/*
 * 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 com.facebook.presto.execution;

import com.facebook.presto.Session;
import com.facebook.presto.spi.PrestoException;
import com.facebook.presto.sql.tree.Statement;
import com.google.common.collect.ImmutableList;
import org.weakref.jmx.MBeanExporter;
import org.weakref.jmx.ObjectNames;

import javax.annotation.PreDestroy;
import javax.annotation.concurrent.ThreadSafe;
import javax.inject.Inject;

import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executor;

import static com.facebook.presto.execution.QueuedExecution.createQueuedExecution;
import static com.facebook.presto.spi.StandardErrorCode.QUERY_QUEUE_FULL;
import static com.facebook.presto.spi.StandardErrorCode.QUERY_REJECTED;
import static java.util.Objects.requireNonNull;

@ThreadSafe
public class SqlQueryQueueManager
        implements QueryQueueManager
{
    private final ConcurrentMap<QueueKey, QueryQueue> queryQueues = new ConcurrentHashMap<>();
    private final List<QueryQueueRule> rules;
    private final MBeanExporter mbeanExporter;

    @Inject
    public SqlQueryQueueManager(List<QueryQueueRule> rules, MBeanExporter mbeanExporter)
    {
        this.mbeanExporter = requireNonNull(mbeanExporter, "mbeanExporter is null");
        this.rules = ImmutableList.copyOf(rules);
    }

    @Override
    public void submit(Statement statement, QueryExecution queryExecution, Executor executor)
    {
        List<QueryQueue> queues;
        try {
            queues = selectQueues(queryExecution.getSession(), executor);
        }
        catch (PrestoException e) {
            queryExecution.fail(e);
            return;
        }

        for (QueryQueue queue : queues) {
            if (!queue.reserve(queryExecution)) {
                // Reject query if we couldn't acquire a permit to enter the queue.
                // The permits will be released when this query fails.
                queryExecution.fail(new PrestoException(QUERY_QUEUE_FULL, "Too many queued queries"));
                return;
            }
        }

        queues.get(0).enqueue(createQueuedExecution(queryExecution, queues.subList(1, queues.size()), executor));
    }

    // Queues returned have already been created and added queryQueues
    private List<QueryQueue> selectQueues(Session session, Executor executor)
    {
        for (QueryQueueRule rule : rules) {
            Optional<List<QueryQueueDefinition>> queues = rule.match(session.toSessionRepresentation());
            if (queues.isPresent()) {
                return getOrCreateQueues(session, executor, queues.get());
            }
        }
        throw new PrestoException(QUERY_REJECTED, "Query did not match any queuing rule");
    }

    private List<QueryQueue> getOrCreateQueues(Session session, Executor executor, List<QueryQueueDefinition> definitions)
    {
        ImmutableList.Builder<QueryQueue> queues = ImmutableList.builder();
        for (QueryQueueDefinition definition : definitions) {
            String expandedName = definition.getExpandedTemplate(session);
            QueueKey key = new QueueKey(definition, expandedName);
            if (!queryQueues.containsKey(key)) {
                QueryQueue queue = new QueryQueue(executor, definition.getMaxQueued(), definition.getMaxConcurrent());
                if (queryQueues.putIfAbsent(key, queue) == null) {
                    // Export the mbean, after checking for races
                    String objectName = ObjectNames.builder(QueryQueue.class, definition.getTemplate()).withProperty("expansion", expandedName).build();
                    mbeanExporter.export(objectName, queue);
                }
            }
            queues.add(queryQueues.get(key));
        }
        return queues.build();
    }

    @PreDestroy
    public void destroy()
    {
        for (QueueKey key : queryQueues.keySet()) {
            String objectName = ObjectNames.builder(QueryQueue.class, key.getQueue().getTemplate()).withProperty("expansion", key.getName()).build();
            mbeanExporter.unexport(objectName);
        }
    }

    private static class QueueKey
    {
        private final QueryQueueDefinition queue;
        private final String name;

        private QueueKey(QueryQueueDefinition queue, String name)
        {
            this.queue = requireNonNull(queue, "queue is null");
            this.name = requireNonNull(name, "name is null");
        }

        public QueryQueueDefinition getQueue()
        {
            return queue;
        }

        public String getName()
        {
            return name;
        }

        @Override
        public boolean equals(Object other)
        {
            if (this == other) {
                return true;
            }
            if (other == null || getClass() != other.getClass()) {
                return false;
            }

            QueueKey queueKey = (QueueKey) other;

            return Objects.equals(name, queueKey.name) && Objects.equals(queue.getTemplate(), queueKey.queue.getTemplate());
        }

        @Override
        public int hashCode()
        {
            return Objects.hash(queue.getTemplate(), name);
        }
    }
}