Messages that check their own times

Problem

I work at a K-12 online learning provider: schools in the US and abroad partner with us so their students can take courses online. I also tutor students one-to-one over video. For every session, the student gets two messages from me: one the day before, confirming the session is booked, and a reminder on the day. Each must give the date, the time and the student’s own time zone, because my students live in many different zones. If the hour is wrong, the student joins an empty room.

Constraints

• Messages go out only through the school’s own messaging system, and only when I send them. Nothing may send itself.
• Session times come from calendar invitations, and not every invitation includes the student’s local time.
• Clocks change in spring and autumn, and some students live where the clocks never change.
• A program that runs in the morning cannot know about sessions booked later that day.

What I built

A small Python program that drafts these messages for me. It reads my tutoring calendar and fills in the team’s standard confirmation and reminder wording for each session.

The tricky part is the time. The program copies the student’s local time from the calendar invitation, then works it out a second time on its own from the session’s start time in UTC (the world’s reference clock). If the two answers do not match, it flags the session instead of guessing. If an invitation has no local time, it uses a time zone already confirmed for that student, and labels every message that relied on it.

It also catches other problems: a missing video link, a session listed twice, or a student who is not on the invitation. It skips days off. On Fridays it covers the weekend and Monday. A second run in the afternoon drafts messages only for sessions booked since the morning, and suggests the exact time to schedule each reminder.

How I proved it worked

Every batch of drafts must pass four automatic checks before it counts as ready:

1. The date and time in each message match the calendar invitation.
2. Every message includes a date, a time and a time zone.
3. The program cannot send anything: there is no sending code anywhere in it.
4. Every message that used a confirmed zone is labelled and names the zone.

A day with nothing to send only passes if every session is accounted for, one by one, so a quiet day cannot hide a missed session.

I replayed every change against earlier days. After adding the afternoon run, every earlier day but one produced exactly the same drafts, and that one differed on purpose. I also broke things deliberately: shifted an hour, removed a label, deleted a message, faked an “already handled” note. Each one made a check fail, and the failure named the message.

Outcome

• The program runs every weekday morning and afternoon. I read each draft and send it myself.
• When the clocks changed in November, the replays gave the right times, including for a place where the clocks never change.
• One real gap came to light: a session at the very start of my working day could not get its reminder in time, because I sent reminders by hand during the day. The afternoon run and the suggested send times came from that case.
• I do not claim an error rate, because none was measured.

What I would do next

• Read the sent messages back from the messaging system and compare them with the drafts.
• Add a check for the subject line. I once wrote a message by hand with the wrong subject, and nothing caught it.

The demo it pairs with

Time-zone message checker. Pick a session and see the confirmation in the student’s time zone. Then break it: change the zone, shift the hour or remove the time zone, and watch which check fails and why.