Fixing the api_streams sensor (#22200)

* Fire events with websocket messages.

* Added tests to validate

* Fixed api_streams sensor to use new sensor

* Delete from coverageac as now works.

* Removed websocket request event.

* Use dispatcher instead of events.

* Moved sensor to under websocket_api

* Changes as per code review

* Fixed tests.

* Modified test

* Patch

homeassistant/components/websocket_api/sensor.py

@@ -0,0 +1,53 @@
+"""Entity to track connections to websocket API."""
+
+from homeassistant.core import callback
+from homeassistant.helpers.entity import Entity
+
+from .const import SIGNAL_WEBSOCKET_CONNECTED, SIGNAL_WEBSOCKET_DISCONNECTED
+
+
+async def async_setup_platform(
+        hass, config, async_add_entities, discovery_info=None):
+    """Set up the API streams platform."""
+    entity = APICount()
+
+    # pylint: disable=protected-access
+    hass.helpers.dispatcher.async_dispatcher_connect(
+        SIGNAL_WEBSOCKET_CONNECTED, entity._increment)
+    hass.helpers.dispatcher.async_dispatcher_connect(
+        SIGNAL_WEBSOCKET_DISCONNECTED, entity._decrement)
+
+    async_add_entities([entity])
+
+
+class APICount(Entity):
+    """Entity to represent how many people are connected to the stream API."""
+
+    def __init__(self):
+        """Initialize the API count."""
+        self.count = 0
+
+    @property
+    def name(self):
+        """Return name of entity."""
+        return "Connected clients"
+
+    @property
+    def state(self):
+        """Return current API count."""
+        return self.count
+
+    @property
+    def unit_of_measurement(self):
+        """Return the unit of measurement."""
+        return "clients"
+
+    @callback
+    def _increment(self):
+        self.count += 1
+        self.async_schedule_update_ha_state()
+
+    @callback
+    def _decrement(self):
+        self.count -= 1
+        self.async_schedule_update_ha_state()