Issue 5931 - Create tests for util package

adblockplussbrowser/src/main/java/org/adblockplus/sbrowser/contentblocker/engine/Engine.java

Index: adblockplussbrowser/src/main/java/org/adblockplus/sbrowser/contentblocker/engine/Engine.java
===================================================================
new file mode 100644
--- /dev/null
+++ b/adblockplussbrowser/src/main/java/org/adblockplus/sbrowser/contentblocker/engine/Engine.java
@@ -0,0 +1,819 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-present eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus 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 Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.adblockplus.sbrowser.contentblocker.engine;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.io.Writer;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.ReentrantLock;
+
+import org.adblockplus.adblockplussbrowser.R;
+import org.adblockplus.sbrowser.contentblocker.util.SharedPrefsUtils;
+import org.adblockplus.sbrowser.contentblocker.util.SubscriptionUtils;
+
+import android.content.Context;
+import android.content.Intent;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+import android.content.pm.ResolveInfo;
+import android.net.ConnectivityManager;
+import android.net.NetworkInfo;
+import android.net.Uri;
+import android.os.Handler;
+import android.os.Looper;
+import android.support.annotation.VisibleForTesting;
+import android.text.TextUtils;
+import android.text.format.DateUtils;
+import android.util.Log;
+
+public final class Engine
+{
+  private static final String TAG = Engine.class.getSimpleName();
+
+  public static final String USER_FILTERS_TITLE = "__filters";
+  public static final String USER_EXCEPTIONS_TITLE = "__exceptions";
+
+  public static final String SBROWSER_APP_ID = "com.sec.android.app.sbrowser";
+  public static final String EASYLIST_URL = "https://easylist-downloads.adblockplus.org/easylist.txt";
+  private static final String ACTION_OPEN_SETTINGS = "com.samsung.android.sbrowser.contentBlocker.ACTION_SETTING";
+  private static final String ACTION_UPDATE = "com.samsung.android.sbrowser.contentBlocker.ACTION_UPDATE";
+
+  public static final String SUBSCRIPTIONS_EXCEPTIONSURL = "subscriptions_exceptionsurl";
+
+  // The value below specifies an interval of [x, 2*x[, where x =
+  // INITIAL_UPDATE_CHECK_DELAY
+  private static final long INITIAL_UPDATE_CHECK_DELAY = 5 * DateUtils.SECOND_IN_MILLIS;
+  private static final long UPDATE_CHECK_INTERVAL = 30 * DateUtils.MINUTE_IN_MILLIS;
+  private static final long BROADCAST_COMBINATION_DELAY = 2500;
+
+  private static final int NO_FLAG = 0;
+  private static final int OLDEST_SAMSUNG_INTERNET_5_VERSIONCODE = 500000000;
+
+  private final ReentrantLock accessLock = new ReentrantLock();
+  private DefaultSubscriptions defaultSubscriptions;
+  private Subscriptions subscriptions;
+  private JSONPrefs jsonPrefs;
+  private AppInfo appInfo;
+  private final LinkedBlockingQueue<EngineEvent> engineEvents = new LinkedBlockingQueue<>();
+  private Thread handlerThread;
+  private Downloader downloader;
+  private SubscriptionUpdateCallback subscriptionUpdateCallback;
+  private final Context serviceContext;
+  private boolean wasFirstRun = false;
+  private long nextUpdateBroadcast = Long.MAX_VALUE;
+
+  private Engine(final Context context)
+  {
+    this.serviceContext = context;
+  }
+
+  public String getPrefsDefault(final String key)
+  {
+    return this.jsonPrefs.getDefaults(key);
+  }
+
+  DefaultSubscriptionInfo getDefaultSubscriptionInfo(final Subscription sub)
+  {
+    return this.defaultSubscriptions.getForUrl(sub.getURL());
+  }
+
+  void lock()
+  {
+    this.accessLock.lock();
+  }
+
+  void unlock()
+  {
+    this.accessLock.unlock();
+  }
+
+  public static boolean openSBrowserSettings(final Context activityContext)
+  {
+    final Intent intent = new Intent(ACTION_OPEN_SETTINGS);
+    final List<ResolveInfo> list = activityContext.getPackageManager()
+        .queryIntentActivities(intent, 0);
+    if (list.size() > 0)
+    {
+      activityContext.startActivity(intent);
+    }
+    return list.size() > 0;
+  }
+
+  public static boolean hasCompatibleSBrowserInstalled(final Context activityContext)
+  {
+    try
+    {
+      return activityContext.getPackageManager()
+          .queryIntentActivities(new Intent(ACTION_OPEN_SETTINGS), 0).size() > 0;
+    }
+    catch (final Throwable t)
+    {
+      return false;
+    }
+  }
+
+  /**
+   * Starting with Samsung Internet 5.0, the way to enable ad blocking has changed. As a result, we
+   * need to check for the version of Samsung Internet and apply text changes to the first run slide.
