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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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package jdk.dns.client.internal.util;

import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Path;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.security.PrivilegedActionException;

import java.security.PrivilegedExceptionAction;

import java.util.concurrent.atomic.AtomicLong;

public class ReloadTracker {

    public static ReloadTracker newInstance(Path fileToTrack, long refreshTimeoutMillis) {

        Path absolutePath = fileToTrack.toAbsolutePath();

        return new ReloadTracker(absolutePath, refreshTimeoutMillis);

    }

    public static class ReloadStatus {

        private final boolean isReloadNeeded;

        private final long lastModificationTimestamp;

        private final boolean fileExists;

        ReloadStatus(boolean fileExists, boolean isReloadNeeded, long lastModificationTimestamp) {

            this.isReloadNeeded = fileExists && isReloadNeeded;

            this.lastModificationTimestamp = lastModificationTimestamp;

            this.fileExists = fileExists;

        }

        public boolean isFileExists() {

            return fileExists;

        }

        public boolean isReloadNeeded() {

            return isReloadNeeded;

        }

        public long getLastModificationTimestamp() {

            return lastModificationTimestamp;

        }

    }

    private ReloadTracker(Path filePath, long refreshTimeoutMillis) {

        this.filePath = filePath;

        this.refreshTimeoutMillis = refreshTimeoutMillis;

    }

    public ReloadStatus getReloadStatus() {

        boolean fileExists;

        var pa = (PrivilegedAction<Boolean>) () -> filePath.toFile().isFile();

        fileExists = System.getSecurityManager() == null ? pa.run() : AccessController.doPrivileged(pa);

        long lastModificationTime = -1;

        long lastReload = lastRefreshed.get();

        // Do not update lastModification time if file doesn't exist

        if (fileExists) {

            try {

                var pea = (PrivilegedExceptionAction<Long>) () -> Files.getLastModifiedTime(filePath).toMillis();

                lastModificationTime = System.getSecurityManager() == null ? pea.run()

                        : AccessController.doPrivileged(pea);

            } catch (Exception e) {

                // In case of Exception the tracked file will be reloaded, ie lastModificationTime == -1

            }

        }

        return new ReloadStatus(fileExists,

                (lastModificationTime != lastSeenChanged.get()) ||

                        (System.currentTimeMillis() - lastReload > refreshTimeoutMillis),

                lastModificationTime);

    }

    public void updateTimestamps(ReloadStatus rs) {

        lastSeenChanged.set(rs.lastModificationTimestamp);

        lastRefreshed.set(System.currentTimeMillis());

    }

    // Last timestamp when tracked file has been reloaded by consumer of this utility class

    private final AtomicLong lastRefreshed = new AtomicLong(-1);

    // Last processed FS last modified timestamp

    private final AtomicLong lastSeenChanged = new AtomicLong(-1);

    // Refresh timeout

    private final long refreshTimeoutMillis;

    // Path of the tracked file

    private final Path filePath;

}