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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 [http://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.dbms.database;

import org.neo4j.graphdb.GraphDatabaseService;
import org.neo4j.util.VisibleForTesting;

import static org.neo4j.kernel.database.NamedDatabaseId.NAMED_SYSTEM_DATABASE_ID;

public abstract class DbmsRuntimeRepository
{
    private final DatabaseManager databaseManager;
    final DbmsRuntimeSystemGraphComponent component;

    private volatile DbmsRuntimeVersion currentVersion;

    protected DbmsRuntimeRepository( DatabaseManager databaseManager, DbmsRuntimeSystemGraphComponent component )
    {
        this.databaseManager = databaseManager;
        this.component = component;
    }

    protected void fetchStateFromSystemDatabase()
    {
        var systemDatabase = getSystemDb();
        currentVersion = component.fetchStateFromSystemDatabase( systemDatabase );
    }

    protected GraphDatabaseService getSystemDb()
    {
        return databaseManager.getDatabaseContext( NAMED_SYSTEM_DATABASE_ID ).orElseThrow(
                () -> new RuntimeException( "Failed to get System Database" ) ).databaseFacade();
    }

    public DbmsRuntimeVersion getVersion()
    {
        if ( currentVersion == null )
        {
            synchronized ( this )
            {
                if ( currentVersion == null )
                {
                    fetchStateFromSystemDatabase();
                }
            }
        }

        return currentVersion;
    }

    /**
     * This must be used only by children and tests!!!
     */
    @VisibleForTesting
    public void setVersion( DbmsRuntimeVersion newVersion )
    {
        currentVersion = newVersion;
    }
}