+   *
+   * @param activityContext
+   * @return a boolean that indicates, if the user has Samsung Internet version 5.x
+   */
+  public static boolean hasSamsungInternetVersion5OrNewer(final Context activityContext)
+  {
+    try
+    {
+      PackageInfo packageInfo = activityContext.getPackageManager().getPackageInfo(SBROWSER_APP_ID, NO_FLAG);
+      return packageInfo.versionCode >= OLDEST_SAMSUNG_INTERNET_5_VERSIONCODE;
+    }
+    catch (PackageManager.NameNotFoundException e)
+    {
+      // Should never happen, as checkAAStatusAndProceed() should not be called if the user
+      // has no compatible SBrowser installed. Nevertheless we have to handle the Exception.
+      Log.d(TAG, "No compatible Samsung Browser found.", e);
+      return false;
+    }
+  }
+
+  public void setSubscriptionUpdateCallback(final SubscriptionUpdateCallback subscriptionUpdateCallback)
+  {
+    this.subscriptionUpdateCallback = subscriptionUpdateCallback;
+  }
+
+  public void requestUpdateBroadcast()
+  {
+    this.nextUpdateBroadcast = System.currentTimeMillis() + BROADCAST_COMBINATION_DELAY;
+  }
+
+  private void writeFileAndSendUpdateBroadcast()
+  {
+    createAndWriteFile();
+
+    runOnUiThread(new Runnable()
+    {
+      @Override
+      public void run()
+      {
+        final Intent intent = new Intent();
+        intent.setAction(ACTION_UPDATE);
+        intent.setData(Uri.parse("package:" + Engine.this.serviceContext.getPackageName()));
+        Engine.this.serviceContext.sendBroadcast(intent);
+      }
+    });
+  }
+
+  boolean canUseInternet()
+  {
+    final ConnectivityManager connManager = (ConnectivityManager) this.serviceContext
+        .getSystemService(Context.CONNECTIVITY_SERVICE);
+    final NetworkInfo current = connManager.getActiveNetworkInfo();
+    if (current == null)
+    {
+      return false;
+    }
+
+    if (wasFirstRun())
+    {
+      return true;
+    }
+
+    final boolean wifiOnly = "1".equals(SharedPrefsUtils.getString(
+        this.serviceContext, R.string.key_automatic_updates , "1"));
+
+    if (wifiOnly)
+    {
+      if (current.isConnected() && !current.isRoaming())
+      {
+        switch (current.getType())
+        {
+          case ConnectivityManager.TYPE_BLUETOOTH:
+          case ConnectivityManager.TYPE_ETHERNET:
+          case ConnectivityManager.TYPE_WIFI:
+          case ConnectivityManager.TYPE_WIMAX:
+            return true;
+          default:
+            return false;
+        }
+      }
+      return false;
+    }
+    return current.isConnected();
+  }
+
+  public List<SubscriptionInfo> getListedSubscriptions()
+  {
+    return this.subscriptions.getSubscriptions(this);
+  }
+
+  public void changeSubscriptionState(final String id, final boolean enabled)
+  {
+    if (this.subscriptionUpdateCallback != null)
+    {
+      subscriptionUpdateCallback.subscriptionUpdateRequested(enabled);
