Studio Booking: Class Packs, Waitlists and Cancellations

Studio Booking: Class Packs, Waitlists and Cancellations

You've joined the team behind the booking backend of a boutique fitness studio. Members buy class packs (a number of credits that expire), spend one credit per class, and join a waitlist when a class is full. Front desk has reported three money-and-seat bugs, and two features are queued behind them. All times are integer minutes; a day is 1440 minutes.

Codebase

How your code is run

run(operations: list[list]) -> list executes the operations in order against a fresh studio and returns one result per operation. Every operation is [name, ts, ...args]; ts is an integer number of minutes and never decreases. Errors are returned as "error: <code>" strings, never raised.

• A name that is not in the table returns "error: unknown operation". A wrong number of arguments, a non-integer (or boolean) where an integer is expected, a non-string or empty id, or a non-integer ts returns "error: invalid arguments".
• add_class: invalid class when start <= ts or capacity < 1. buy_pack: invalid pack when credits < 1 or valid_days < 1.
• Packs. Pack ids are "p-1", "p-2", ... in purchase order across the whole studio. A pack bought at ts expires at ts + valid_days * 1440; it is usable at time t only while t < expires. credits counts the credits left in the member's packs that are usable at ts.
• Spending. Booking a seat spends one credit from the member's usable pack that expires soonest (ties: lower pack id). A booking remembers which pack paid for it.
• Booking a full class puts the member on the waitlist (position 1 = first in line) and costs nothing; the credit is only spent if they are later promoted. A class is full when booked == capacity.
• A booking, waitlist join or cancel needs ts < start; at ts >= start the answer is class started.
• Cancelling. A waitlisted member leaves the waitlist (left waitlist, no credit involved). A booked member frees the seat and the cancel is late if the class starts in less than 720 minutes (12 hours); exactly 720 is still on time. A late cancel returns forfeited and the credit is gone. An on-time cancel returns refunded and the credit goes back to the pack that paid for that seat, even if that pack has expired in the meantime (an expired pack cannot spend it, so the credit is simply lost).
• roster lists booked members in the order seats were taken and the waitlist in line order.

Worked example

[["add_class", 0, "yoga", 3000, 2],
 ["buy_pack", 1, "ana", 5, 30],
 ["book", 2, "ana", "yoga"],
 ["credits", 3, "ana"],
 ["cancel", 100, "ana", "yoga"],
 ["credits", 101, "ana"]]

returns

[true, "p-1", "booked", 4, "refunded", 5]

Part 1: Fix three booking bugs (STU-412, STU-419, STU-427)

Goal: make booking, cancelling and refunding follow the rules above.

Reports from the front desk:

1. "Ana cancelled exactly 12 hours before class and lost her credit."
2. "Ben bought a 2-credit pack that expires this week and a 20-credit pack that expires in two months. The system spent from the big pack first and his small pack expired unused."
3. "Cy cancelled in time and got his credit back, but into the wrong pack: his short pack still expired with a credit in it, and his long pack grew by one."

tests/test_booking.py::test_cancel_exactly_twelve_hours_before_is_refunded currently fails. Waitlists still never get promoted; that is Part 2.

Rules: everything in the section above; the table's error order holds.

Part 2: Waitlist auto-promotion (STU-431)

Goal: when a booked member cancels, offer the freed seat to the waitlist.

Rules

1. After a cancel of a booked seat (refunded or forfeited alike), if the class starts more than 120 minutes after ts (PROMOTION_CUTOFF_MINUTES; exactly 120 is too late), try to promote one waitlisted member. At 120 minutes or less, nobody is promoted and the seat stays open for walk-ins.
2. Go through the waitlist in line order. A member is promoted if they have a usable credit at ts: one credit is spent exactly as for book (soonest-expiring usable pack), they get a seat appended to the bookings, and they leave the waitlist. Members with no usable credit are skipped and keep their place. At most one member is promoted per cancel. Cancelling a waitlist spot never promotes anyone.
3. An open seat with a non-empty waitlist (rule 1 cutoff, or everyone was skipped) can be taken by a book from anyone not already booked or waitlisted: it books directly ("booked"). A waitlisted member calling book still gets already waitlisted.
4. A promoted member's booking remembers the pack that paid at promotion time; their own later cancel follows the Part 1 rules against that pack.

Example

[["add_class", 0, "spin", 3000, 1],
 ["buy_pack", 1, "ana", 5, 30], ["buy_pack", 1, "ben", 5, 30], ["buy_pack", 1, "cy", 5, 30],
 ["book", 2, "ana", "spin"], ["book", 3, "ben", "spin"], ["book", 4, "cy", "spin"],
 ["cancel", 100, "ana", "spin"],
 ["roster", 101, "spin"], ["credits", 101, "ben"], ["credits", 101, "ana"]]

returns [true, "p-1", "p-2", "p-3", "booked", "waitlisted:1", "waitlisted:2", "refunded", {"booked": ["ben"], "waitlist": ["cy"]}, 4, 5].

Part 3: Instructor-cancelled classes (STU-448)

Goal: the studio can cancel a whole class. Everyone who booked must be made whole, and this changes how refunds to expired packs work for that case.

New operation: ["cancel_class", ts, class_id] returns {"refunded": <int>, "makeup_packs": <int>, "cleared": <int>}. Errors, in order: class not found, class cancelled, class started (ts >= start).

Rules

1. Every booked member gets their credit back regardless of how close the class is; the late-cancel window does not apply. Bookings are processed in booking order. If the pack that paid is still usable at ts the credit goes back to it. If it has expired, the credit instead goes into a new makeup pack: 1 credit, valid for 14 days (ts + 14 * 1440), with the next pack id ("p-N" continues the same sequence, so ids follow booking order).
2. The waitlist is cleared; waitlisted members were never charged, so nothing is refunded to them. Nobody is promoted.
3. Members who cancelled earlier (including late cancels) get nothing from cancel_class. The Part 1 rule for a member's own cancel is unchanged: their credit returns to the original pack even if it expired.
4. refunded = number of bookings refunded, makeup_packs = how many of them got a makeup pack, cleared = waitlist size removed.
5. Afterwards the class stays in the catalogue: roster returns two empty lists, and book and cancel return class cancelled (checked right after class not found, before class started, even after the original start time). add_class with the same id is still class exists.

Example (ana, ben, cy each own a fresh 5-credit pack)

[["add_class", 0, "pilates", 3000, 2],
 ["buy_pack", 1, "ana", 5, 30], ["buy_pack", 1, "ben", 5, 30], ["buy_pack", 1, "cy", 5, 30],
 ["book", 2, "ana", "pilates"], ["book", 3, "ben", "pilates"], ["book", 4, "cy", "pilates"],
 ["cancel_class", 2900, "pilates"],
 ["credits", 2901, "ana"], ["credits", 2901, "cy"],
 ["roster", 2902, "pilates"], ["book", 2903, "cy", "pilates"]]

returns [true, "p-1", "p-2", "p-3", "booked", "booked", "waitlisted:1", {"refunded": 2, "makeup_packs": 0, "cleared": 1}, 5, 5, {"booked": [], "waitlist": []}, "error: class cancelled"].

Notes

• You may use the AI assistant freely; you are expected to verify what it produces.
• Later parts must not break earlier ones; hidden tests re-check earlier behaviour.
• schedule.py and models.py are known-good.