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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.

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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.query;

import org.neo4j.collection.Dependencies;
import org.neo4j.configuration.Config;
import org.neo4j.kernel.api.Kernel;
import org.neo4j.kernel.internal.GraphDatabaseAPI;
import org.neo4j.kernel.lifecycle.LifeSupport;
import org.neo4j.logging.InternalLogProvider;
import org.neo4j.monitoring.Monitors;
import org.neo4j.scheduler.JobScheduler;

public abstract class QueryEngineProvider {
    protected abstract QueryExecutionEngine createEngine(
            Dependencies deps, GraphDatabaseAPI graphAPI, boolean isSystemDatabase, SPI spi);

    protected abstract int enginePriority();

    public static QueryExecutionEngine initialize(
            Dependencies deps,
            GraphDatabaseAPI graphAPI,
            QueryEngineProvider provider,
            boolean isSystemDatabase,
            SPI spi) {
        if (provider == null) {
            return noEngine();
        }
        QueryExecutionEngine engine = provider.createEngine(deps, graphAPI, isSystemDatabase, spi);
        return deps.satisfyDependency(engine);
    }

    public static QueryExecutionEngine noEngine() {
        return NoQueryEngine.INSTANCE;
    }

    public interface SPI {
        InternalLogProvider logProvider();

        Monitors monitors();

        JobScheduler jobScheduler();

        LifeSupport lifeSupport();

        Kernel kernel();

        Config config();
    }

    public static SPI spi(
            InternalLogProvider logProvider,
            Monitors monitors,
            JobScheduler jobScheduler,
            LifeSupport lifeSupport,
            Kernel kernel,
            Config config) {
        return new SPI() {
            @Override
            public InternalLogProvider logProvider() {
                return logProvider;
            }

            @Override
            public Monitors monitors() {
                return monitors;
            }

            @Override
            public JobScheduler jobScheduler() {
                return jobScheduler;
            }

            @Override
            public LifeSupport lifeSupport() {
                return lifeSupport;
            }

            @Override
            public Kernel kernel() {
                return kernel;
            }

            @Override
            public Config config() {
                return config;
            }
        };
    }
}