Change to a notification based approach to getting the focused app's name

mac-agent/kb-focus.py

@@ -1,6 +1,6 @@
-import signal, sys
+import signal, sys, objc
 from AppKit import NSWorkspace
-from Foundation import NSRunLoop, NSDate
+from Foundation import NSRunLoop, NSDate, NSObject
 import hid
 
 VID, PID = 0x3384, 0x0009
@@ -20,47 +20,60 @@ def send_app_name(dev, name):
     dev.write(data)
     dev.read(32, timeout=1000)
 
+class AppObserver(NSObject):
+    def init(self):
+        self = objc.super(AppObserver, self).init()
+        self.dev = None
+        self.last_app = None
+        self.current_app = NSWorkspace.sharedWorkspace().frontmostApplication().localizedName()
+        return self
+
+    def appChanged_(self, notification):
+        app = notification.userInfo()["NSWorkspaceApplicationKey"].localizedName()
+        self.current_app = app
+        if self.dev is not None:
+            self.last_app = app
+            print(f"App: {app}")
+            try:
+                send_app_name(self.dev, app)
+            except Exception:
+                print("Keyboard disconnected")
+                self.dev = None
+                self.last_app = None
+
 def main():
     signal.signal(signal.SIGINT, lambda *_: sys.exit(0))
     ws = NSWorkspace.sharedWorkspace()
-    dev = None
-    last_app = None
+
+    observer = AppObserver.alloc().init()
+    ws.notificationCenter().addObserver_selector_name_object_(
+        observer, "appChanged:", "NSWorkspaceDidActivateApplicationNotification", None
+    )
 
     while True:
         connected = find_keyboard_path() is not None
 
         # Detect disconnect
-        if dev is not None and not connected:
+        if observer.dev is not None and not connected:
             print("Keyboard disconnected")
-            dev = None
-            last_app = None
+            observer.dev = None
+            observer.last_app = None
 
         # Connect and send current app
-        if dev is None and connected:
+        if observer.dev is None and connected:
             try:
-                dev = hid.Device(path=find_keyboard_path())
+                observer.dev = hid.Device(path=find_keyboard_path())
                 print("Keyboard connected")
-                last_app = ws.frontmostApplication().localizedName()
-                print(f"App: {last_app}")
-                send_app_name(dev, last_app)
+                observer.last_app = observer.current_app
+                print(f"App: {observer.current_app}")
+                send_app_name(observer.dev, observer.current_app)
             except Exception:
-                dev = None
-
-        # App change
-        if dev is not None:
-            app = ws.frontmostApplication().localizedName()
-            if app != last_app:
-                print(f"App: {app}")
-                last_app = app
-                try:
-                    send_app_name(dev, app)
-                except Exception:
-                    print("Keyboard disconnected")
-                    dev = None
-                    last_app = None
+                observer.dev = None
 
+        # Pump run loop — notifications fire here and send immediately;
+        # 2s is enough for connect/disconnect detection
         NSRunLoop.currentRunLoop().runUntilDate_(
-            NSDate.dateWithTimeIntervalSinceNow_(0.25)
+            NSDate.dateWithTimeIntervalSinceNow_(2.0)
         )
 
 if __name__ == "__main__":