webapps: introduce helper class to store extended set of data

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappDataStorage.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.graphics.Bitmap;
+import android.os.AsyncTask;
+
+import org.chromium.chrome.browser.ShortcutHelper;
+
+/**
+ * This is a class used to store data about an installed webapp. It uses SharedPreferences
+ * to persist the data to disk.

[mlamouri (slow - plz ping), 2015/08/27 16:18:23]

nit: I would add a comment explaining that every time .open() is called, the
LAST_USED time is update. It can be checked without updating it using
.getLastUsedTime()

+ */
+public class WebappDataStorage {
+
+    static final String SHARED_PREFS_FILE_PREFIX = "webapp_";
+    static final String KEY_SPLASH_ICON = "splash_icon";
+    static final String KEY_LAST_USED = "last_used";
+
+    private final SharedPreferences mPreferences;
+
+    /**
+     * Opens an instance of WebappDataStorage for the webapp specified.
+     * @param context  The context to open the SharedPreferences.
+     * @param webappId The ID of the webapp which is being opened.
+     */
+    public static WebappDataStorage open(Context context, String webappId) {
+        WebappDataStorage storage = new WebappDataStorage(
+                context.getApplicationContext(), webappId);
+        storage.updateLastUsedTime();
+        return storage;
+    }
+
+    /**
+     * Asynchronously retrieves the time which this WebappDataStorage was last
+     * opened using {@link WebappDataStorage#open(Context, String)}.
+     * @param context  The context to read the SharedPreferences file.
+     * @param webappId The ID of the webapp the used time is being read for.
+     * @param callback Called when the last used time has been retrieved.
+     */
+    public static void getLastUsedTime(Context context, String webappId,
+            final FetchCallback<Long> callback) {
+        new WebappDataStorage(context.getApplicationContext(), webappId)
+                .getLastUsedTime(callback);
+    }
+
+    private WebappDataStorage(Context context, String webappId) {
+        mPreferences = context.getSharedPreferences(
+                SHARED_PREFS_FILE_PREFIX + webappId, Context.MODE_PRIVATE);
+    }
+
+    /*
+     * Asynchronously retrieves the splash screen image associated with the
+     * current webapp.
+     * @param callback Called when the splash screen image has been retrieved.
+     *                 May be null if no image was found.
+     */
+    public void getSplashScreenImage(final FetchCallback<Bitmap> callback) {
+        new BitmapFetchTask(KEY_SPLASH_ICON, callback).execute();
+    }
+
+    /*
+     * Update the information associated with the webapp with the specified data.
+     * @param splashScreenImage The image which should be shown on the splash screen of the webapp.
+     */
+    public void updateSplashScreenImage(final Bitmap splashScreenImage) {
+        new UpdateTask(splashScreenImage).execute();
+    }
+
+    private void getLastUsedTime(final FetchCallback<Long> callback) {
+        new AsyncTask<Void, Void, Long>() {
+            @Override
+            protected final Long doInBackground(Void... nothing) {
+                return mPreferences.getLong(KEY_LAST_USED, -1L);
+            }
+
+            @Override
+            protected final void onPostExecute(Long result) {
+                callback.onDataRetrieved(result == -1L ? null : result);

[mlamouri (slow - plz ping), 2015/08/27 16:18:23]

-1 shouldn't happen, right? Should that assert?

[Lalit Maganti, 2015/08/27 16:24:34]

-1 will be returned if there is no last used time. Although extremely unlikely
that getLastUsedTime would be called without a webapp existing it could
theoretically happen.

[mlamouri (slow - plz ping), 2015/08/27 16:29:30]

That's the point. Can you add an assert?

[Lalit Maganti, 2015/08/27 16:40:30]

OK done.

+            }
+        }.execute();
+    }
+
+    private WebappDataStorage updateLastUsedTime() {
+        new AsyncTask<Void, Void, Void>() {
+            @Override
+            protected final Void doInBackground(Void... nothing) {
+                mPreferences.edit()
+                        .putLong(KEY_LAST_USED, System.currentTimeMillis())
+                        .commit();
+                return null;
+            }
+        }.execute();
+        return this;
+    }
+
+    /**
+     * Called after data has been retrieved from storage.
+     */
+    public interface FetchCallback<T> {
+        public void onDataRetrieved(T readObject);
+    }
+
+    private final class BitmapFetchTask extends AsyncTask<Void, Void, Bitmap> {
+
+        private final String mKey;
+        private final FetchCallback<Bitmap> mCallback;
+
+        public BitmapFetchTask(String key, FetchCallback<Bitmap> callback) {
+            mKey = key;
+            mCallback = callback;
+        }
+
+        @Override
+        protected final Bitmap doInBackground(Void... nothing) {
+            System.out.println(mPreferences.getString(mKey, null));

[mlamouri (slow - plz ping), 2015/08/27 16:18:23]

nit: remove?

[Lalit Maganti, 2015/08/27 16:24:34]

Whoops missed removing this one.

Done.

+            return ShortcutHelper.decodeBitmapFromString(mPreferences.getString(mKey, null));
+        }
+
+        @Override
+        protected final void onPostExecute(Bitmap result) {
+            mCallback.onDataRetrieved(result);
+        }
+    }
+
+    private final class UpdateTask extends AsyncTask<Void, Void, Void> {
+
+        private final Bitmap mSplashImage;
+
+        public UpdateTask(Bitmap splashImage) {
+            mSplashImage = splashImage;
+        }
+
+        @Override
+        protected Void doInBackground(Void... nothing) {
+            mPreferences.edit()
+                    .putString(KEY_SPLASH_ICON, ShortcutHelper.encodeBitmapAsString(mSplashImage))
+                    .commit();
+            return null;
+        }
+    }
+}