do not notify for messages from strangers by default

src/main/java/de/pixart/messenger/entities/Conversation.java

@@ -1036,6 +1036,26 @@ public class Conversation extends AbstractEntity implements Blockable, Comparabl
         }
     }
 
+    private int sentMessagesCount() {
+        int count = 0;
+        synchronized (this.messages) {
+            for (Message message : messages) {
+                if (message.getStatus() != Message.STATUS_RECEIVED) {
+                    ++count;
+                }
+            }
+        }
+        return count;
+    }
+
+    public boolean isWithStranger() {
+        if (mode == MODE_SINGLE) {
+            return !getContact().mutualPresenceSubscription() && sentMessagesCount() == 0;
+        } else {
+            return false;
+        }
+    }
+
     public class Smp {
         public static final int STATUS_NONE = 0;
         public static final int STATUS_CONTACT_REQUESTED = 1;

src/main/java/de/pixart/messenger/services/NotificationService.java

@@ -65,10 +65,11 @@ public class NotificationService {
     }
 
     public boolean notify(final Message message) {
-        return (message.getStatus() == Message.STATUS_RECEIVED)
+        return message.getStatus() == Message.STATUS_RECEIVED
                 && notificationsEnabled()
                 && !message.getConversation().isMuted()
-                && (message.getConversation().alwaysNotify() || wasHighlightedOrPrivate(message)
+                && (message.getConversation().alwaysNotify() || wasHighlightedOrPrivate(message))
+                && (!message.getConversation().isWithStranger() || notificationsFromStrangers()
         );
     }
 
@@ -76,6 +77,11 @@ public class NotificationService {
         return mXmppConnectionService.getPreferences().getBoolean("show_notification", true);
     }
 
+    private boolean notificationsFromStrangers() {
+        return mXmppConnectionService.getPreferences().getBoolean("notifications_from_strangers",
+                mXmppConnectionService.getResources().getBoolean(R.bool.notifications_from_strangers));
+    }
+
     public boolean isQuietHours() {
         if (!mXmppConnectionService.getPreferences().getBoolean("enable_quiet_hours", false)) {
             return false;

src/main/res/values/defaults.xml

@@ -3,4 +3,5 @@
     <string name="default_resource" translatable="false">Phone</string>
     <bool name="portrait_only">true</bool>
     <bool name="enter_is_send">false</bool>
+    <bool name="notifications_from_strangers">false</bool>
 </resources>

src/main/res/values/strings.xml

@@ -749,4 +749,6 @@
     <string name="block_jabber_id">Block Jabber ID</string>
     <string name="corresponding_conversations_closed">Corresponding conversations closed.</string>
     <string name="contact_blocked_past_tense">Contact blocked.</string>
+    <string name="pref_notifications_from_strangers">Notifications from strangers</string>
+    <string name="pref_notifications_from_strangers_summary">Notify for messages received from strangers.</string>
 </resources>

src/main/res/xml/preferences.xml

@@ -86,6 +86,12 @@
             android:ringtoneType="notification"
             android:summary="@string/pref_sound_summary"
             android:title="@string/pref_sound" />
+        <CheckBoxPreference
+            android:defaultValue="@bool/notifications_from_strangers"
+            android:dependency="show_notification"
+            android:key="notifications_from_strangers"
+            android:summary="@string/pref_notifications_from_strangers_summary"
+            android:title="@string/pref_notifications_from_strangers" />
     </PreferenceScreen>
     <!--Attachments-->
     <PreferenceScreen