AbstractUpdateOperation.java

/*******************************************************************************
 * Copyright 2013 André Rouél
 * 
 * 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.
 ******************************************************************************/
package net.sf.uadetector.datastore;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.concurrent.ExecutorService;
import java.util.regex.Pattern;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import net.sf.qualitycheck.Check;
import net.sf.uadetector.internal.util.ExecutorServices;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Provides a basic implementation to update UAS data in the background when calling {@link #run()}.
 * 
 * @author André Rouél
 */
public abstract class AbstractUpdateOperation implements UpdateOperation {

    /**
     * Defines an empty version string
     */
    private static final String EMPTY_VERSION = "";

    /**
     * Corresponding default logger for this class
     */
    private static final Logger LOG = LoggerFactory.getLogger(AbstractUpdateOperation.class);

    /**
     * Message for the log when no update is available.<br>
     * <br>
     * <b>Message sample</b>: No update available. Current version is '<em>20120301-01</em>'.<br>
     * <b>First placeholder</b>: current version
     */
    private static final String MSG_NO_UPDATE_AVAILABLE = "No update available. Current version is '%s'.";

    /**
     * Message for the log when an online update check is not possible.<br>
     * <br>
     * <b>Message sample</b>: Can not check for an updated version. Are you sure you have an established internet
     * connection?
     */
    private static final String MSG_NO_UPDATE_CHECK_POSSIBLE = "Can not check for an updated version. Are you sure you have an established internet connection?";

    /**
     * Message for the log when an exception occur during the update check.<br>
     * <br>
     * <b>Message sample</b>: Can not check for an updated version: <em>java.net.ConnectException</em>:
     * <em>Connection refused</em><br>
     * <b>First placeholder</b>: class name of exception<br>
     * <b>Second placeholder</b>: exception message
     */
    private static final String MSG_NO_UPDATE_CHECK_POSSIBLE__DEBUG = "Can not check for an updated version: %s: %s";

    /**
     * Message for the log when an update is available.<br>
     * <br>
     * <b>Message sample</b>: An update is available. Current version is '<em>20120301-01</em>' and remote version is '
     * <em>20120401-01</em>'.<br>
     * <b>First placeholder</b>: current version<br>
     * <b>Second placeholder</b>: new remote version
     */
    private static final String MSG_UPDATE_AVAILABLE = "An update is available. Current version is '%s' and remote version is '%s'.";

    /**
     * Pattern of a typical version of <i>UAS data</i>
     */
    private static final Pattern VERSION_PATTERN = Pattern.compile("\\d{8}\\-\\d{2}");

    /**
     * Checks a given newer version against an older one.
     * 
     * @param newer
     *            possible newer version
     * @param older
     *            possible older version
     * @return {@code true} if the first argument is newer than the second argument, otherwise {@code false}
     */
    static boolean hasUpdate(final String newer, final String older) {
        return VERSION_PATTERN.matcher(newer).matches() && VERSION_PATTERN.matcher(older).matches() ? newer.compareTo(older) > 0 : false;
    }

    /**
     * Reads the current User-Agent data version from <a
     * href="http://user-agent-string.info">http://user-agent-string.info</a>.
     * 
     * @param url
     *            a URL which the version information can be loaded
     * @return a version string or {@code null}
     * @throws IOException
     *             if an I/O exception occurs
     */
    @Nullable
    private static String retrieveRemoteVersion(@Nonnull final URL url, @Nonnull final Charset charset) throws IOException {
        final InputStream stream = url.openStream();
        final InputStreamReader reader = new InputStreamReader(stream, charset);
        final LineNumberReader lnr = new LineNumberReader(reader);
        final String line = lnr.readLine();
        lnr.close();
        reader.close();
        stream.close();
        return line;
    }

    /**
     * {@link ExecutorService} to run the update operation of the UAS data in background
     */
    private final ExecutorService executorService = ExecutorServices.createBackgroundExecutor();

    /**
     * Time of last update check in milliseconds
     */
    private long lastUpdateCheck = 0;

    /**
     * The data store for instances that implements {@link net.sf.uadetector.internal.data.Data}
     */
    private final RefreshableDataStore store;

    public AbstractUpdateOperation(@Nonnull final RefreshableDataStore dataStore) {
        Check.notNull(dataStore, "dataStore");
        store = dataStore;
    }

    /**
     * Shortcut to get the current version of the UAS data in the {@link net.sf.uadetector.datastore.DataStore}.
     * 
     * @return current version of UAS data
     */
    @Nonnull
    private String getCurrentVersion() {
        return store.getData().getVersion();
    }

    /**
     * Gets the time of the last update check in milliseconds.
     * 
     * @return time of the last update check in milliseconds
     */
    @Override
    public long getLastUpdateCheck() {
        return lastUpdateCheck;
    }

    /**
     * Fetches the current version information over HTTP and compares it with the last version of the most recently
     * imported data.
     * 
     * @return {@code true} if an update exists, otherwise {@code false}
     */
    protected boolean isUpdateAvailable() {
        boolean result = false;
        String version = EMPTY_VERSION;
        try {
            version = retrieveRemoteVersion(store.getVersionUrl(), store.getCharset());
        } catch (final IOException e) {
            LOG.info(MSG_NO_UPDATE_CHECK_POSSIBLE);
            LOG.debug(String.format(MSG_NO_UPDATE_CHECK_POSSIBLE__DEBUG, e.getClass().getName(), e.getLocalizedMessage()));
        }
        if (hasUpdate(version, getCurrentVersion())) {
            LOG.debug(String.format(MSG_UPDATE_AVAILABLE, getCurrentVersion(), version));
            result = true;
        } else {
            LOG.debug(String.format(MSG_NO_UPDATE_AVAILABLE, getCurrentVersion()));
        }
        lastUpdateCheck = System.currentTimeMillis();
        return result;
    }

    /**
     * Executes the update at some time in the future (as soon as possible) within a new thread.
     */
    @Override
    public void run() {
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                call();
            }
        });
    }

    /**
     * Shuts down the corresponding background executor as soon as possible, but at the latest specified default time.
     * 
     * @see ExecutorServices#shutdown(ExecutorService)
     */
    @Override
    public void shutdown() {
        ExecutorServices.shutdown(executorService);
    }

}