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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.commandline.dbms;

import java.io.Closeable;
import java.io.IOException;
import java.nio.file.Files;
import org.neo4j.io.IOUtils;
import org.neo4j.io.fs.DefaultFileSystemAbstraction;
import org.neo4j.io.fs.FileSystemAbstraction;
import org.neo4j.io.layout.DatabaseLayout;
import org.neo4j.io.layout.Neo4jLayout;
import org.neo4j.io.locker.FileLockException;
import org.neo4j.io.locker.Locker;
import org.neo4j.kernel.internal.locker.DatabaseLocker;
import org.neo4j.kernel.internal.locker.GlobalLocker;

public final class LockChecker implements Closeable {
    private final FileSystemAbstraction fileSystem;
    private final Locker locker;

    private LockChecker(FileSystemAbstraction fileSystem, Locker locker) {
        this.fileSystem = fileSystem;
        this.locker = locker;
    }

    public static Closeable checkDbmsLock(Neo4jLayout neo4jLayout) throws CannotWriteException {
        var fileSystem = new DefaultFileSystemAbstraction();
        var locker = new GlobalLocker(fileSystem, neo4jLayout);
        return check(locker, fileSystem);
    }

    public static Closeable checkDatabaseLock(DatabaseLayout databaseLayout) throws CannotWriteException {
        var fileSystem = new DefaultFileSystemAbstraction();
        var locker = new DatabaseLocker(fileSystem, databaseLayout);
        return check(locker, fileSystem);
    }

    private static Closeable check(Locker locker, FileSystemAbstraction fileSystem) throws CannotWriteException {
        var lockFile = locker.lockFile();

        if (Files.isWritable(lockFile.getParent())) {
            if (Files.exists(lockFile) && !Files.isWritable(lockFile)) {
                throw new CannotWriteException(lockFile);
            }
            LockChecker lockChecker = new LockChecker(fileSystem, locker);
            try {
                lockChecker.checkLock();
                return lockChecker;
            } catch (FileLockException le) {
                try {
                    locker.close();
                } catch (IOException e) {
                    le.addSuppressed(e);
                }
                throw le;
            }
        } else {
            throw new CannotWriteException(lockFile);
        }
    }

    private void checkLock() {
        locker.checkLock();
    }

    @Override
    public void close() throws IOException {
        IOUtils.closeAll(locker, fileSystem);
    }
}