/*
 * 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 <http://www.gnu.org/licenses/>.
 */
package org.neo4j.dbms.database;

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

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

public abstract class DbmsRuntimeRepository {
    private final DatabaseContextProvider<?> databaseContextProvider;
    protected final DbmsRuntimeSystemGraphComponent component;

    private volatile DbmsRuntimeVersion currentVersion;

    protected DbmsRuntimeRepository(
            DatabaseContextProvider<?> databaseContextProvider, DbmsRuntimeSystemGraphComponent component) {
        this.databaseContextProvider = databaseContextProvider;
        this.component = component;
    }

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

    protected GraphDatabaseService getSystemDb() {
        return databaseContextProvider
                .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;
    }
}
