added preprocess fromto date, does not work properly yet

pyfacts/utils.py

@@ -144,13 +144,43 @@ def _preprocess_match_options(as_on_match: str, prior_match: str, closest: str)
     return as_on_delta, prior_delta
 
 
+def _preprocess_from_to_date(
+    from_date: datetime.date | str,
+    to_date: datetime.date | str,
+    time_series: Mapping = None,
+    align_dates: bool = True,
+    return_period_unit: Literal["years", "months", "days"] = None,
+    return_period_value: int = None,
+    as_on_match: str = "closest",
+    prior_match: str = "closest",
+    closest: Literal["previous", "next", "exact"] = "previous",
+) -> tuple:
+
+    as_on_match, prior_match = _preprocess_match_options(as_on_match, prior_match, closest)
+
+    if (from_date is None or to_date is None) and time_series is None:
+        raise ValueError("Provide either to_date and from_date or time_series data")
+
+    if time_series is not None and (return_period_unit is None or return_period_value is None):
+        raise ValueError("Provide return period for calculation of from_date")
+
+    if from_date is None:
+        expected_start_date = time_series.start_date + relativedelta(**{return_period_unit: return_period_value})
+        from_date = _find_closest_date(time_series.data, expected_start_date, 999, as_on_match, "fail")[0]
+
+    if to_date is None:
+        to_date = time_series.end_date
+
+    return from_date, to_date
+
+
 def _find_closest_date(
     data: Mapping[datetime.datetime, float],
     date: datetime.datetime,
     limit_days: int,
     delta: datetime.timedelta,
     if_not_found: Literal["fail", "nan"],
-):
+) -> Tuple[datetime.datetime, float]:
     """Helper function to find data for the closest available date"""
 
     if delta.days < 0 and date < min(data):