Issue 1399: Restore app_id style behaviour

The man page says that app_id should only be set as a class when it is
the only window in the workspace. This commit restores this behaviour.

Author: RobertMueller2

src/modules/sway/window.cpp

@@ -93,9 +93,6 @@ void Window::updateAppIcon() {
 }
 
 auto Window::update() -> void {
-  if (!old_app_id_.empty()) {
-    bar_.window.get_style_context()->remove_class(old_app_id_);
-  }
   spdlog::trace("workspace layout {}, tiled count {}, floating count {}", layout_, app_nb_, floating_count_ );
 
   int mode = 0;
@@ -121,14 +118,21 @@ auto Window::update() -> void {
     }
   }
 
+  if (!old_app_id_.empty() && ((mode &2) == 0 || old_app_id_ != app_id_) && bar_.window.get_style_context()->has_class(old_app_id_)) {
+    spdlog::trace("Removing app_id class: {}", old_app_id_);
+    bar_.window.get_style_context()->remove_class(old_app_id_);
+    old_app_id_="";
+  }
+
   setClass("empty", ((mode &1) > 0));
   setClass("solo", ((mode &2) > 0));
   setClass("floating", ((mode &4) > 0));
   setClass("tabbed", ((mode &8) > 0));
   setClass("stacked", ((mode &16) > 0));
   setClass("tiled", ((mode &32) > 0));
 
-  if (!app_id_.empty() && !bar_.window.get_style_context()->has_class(app_id_)) {
+  if ((mode &2) > 0 && !app_id_.empty() && !bar_.window.get_style_context()->has_class(app_id_)) {
+    spdlog::trace("Adding app_id class: {}", app_id_);
     bar_.window.get_style_context()->add_class(app_id_);
     old_app_id_ = app_id_;
   }