Add a load_platform mechanism (home-assistant#2012)

* discovery.load_platform method

* rm grep

.gitignore

@@ -83,3 +83,5 @@ venv
 # vimmy stuff
 *.swp
 *.swo
+
+ctags.tmp

homeassistant/components/discovery.py

@@ -19,6 +19,8 @@
 
 SCAN_INTERVAL = 300  # seconds
 
+LOAD_PLATFORM = 'load_platform'
+
 SERVICE_WEMO = 'belkin_wemo'
 SERVICE_HUE = 'philips_hue'
 SERVICE_CAST = 'google_cast'
@@ -73,6 +75,32 @@ def discover(hass, service, discovered=None, component=None, hass_config=None):
     hass.bus.fire(EVENT_PLATFORM_DISCOVERED, data)
 
 
+def load_platform(hass, component, platform, info=None, hass_config=None):
+    """Helper method for generic platform loading.
+
+    This method allows a platform to be loaded dynamically without it being
+    known at runtime (in the DISCOVERY_PLATFORMS list of the component).
+    Advantages of using this method:
+    - Any component & platforms combination can be dynamically added
+    - A component (i.e. light) does not have to import every component
+      that can dynamically add a platform (e.g. wemo, wink, insteon_hub)
+    - Custom user components can take advantage of discovery/loading
+
+    Target components will be loaded and an EVENT_PLATFORM_DISCOVERED will be
+    fired to load the platform. The event will contain:
+        { ATTR_SERVICE = LOAD_PLATFORM + '.' + <<component>>
+          ATTR_DISCOVERED = {LOAD_PLATFORM: <<platform>>} }
+
+    * dev note: This listener can be found in entity_component.py
+    """
+    if info is None:
+        info = {LOAD_PLATFORM: platform}
+    else:
+        info[LOAD_PLATFORM] = platform
+    discover(hass, LOAD_PLATFORM + '.' + component, info, component,
+             hass_config)
+
+
 def setup(hass, config):
     """Start a discovery service."""
     logger = logging.getLogger(__name__)

homeassistant/helpers/entity_component.py

@@ -55,12 +55,24 @@ def setup(self, config):
             self._setup_platform(p_type, p_config)
 
         if self.discovery_platforms:
+            # Discovery listener for all items in discovery_platforms array
+            # passed from a component's setup method (e.g. light/__init__.py)
             discovery.listen(
                 self.hass, self.discovery_platforms.keys(),
                 lambda service, info:
                 self._setup_platform(self.discovery_platforms[service], {},
                                      info))
 
+            # Generic discovery listener for loading platform dynamically
+            # Refer to: homeassistant.components.discovery.load_platform()
+            def load_platform_callback(service, info):
+                """Callback to load a platform."""
+                platform = info.pop(discovery.LOAD_PLATFORM)
+                self._setup_platform(platform, {}, info if info else None)
+            discovery.listen(
+                self.hass, discovery.LOAD_PLATFORM + '.' + self.domain,
+                load_platform_callback)
+
     def extract_from_service(self, service):
         """Extract all known entities from a service call.