handled multiple race conditions

main.py

@@ -46,24 +46,46 @@ def main():
     with serial.Serial(device_name, 115200, timeout=1) as ser:
         shutdown_triggered = False
         inverter_online = True
+        last_online = time.monotonic()
+        receiving_data = True
+        last_logged = -1
+        try:
             while running:
                 line = ser.readline().decode(errors="ignore").strip()
-            if line == "":
-                logger.warning("No serial data")
-                continue
-            elif line == "0":
-                logger.debug("Inverter Online")
+
+                if line != "" and not receiving_data:
+                    receiving_data = True
+                    logger.info("Serial data restored")
+
+                if line == "0":
+                    if not inverter_online:
+                        logger.info("Inverter restored")
                     inverter_online = True
-            elif not inverter_online:
-                if time.time() - last_online > shutdown_timer:
-                    shutdown_triggered = True
-                    break
-            else:
+                    last_online = time.monotonic()
+
+                elif line == "1":
                     if inverter_online:
                         inverter_online = False
-                    last_online = time.time()
-                    logger.info(f"Running on UPS reserve, offline for {time.time()-last_online}s")
+                        logger.info("Running on UPS reserve")
 
+                elif line == "":
+                    if receiving_data:
+                        receiving_data = False
+                        logger.warning("No serial data")
+
+                else:
+                    logger.warning(f"Unexpected serial data: {line}")
+
+                if not inverter_online:
+                    sec = int(time.monotonic() - last_online)
+
+                    if sec % 10 == 0 and sec != last_logged:
+                        logger.info(f"Offline for {sec}s")
+                        last_logged = sec
+
+                    if sec >= shutdown_timer:
+                        shutdown_triggered = True
+                        break
             if shutdown_triggered:
                 logger.info(f"Inverter offline for {shutdown_timer} seconds")
                 try:
@@ -81,6 +103,9 @@ def main():
                 os.system("shutdown now")
             else:
                 logger.info("Exited cleanly (service stop)")
+        except serial.SerialException as e:
+            logger.error(f"Serial device error: {e}")
+            raise
 
 if __name__ == "__main__":
     main()