/*
 * ============LICENSE_START=======================================================
 * ONAP : ccsdk features
 * ================================================================================
 * Copyright (C) 2019 highstreet technologies GmbH Intellectual Property.
 * All rights reserved.
 * ================================================================================
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * ============LICENSE_END=========================================================
 *
 */
package org.onap.ccsdk.features.sdnr.wt.common.file;

import java.io.File;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Check every now and then that a certain file has not changed. If it has, then call the {@link #doOnChange} method.
 *
 * @author JunHo Yoon
 * @since 3.1.1
 */
public abstract class FileWatchdog extends Thread {
    private static final Logger LOGGER = LoggerFactory.getLogger(FileWatchdog.class);
    /**
     * The default delay between every file modification check, set to 60 seconds.
     */
    public static final long DEFAULT_DELAY = 60000;
    /**
     * The name of the file to observe for changes.
     */
    private final String filename;

    /**
     * The delay to observe between every check. By default set {@link #DEFAULT_DELAY}.
     */
    private long delay = DEFAULT_DELAY;

    private final File file;
    private long lastModified = 0;
    private boolean warnedAlready = false;

    protected FileWatchdog(String filename) {
        this.filename = filename;
        file = new File(filename);
        setDaemon(true);
        checkAndConfigure();
    }

    /**
     * Set the delay to observe between each check of the file changes.
     *
     * @param delay the frequency of file watch.
     */
    public void setDelay(long delay) {
        this.delay = delay;
    }

    /**
     * abstract method to be run when the file is changed.
     */
    protected abstract void doOnChange();

    protected void checkAndConfigure() {
        boolean fileExists;
        try {
            fileExists = file.exists();
        } catch (SecurityException e) {
            LOGGER.warn("Was not allowed to read check file existence, file:[{}].", filename);
            this.interrupt(); // there is no point in continuing
            return;
        }

        if (fileExists) {
            long l = file.lastModified(); // this can also throw a
            if (lastModified == 0) {
                lastModified = l; // is very unlikely.
            }
            if (l > lastModified) { // however, if we reached this point this
                lastModified = l; // is very unlikely.
                doOnChange();
                warnedAlready = false;
            }
        } else {
            if (!warnedAlready) {
                LOGGER.debug("[{}] does not exist.", filename);
                warnedAlready = true;
            }
        }
    }

    @Override
    public void run() {
        while (!isInterrupted()) {
            checkAndConfigure();
            try {
                Thread.sleep(delay);
            } catch (InterruptedException e) {
                LOGGER.debug("Interrupted sleep. {}", e.getMessage());
                Thread.currentThread().interrupt();
            }
        }
        LOGGER.debug("Stoppen file watchdog for file {}", filename);
    }
}