Improve emeterstatus API, move into own module (#205)

Adds the following properties to EmeterStatus for saner API:
* voltage (in V)
* power (in W)
* current (in A)
* total (in kWh)

kasa/emeterstatus.py

@@ -0,0 +1,82 @@
+"""Module for emeter container."""
+import logging
+from typing import Optional
+
+_LOGGER = logging.getLogger(__name__)
+
+
+class EmeterStatus(dict):
+    """Container for converting different representations of emeter data.
+
+    Newer FW/HW versions postfix the variable names with the used units,
+    where-as the olders do not have this feature.
+
+    This class automatically converts between these two to allow
+    backwards and forwards compatibility.
+    """
+
+    @property
+    def voltage(self) -> Optional[float]:
+        """Return voltage in V."""
+        try:
+            return self["voltage"]
+        except ValueError:
+            return None
+
+    @property
+    def power(self) -> Optional[float]:
+        """Return power in W."""
+        try:
+            return self["power"]
+        except ValueError:
+            return None
+
+    @property
+    def current(self) -> Optional[float]:
+        """Return current in A."""
+        try:
+            return self["current"]
+        except ValueError:
+            return None
+
+    @property
+    def total(self) -> Optional[float]:
+        """Return total in kWh."""
+        try:
+            return self["total"]
+        except ValueError:
+            return None
+
+    def __repr__(self):
+        return f"<EmeterStatus power={self.power} voltage={self.voltage} current={self.current} total={self.total}>"
+
+    def __getitem__(self, item):
+        valid_keys = [
+            "voltage_mv",
+            "power_mw",
+            "current_ma",
+            "energy_wh",
+            "total_wh",
+            "voltage",
+            "power",
+            "current",
+            "total",
+            "energy",
+        ]
+
+        # 1. if requested data is available, return it
+        if item in super().keys():
+            return super().__getitem__(item)
+        # otherwise decide how to convert it
+        else:
+            if item not in valid_keys:
+                raise KeyError(item)
+            if "_" in item:  # upscale
+                return super().__getitem__(item[: item.find("_")]) * 1000
+            else:  # downscale
+                for i in super().keys():
+                    if i.startswith(item):
+                        return self.__getitem__(i) / 1000
+
+                _LOGGER.debug(f"Unable to find value for '{item}'")
+                return None