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/*
 * 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 io.prestosql.plugin.session.db;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableList;
import io.airlift.log.Logger;
import io.airlift.stats.CounterStat;
import io.prestosql.plugin.session.SessionMatchSpec;
import org.weakref.jmx.Managed;
import org.weakref.jmx.Nested;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.inject.Inject;

import java.util.List;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

import static io.airlift.concurrent.Threads.daemonThreadsNamed;
import static java.util.Objects.requireNonNull;
import static java.util.concurrent.Executors.newSingleThreadScheduledExecutor;

/**
 * Periodically schedules the loading of specs from the database during initialization. Returns the most recent successfully
 * loaded specs on every get() invocation.
 */
public class RefreshingDbSpecsProvider
        implements DbSpecsProvider
{
    private static final Logger log = Logger.get(RefreshingDbSpecsProvider.class);

    private final AtomicReference> sessionMatchSpecs = new AtomicReference<>(ImmutableList.of());
    private final SessionPropertiesDao dao;

    private final ScheduledExecutorService executor = newSingleThreadScheduledExecutor(daemonThreadsNamed("RefreshingDbSpecsProvider"));
    private final AtomicBoolean started = new AtomicBoolean();
    private final long refreshPeriodMillis;
    private final CounterStat dbLoadFailures = new CounterStat();

    @Inject
    public RefreshingDbSpecsProvider(DbSessionPropertyManagerConfig config, SessionPropertiesDao dao)
    {
        requireNonNull(config, "config is null");
        this.dao = requireNonNull(dao, "dao is null");
        this.refreshPeriodMillis = config.getSpecsRefreshPeriod().toMillis();

        dao.createSessionSpecsTable();
        dao.createSessionClientTagsTable();
        dao.createSessionPropertiesTable();
    }

    @PostConstruct
    public void initialize()
    {
        if (!started.getAndSet(true)) {
            executor.scheduleWithFixedDelay(this::refresh, 0, refreshPeriodMillis, TimeUnit.MILLISECONDS);
        }
    }

    @VisibleForTesting
    void refresh()
    {
        requireNonNull(dao, "dao is null");

        try {
            sessionMatchSpecs.set(ImmutableList.copyOf(dao.getSessionMatchSpecs()));
        }
        catch (Throwable e) {
            // Catch all exceptions here since throwing an exception from executor#scheduleWithFixedDelay method
            // suppresses all future scheduled invocations
            dbLoadFailures.update(1);
            log.error(e, "Error loading configuration from database");
        }
    }

    @PreDestroy
    public void destroy()
    {
        executor.shutdownNow();
    }

    @Override
    public List get()
    {
        return sessionMatchSpecs.get();
    }

    @Managed
    @Nested
    public CounterStat getDbLoadFailures()
    {
        return dbLoadFailures;
    }
}