+    }
+    this.engineEvents.add(new ChangeEnabledStateEvent(id, enabled));
+  }
+
+  public void subscriptionStateChanged()
+  {
+    if (this.subscriptionUpdateCallback != null)
+    {
+      subscriptionUpdateCallback.subscriptionUpdatedApplied();
+    }
+  }
+
+  public void createAndAddSubscriptionFromUrl(final String url,
+      final SubscriptionAddedCallback callback) throws IOException
+  {
+    final Subscription sub = Subscription.create(url);
+    sub.putMeta(Subscription.KEY_TITLE, url);
+    sub.setEnabled(true);
+    subscriptions.add(sub);
+    subscriptions.persistSubscription(sub);
+    callback.subscriptionAdded();
+  }
+
+  public void removeSubscriptionById(final String subscriptionId)
+  {
+    subscriptions.remove(subscriptionId);
+  }
+
+  void downloadFinished(final String id, final int responseCode, final String response,
+      final Map<String, String> headers)
+  {
+    this.engineEvents.add(new DownloadFinishedEvent(id, responseCode, response, headers));
+  }
+
+  private void createAndWriteFile()
+  {
+    this.lock();
+    try
+    {
+      Log.d(TAG, "Writing filters...");
+      final File filterFile = this.subscriptions.createAndWriteFile();
+      writeWhitelistedWebsites(this.serviceContext, filterFile);
+
+      SharedPrefsUtils.putString(
+          this.serviceContext, R.string.key_cached_filter_path, filterFile.getAbsolutePath());
+
+      Log.d(TAG, "Cleaning up cache...");
+      final File dummyFile = getDummyFilterFile(this.serviceContext);
+      final File[] cacheDirFiles = getFilterCacheDir(this.serviceContext).listFiles();
+      if (cacheDirFiles != null)
+      {
+        for (final File file : cacheDirFiles)
+        {
+          if (!file.equals(dummyFile) && !file.equals(filterFile))
+          {
+            Log.d(TAG, "Deleting file:" + file);
+            file.delete();
+          }
+        }
+      }
+    }
+    catch (IOException e)
+    {
+      Log.e(TAG, "Failed to write filters", e);
+    }
+    finally
+    {
+      this.unlock();
+    }
+  }
+
+  public static void runOnUiThread(final Runnable runnable)
+  {
+    new Handler(Looper.getMainLooper()).post(runnable);
+  }
+
+  public boolean isAcceptableAdsEnabled()
+  {
+    this.lock();
+    try
+    {
+      return this.subscriptions.isSubscriptionEnabled("url:"
+          + this.getPrefsDefault(SUBSCRIPTIONS_EXCEPTIONSURL));
+    }
+    finally
+    {
+      this.unlock();
+    }
+  }
+
+  public DefaultSubscriptionInfo getDefaultSubscriptionInfoForUrl(final String url)
+  {
+    return this.defaultSubscriptions.getForUrl(url);
+  }
+
+  /**
+   * If the user starts the app for the first time, we force to update the subscription which was
+   * selected as the default, no matter if he has a WIFI connection or not. From the second start
+   * we only update when the user has a WIFI connection.
