update interval no longer shrinks with recursion

Previously, the endtime-starttime interval being processed by the run_as_update method would shrink by 1 (second) with each recursion. This ultimately broke run_as_update when processing anything other than 1-second data, but it wasn't obvious because we rarely had to actually recurse. There is a little trickery now to ensure that user- provided starttime and endtime are inclusive of the full first (most recent) update interval, while subsequent, calculated, endtimes are set equal to the prior starttime minus specified output_interval (e.g., 'second', 'minute', etc.).

geomagio/Controller.py

@@ -426,9 +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
-                interval = endtime - starttime
-                recurse_starttime = starttime - interval
-                recurse_endtime = starttime - 1
+                recurse_starttime, recurse_endtime = get_previous_interval(
+                    start=starttime,
+                    end=endtime,
+                )
                 self.run_as_update(
                     algorithm=algorithm,
                     observatory=observatory,
@@ -636,6 +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()