Toll Road: Trip Billing

Toll Road: Trip Billing

You've joined the tolling team of a highway operator. Vehicles pass plazas along one straight road; an entry read followed by an exit read forms a trip, and the trip is billed by distance. Customer support has three open fare complaints, and two billing features are queued behind them. All money is integer cents; fares are *computed* in tenths of a cent so per-km rates like 12.5 cents stay exact.

Codebase

How your code is run

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

• The road: plazas A 0 km, B 9, C 26, D 41, E 77. Directions are "up" (towards E) and "down" (towards A). Classes and rates are in toll/config.py.
• A wrong number of arguments, a non-integer ts or a non-string/empty string argument returns "error: invalid arguments"; an unknown operation name returns "error: unknown operation".
• A trip is a dict with exactly these keys: id ("t-1", "t-2", ... in the order trips are *closed*), vehicle, from, to (plaza ids), km, fare (cents), fee (cents, see Part 3), kind, opened (ts of the entry), closed (ts the trip was billed).
• A rejected operation changes nothing: no trip id is used and no state moves.

Worked example

[["enroll", 1, "T100", "car"],
 ["enroll", 2, "T200", "moto"],
 ["entry", 10, "T100", "B", "up"],
 ["exit", 30, "T100", "C"],
 ["entry", 40, "T200", "A", "up"],
 ["exit", 50, "T200", "B"],
 ["exit", 51, "T200", "B"],
 ["trips", 60, "T100"]]

returns

[true, true, true,
 {"id": "t-1", "vehicle": "T100", "from": "B", "to": "C", "km": 17, "fare": 213, "fee": 0, "kind": "normal", "opened": 10, "closed": 30},
 true,
 {"id": "t-2", "vehicle": "T200", "from": "A", "to": "B", "km": 9, "fare": 150, "fee": 0, "kind": "normal", "opened": 40, "closed": 50},
 "error: no open trip",
 [{"id": "t-1", "vehicle": "T100", "from": "B", "to": "C", "km": 17, "fare": 213, "fee": 0, "kind": "normal", "opened": 10, "closed": 30}]]

Part 1 — Fix three fare complaints (TOLL-412, TOLL-418, TOLL-431)

Goal: make completed trips (kind "normal") bill and close exactly as specified.

Support tickets: "My 17 km trip cost 212 cents; the sign says 12.5 cents per km, so 212.5 should be 213." "My motorbike was charged 58 cents for a 9 km hop — I thought there was a minimum." "When the camera double-reads an exit we get two bills for one trip."

Rules

1. Exact fare = km x rate (tenths of a cent); km is the distance between entry and exit plaza.
2. The minimum fare of MIN_FARE_CENTS applies to the exact fare: a trip is never billed less than 150 cents.
3. Whole cents = exact fare rounded half up (x.5 cents goes up). Never use floats.
4. exit bills a trip only if the vehicle has an open trip, and billing closes it: a second exit read returns no open trip. Trip ids are given out at billing time.
5. The exit plaza must be at or beyond the entry plaza in the entry's direction (the same plaza is allowed, distance 0, minimum fare). Otherwise wrong direction, and the trip stays open.
6. entry while the vehicle already has an open trip is not defined yet (Part 2).

tests/test_fares.py and tests/test_service.py contain failing tests for these.

Part 2 — Missed exits and abandoned trips (TOLL-440)

Goal: a trip that never gets an exit read must still be billed, as a max-fare trip from its entry plaza to the *last plaza in its direction of travel* (E for "up", A for "down"), priced with the normal formula (class rate, minimum fare; an entry already at the last plaza is a 0 km trip at the minimum fare).

