Add support for controlling homekit lights and switches (#13346)

* Add support for controlling homekit lights and switches

This adds support for controlling lights and switches that expose a HomeKit
control interface, avoiding the requirement to implement protocol-specific
components.

* Comment out the homekit requirement

This needs to build native code, so leave it commented for now

* Review updates

* Make HomeKit auto-discovery optional

Add an "enable" argument to the discovery component and add a list of
optional devices types (currently just HomeKit) to discover

* Further review comments

* Update requirements_all.txt

* Fix houndci complaints

* Further review updates

* Final review fixup

* Lint fixups

* Fix discovery tests

* Further review updates

homeassistant/components/switch/homekit_controller.py

@@ -0,0 +1,68 @@
+"""
+Support for Homekit switches.
+
+For more details about this platform, please refer to the documentation at
+https://home-assistant.io/components/switch.homekit_controller/
+"""
+import json
+import logging
+
+from homeassistant.components.homekit_controller import (HomeKitEntity,
+                                                         KNOWN_ACCESSORIES)
+from homeassistant.components.switch import SwitchDevice
+
+DEPENDENCIES = ['homekit_controller']
+
+_LOGGER = logging.getLogger(__name__)
+
+
+def setup_platform(hass, config, add_devices, discovery_info=None):
+    """Set up Homekit switch support."""
+    if discovery_info is not None:
+        accessory = hass.data[KNOWN_ACCESSORIES][discovery_info['serial']]
+        add_devices([HomeKitSwitch(accessory, discovery_info)], True)
+
+
+class HomeKitSwitch(HomeKitEntity, SwitchDevice):
+    """Representation of a Homekit switch."""
+
+    def __init__(self, *args):
+        """Initialise the switch."""
+        super().__init__(*args)
+        self._on = None
+
+    def update_characteristics(self, characteristics):
+        """Synchronise the switch state with Home Assistant."""
+        # pylint: disable=import-error
+        import homekit
+
+        for characteristic in characteristics:
+            ctype = characteristic['type']
+            ctype = homekit.CharacteristicsTypes.get_short(ctype)
+            if ctype == "on":
+                self._chars['on'] = characteristic['iid']
+                self._on = characteristic['value']
+            elif ctype == "outlet-in-use":
+                self._chars['outlet-in-use'] = characteristic['iid']
+
+    @property
+    def is_on(self):
+        """Return true if device is on."""
+        return self._on
+
+    def turn_on(self, **kwargs):
+        """Turn the specified switch on."""
+        self._on = True
+        characteristics = [{'aid': self._aid,
+                            'iid': self._chars['on'],
+                            'value': True}]
+        body = json.dumps({'characteristics': characteristics})
+        self._securecon.put('/characteristics', body)
+
+    def turn_off(self, **kwargs):
+        """Turn the specified switch off."""
+        characteristics = [{'aid': self._aid,
+                            'iid': self._chars['on'],
+                            'value': False}]
+        body = json.dumps({'characteristics': characteristics})
+        self._securecon.put('/characteristics', body)