/*
* Copyright 2012 Google Inc. 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.
*/
package net.coding.program.login.auth;
import android.content.Context;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;
/**
* Clock input for the time-based OTPs (TOTP). The input is based on the current system time
* and is adjusted by a persistently stored correction value (offset in minutes).
*
* @author klyubin@google.com (Alex Klyubin)
*/
public class TotpClock implements SharedPreferences.OnSharedPreferenceChangeListener {
// @VisibleForTesting
static final String PREFERENCE_KEY_OFFSET_MINUTES = "timeCorrectionMinutes";
private final SharedPreferences mPreferences;
private final Object mLock = new Object();
/**
* Cached value of time correction (in minutes) or {@code null} if not cached. The value is cached
* because it's read very frequently (once every 100ms) and is modified very infrequently.
*
* @GuardedBy {@link #mLock}
*/
private Integer mCachedCorrectionMinutes;
public TotpClock(Context context) {
mPreferences = PreferenceManager.getDefaultSharedPreferences(context);
mPreferences.registerOnSharedPreferenceChangeListener(this);
}
/**
* Gets the number of milliseconds since epoch.
*/
public long currentTimeMillis() {
return System.currentTimeMillis() + getTimeCorrectionMinutes() * Utilities.MINUTE_IN_MILLIS;
}
/**
* Gets the currently used time correction value.
*
* @return number of minutes by which this device is behind the correct time.
*/
public int getTimeCorrectionMinutes() {
synchronized (mLock) {
if (mCachedCorrectionMinutes == null) {
try {
mCachedCorrectionMinutes = mPreferences.getInt(PREFERENCE_KEY_OFFSET_MINUTES, 0);
} catch (ClassCastException e) {
mCachedCorrectionMinutes = Integer.valueOf(mPreferences.getString(PREFERENCE_KEY_OFFSET_MINUTES, "0"));
}
}
return mCachedCorrectionMinutes;
}
}
/**
* Sets the currently used time correction value.
*
* @param minutes number of minutes by which this device is behind the correct time.
*/
public void setTimeCorrectionMinutes(int minutes) {
synchronized (mLock) {
mPreferences.edit().putInt(PREFERENCE_KEY_OFFSET_MINUTES, minutes).commit();
// Invalidate the cache to force reading actual settings from time to time
mCachedCorrectionMinutes = null;
}
}
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
if (key.equals(PREFERENCE_KEY_OFFSET_MINUTES)) {
// Invalidate the cache
mCachedCorrectionMinutes = null;
}
}
}