Rules

1. Timeout. An open trip is billed as a max-fare trip with kind "timeout" once ts >= opened + 43200 (12 hours; OPEN_TRIP_TIMEOUT_S). Its closed is opened + 43200, not the ts of the operation that noticed.
2. Timeouts are checked before every operation whose ts is an integer — reads, queries, failing and unknown operations included. Several expiring trips are billed in order of opened, ties by the order they were opened, and take trip ids in that order.
3. Missed exit. A valid entry for a vehicle that still has an open trip first bills that old trip as a max-fare trip with kind "missed_exit" and closed = the new entry's ts, then opens the new trip. An entry that is rejected leaves the old trip open.
4. An exit that arrives at or after the timeout finds no open trip (no open trip); one arriving earlier is a normal exit. exit still returns the trip it closed.
5. trips lists max-fare trips with the same shape; to is the last plaza reached.

Example (after enrolling T100 as a car)

[["entry", 100, "T100", "B", "up"],
 ["entry", 200, "T100", "C", "up"],
 ["exit", 43400, "T100", "D"],
 ["trips", 43401, "T100"]]

returns true, true, "error: no open trip" and then two trips: t-1 from B to E (68 km, fare 850, missed_exit, opened 100, closed 200) and t-2 from C to E (51 km, fare 638, timeout, opened 200, closed 43400). The exit at 43400 is exactly 200 + 43200, so the timeout already billed the trip.

Part 3 — Camera-only vehicles and monthly statements (TOLL-455)

Goal: vehicles without a transponder are read by plate camera, pay an admin fee, and every vehicle gets a monthly statement.

New operations: register_plate (plate, class) returns true (errors in order: invalid class, plate registered); statement (period) returns the statement below (period must be an integer >= 0, otherwise invalid arguments). enroll of a vehicle id that starts with "plate:" returns invalid arguments.

Rules

1. A vehicle id starting with "plate:" is a camera read ("plate:XYZ9" is plate XYZ9). Plates need no enroll; unknown vehicle never applies to them. Everything else (entry, exit, max-fare trips, timeouts) works exactly as before.
2. A plate trip is priced when it is billed, using the class the plate is registered under *at that moment*, else car. A later registration never re-prices a trip. (A timed-out trip is billed *before* the operation that notices it runs, so a register_plate arriving after the timeout does not affect its price.)
3. Every plate trip owes a 150 cent fee, unless the plate is registered with a registration ts <= closed + 604800 (7 days). That includes plates registered before the trip. The fee is judged whenever a trip is shown, so registering a plate within a week of a trip waives that trip's fee retroactively. Transponder trips have fee 0.
4. statement(period) covers trips with period * 2592000 <= closed < (period + 1) * 2592000 (30-day periods), by billing time (closed), never by opened.
5. The result is {"period": p, "lines": [...]} with one line per vehicle that has trips in the period, sorted by vehicle id (plain string order): {"vehicle", "trips", "fares", "fees", "total"}. fees is the sum of the trips' current fees and total = fares + fees.
6. fares is the sum of the exact fares (tenths) rounded half up once, so it can differ from the sum of the individual trips' rounded fare values by a few cents. Individual trip fare values keep Part 1's rounding.

Example

[["enroll", 1, "T100", "car"],
 ["entry", 100, "plate:XYZ9", "B", "up"],
 ["exit", 200, "plate:XYZ9", "C"],
 ["register_plate", 300, "XYZ9", "truck"],
 ["trips", 301, "plate:XYZ9"],
 ["entry", 400, "T100", "B", "up"], ["exit", 500, "T100", "C"],
 ["entry", 600, "T100", "B", "up"], ["exit", 700, "T100", "C"],
 ["statement", 800, 0]]

The plate trip is first returned (by exit) with fare 213 and fee 150; after the registration the trips call shows the same fare 213 with fee 0. The statement is {"period": 0, "lines": [{"vehicle": "T100", "trips": 2, "fares": 425, "fees": 0, "total": 425}, {"vehicle": "plate:XYZ9", "trips": 1, "fares": 213, "fees": 0, "total": 213}]} — T100's two trips each show 213, but 2 x 212.5 is exactly 425.

Notes

• highway.py is known-good.
• 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.