Enables the use of owntracks transition events

By using the configuration option "use_events:yes" in the device_tracker section,
only 'enter'/'leave' events are considered to calculate the state of a tracker device.
The home zone is defined as the owntracks region 'home'. Other regions may also be defined, the name of
the region is then used as state for the device. All owntracks regions, the 'Share' setting must be enabled in the app.

homeassistant/components/device_tracker/owntracks.py

@@ -1,6 +1,6 @@
 """
 homeassistant.components.device_tracker.owntracks
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 OwnTracks platform for the device tracker.
 
 For more details about this platform, please refer to the documentation at
@@ -10,14 +10,16 @@ import json
 import logging
 
 import homeassistant.components.mqtt as mqtt
+from homeassistant.const import (STATE_HOME, STATE_NOT_HOME)
 
 DEPENDENCIES = ['mqtt']
 
+CONF_TRANSITION_EVENTS = 'use_events'
 LOCATION_TOPIC = 'owntracks/+/+'
-
+EVENT_TOPIC = 'owntracks/+/+/event'
 
 def setup_scanner(hass, config, see):
-    """ Set up a OwnTracksks tracker. """
+    """ Set up an OwnTracks tracker. """
 
     def owntracks_location_update(topic, payload, qos):
         """ MQTT message received. """
@@ -47,7 +49,58 @@ def setup_scanner(hass, config, see):
             kwargs['battery'] = data['batt']
 
         see(**kwargs)
+        
+    
+    def owntracks_event_update(topic, payload, qos):
+        """ MQTT event (geofences) received. """
 
-    mqtt.subscribe(hass, LOCATION_TOPIC, owntracks_location_update, 1)
+        # Docs on available data:
+        # http://owntracks.org/booklet/tech/json/#_typetransition
+        try:
+            data = json.loads(payload)
+        except ValueError:
+            # If invalid JSON
+            logging.getLogger(__name__).error(
+                'Unable to parse payload as JSON: %s', payload)
+            return
+
+        if not isinstance(data, dict) or data.get('_type') != 'transition':
+            return
+
+            
+        # check if in "home" fence or other zone
+        location = ''
+        if data['event'] == 'enter':
+            
+            if data['desc'] == 'home':
+                location = STATE_HOME
+            else:
+                location = data['desc']
+            
+        elif data['event'] == 'leave':
+            location = STATE_NOT_HOME
+        else:
+            logging.getLogger(__name__).error('Misformatted mqtt msgs, _type=transition, event=%s', data['event'])
+            return
+
+        parts = topic.split('/')
+        kwargs = {
+            'dev_id': '{}_{}'.format(parts[1], parts[2]),
+            'host_name': parts[1],
+            'gps': (data['lat'], data['lon']),
+            'location_name': location,
+        }
+        if 'acc' in data:
+            kwargs['gps_accuracy'] = data['acc']
+
+        see(**kwargs)
+    
+        
+    use_events = config.get(CONF_TRANSITION_EVENTS)
+   
+    if use_events:
+        mqtt.subscribe(hass, EVENT_TOPIC, owntracks_event_update, 1)
+    else:
+        mqtt.subscribe(hass, LOCATION_TOPIC, owntracks_location_update, 1)
 
     return True