Add support for WA7BNM Contest Calendar. Closes #106

providers/alert/ical_alert_provider.py

@@ -0,0 +1,47 @@
+from datetime import datetime, time
+from typing import cast
+
+import pytz
+from icalendar import Calendar, Event
+
+from data.alert import Alert
+from providers.alert.http_alert_provider import HTTPAlertProvider
+
+
+class ICALAlertProvider(HTTPAlertProvider):
+    """Generic alert provider for iCal calendars. Defines an abstract method event_to_alert(event) that subclasses must
+    implement, and use it to convert an iCal event to an Alert object based on whatever format their iCal events use."""
+
+    def __init__(self, name, provider_config, url, poll_interval):
+        super().__init__(name, provider_config, url, poll_interval)
+
+    def _http_response_to_alerts(self, http_response):
+        new_alerts = []
+        cal = Calendar.from_ical(http_response.content)
+
+        # Iterate through events, passing each one in turn to the subclass' event_to_alert method to turn it into
+        # a Spothole alert object
+        for component in cal.walk():
+            if component.name != "VEVENT":
+                continue
+
+            event = cast(Event, component)
+            alert = self.event_to_alert(event)
+            new_alerts.append(alert)
+        return new_alerts
+
+    def event_to_alert(self, event: Event) -> Alert:
+        """Convert an ICal event to an Alert object. Subclasses must implement this method."""
+
+    @staticmethod
+    def _to_utc_timestamp(value):
+        """Convert a date or datetime value from an iCal field into a UTC UNIX timestamp."""
+
+        # Datetime object so we can treat it as-is, check if it has a non-UTC tz and convert it if necessary
+        if isinstance(value, datetime):
+            if value.tzinfo is None:
+                value = pytz.UTC.localize(value)
+            return value.astimezone(pytz.UTC).timestamp()
+
+        # Date object so this is an all day event
+        return pytz.UTC.localize(datetime.combine(value, time.min)).timestamp()