Calendar Subscribe

Turn a timetable file into a subscription calendar (one HTTPS .ics + a tiny landing page). Classmates add it once; you update the file when the schedule changes.

When this skill is on

User wants classmates / family to subscribe, not import a one-shot dump. Typical: school timetable, weekend MBA grid, recurring office hours.

Workflow

1. Parse the source (xlsx grid or csv event list). Skip holiday / "no class" cells.
2. Split each teaching block into the actual session times (do not merge a whole morning into one 3-hour event unless the user asks).
3. ICS with a real timezone (TZID, not floating local), CRLF, UTF-8 line fold on character boundaries.
4. Travel alarm once per calendar day, on the earliest class only. Default offset 90 minutes. Later sessions that day get no commute alarm.
5. Host the .ics on any public HTTPS static path. Content-Type: text/calendar.
6. Landing page that branches: WeChat → "open in browser"; iOS → webcal://; Android → Google Calendar cid= + raw ICS.
7. Verify in the same turn: curl -sI both /path and /path/; count BEGIN:VEVENT and BEGIN:VALARM; VALARM count must equal distinct class days.

Source formats

A. Event list CSV (preferred when you can export it)

date,start,end,title,location,notes
2026-09-12,09:00,10:30,Finance,Room 222,week 1

B. Chinese-university weekend grid xlsx

• Row of week labels, row of Excel serial dates, row of 周六/周日
• Time-slot rows (morning / afternoon / evening)
• Merged holiday cells: read the merge origin; if text matches skip patterns, emit nothing

Default skip regex: 不上课|放假|补班

If the sheet only lists two clock ranges per period (e.g. 09:00–10:30 and 10:45–12:15), emit two events, not four 45-minute 节.

ICS rules

• METHOD:PUBLISH, X-WR-CALNAME, X-WR-TIMEZONE, REFRESH-INTERVAL;VALUE=DURATION:P1D
• DTSTART / DTEND with TZID=<IANA> (default Asia/Shanghai)
• Stable UID from date+start+title so republishing does not duplicate on clients that key on UID
• Fold lines at ≤73 UTF-8 bytes on codepoint boundaries (do not split a Chinese character)
• Escape \, ;, ,, newlines
• VALARM TRIGGER:-PT{N}M only on the day's first event

Use scripts/build_ics.py. Example:

python3 scripts/build_ics.py \
  --xlsx timetable.xlsx \
  --out timetable.ics \
  --name "Fall timetable" \
  --location "Room 222" \
  --tz Asia/Shanghai \
  --travel-minutes 90

CSV path: --csv events.csv instead of --xlsx.

Hosting

Any HTTPS static file is enough. Apple Calendar, Google Calendar, and most Android calendars fetch from their servers, so the URL must be reachable from the public internet, not only the author's LAN.

Minimum nginx (adapt root and URL prefix):

location = /cal {
    return 301 /cal/;
}
location ^~ /cal/ {
    alias /var/www/cal/;
    index index.html;
    types {
        text/calendar ics;
        text/html html;
        image/jpeg jpg jpeg;
        image/png png;
    }
    add_header Cache-Control "public, max-age=3600";
}

Landing template: references/landing.html. Replace ICS_URL and PAGE_URL.

Poster / QR: generate a real QR of PAGE_URL (script or qrcode lib). Never let an image model draw the code. Leave a square hole on the poster and composite.

Verify (same turn, or do not claim it works)

curl -sI https://example.com/cal      # must 301 → /cal/
curl -sI https://example.com/cal/     # text/html 200
curl -sI https://example.com/cal/timetable.ics   # text/calendar

Count:

• BEGIN:VEVENT = number of real sessions (not holidays)
• BEGIN:VALARM = number of distinct class days
• zero holiday phrases in summaries

Gotchas

• /cal without a trailing slash is not /cal/. A prefix location ^~ /cal/ misses /cal. On a SPA host the bare path falls through to index.html. If that app sends Cross-Origin-Embedder-Policy: require-corp, the page looks "broken" or blank. Always add location = /cal { return 301 /cal/; }.
• Do not write nginx backups into sites-enabled/. A .bak is loaded as a second server; duplicate listen 443 fails nginx -t.
• Port 80 return 404 (leftover certbot) makes http links look dead. 301 to https.
• A location that sets any add_header drops parent add_headers. COOP/COEP on the server block will not apply — usually what you want for a calendar page.
• WeChat in-app browser cannot add calendars. Detect MicroMessenger and tell the user to open in the system browser first.
• Google Calendar mobile app cannot subscribe from a URL. The https://calendar.google.com/calendar/r?cid= link works in a browser; OEM calendars can open the raw .ics as a one-shot import (no later refresh).
• Commute alarm is per day, not per session. 09:00 class → 07:30 leave. Do not also alarm 10:45 / afternoon / evening.
• UTF-8 fold: taking bytes[:73] can land inside a 3-byte Chinese character and crash encode. Fold on characters, measuring encoded length.
• Excel dates are serials from 1899-12-30 when data_only=True.
• Image-model QR codes do not scan.
• Domestic clients vs a US VPS: the author's phone may not reach the host. Give the raw ICS URL as a fallback; Google/Apple fetchers are usually outside the same firewall.

Examples

User: 把这张课表做成可以分享的日历订阅
→ parse xlsx → ICS → host → landing → verify VEVENT/VALARM

User: 通勤提前一个半小时，别每节课都响
→ --travel-minutes 90, first class of each day only