+   *
+   * @return a boolean that indicated if this is the first start of the app
+   */
+  @VisibleForTesting
+  private boolean wasFirstRun()
+  {
+    if (wasFirstRun)
+    {
+      this.wasFirstRun = false;
+      return true;
+    }
+    else
+    {
+      return false;
+    }
+  }
+
+  private void migrateFromPreviousVersion(final Context context)
+  {
+    try
+    {
+      final int versionCode = context.getPackageManager().getPackageInfo(context.getPackageName(),
+          0).versionCode;
+
+      final int previousVersionCode = SharedPrefsUtils.getInt(
+          context, R.string.key_previous_version_code, 0);
+
+      if (versionCode > previousVersionCode)
+      {
+        if (previousVersionCode > 0)
+        {
+          // We can do possible migration stuff here
+          // Currently we only persist the new version code
+        }
+        SharedPrefsUtils.putInt(context, R.string.key_previous_version_code, versionCode);
+      }
+    }
+    catch (final Throwable t)
+    {
+      Log.e(TAG, "Failed on migration, please clear all application data", t);
+    }
+  }
+
+  static Engine create(final Context context) throws IOException
+  {
+    final Engine engine = new Engine(context);
+
+    // Migration data from previous version (if needed)
+    engine.migrateFromPreviousVersion(context);
+    Log.d(TAG, "Migration done");
+
+    engine.appInfo = AppInfo.create(context);
+
+    Log.d(TAG, "Creating engine, appInfo=" + engine.appInfo.toString());
+
+    try (final InputStream subscriptionsXml = context.getResources()
+        .openRawResource(R.raw.subscriptions))
+    {
+      engine.defaultSubscriptions = DefaultSubscriptions.fromStream(subscriptionsXml);
+    }
+
+    Log.d(TAG, "Finished reading 'subscriptions.xml'");
+    engine.subscriptions = Subscriptions.initialize(engine, getSubscriptionsDir(context),
+        getFilterCacheDir(context));
+
+    try (final InputStream prefsJson = context.getResources().openRawResource(R.raw.prefs))
+    {
+      engine.jsonPrefs = JSONPrefs.create(prefsJson);
+    }
+
+    Log.d(TAG, "Finished reading JSON preferences");
+
+    // Check if this is a fresh start, if so: initialize bundled easylist.
+    engine.wasFirstRun = engine.subscriptions.wasUnitialized();
+    if (engine.subscriptions.wasUnitialized())
+    {
+      Log.d(TAG, "Subscription storage was uninitialized, initializing...");
+
+      try (final InputStream easylistTxt = context.getResources().openRawResource(R.raw.easylist))
+      {
+        final Subscription easylist = engine.subscriptions.add(Subscription
+            // Use bundled EasyList as default and update it with locale specific list later
+            // see: https://issues.adblockplus.org/ticket/5237
+            .create(SubscriptionUtils.chooseDefaultSubscriptionUrl(
+                engine.defaultSubscriptions.getAdsSubscriptions()))
+            .parseLines(readLines(easylistTxt)));
+        easylist.putMeta(Subscription.KEY_UPDATE_TIMESTAMP, "0");
+        easylist.setEnabled(true);
+      }
+      Log.d(TAG, "Added and enabled bundled easylist");
+
+      try (final InputStream exceptionsTxt = context.getResources()
+          .openRawResource(R.raw.exceptionrules))
+      {
+        final Subscription exceptions = engine.subscriptions.add(Subscription
+            .create(engine.getPrefsDefault(SUBSCRIPTIONS_EXCEPTIONSURL))
+            .parseLines(readLines(exceptionsTxt)));
+        exceptions.putMeta(Subscription.KEY_UPDATE_TIMESTAMP, "0");
+        exceptions.setEnabled(true);
+      }
+      Log.d(TAG, "Added and enabled bundled exceptionslist");
+
+      int additional = 0;
+      for (final Subscription sub : engine.defaultSubscriptions.createSubscriptions())
+      {
