Add unique_id to mqtt_json light (#16721)

Applies changes from #16303 to mqtt_json component.
Fixes #16600.

homeassistant/components/light/mqtt_json.py

@@ -53,6 +53,7 @@
 CONF_FLASH_TIME_LONG = 'flash_time_long'
 CONF_FLASH_TIME_SHORT = 'flash_time_short'
 CONF_HS = 'hs'
+CONF_UNIQUE_ID = 'unique_id'
 
 # Stealing some of these from the base MQTT configs.
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
@@ -67,6 +68,7 @@
     vol.Optional(CONF_FLASH_TIME_LONG, default=DEFAULT_FLASH_TIME_LONG):
         cv.positive_int,
     vol.Optional(CONF_NAME, default=DEFAULT_NAME): cv.string,
+    vol.Optional(CONF_UNIQUE_ID): cv.string,
     vol.Optional(CONF_OPTIMISTIC, default=DEFAULT_OPTIMISTIC): cv.boolean,
     vol.Optional(CONF_QOS, default=mqtt.DEFAULT_QOS):
         vol.All(vol.Coerce(int), vol.In([0, 1, 2])),
@@ -87,6 +89,7 @@ async def async_setup_platform(hass: HomeAssistantType, config: ConfigType,
         config = PLATFORM_SCHEMA(discovery_info)
     async_add_entities([MqttJson(
         config.get(CONF_NAME),
+        config.get(CONF_UNIQUE_ID),
         config.get(CONF_EFFECT_LIST),
         {
             key: config.get(key) for key in (
@@ -120,14 +123,15 @@ async def async_setup_platform(hass: HomeAssistantType, config: ConfigType,
 class MqttJson(MqttAvailability, Light):
     """Representation of a MQTT JSON light."""
 
-    def __init__(self, name, effect_list, topic, qos, retain, optimistic,
-                 brightness, color_temp, effect, rgb, white_value, xy, hs,
-                 flash_times, availability_topic, payload_available,
+    def __init__(self, name, unique_id, effect_list, topic, qos, retain,
+                 optimistic, brightness, color_temp, effect, rgb, white_value,
+                 xy, hs, flash_times, availability_topic, payload_available,
                  payload_not_available, brightness_scale):
         """Initialize MQTT JSON light."""
         super().__init__(availability_topic, qos, payload_available,
                          payload_not_available)
         self._name = name
+        self._unique_id = unique_id
         self._effect_list = effect_list
         self._topic = topic
         self._qos = qos
@@ -316,6 +320,11 @@ def name(self):
         """Return the name of the device if any."""
         return self._name
 
+    @property
+    def unique_id(self):
+        """Return a unique ID."""
+        return self._unique_id
+
     @property
     def is_on(self):
         """Return true if device is on."""