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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.database;

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

import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Supplier;
import org.neo4j.dbms.api.DatabaseManagementException;
import org.neo4j.dbms.database.DatabaseContext;
import org.neo4j.dbms.systemgraph.CommunityTopologyGraphDbmsModel;
import org.neo4j.dbms.systemgraph.TopologyGraphDbmsModel;
import org.neo4j.graphdb.DatabaseShutdownException;

public class SystemGraphDatabaseReferenceRepository implements DatabaseReferenceRepository {
    private static final DatabaseReference SYSTEM_DATABASE_REFERENCE = new DatabaseReferenceImpl.Internal(
            new NormalizedDatabaseName(SYSTEM_DATABASE_NAME), NAMED_SYSTEM_DATABASE_ID, true);

    private final Supplier systemDatabaseSupplier;

    public SystemGraphDatabaseReferenceRepository(Supplier systemDatabaseSupplier) {
        this.systemDatabaseSupplier = systemDatabaseSupplier;
    }

    @Override
    public Optional getByAlias(NormalizedDatabaseName databaseAlias) {
        if (Objects.equals(SYSTEM_DATABASE_NAME, databaseAlias.name())) {
            return Optional.of(SYSTEM_DATABASE_REFERENCE);
        }
        return execute(model -> model.getDatabaseRefByAlias(databaseAlias.name()));
    }

    @Override
    public Set getAllDatabaseReferences() {
        return execute(TopologyGraphDbmsModel::getAllDatabaseReferences);
    }

    @Override
    public Set getInternalDatabaseReferences() {
        return execute(TopologyGraphDbmsModel::getAllInternalDatabaseReferences);
    }

    @Override
    public Set getExternalDatabaseReferences() {
        return execute(TopologyGraphDbmsModel::getAllExternalDatabaseReferences);
    }

    @Override
    public Set getCompositeDatabaseReferences() {
        return execute(TopologyGraphDbmsModel::getAllCompositeDatabaseReferences);
    }

    private  T execute(Function operation) {
        var databaseContext = systemDatabaseSupplier.get();
        var systemDb = databaseContext.databaseFacade();
        if (!systemDb.isAvailable(100)) {
            throw new DatabaseShutdownException(
                    new DatabaseManagementException("System database is not (yet) available"));
        }
        try (var tx = systemDb.beginTx()) {
            var model = new CommunityTopologyGraphDbmsModel(tx);
            return operation.apply(model);
        }
    }
}