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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.kernel.database;

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

public class MapCachingDatabaseReferenceRepository implements DatabaseReferenceRepository.Caching
{
    private final DatabaseReferenceRepository delegate;
    private volatile Map databaseRefsByName;

    public MapCachingDatabaseReferenceRepository( DatabaseReferenceRepository delegate )
    {
        this.databaseRefsByName = new ConcurrentHashMap<>();
        this.delegate = delegate;
    }

    @Override
    public Optional getByName( NormalizedDatabaseName databaseName )
    {
        return Optional.ofNullable( databaseRefsByName.computeIfAbsent( databaseName, this::lookupReferenceOnDelegate ) );
    }

    /**
     * May return null, as {@link ConcurrentHashMap#computeIfAbsent} uses null as a signal not to add an entry to for the given key.
     */
    private DatabaseReference lookupReferenceOnDelegate( NormalizedDatabaseName databaseName )
    {
        return delegate.getByName( databaseName ).orElse( null );
    }

    @Override
    public Set getAllDatabaseReferences()
    {
        // Can't cache getAll call
        return delegate.getAllDatabaseReferences();
    }

    @Override
    public Set getInternalDatabaseReferences()
    {
        // Can't cache getAll call
        return delegate.getInternalDatabaseReferences();
    }

    @Override
    public Set getExternalDatabaseReferences()
    {
        // Can't cache getAll call
        return delegate.getExternalDatabaseReferences();
    }

    @Override
    public void invalidateAll()
    {
        this.databaseRefsByName = new ConcurrentHashMap<>();
    }
}