Paws & Play: Daycare Check-In

Paws & Play: Daycare Check-In

You've joined the small team behind the front-desk system of Paws & Play, a dog daycare. The system decides whether a dog may come in, which play room it goes to, and what the owner pays at pickup. Three tickets are open: front desk is reporting wrong answers, billing wants households to be priced fairly, and the behaviour team wants reactive dogs handled safely. All prices are integer cents.

Codebase

All rates, hours, rooms and size units live in config.py; the examples below use those values.

How your code is run

run(operations: list[list]) -> list executes the operations in order against a fresh daycare and returns one result per operation. Every operation is [name, date, time, ...args]. date is a "YYYY-MM-DD" string (only the shape is checked; ISO dates compare correctly as plain strings) and time is "HH:MM" from 00:00 to 23:59. Errors are returned as "error: <message>", never raised.

• An unknown operation name returns "error: unknown operation". A malformed operation (not a list, fewer than three elements, bad date or time, wrong number of arguments, an id that is not a non-empty string, an expires that is not a YYYY-MM-DD string) returns "error: invalid arguments"; this is checked before anything else.
• size is "S", "M" or "L". The only vaccines are rabies, dhpp and bordetella. Every dog needs all three.
• A vaccine is valid through its expiry date: it covers every date <= expires. vaccinate never shortens an existing record (a later expires replaces it, an earlier one is ignored). The first uncovered vaccine, in the order rabies, dhpp, bordetella, is the one reported: missing if no record exists, expired otherwise.
• Check-in is allowed from 07:00 up to but not including 18:00; otherwise daycare closed.
• Rooms. Capacity is counted in size units (S=1, M=2, L=3). Large dogs are never placed in cozy. A room is *eligible* for a dog if it allows the dog's size and has enough free units. The dog goes to the eligible room that would have the fewest free units left after placing it; on a tie, the room listed first in config.py. If no room is eligible: no room available and the dog is not checked in.
• A dog must be picked up on the day it checked in (day mismatch otherwise). Pickup frees the dog's space.
• Bill returned by check_out: {"dogs": [[dog_id, charge]], "late_fee": n, "total": n}. A pickup at or before 13:00 is a half day, later pickups are a full day (rates in config.py). The late fee is 500 for every *started* 15 minutes after 18:00: nothing at 18:00, 500 for 18:01 through 18:15, 1000 for 18:16, and so on. total is the sum of all charges plus the late fee.

Worked example

[["register", "2025-03-10", "07:00", "rex", "o1", "M"],
 ["vaccinate", "2025-03-10", "07:00", "rex", "rabies", "2025-03-10"],
 ["vaccinate", "2025-03-10", "07:00", "rex", "dhpp", "2026-01-01"],
 ["vaccinate", "2025-03-10", "07:00", "rex", "bordetella", "2025-09-01"],
 ["check_in", "2025-03-10", "08:05", "rex"],
 ["check_out", "2025-03-10", "18:20", "rex"]]

returns

[true, true, true, true, "cozy", {"dogs": [["rex", 3650]], "late_fee": 1000, "total": 4650}]

Rex's rabies certificate runs out on the day he visits, which still counts. He is picked up 20 minutes late, which is two started quarter-hours.

Part 1: Fix three front-desk defects (SUP-410, SUP-418, SUP-425)

Goal: make check-in, rooms and billing follow the rules above. Reports from the front desk:

1. "We turned Max away on the exact day his rabies certificate expires."
2. "A family picking up at 18:05 paid no late fee, and at 18:20 they were charged only one block."
3. "Once a few medium dogs go home, the cozy room still says it is full, so new small and medium dogs get pushed into the meadow."

Rules

1. A vaccine whose expires equals the visit date covers that visit; the next day it does not.
2. The late fee counts every *started* 15-minute block after 18:00.
3. After pickup the room has exactly as much free capacity as before the dog arrived, whatever its size.

The failing tests in tests/test_daycare.py show the symptoms. Everything not mentioned here already works and must keep working, including the order in which check-in errors are reported.

Part 2: Household pickups (BILL-77)

Goal: an owner usually collects several dogs at once. check_out now accepts one or more dog ids and bills them as one pickup with a multi-dog discount.

["check_out", date, time, dog_id, dog_id, ...]

Rules

1. All listed dogs must belong to the same owner. Dogs are validated in the listed order: unknown dog, then not checked in, then day mismatch for each dog in turn; only after every dog passes is the owner check made (different owners). Listing the same dog twice, or a non-string id, is invalid arguments and is checked before any of these. If any error occurs, nobody leaves and nothing changes.
2. Each dog's *base charge* is its half-day or full-day rate, decided once by the pickup time.
3. The dog with the highest base charge pays it in full (if several are tied, the one listed first). Every other dog pays base - base // 4 (integer arithmetic; a quarter off, rounded so the customer pays the extra cent).
4. The late fee is charged once per pickup, not per dog, and is never discounted.
5. The bill lists the dogs in the order given; total is the sum of their charges plus the late fee. With a single dog the bill is exactly what Part 1 produced.
6. All dogs in the pickup leave their rooms.

Example (all three dogs already checked in on 2025-03-10; bruno is an L, rex an M, pip an S, all owned by o1)

[["check_out", "2025-03-10", "12:30", "rex", "bruno", "pip"]]

returns

[{"dogs": [["rex", 1613], ["bruno", 2500], ["pip", 1275]], "late_fee": 0, "total": 5388}]

bruno has the highest half-day rate (2500) and pays it. rex: 2150 - 537 = 1613. pip: 1700 - 425 = 1275.

Part 3: Reactive dogs (BEH-31)

Goal: the behaviour team flags some dogs as *reactive*. A reactive dog must never share a room with more than two other dogs. The old rule "a room accepts a dog if the units fit" is no longer enough.

register takes an optional fourth argument after size: the dog's temperament, "calm" (default) or "reactive". Any other value is error: invalid temperament (checked after invalid size).

Rules

1. A reactive dog may only be placed in a room that currently holds at most 2 other dogs (any sizes; count dogs, not units).
2. While a reactive dog is in a room, no dog of any temperament may join it once it already holds 3 or more dogs, even when units are free. (So a room with a reactive dog never has more than 3 dogs, and a calm newcomer is refused a room where a reactive dog already shares with two others.)
3. The existing rules still apply on top: size restrictions (cozy has no large dogs), unit capacity, and the tightest-fit room choice among the rooms that are eligible under all rules. Dogs already in a room are never moved. Once the reactive dog leaves, the limit stops applying to that room.
4. A reactive dog's charge at pickup includes a surcharge of 800, added after the household discount: the surcharge is never discounted, and it does not change which dog is the highest-charged one (that is decided by base charge alone).
5. Everything from Parts 1 and 2 still holds. The late fee is still charged once per pickup.

Example (all dogs owned by different people, fully vaccinated, size S; a, b, c calm, r reactive)

[["check_in", "2025-03-10", "08:00", "a"],
 ["check_in", "2025-03-10", "08:01", "b"],
 ["check_in", "2025-03-10", "08:02", "c"],
 ["check_in", "2025-03-10", "08:03", "r"]]

returns ["cozy", "cozy", "cozy", "meadow"]. cozy holds three dogs, which is more than two, so the reactive dog cannot go there even though units are free, and meadow is the next-best eligible room. A fourth *calm* dog arriving now still gets cozy (3 dogs, 4 of 6 units used, no reactive dog in it).

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.