Add support for the protocol used by TAPO devices and some newer KASA devices. (#552)

* Add Tapo protocol support

* Update get_device_instance and test_unsupported following review

kasa/tapo/tapoplug.py

@@ -0,0 +1,73 @@
+"""Module for a TAPO Plug."""
+import logging
+from datetime import datetime, timedelta
+from typing import Any, Dict, Optional, cast
+
+from ..credentials import Credentials
+from ..emeterstatus import EmeterStatus
+from ..smartdevice import DeviceType
+from .tapodevice import TapoDevice
+
+_LOGGER = logging.getLogger(__name__)
+
+
+class TapoPlug(TapoDevice):
+    """Class to represent a TAPO Plug."""
+
+    def __init__(
+        self,
+        host: str,
+        *,
+        port: Optional[int] = None,
+        credentials: Optional[Credentials] = None,
+        timeout: Optional[int] = None,
+    ) -> None:
+        super().__init__(host, port=port, credentials=credentials, timeout=timeout)
+        self._device_type = DeviceType.Plug
+
+    async def update(self, update_children: bool = True):
+        """Call the device endpoint and update the device data."""
+        await super().update(update_children)
+
+        self._energy = await self.protocol.query("get_energy_usage")
+        self._emeter = await self.protocol.query("get_current_power")
+
+        self._data["energy"] = self._energy
+        self._data["emeter"] = self._emeter
+
+        _LOGGER.debug("Got an update: %s %s", self._energy, self._emeter)
+
+    @property
+    def state_information(self) -> Dict[str, Any]:
+        """Return the key state information."""
+        return {
+            **super().state_information,
+            **{
+                "On since": self.on_since,
+                "auto_off_status": self._info.get("auto_off_status"),
+                "auto_off_remain_time": self._info.get("auto_off_remain_time"),
+            },
+        }
+
+    @property
+    def emeter_realtime(self) -> EmeterStatus:
+        """Get the emeter status."""
+        return EmeterStatus({"power_mw": self._energy.get("current_power")})
+
+    @property
+    def emeter_today(self) -> Optional[float]:
+        """Get the emeter value for today."""
+        return None
+
+    @property
+    def emeter_this_month(self) -> Optional[float]:
+        """Get the emeter value for this month."""
+        return None
+
+    @property
+    def on_since(self) -> Optional[datetime]:
+        """Return the time that the device was turned on or None if turned off."""
+        if not self._info.get("device_on"):
+            return None
+        on_time = cast(float, self._info.get("on_time"))
+        return datetime.now().replace(microsecond=0) - timedelta(seconds=on_time)