Update legacy

Implements script to fill gaps in legacy data.

geomagio/TimeseriesUtility.py

@@ -568,3 +568,32 @@ def round_usecs(time):
     if rounded_usecs != usecs:
         time = time.replace(microsecond=rounded_usecs)
     return time
+
+
+def get_previous_interval(interval: str):
+    """Gets previous available interval from input interval.
+
+    Parameters
+    ----------
+    interval: str
+        string containing current interval
+
+    Returns
+    ----------
+    interval: str
+        string containing previous available interval
+    """
+    current_delta = get_delta_from_interval(interval)
+    if interval == "second":
+        return "tenhertz"
+
+    elif interval == "minute":
+        return "second"
+
+    elif interval in ["hour", "day"]:
+        return "minute"
+
+    else:
+        raise ValueError(
+            "Method cannot determine intervals smaller than ten hertz or larger than one minute"
+        )