webapps: Add cleanup task when opening up WebappActivity to clean old web apps

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.webapps;
 
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.os.AsyncTask;
 
@@ skipping 10 matching lines @@
  *
  * It is NOT intended to be 100% accurate nor a comprehensive list of all installed web apps
  * because it is impossible to track when the user removes a web app from the Home screen and it
  * is similarily impossible to track pre-registry era web apps (this case is not a problem anyway
  * as these web apps have no external data to cleanup).
  */
 public class WebappRegistry {
 
     static final String REGISTRY_FILE_NAME = "webapp_registry";
     static final String KEY_WEBAPP_SET = "webapp_set";
+    static final String KEY_LAST_CLEANUP = "last_cleanup";
+
+    /** Represents a period of 4 weeks in milliseconds */
+    static final long FULL_CLEANUP_DURATION = 4 * 7 * 24 * 60 * 60 * 1000;

[mlamouri (slow - plz ping), 2015/09/24 15:20:04]

Could you use
http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html :)

[Lalit Maganti, 2015/09/24 16:09:38]

Done.

+
+    /** Represents a period of 13 weeks in milliseconds */
+    static final long WEBAPP_UNOPENED_CLEANUP_DURATION = 13 * 7 * 24 * 60 * 60 * 1000;

[mlamouri (slow - plz ping), 2015/09/24 15:20:04]

ditto

[Lalit Maganti, 2015/09/24 16:09:37]

Done.

 
     /**
      * Called when a retrieval of the stored web apps occurs.
      */
     public interface FetchCallback {
         public void onWebappIdsRetrieved(Set<String> readObject);
     }
 
     /**
      * Registers the existence of a web app and creates the SharedPreference for it.
@@ skipping 33 matching lines @@
             }
 
             @Override
             protected final void onPostExecute(Set<String> result) {
                 callback.onWebappIdsRetrieved(result);
             }
         }.execute();
     }
 
     /**
+     * Deletes the data for all "old" web apps. i.e. web apps which have not been opened by the user
+     * in the last 3 months. Cleanup is run, at most, once a month.
+     * @param context     Context to open the registry with.
+     * @param currentTime The current time which will be checked to decide if the task should be run
+     *                    and if a web app should be cleaned up.
+     */
+    static void unregisterOldWebapps(final Context context, final long currentTime) {
+        new AsyncTask<Void, Void, Void>() {
+            @Override
+            protected final Void doInBackground(Void... nothing) {
+                SharedPreferences preferences = openSharedPreferences(context);
+                long lastCleanup = preferences.getLong(KEY_LAST_CLEANUP, 0);
+                if (currentTime - lastCleanup < FULL_CLEANUP_DURATION) return null;

[mlamouri (slow - plz ping), 2015/09/24 15:20:04]

nit: I would use parenthesis: |if ((currentTime - lastUsed) <
FULL_CLEANUP_DURATION) continue;

[Lalit Maganti, 2015/09/24 16:09:37]

Done.

+
+                Set<String> currentWebapps = getRegisteredWebappIds(preferences);
+                Set<String> retainedWebapps = new HashSet<String>(currentWebapps);
+                for (String id : currentWebapps) {
+                    long lastUsed = new WebappDataStorage(context, id).getLastUsedTime();
+                    if (currentTime - lastUsed < WEBAPP_UNOPENED_CLEANUP_DURATION) continue;

[mlamouri (slow - plz ping), 2015/09/24 15:20:04]

ditto

[Lalit Maganti, 2015/09/24 16:09:37]

Done.

+
+                    WebappDataStorage.deleteDataForWebapp(context, id);
+                    retainedWebapps.remove(id);
+                }
+
+                preferences.edit()
+                        .putLong(KEY_LAST_CLEANUP, currentTime)
+                        .putStringSet(KEY_WEBAPP_SET, retainedWebapps)
+                        .commit();
+                return null;
+            }
+        }.execute();
+    }
+
+    /**
      * Deletes the data of all web apps, as well as the registry tracking the web apps.
      */
     @VisibleForTesting
     static void unregisterAllWebapps(final Context context, final Runnable callback) {
         new AsyncTask<Void, Void, Void>() {
             @Override
             protected final Void doInBackground(Void... nothing) {
                 SharedPreferences preferences = openSharedPreferences(context);
                 for (String id : getRegisteredWebappIds(preferences)) {
                     WebappDataStorage.deleteDataForWebapp(context, id);
@@ skipping 26 matching lines @@
 
     private static Set<String> getRegisteredWebappIds(SharedPreferences preferences) {
         return preferences.getStringSet(KEY_WEBAPP_SET, Collections.<String>emptySet());
     }
 
     private WebappRegistry() {
     }
 
     private static native void nativeOnWebappsUnregistered(long callbackPointer);
 }