Allow update entities on add_entities callback (#4114)

* Allow udpate entities on add_entities callback

* fix wrong position

* update force_update to update_before_add

* add unittest for update_befor_add

* fix unittest

* change mocking

homeassistant/helpers/entity_component.py

@@ -155,14 +155,15 @@ class EntityComponent(object):
             self.logger.exception(
                 'Error while setting up platform %s', platform_type)
 
-    def add_entity(self, entity, platform=None):
+    def add_entity(self, entity, platform=None, update_before_add=False):
         """Add entity to component."""
         return run_coroutine_threadsafe(
-            self.async_add_entity(entity, platform), self.hass.loop
+            self.async_add_entity(entity, platform, update_before_add),
+            self.hass.loop
         ).result()
 
     @asyncio.coroutine
-    def async_add_entity(self, entity, platform=None):
+    def async_add_entity(self, entity, platform=None, update_before_add=False):
         """Add entity to component.
 
         This method must be run in the event loop.
@@ -172,6 +173,13 @@ class EntityComponent(object):
 
         entity.hass = self.hass
 
+        # update/init entity data
+        if update_before_add:
+            if hasattr(entity, 'async_update'):
+                yield from entity.async_update()
+            else:
+                yield from self.hass.loop.run_in_executor(None, entity.update)
+
         if getattr(entity, 'entity_id', None) is None:
             object_id = entity.name or DEVICE_DEFAULT_NAME
 
@@ -274,19 +282,21 @@ class EntityPlatform(object):
         self.platform_entities = []
         self._async_unsub_polling = None
 
-    def add_entities(self, new_entities):
+    def add_entities(self, new_entities, update_before_add=False):
         """Add entities for a single platform."""
         run_coroutine_threadsafe(
-            self.async_add_entities(new_entities), self.component.hass.loop
+            self.async_add_entities(new_entities, update_before_add),
+            self.component.hass.loop
         ).result()
 
     @asyncio.coroutine
-    def async_add_entities(self, new_entities):
+    def async_add_entities(self, new_entities, update_before_add=False):
         """Add entities for a single platform async.
 
         This method must be run in the event loop.
         """
-        tasks = [self._async_process_entity(entity) for entity in new_entities]
+        tasks = [self._async_process_entity(entity, update_before_add)
+                 for entity in new_entities]
 
         yield from asyncio.gather(*tasks, loop=self.component.hass.loop)
         yield from self.component.async_update_group()
@@ -301,9 +311,11 @@ class EntityPlatform(object):
             second=range(0, 60, self.scan_interval))
 
     @asyncio.coroutine
-    def _async_process_entity(self, new_entity):
+    def _async_process_entity(self, new_entity, update_before_add):
         """Add entities to StateMachine."""
-        ret = yield from self.component.async_add_entity(new_entity, self)
+        ret = yield from self.component.async_add_entity(
+            new_entity, self, update_before_add=update_before_add
+        )
         if ret:
             self.platform_entities.append(new_entity)