import pyudev
import threading

class DevicePoller:
   def __init__(self, dev):
      self.device_added = threading.Event()
      self.device_removed = threading.Event()
      self.device = dev
      self.wait_add = self.device_added.wait
      self.wait_remove = self.device_removed.wait
      self.have = self.device_added.is_set

      if dev:
         self.device_added.set()

   def launch_observer(self, monitor, device_match):

      if not monitor:
         monitor = pyudev.Monitor.from_netlink(pyudev.Context())

      def handle_event(action, device):
         if action == 'add' and device_match(device):
            self.device = device
            self.device_removed.clear()
            self.device_added.set()
         elif action == 'remove' and device == self.device:
            self.device = None
            self.device_added.clear()
            self.device_removed.set()

      self.observer = pyudev.MonitorObserver(monitor, handle_event)
      self.observer.start()

   def stop_observer():
      self.observer.stop()

def simple_devicer(subsystem, predicate):
   dev = None
   context = pyudev.Context()
   for try_dev in context.list_devices(subsystem=subsystem):
      if predicate(try_dev):
         dev = try_dev
         break

   monitor = pyudev.Monitor.from_netlink(context)
   monitor.filter_by(subsystem)

   devicer = DevicePoller(dev)
   devicer.launch_observer(monitor, predicate)

   return devicer

if __name__ == '__main__':

   dexcom_g5_product = '22a3/47/100'

   def is_dexcom_g5(dev):
      try: return dev.parent.get('PRODUCT') == dexcom_g5_product
      except: return False

   devicer = simple_devicer('tty', is_dexcom_g5)

   while True:
      print("waiting for device")
      devicer.wait_add()
      while devicer.have():
         print("poll device {0}".format(devicer.device))
         print("sleep(5)")
         if devicer.wait_remove(5):
            print("device removed")

   devicer.stop_observer()