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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 java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;

public class MapCachingDatabaseIdRepository implements DatabaseIdRepository.Caching {
    private static final Optional OPT_SYS_DB = Optional.of(NamedDatabaseId.NAMED_SYSTEM_DATABASE_ID);

    private volatile DatabaseIdRepository delegate;
    private volatile Map databaseIdsByName;
    private volatile Map databaseIdsByUuid;

    public MapCachingDatabaseIdRepository(DatabaseIdRepository delegate) {
        this.delegate = delegate;
        this.databaseIdsByName = new ConcurrentHashMap<>();
        this.databaseIdsByUuid = new ConcurrentHashMap<>();
    }

    public MapCachingDatabaseIdRepository() {
        this(null);
    }

    public void setDelegate(DatabaseIdRepository databaseIdRepository) {
        delegate = databaseIdRepository;
    }

    @Override
    public Optional getByName(NormalizedDatabaseName databaseName) {
        if (NamedDatabaseId.NAMED_SYSTEM_DATABASE_ID.name().equals(databaseName.name())) {
            return OPT_SYS_DB;
        }
        var dbId = Optional.ofNullable(databaseIdsByName.computeIfAbsent(
                databaseName.name(), name -> delegate.getByName(name).orElse(null)));
        dbId.ifPresent(id -> databaseIdsByUuid.put(id.databaseId(), id));
        return dbId;
    }

    @Override
    public Optional getById(DatabaseId uuid) {
        if (DatabaseId.SYSTEM_DATABASE_ID.equals(uuid)) {
            return OPT_SYS_DB;
        }
        var dbId = Optional.ofNullable(databaseIdsByUuid.computeIfAbsent(
                uuid, id -> delegate.getById(id).orElse(null)));
        dbId.ifPresent(id -> databaseIdsByName.put(id.name(), id));
        return dbId;
    }

    /**
     * We recreate the maps rather than .clear() because .clear() is not atomic
     *  and a concurrent .computeIfAbsent() could preserve a stale value.
     */
    @Override
    public void invalidateAll() {
        this.databaseIdsByName = new ConcurrentHashMap<>();
        this.databaseIdsByUuid = new ConcurrentHashMap<>();
    }
}