+        if (!engine.subscriptions.hasSubscription(sub.getId()))
+        {
+          additional++;
+          engine.subscriptions.add(sub);
+        }
+      }
+
+      Log.d(TAG, "Added " + additional + " additional default/built-in subscriptions");
+      engine.subscriptions.persistSubscriptions();
+    }
+
+    engine.handlerThread = new Thread(new EventHandler(engine));
+    engine.handlerThread.setDaemon(true);
+    engine.handlerThread.start();
+
+    engine.downloader = Downloader.create(engine);
+
+    final File cachedFilterFile = getCachedFilterFile(context);
+    if (cachedFilterFile == null || !cachedFilterFile.exists())
+    {
+      engine.writeFileAndSendUpdateBroadcast();
+    }
+
+    return engine;
+  }
+
+  public static String readFileAsString(InputStream instream) throws IOException
+  {
+    final StringBuilder sb = new StringBuilder();
+    try (final BufferedReader r = new BufferedReader(new InputStreamReader(
+        instream, StandardCharsets.UTF_8)))
+    {
+      for (int ch = r.read(); ch != -1; ch = r.read())
+      {
+        sb.append((char) ch);
+      }
+    }
+    return sb.toString();
+  }
+
+  public static List<String> readLines(InputStream instream) throws IOException
+  {
+    final ArrayList<String> list = new ArrayList<>();
+    try (final BufferedReader r = new BufferedReader(new InputStreamReader(
+        instream, StandardCharsets.UTF_8)))
+    {
+      for (String line = r.readLine(); line != null; line = r.readLine())
+      {
+        list.add(line);
+      }
+    }
+    return list;
+  }
+
+  public static File getOrCreateCachedFilterFile(Context context) throws IOException
+  {
+    final File cachedFilterFile = getCachedFilterFile(context);
+    if (cachedFilterFile != null && cachedFilterFile.exists())
+    {
+      Log.d(TAG, "Cached filter file found: " + cachedFilterFile);
+      return cachedFilterFile;
+    }
+
+    Log.d(TAG, "Cached filter file not found. Using dummy filter file");
+    final File dummyFilterFile = getDummyFilterFile(context);
+    if (!dummyFilterFile.exists())
+    {
+      Log.d(TAG, "Creating dummy filter file...");
+      dummyFilterFile.getParentFile().mkdirs();
+      try (final BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(
+          new FileOutputStream(dummyFilterFile), StandardCharsets.UTF_8)))
+      {
+        writeFilterHeaders(writer);
+      }
+    }
+    return dummyFilterFile;
+  }
+
+  public static void writeFilterHeaders(Writer writer) throws IOException
+  {
+    writer.write("[Adblock Plus 2.0]\n");
+    writer.write("! This file was automatically created.\n");
+  }
+
+  private static void writeWhitelistedWebsites(Context context, File filterFile) throws IOException
+  {
+    Log.d(TAG, "Writing whitelisted websites...");
+    final Set<String> whitelistedWebsites = new TreeSet<>();
+    whitelistedWebsites.addAll(SharedPrefsUtils.getStringSet(
+        context, R.string.key_whitelisted_websites, Collections.<String>emptySet()));
+
+    try (final BufferedWriter w = new BufferedWriter( new OutputStreamWriter(
+        new FileOutputStream(filterFile, true), StandardCharsets.UTF_8)))
+    {
+      for (final String url : whitelistedWebsites)
+      {
+        try
+        {
+          final URI uri = new URI(url);
+          final String host = uri.getHost() != null ? uri.getHost() : uri.getPath();
+          w.write("@@||" + host + "^$document");
+          w.write('\n');
+        }
+        catch (URISyntaxException e)
+        {
+          Log.w(TAG, "Failed to parse whitelisted website: " + url);
+        }
+      }
+    }
+  }
+
+  private static File getCachedFilterFile(Context context)
+  {
+    final String cachedFilterPath = SharedPrefsUtils.getString(
+        context, R.string.key_cached_filter_path, null);
