Use at method in getitem magic of moving window

The incomplete implementation of single element access in the getitem
magic is replaced by using the `at` method.

Signed-off-by: cwasicki <[email protected]>

Author: cwasicki

RELEASE_NOTES.md

@@ -28,11 +28,12 @@
 - In `OrderedRingBuffer` and `MovingWindow`:
   - Support for integer indices is added.
   - Add `count_covered` method to count the number of elements covered by the used time range.
-
+- Add `at` method to `MovingWindow` to access a single element and use it in `__getitem__` magic to fully support single element access.
 
 
 
 ## Bug Fixes
 
 - Fix rendering of diagrams in the documentation.
 - The `__getitem__` magic of the `MovingWindow` is fixed to support the same functionality that the `window` method provides.
+- Fixes incorrect implementation of single element access in `__getitem__` magic of `MovingWindow`.

src/frequenz/sdk/timeseries/_moving_window.py

@@ -418,15 +418,11 @@ def __getitem__(self, key: SupportsIndex | datetime | slice) -> float | ArrayLik
                 raise ValueError("Slicing with a step other than 1 is not supported.")
             return self.window(key.start, key.stop)
 
-        if self._buffer.count_valid() == 0:
-            raise IndexError("The buffer is empty.")
-
         if isinstance(key, datetime):
-            _logger.debug("Returning value at time %s ", key)
-            return self._buffer[self._buffer.to_internal_index(key)]
+            return self.at(key)
+
         if isinstance(key, SupportsIndex):
-            _logger.debug("Returning value at index %s ", key)
-            return self._buffer[key]
+            return self.at(key.__index__())
 
         raise TypeError(
             "Key has to be either a timestamp or an integer "

tests/timeseries/test_moving_window.py

@@ -83,10 +83,10 @@ async def test_access_window_by_index() -> None:
     window, sender = init_moving_window(timedelta(seconds=2))
     async with window:
         await push_logical_meter_data(sender, [1, 2, 3])
-        assert np.array_equal(window[0], 3.0)  # bug: should be 2
-        assert np.array_equal(window[1], 2.0)  # bug: should be 3
-        assert np.array_equal(window[-1], 2.0)  # bug: should be 3
-        assert np.array_equal(window[-2], 3.0)  # bug: should be 2
+        assert np.array_equal(window[0], 2.0)
+        assert np.array_equal(window[1], 3.0)
+        assert np.array_equal(window[-1], 3.0)
+        assert np.array_equal(window[-2], 2.0)
         with pytest.raises(IndexError):
             _ = window[3]
         with pytest.raises(IndexError):
@@ -102,13 +102,12 @@ async def test_access_window_by_timestamp() -> None:
         assert np.array_equal(window.at(dt(1)), 1.0)
         assert np.array_equal(window[dt(2)], 2.0)
         assert np.array_equal(window.at(dt(2)), 2.0)
-        assert np.array_equal(window[dt(3)], 1.0)  # bug: should raise
         with pytest.raises(IndexError):
             _ = window[dt(0)]
         with pytest.raises(IndexError):
             _ = window.at(dt(0))
         with pytest.raises(IndexError):
-            _ = window[dt(4)]
+            _ = window[dt(3)]
         with pytest.raises(IndexError):
             _ = window.at(dt(3))