Add get_previous_interval method and test

geomagio/Controller.py

@@ -426,11 +426,10 @@ class Controller(object):
             # check for fillable gap at start
             if output_gap[0] == starttime:
                 # found fillable gap at start, recurse to previous interval
-                delta = TimeseriesUtility.get_delta_from_interval(output_interval)
-                recurse_starttime = (
-                    starttime - (endtime - starttime) - delta * bool(update_count)
+                recurse_starttime, recurse_endtime = get_previous_interval(
+                    start=starttime,
+                    end=endtime,
                 )
-                recurse_endtime = starttime - delta
                 self.run_as_update(
                     algorithm=algorithm,
                     observatory=observatory,
@@ -638,6 +637,29 @@ def get_output_factory(args):
     return output_factory
 
 
+def get_previous_interval(
+    start: UTCDateTime,
+    end: UTCDateTime,
+) -> Tuple[UTCDateTime, UTCDateTime]:
+    """Get previous interval for given interval.
+
+    Parameters
+    ----------
+    start
+        start of interval
+    end
+        end of interval
+
+    Returns
+    -------
+    Previous interval of approximately the same size.
+    Interval is rounded to nearest second, and ends one microsecond earlier.
+    """
+    # round to nearest second to recover removed microsecond from repeated calls
+    interval_size = round(end - start)
+    return (start - interval_size, start - 1e-6)
+
+
 def get_realtime_interval(interval_seconds: int) -> Tuple[UTCDateTime, UTCDateTime]:
     # calculate endtime/starttime
     now = UTCDateTime()

test/Controller_test.py

@@ -6,7 +6,7 @@ from geomagio.algorithm import Algorithm
 from geomagio.iaga2002 import IAGA2002Factory
 
 # needed to emulate geomag.py script
-from geomagio.Controller import _main, parse_args
+from geomagio.Controller import _main, get_previous_interval, parse_args
 
 # needed to copy SqDistAlgorithm statefile
 from shutil import copy
@@ -290,3 +290,23 @@ def test_controller_update_sqdist():
     )
     expected = expected_factory.get_timeseries(starttime=starttime1, endtime=endtime6)
     assert_allclose(actual, expected)
+
+
+def test_get_previous_interval():
+    """Test get_previous_interval produces stable interval sizes"""
+    # initial interval is one hour
+    start = UTCDateTime("2022-01-05T00:00:00Z")
+    end = UTCDateTime("2022-01-05T01:00:00Z")
+    # previous interval starts at beginning of previous hour
+    previous = get_previous_interval(start=start, end=end)
+    assert previous == (
+        UTCDateTime("2022-01-04T23:00:00"),
+        UTCDateTime("2022-01-04T23:59:59.999999Z"),
+    )
+    # previous interval still starts at beginning of previous hour
+    # even though interval is one microsecond smaller
+    previous = get_previous_interval(*previous)
+    assert previous == (
+        UTCDateTime("2022-01-04T22:00:00"),
+        UTCDateTime("2022-01-04T22:59:59.999999Z"),
+    )