my.calendar.holidays: unhardcode calendar, detect it from the location data

my/calendar/holidays.py

@@ -6,14 +6,24 @@ REQUIRES = [
 ]
 
 from datetime import date, datetime, timedelta
+from functools import lru_cache
 from typing import Union
 
+from ..core.time import zone_to_countrycode
 
-# TODO would be nice to do it dynamically depending on the past timezones...
-from workalendar.europe import UnitedKingdom # type: ignore
-cal = UnitedKingdom()
-# TODO that should depend on country/'location' of residence I suppose?
 
+@lru_cache(1)
+def _calendar():
+    from workalendar.registry import registry # type: ignore
+    # todo switch to using time.tz.main once _get_tz stabilizes?
+    from ..time.tz import via_location as LTZ
+    # TODO would be nice to do it dynamically depending on the past timezones...
+    tz = LTZ._get_tz(datetime.now())
+    assert tz is not None
+
+    code = zone_to_countrycode(tz.zone)
+    Cal = registry.get_calendars()[code]
+    return Cal()
 
 # todo move to common?
 DateIsh = Union[datetime, date, str]
@@ -29,7 +39,7 @@ def as_date(dd: DateIsh) -> date:
 
 def is_holiday(d: DateIsh) -> bool:
     day = as_date(d)
-    return not cal.is_working_day(day)
+    return not _calendar().is_working_day(day)
 
 
 def is_workday(d: DateIsh) -> bool:

my/core/time.py

@@ -15,3 +15,18 @@ tz_lookup['UTC'] = pytz.utc # ugh. otherwise it'z Zulu...
 @lru_cache(None)
 def abbr_to_timezone(abbr: str) -> tzinfo:
     return tz_lookup[abbr]
+
+
+def zone_to_countrycode(zone: str) -> str:
+    # todo make optional?
+    return _zones_to_countrycode()[zone]
+
+
+@lru_cache(1)
+def _zones_to_countrycode():
+    # https://stackoverflow.com/a/13020785/706389
+    res = {}
+    for countrycode, timezones in pytz.country_timezones.items():
+        for timezone in timezones:
+            res[timezone] = countrycode
+    return res

my/time/tz/via_location.py

@@ -119,6 +119,7 @@ def _get_home_tz(loc) -> Optional[pytz.BaseTzInfo]:
         return pytz.timezone(zone)
 
 
+# TODO expose? to main as well?
 def _get_tz(dt: datetime) -> Optional[pytz.BaseTzInfo]:
     res = _get_day_tz(d=dt.date())
     if res is not None: