Record max idle time

app/src/main/java/eu/faircode/email/Core.java

@@ -3308,6 +3308,22 @@ class Core {
                 }
         }
 
+        private long maxIdle = 0;
+        private long lastActivity = 0;
+
+        synchronized void activity() {
+            long now = SystemClock.elapsedRealtime();
+            if (lastActivity > 0 && now - lastActivity > maxIdle) {
+                maxIdle = now - lastActivity;
+                Log.i("Max idle=" + (maxIdle / 1000));
+            }
+            lastActivity = now;
+        }
+
+        long getMaxIdle() {
+            return maxIdle;
+        }
+
         @NonNull
         @Override
         public String toString() {

app/src/main/java/eu/faircode/email/ServiceSynchronize.java

@@ -1020,6 +1020,7 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                                         while (ifolder.isOpen() && state.isRunning() && state.isRecoverable()) {
                                             Log.i(folder.name + " do idle");
                                             ifolder.idle(false);
+                                            state.activity();
                                         }
                                     } catch (Throwable ex) {
                                         Log.e(folder.name, ex);