Avoid linear search for emeter realtime and emeter_today (#622)

* Avoid linear search for emeter realtime and emeter_today

Most of the time the data we want is at the end of the
list so we now search backwards to avoid having to
scale all the data and throw most of it away

* more tweaks

* coverage

* coverage

* preen

* coverage

* branch cover

kasa/modules/emeter.py

@@ -1,6 +1,6 @@
 """Implementation of the emeter module."""
 from datetime import datetime
-from typing import Dict, Optional
+from typing import Dict, List, Optional, Union
 
 from ..emeterstatus import EmeterStatus
 from .usage import Usage
@@ -19,8 +19,7 @@ class Emeter(Usage):
         """Return today's energy consumption in kWh."""
         raw_data = self.daily_data
         today = datetime.now().day
-        data = self._convert_stat_data(raw_data, entry_key="day")
-
+        data = self._convert_stat_data(raw_data, entry_key="day", key=today)
         return data.get(today)
 
     @property
@@ -28,8 +27,7 @@ class Emeter(Usage):
         """Return this month's energy consumption in kWh."""
         raw_data = self.monthly_data
         current_month = datetime.now().month
-        data = self._convert_stat_data(raw_data, entry_key="month")
-
+        data = self._convert_stat_data(raw_data, entry_key="month", key=current_month)
         return data.get(current_month)
 
     async def erase_stats(self):
@@ -61,7 +59,13 @@ class Emeter(Usage):
         data = self._convert_stat_data(data["month_list"], entry_key="month", kwh=kwh)
         return data
 
-    def _convert_stat_data(self, data, entry_key, kwh=True) -> Dict:
+    def _convert_stat_data(
+        self,
+        data: List[Dict[str, Union[int, float]]],
+        entry_key: str,
+        kwh: bool=True,
+        key: Optional[int] = None,
+    ) -> Dict[Union[int, float], Union[int, float]]:
         """Return emeter information keyed with the day/month.
 
         The incoming data is a list of dictionaries::
@@ -89,6 +93,19 @@ class Emeter(Usage):
             if not kwh:
                 scale = 1000
 
-        data = {entry[entry_key]: entry[value_key] * scale for entry in data}
+        if key is None:
+            # Return all the data
+            return {entry[entry_key]: entry[value_key] * scale for entry in data}
 
-        return data
+        # In this case we want a specific key in the data
+        # i.e. the current day or month.
+        #
+        # Since we usually want the data at the end of the list so we can
+        # optimize the search by starting at the end and avoid scaling
+        # the data we don't need.
+        #
+        for entry in reversed(data):
+            if entry[entry_key] == key:
+                return {entry[entry_key]: entry[value_key] * scale}
+
+        return {}

kasa/modules/usage.py

@@ -10,8 +10,9 @@ class Usage(Module):
 
     def query(self):
         """Return the base query."""
-        year = datetime.now().year
-        month = datetime.now().month
+        now = datetime.now()
+        year = now.year
+        month = now.month
 
         req = self.query_for_command("get_realtime")
         req = merge(
@@ -40,21 +41,21 @@ class Usage(Module):
     def usage_today(self):
         """Return today's usage in minutes."""
         today = datetime.now().day
-        converted = [x["time"] for x in self.daily_data if x["day"] == today]
-        if not converted:
-            return None
-
-        return converted.pop()
+        # Traverse the list in reverse order to find the latest entry.
+        for entry in reversed(self.daily_data):
+            if entry["day"] == today:
+                return entry["time"]
+        return None
 
     @property
     def usage_this_month(self):
         """Return usage in this month in minutes."""
         this_month = datetime.now().month
-        converted = [x["time"] for x in self.monthly_data if x["month"] == this_month]
-        if not converted:
-            return None
-
-        return converted.pop()
+        # Traverse the list in reverse order to find the latest entry.
+        for entry in reversed(self.monthly_data):
+            if entry["month"] == this_month:
+                return entry["time"]
+        return None
 
     async def get_raw_daystat(self, *, year=None, month=None) -> Dict:
         """Return raw daily stats for the given year & month."""