+
+    if (cachedFilterPath != null)
+    {
+      return new File(cachedFilterPath);
+    }
+
+    return null;
+  }
+
+  private static File getDummyFilterFile(Context context)
+  {
+    return new File(getFilterCacheDir(context), "dummy.txt");
+  }
+
+  private static File getFilterCacheDir(Context context)
+  {
+    return new File(context.getCacheDir(), "subscriptions");
+  }
+
+  private static File getSubscriptionsDir(Context context)
+  {
+    return new File(context.getFilesDir(), "subscriptions");
+  }
+
+  URL createDownloadURL(final Subscription sub) throws IOException
+  {
+    final StringBuilder sb = new StringBuilder();
+
+    sb.append(sub.getURL());
+    if (sub.getURL().getQuery() != null)
+    {
+      sb.append('&');
+    }
+    else
+    {
+      sb.append('?');
+    }
+
+    sb.append("addonName=");
+    sb.append(URLEncoder.encode(this.appInfo.addonName, StandardCharsets.UTF_8.name()));
+    sb.append("&addonVersion=");
+    sb.append(URLEncoder.encode(this.appInfo.addonVersion, StandardCharsets.UTF_8.name()));
+    sb.append("&application=");
+    sb.append(URLEncoder.encode(this.appInfo.application, StandardCharsets.UTF_8.name()));
+    sb.append("&applicationVersion=");
+    sb.append(URLEncoder.encode(this.appInfo.applicationVersion, StandardCharsets.UTF_8.name()));
+    sb.append("&platform=");
+    sb.append(URLEncoder.encode(this.appInfo.platform, StandardCharsets.UTF_8.name()));
+    sb.append("&platformVersion=");
+    sb.append(URLEncoder.encode(this.appInfo.platformVersion, StandardCharsets.UTF_8.name()));
+    sb.append("&lastVersion=");
+    sb.append(sub.getVersion());
+    sb.append("&downloadCount=");
+    final long downloadCount = sub.getDownloadCount();
+    if (downloadCount < 5)
+    {
+      sb.append(downloadCount);
+    }
+    else
+    {
+      sb.append("4%2B"); // "4+" URL encoded
+    }
+
+    return new URL(sb.toString());
+  }
+
+  public boolean isAcceptableAdsUrl(final SubscriptionInfo subscriptionInfo)
+  {
+    return getPrefsDefault(SUBSCRIPTIONS_EXCEPTIONSURL).equals(subscriptionInfo.getUrl());
+  }
+
+  private static class EventHandler implements Runnable
+  {
+    private static final String TAG = EventHandler.class.getSimpleName();
+    private final Engine engine;
+
+    public EventHandler(final Engine engine)
+    {
+      this.engine = engine;
+    }
+
+    @Override
+    public void run()
+    {
+      Log.d(TAG, "Handler thread started");
+      boolean interrupted = false;
+      long nextUpdateCheck = System.currentTimeMillis()
+          + (long) ((1 + Math.random()) * INITIAL_UPDATE_CHECK_DELAY);
+      while (!interrupted)
+      {
+        try
+        {
+          final EngineEvent event = this.engine.engineEvents.poll(100, TimeUnit.MILLISECONDS);
+          engine.lock();
+          try
+          {
+            if (event != null)
+            {
+              switch (event.getType())
+              {
+                case CHANGE_ENABLED_STATE:
+                {
+                  final ChangeEnabledStateEvent cese = (ChangeEnabledStateEvent) event;
+                  Log.d(TAG, "Changing " + cese.id + " to enabled: " + cese.enabled);
+                  engine.subscriptions.changeSubscriptionState(cese.id, cese.enabled);
+                  break;
+                }
+                case DOWNLOAD_FINISHED:
+                {
+                  final DownloadFinishedEvent dfe = (DownloadFinishedEvent) event;
+                  Log.d(TAG, "Download finished for '" + dfe.id + "' with response code "
+                      + dfe.responseCode);
+                  this.engine.subscriptions.updateSubscription(dfe.id, dfe.responseCode,
+                      dfe.response, dfe.headers);
+                  break;
