calendar: add EXDATE support for cancelling single occurrences of recurring events

event delete on a recurring event previously deleted the entire .ics file,
killing the whole series. Now requires --date (adds EXDATE) or --all (deletes
series) for recurring events, refusing to act without either flag.

skills/calendar/scripts/cal_tool.py

@@ -729,7 +729,14 @@ def cmd_event_list(args):
 
 
 def cmd_event_delete(args):
-    """Delete a calendar event by UID or summary match."""
+    """Delete a calendar event or cancel a single occurrence of a recurring event.
+
+    For recurring events:
+      --date YYYY-MM-DD   Cancel one occurrence by adding EXDATE (keeps the series)
+      --all               Delete the entire series (required safety flag)
+
+    Without --date or --all on a recurring event, the command refuses to act.
+    """
     if not args.uid and not args.match:
         print("Error: --uid or --match is required", file=sys.stderr)
         sys.exit(1)
@@ -755,9 +762,9 @@ def cmd_event_delete(args):
                 uid = str(component.get("uid", ""))
                 summary = str(component.get("summary", ""))
                 if args.uid and args.uid in uid:
-                    matches.append((ics_path, uid, summary))
+                    matches.append((ics_path, uid, summary, component))
                 elif args.match and args.match in summary:
-                    matches.append((ics_path, uid, summary))
+                    matches.append((ics_path, uid, summary, component))
 
     if not matches:
         target = args.uid or args.match
@@ -765,16 +772,72 @@ def cmd_event_delete(args):
         sys.exit(1)
     if len(matches) > 1:
         print(f"Error: Multiple events match:", file=sys.stderr)
-        for _, uid, summary in matches:
+        for _, uid, summary, _ in matches:
             print(f"  - {summary} (uid: {uid})", file=sys.stderr)
         sys.exit(1)
 
-    ics_path, uid, summary = matches[0]
-    ics_path.unlink()
-    print(f"Deleted event: {summary} (uid: {uid})")
+    ics_path, uid, summary, vevent = matches[0]
+    has_rrule = vevent.get("rrule") is not None
+
+    if has_rrule and not args.date and not args.all:
+        print(
+            f"Error: '{summary}' is a recurring event. Use one of:\n"
+            f"  --date YYYY-MM-DD   Cancel a single occurrence\n"
+            f"  --all               Delete the entire series",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
+    if args.date and has_rrule:
+        # Add EXDATE to cancel a single occurrence
+        _add_exdate(ics_path, vevent, args.date, summary, uid)
+    else:
+        # Delete the entire event (single event, or recurring with --all)
+        ics_path.unlink()
+        if has_rrule:
+            print(f"Deleted recurring event series: {summary} (uid: {uid})")
+        else:
+            print(f"Deleted event: {summary} (uid: {uid})")
+
     _sync_calendar()
 
 
+def _add_exdate(ics_path, vevent, date_str, summary, uid):
+    """Add an EXDATE to a recurring event to cancel a single occurrence."""
+    exclude_date = _parse_date(date_str)
+
+    # Verify the date is a valid occurrence (matches the RRULE pattern)
+    dtstart = vevent.get("dtstart").dt
+    rrule = vevent.get("rrule")
+
+    # Check if dtstart is a datetime or date
+    if isinstance(dtstart, datetime):
+        start_date = dtstart.date() if hasattr(dtstart, 'date') else dtstart
+    else:
+        start_date = dtstart
+
+    if exclude_date < start_date:
+        print(f"Error: --date {date_str} is before the event start ({start_date})", file=sys.stderr)
+        sys.exit(1)
+
+    # Re-read and modify the ICS file to add EXDATE
+    cal = Calendar.from_ical(ics_path.read_bytes())
+    for component in cal.walk():
+        if component.name == "VEVENT" and str(component.get("uid", "")) == uid:
+            # EXDATE value type must match DTSTART value type
+            if isinstance(dtstart, datetime):
+                # Use a datetime with the same time as DTSTART
+                exclude_dt = datetime.combine(exclude_date, dtstart.time())
+                component.add("exdate", [exclude_dt], parameters={"TZID": vevent.get("dtstart").params.get("TZID", DEFAULT_TIMEZONE)})
+            else:
+                component.add("exdate", [exclude_date])
+            break
+
+    ics_path.write_bytes(cal.to_ical())
+    print(f"Cancelled {summary} on {date_str} (added EXDATE, series continues)")
+    print(f"Updated: {ics_path}")
+
+
 # ---------------------------------------------------------------------------
 # CLI
 # ---------------------------------------------------------------------------
@@ -823,9 +886,11 @@ def main():
     elist_p.add_argument("--format", default="", help="khal format string (e.g. '{uid} {title}')")
 
     # event delete
-    edel_p = event_sub.add_parser("delete", help="Delete an event")
+    edel_p = event_sub.add_parser("delete", help="Delete an event or cancel one occurrence")
     edel_p.add_argument("--uid", default="", help="Event UID")
     edel_p.add_argument("--match", default="", help="Match on summary text")
+    edel_p.add_argument("--date", default="", help="Cancel single occurrence on this date (YYYY-MM-DD, for recurring events)")
+    edel_p.add_argument("--all", action="store_true", help="Delete entire recurring series (safety flag)")
 
     # --- todo ---
     todo_p = subparsers.add_parser("todo", help="Manage VTODO tasks")