Implemented Timezone Change broadcast receiver & Calibrated notificat…

…ion.

AnkiDroid/src/main/AndroidManifest.xml

@@ -450,6 +450,12 @@
                 <action android:name="android.intent.action.BOOT_COMPLETED" />
             </intent-filter>
         </receiver>
+        <receiver android:name=".receiver.TimeZoneChangeReceiver"
+            android:exported="false">
+            <intent-filter>
+                <action android:name="android.intent.action.TIMEZONE_CHANGED" />
+            </intent-filter>
+        </receiver>
 
         <!-- stuff for Samsung Multi-Window -->
         <uses-library

AnkiDroid/src/main/java/com/ichi2/anki/AnkiDroidApp.java

@@ -41,6 +41,7 @@
 import com.ichi2.anki.contextmenu.AnkiCardContextMenu;
 import com.ichi2.anki.contextmenu.CardBrowserContextMenu;
 import com.ichi2.anki.exception.StorageAccessException;
+import com.ichi2.anki.receiver.TimeZoneChangeReceiver;
 import com.ichi2.anki.services.BootService;
 import com.ichi2.anki.services.NotificationService;
 import com.ichi2.compat.CompatHelper;
@@ -251,6 +252,9 @@ public void onCreate() {
         Timber.i("AnkiDroidApp: Starting Services");
         new BootService().onReceive(this, new Intent(this, BootService.class));
 
+        Timber.i("AnkiDroidApp: Registering Broadcast Receivers");
+        TimeZoneChangeReceiver.Companion.registerTimeZoneChangeReceiver(this, new TimeZoneChangeReceiver());
+
         // TODO: Notification CleanUP. Delete the Notification Service after successful implementation of Notification Work Manager.
         // Register for notifications
         mNotifications.observeForever(unused -> NotificationService.triggerNotificationFor(this));

AnkiDroid/src/main/java/com/ichi2/anki/receiver/TimeZoneChangeReceiver.kt

@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2022 Prateek Singh <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * This program 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
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.ichi2.anki.receiver
+
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+import android.content.IntentFilter
+import com.ichi2.anki.NotificationDatastore
+import com.ichi2.anki.NotificationHelper
+import com.ichi2.libanki.utils.TimeManager
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import timber.log.Timber
+import java.util.*
+
+/**
+ * Broadcast receiver to listen timezone change of user.
+ * Changes the notification triggering time when user timezone changes.
+ * */
+class TimeZoneChangeReceiver : BroadcastReceiver() {
+
+    override fun onReceive(context: Context, intent: Intent) {
+        Timber.d("TimeZoneChangeReceiver Started...")
+
+        CoroutineScope(Dispatchers.Default).launch {
+            val notificationDatastore = NotificationDatastore.getInstance(context)
+
+            val oldTimezone: String = notificationDatastore.getString(TIMEZONE_KEY, "null")
+            val newTimezone: String = TimeZone.getDefault().id
+            val now = TimeManager.time.intTimeMS()
+
+            /**
+             * Get the current offset according to given TimeZone.
+             * */
+            fun getOffsetFromNow(timezone: String) = TimeZone.getTimeZone(timezone).getOffset(now)
+
+            if (oldTimezone != "null" || getOffsetFromNow(oldTimezone) == getOffsetFromNow(newTimezone)) {
+                Timber.d("No Timezone changed found...")
+                return@launch
+            }
+
+            Timber.d("Timezone changed...")
+            // Change the timezone to new timezone and recalculate the notification according to new time zone.
+            notificationDatastore.putStringAsync(TIMEZONE_KEY, newTimezone)
+
+            val oldCurrTimeMS = getZonedCurrTimeMS(oldTimezone)
+            val newCurrTimeMS = getZonedCurrTimeMS(newTimezone)
+            val timeDiffMS = oldCurrTimeMS - newCurrTimeMS
+
+            // Calibrate notification time.
+            NotificationHelper(context).calibrateNotificationTime(newCurrTimeMS, timeDiffMS)
+        }
+    }
+
+    companion object {
+        private const val TIMEZONE_KEY = "TIMEZONE"
+
+        /**
+         * Registers timezone change receiver on app start.
+         * */
+        fun registerTimeZoneChangeReceiver(context: Context, receiver: BroadcastReceiver) {
+            Timber.d("Registering Timezone change receiver...")
+
+            val filter = IntentFilter(Intent.ACTION_TIMEZONE_CHANGED)
+            context.registerReceiver(receiver, filter)
+        }
+
+        /**
+         * Get current time according the timezone of user.
+         * @return epoch time in milliseconds
+         * */
+        fun getZonedCurrTimeMS(zoneId: String): Long {
+            val currTimeMS = TimeManager.time.intTimeMS()
+            val offset = TimeZone.getTimeZone(zoneId).getOffset(currTimeMS)
+            return currTimeMS + offset
+        }
+    }
+}