+                }
+                default:
+                  Log.d(TAG, "Unhandled type: " + event.getType());
+                  break;
+              }
+            }
+
+            final long currentTime = System.currentTimeMillis();
+            if (currentTime > nextUpdateCheck)
+            {
+              nextUpdateCheck = currentTime + UPDATE_CHECK_INTERVAL;
+
+              this.engine.subscriptions.checkForUpdates();
+            }
+
+            if (currentTime > this.engine.nextUpdateBroadcast)
+            {
+              this.engine.nextUpdateBroadcast = Long.MAX_VALUE;
+              Log.d(TAG, "Sending update broadcast");
+              this.engine.writeFileAndSendUpdateBroadcast();
+            }
+          }
+          finally
+          {
+            engine.unlock();
+          }
+        }
+        catch (final InterruptedException e)
+        {
+          Log.d(TAG, "Handler interrupted", e);
+          interrupted = true;
+        }
+        catch (final Throwable t)
+        {
+          Log.e(TAG, "Event processing failed: " + t.getMessage(), t);
+        }
+      }
+      Log.d(TAG, "Handler thread finished");
+    }
+  }
+
+  private static class EngineEvent
+  {
+    public enum EngineEventType
+    {
+      CHANGE_ENABLED_STATE,
+      FORCE_DOWNLOAD,
+      DOWNLOAD_FINISHED
+    }
+
+    private final EngineEventType type;
+
+    EngineEvent(final EngineEventType type)
+    {
+      this.type = type;
+    }
+
+    public EngineEventType getType()
+    {
+      return this.type;
+    }
+  }
+
+  private static class ChangeEnabledStateEvent extends EngineEvent
+  {
+    private final String id;
+    private final boolean enabled;
+
+    public ChangeEnabledStateEvent(final String id, final boolean enabled)
+    {
+      super(EngineEvent.EngineEventType.CHANGE_ENABLED_STATE);
+      this.id = id;
+      this.enabled = enabled;
+    }
+  }
+
+  private static class DownloadFinishedEvent extends EngineEvent
+  {
+    private final String id;
+    private final int responseCode;
+    private final String response;
+    private final HashMap<String, String> headers = new HashMap<>();
+
+    public DownloadFinishedEvent(final String id,
+        final int responseCode,
+        final String response,
+        final Map<String, String> headers)
+    {
+      super(EngineEvent.EngineEventType.DOWNLOAD_FINISHED);
+      this.id = id;
+      this.responseCode = responseCode;
+      this.response = response;
+      if (headers != null)
+      {
+        this.headers.putAll(headers);
+      }
+    }
+  }
+
+  public void enqueueDownload(final Subscription sub, final boolean forced) throws IOException
+  {
+    if (sub.getURL() != null && sub.shouldUpdate(forced))
+    {
+      final HashMap<String, String> headers = new HashMap<>();
+      if (sub.isMetaDataValid() && sub.isFiltersValid())
+      {
+        final String lastModified = sub.getMeta(Subscription.KEY_HTTP_LAST_MODIFIED);
+        if (!TextUtils.isEmpty(lastModified))
+        {
+          headers.put("If-Modified-Since", lastModified);
+        }
+        final String etag = sub.getMeta(Subscription.KEY_HTTP_ETAG);
+        if (!TextUtils.isEmpty(etag))
+        {
+          headers.put("If-None-Match", etag);
+        }
+      }
+      Log.d(TAG, headers.toString());
+      this.downloader.enqueueDownload(this.createDownloadURL(sub), sub.getId(), headers);
+    }
+  }
+
+  public void connectivityChanged()
+  {
+    this.downloader.connectivityChanged();
+  }
+
+  public interface SubscriptionUpdateCallback
+  {
+    void subscriptionUpdateRequested(boolean enabled);
+    void subscriptionUpdatedApplied();
+  }
+
+  public interface SubscriptionAddedCallback
+  {
+    void subscriptionAdded();
+  }
+}