RingBuffer: Fix gaps being ignored in __len__()

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

src/frequenz/sdk/timeseries/_ringbuffer/buffer.py

@@ -517,10 +517,24 @@ def __len__(self) -> int:
         if self._datetime_newest == self._DATETIME_MIN:
             return 0
 
+        # Sum of all elements in the gap ranges
+        sum_missing_entries = max(
+            0,
+            sum(
+                (
+                    gap.end
+                    # Don't look further back than oldest timestamp
+                    - max(gap.start, self._datetime_oldest)
+                )
+                // self._sampling_period
+                for gap in self._gaps
+            ),
+        )
+
         start_index = self.datetime_to_index(self._datetime_oldest)
         end_index = self.datetime_to_index(self._datetime_newest)
 
         if end_index < start_index:
-            return len(self._buffer) - start_index + end_index + 1
+            return len(self._buffer) - start_index + end_index + 1 - sum_missing_entries
 
-        return end_index + 1 - start_index
+        return end_index + 1 - start_index - sum_missing_entries

tests/timeseries/test_ringbuffer.py

@@ -289,6 +289,21 @@ def test_len_ringbuffer_samples_fit_buffer_size() -> None:
         assert len(buffer) == len(test_samples)
 
 
+def test_len_with_gaps() -> None:
+    """Test the length when there are gaps in the buffer."""
+    buffer = OrderedRingBuffer(
+        np.empty(shape=10, dtype=float),
+        sampling_period=timedelta(seconds=1),
+        align_to=datetime(1, 1, 1, tzinfo=timezone.utc),
+    )
+
+    for i in range(10):
+        buffer.update(
+            Sample(datetime(2, 2, 2, 0, 0, i, tzinfo=timezone.utc), Quantity(float(i)))
+        )
+        assert len(buffer) == i + 1
+
+
 def test_len_ringbuffer_samples_overwrite_buffer() -> None:
     """Test the length of ordered ring buffer.