Use coordinate-based timezone lookup for trip destinations

requirements.txt

@@ -10,3 +10,4 @@ ephem
 flask
 requests
 emoji
+timezonefinder

web_view.py

@@ -3,7 +3,9 @@
 """Web page to show upcoming events."""
 
 import decimal
+import functools
 import hashlib
+import importlib
 import inspect
 import json
 import operator
@@ -789,9 +791,35 @@ def _format_offset_from_bristol(offset_minutes: int) -> str:
     return f"{sign}{hours:02d}:{mins:02d} vs Bristol"
 
 
+def _timezone_from_coordinates(latitude: float, longitude: float) -> str | None:
+    """Resolve IANA timezone name from coordinates."""
+    timezone_finder = _get_timezone_finder()
+    if timezone_finder is None:
+        return None
+
+    tz_name = timezone_finder.timezone_at(lng=longitude, lat=latitude)
+    return tz_name if isinstance(tz_name, str) else None
+
+
+@functools.lru_cache(maxsize=1)
+def _get_timezone_finder() -> typing.Any:
+    """Get timezone finder instance if dependency is available."""
+    try:
+        timezonefinder_module = importlib.import_module("timezonefinder")
+    except ModuleNotFoundError:
+        return None
+
+    timezone_finder_cls = getattr(timezonefinder_module, "TimezoneFinder", None)
+    if timezone_finder_cls is None:
+        return None
+
+    return timezone_finder_cls()
+
+
 def get_destination_timezones(trip: Trip) -> list[StrDict]:
     """Build destination timezone metadata for the trip page."""
     per_location: dict[tuple[str, str], list[str]] = defaultdict(list)
+    location_coords: dict[tuple[str, str], tuple[float, float]] = {}
     for item in trip.accommodation + trip.conferences + trip.events:
         location = item.get("location")
         country = item.get("country")
@@ -803,6 +831,11 @@ def get_destination_timezones(trip: Trip) -> list[StrDict]:
         if isinstance(timezone_name, str):
             per_location[key].append(timezone_name)
 
+        latitude = item.get("latitude")
+        longitude = item.get("longitude")
+        if isinstance(latitude, (int, float)) and isinstance(longitude, (int, float)):
+            location_coords[key] = (float(latitude), float(longitude))
+
         for field in (
             "from",
             "to",
@@ -832,6 +865,12 @@ def get_destination_timezones(trip: Trip) -> list[StrDict]:
             except Exception:
                 continue
 
+        if not timezone_name and key in location_coords:
+            latitude, longitude = location_coords[key]
+            coordinate_timezone = _timezone_from_coordinates(latitude, longitude)
+            if coordinate_timezone:
+                timezone_name = coordinate_timezone
+
         if not timezone_name:
             country_timezones = pytz.country_timezones.get(country_code, [])
             if len(country_timezones) == 1: