(event);
			return true;
		}

		return false;
	}

	/**
	 * Removes all registered event handlers.
	 */
	public void clearAll() {
		synchronized (registeredHandlers) {
			registeredHandlers.clear();
		}
	}
}