@@ -1,12 +1,13 @@
 from icalendar.cal import Calendar, FreeBusy
+import icalendar
+
 import requests
 from flask import Flask
-from datetime import date, datetime, timedelta, time
+from datetime import date, datetime, timedelta, time, timezone
 import zoneinfo
 from dataclasses import dataclass
 from danoan.toml_dataclass import TomlDataClassIO
 from os import environ
-import calendar
 
 @dataclass
 class CalendarConfig(TomlDataClassIO):
@@ -51,6 +52,13 @@ return dt.replace(tzinfo=tz)
     else:
         return dt.astimezone(tz)
 
+def to_utc(dt):
+    return dt.astimezone(tz=timezone.utc)
+
+def looks_tentative(component):
+    summary = str(component.get('summary'))
+    return component.get('status') == 'TENTATIVE' or 'TBD' in summary or summary.endswith("?")
+
 @app.route(f'/{str.lower(config.name)}.ics')
 def index():
     today = date.today()
@@ -69,12 +77,21 @@ for component in input.walk():
             if component.name == "VEVENT":
                 dtstart = fixup_date(component.get('dtstart').dt)
                 dtend = fixup_date(component.get('dtend', component.get('dtstart')).dt)
+                dtstamp = fixup_date(component.get('dtstamp').dt)
                 if dtstart >= start_date and dtend <= end_date:
-                    busy = FreeBusy()
+                    busy = FreeBusy(uid=component.get('uid'))
+                    vp = icalendar.prop.vPeriod([ to_utc(d) for d in [dtstart, dtend] ])
+
+                    if looks_tentative(component):
+                        vp.FBTYPE = icalendar.enums.FBTYPE.BUSY_TENTATIVE
+                    else:
+                        vp.FBTYPE = icalendar.enums.FBTYPE.BUSY_UNAVAILABLE
+
+                    busy.add('freebusy', vp)
                     busy.add('summary', f'{config.name} Busy')
-                    busy.uid = component.get('uid')
                     busy.add('dtstart', dtstart)
                     busy.add('dtend', dtend)
+                    busy.add('dtstamp', dtstamp)
                     output.add_component(busy)
         return output.to_ical(), { "Content-Type": "text/plain" }
     except Exception as e: