Extract per-stop arrivals core into shared functions - #1407
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The arrivals-and-departures-for-stop handler carried its entire pipeline inline: the +/-1 day service window scan, the batch route and trip resolution, the per-row arrival construction, and the reference assembly. Nothing was callable from anywhere else, so a second endpoint needing arrivals for many stops would have to duplicate all of it. Move that pipeline into arrivals_core.go behind arrivalsForStop and buildArrivalsReferences, with an arrivalsAccumulator gathering the routes, trips, stops and situations that the arrivals reference. The accumulator is what makes the code reusable across several stops: a caller loops over stops sharing one accumulator and gets a single deduplicated references block. Behavior is unchanged; the test suite passes without modification. Two details worth noting for review: BuildTripStatus now receives the vehicle the caller already looked up rather than nil. It is not a fix -- BuildTripStatus falls back to the same GetVehicleForTrip call when handed nil -- so the result is identical, but it drops one redundant lookup per arrival row. The extracted stop reference deliberately keeps its inline literal instead of calling buildStopModel. That helper defaults Code to the stop ID when stops.code is NULL, where this endpoint emits an empty string, so adopting it would be a response change rather than a refactor.
📝 WalkthroughWalkthroughThe handler now delegates stop-arrival computation and reference assembly to shared helpers. The new core queries active stop times, builds arrivals with real-time data, accumulates related entities, and short-circuits unmatched windows. ChangesStop arrivals flow
Estimated code review effort: 4 (Complex) | ~60 minutes Merge Risk: 🟡 Moderate · up to The refactor can currently convert database lookup failures into successful responses with missing arrivals or stop references, causing clients to receive incomplete data while masking a server-side failure. Merge readiness is moderate until both errors are propagated and handled as server errors. Sequence Diagram(s)sequenceDiagram
participant StopArrivalsHandler
participant ArrivalsForStop
participant GTFSDatabase
participant BuildArrival
participant BuildTripStatus
participant BuildArrivalsReferences
StopArrivalsHandler->>ArrivalsForStop: stopArrivalsInput
ArrivalsForStop->>GTFSDatabase: query active stop times and entities
GTFSDatabase-->>ArrivalsForStop: matched stop times and entities
ArrivalsForStop->>BuildArrival: arrivalInput
BuildArrival->>BuildTripStatus: vehicle and trip data
BuildTripStatus-->>BuildArrival: trip status and metrics
BuildArrival-->>ArrivalsForStop: ArrivalAndDeparture
StopArrivalsHandler->>BuildArrivalsReferences: accumulated entities
BuildArrivalsReferences-->>StopArrivalsHandler: ReferencesModel
Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@internal/restapi/arrivals_core.go`:
- Line 152: Reduce cognitive complexity below the quality-gate threshold by
extracting the per-day logic from activeStopTimesForWindow into
stopTimesForServiceDay, unique ID and trip-stop count preparation from
batchArrivalEntities into uniqueIDs and tripStopCounts, prediction and
trip-status/metric resolution from buildArrival into separate helpers, and batch
lookup loading from appendStopReferences into a stopReferenceData loader while
preserving existing behavior.
- Around line 557-567: Update appendStopReferences so a GetStopsByIDs failure is
returned to the caller instead of setting batchStops to nil and continuing;
preserve the existing successful stop-reference processing and the
warn-and-continue behavior for GetRoutesForStops, which may still set
batchRoutesForStops to nil.
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internal/restapi/arrivals_and_departures_for_stop_handler.gointernal/restapi/arrivals_core.go
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Four functions in the extracted core sat above the quality gate's
cognitive complexity threshold of 15: activeStopTimesForWindow at 21,
appendStopReferences at 18, buildArrival at 17 and batchArrivalEntities
at 16.
Pull the distinct sub-tasks out of each:
- stopTimesForServiceDay, the per-service-day scan
- uniqueRouteAndTripIDs and tripStopCounts, the batch input and
stop-count preparation
- combinedVehicleID and tripStatusForArrival, the vehicle and trip
status resolution
- loadStopReferenceData and collectStopRoutes, the reference batch
load and per-stop route rendering
One behaviour does change. A failed GetStopsByIDs in the stop reference
load is now returned rather than logged and skipped past. Swallowing it
dropped every stop reference and still answered 200, so the entry named
stops the client had no way to resolve; the handler now surfaces it as
a 500. The routes lookup keeps its warn-and-continue, since losing it
only costs each stop its routeIds.
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Addressed both review points in f32e903. Quality gate is now green (0 issues). Cognitive complexity — four functions were over the threshold of 15. Split each into its distinct sub-tasks:
One thing to be careful of if you review that extraction: the per-day loop has two different failure modes. Failing to resolve a day's active services is fatal on day 0 but tolerable on ±1, while failing to read that day's
Note that this second fix does make the PR no longer strictly behaviour-preserving — it only fires on a DB failure, so the suite still passes with no test changes, but the description's "no behavior change" is slightly overstated now. Happy to reword it if you'd prefer. |
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Review summary
Automated review (medium effort) plus manual verification of the merge state against current main. Two correctness/behavior issues should block merge; the rest are cleanup findings worth addressing in follow-up commits.
1. Frequency support is missing, and this PR conflicts with main's frequency work — internal/restapi/arrivals_core.go
This branch predates main's frequency-support work (BuildTripStatus gained a freqMap parameter and callers now populate arrival.Frequency). Verified directly:
git merge maininto this branch produces a realCONFLICT (content)inarrivals_and_departures_for_stop_handler.go, spanning ~383 lines — this PR's side is a 3-line stub, main's side is the full old inline block that includes all frequency handling.- On the clean PR branch (no merge in progress),
grep -n "freq\|Freq"returns zero matches inarrivals_core.go,arrivals_and_departures_for_stop_handler.go, andarrival_and_departure_for_stop_handler.go.
So today, any stop served by a frequencies.txt-based (headway) trip gets "frequency": null in /api/where/arrivals-and-departures-for-stop/{id} responses instead of the populated block clients use for "every N minutes" countdown UIs. This isn't something git resolves automatically — whoever merges has to manually re-port frequency support into the new accumulator-based structure. Please rebase onto main and reintroduce frequency handling in arrivals_core.go before merge.
2. GetStopsByIDs failure now returns a hard 500 instead of degrading gracefully — internal/restapi/arrivals_core.go (loadStopReferenceData)
The old handler logged a warning on GetStopsByIDs error and continued with batchStops = nil, still returning 200 with arrivals populated but references.stops incomplete. The new code does:
if err != nil {
return nil, nil, fmt.Errorf("batch fetch stop references: %w", err)
}which propagates all the way to api.serverErrorResponse(w, r, err) — a 500. A transient DB blip on the stop-reference batch query (unrelated to the arrivals already computed) now fails the whole request. This is an undisclosed behavior change; the PR description states "no behavior change." Since this sits in the exact region that conflicts with main (see #1), it's worth fixing while resolving that conflict rather than as a separate patch.
3. Dead code: RouteTypes / isRouteTypeAllowed filter is never wired up
stopArrivalsInput.RouteTypes is never set by the only caller (handler_new.go's construction of stopArrivalsInput), so isRouteTypeAllowed is always called with allowed == nil and always returns true. This adds an unreachable branch to the hot per-row loop and a predicate function that looks like live functionality but is untested and unused. Either wire it up or drop it until it's needed.
4. Dead code: arrivalsReferencesInput.stopAgencies is never populated
Same pattern — the only call site never sets stopAgencies, so the per-stop agency lookup in appendStopReferences can never hit. A future contributor could reasonably assume per-stop agency overrides are already implemented and tested.
5. Reuse: route/stop reference building bypasses existing helpers in reference_utils.go
appendRouteReferenceshand-buildsmodels.Routeviamodels.NewRouteinstead of reusingbuildRouteModels, the documented single source of truth forgtfsdb.Route -> models.Routemapping.collectStopRoutesmanually copies aGetRoutesForStopsRowinto a freshgtfsdb.Routeinstead of reusingrouteReferenceFromStopRow/routeReferencesForStops.
Per CONTRIBUTING.md's Code Reuse guidance, these should call the existing helpers rather than duplicating the conversion logic — otherwise a future schema/null-handling fix applied to the shared helpers won't apply here.
6. Duplication: the singular arrival-and-departure handler still has its own inline reference-building logic
internal/restapi/arrival_and_departure_for_stop_handler.go hand-rolls the same ~110-line stop/route reference-building logic this PR just extracted into arrivals_core.go, leaving two parallel implementations that will drift over time. Worth a follow-up to migrate the singular handler onto the new shared helpers.
7. Design note: arrivalsAccumulator.alertAgencyID is a single scalar despite being documented as multi-stop/multi-agency
If a future arrivals-for-location endpoint loops arrivalsForStop across stops from different agencies while sharing one accumulator (the PR's stated purpose for this type), acc.alertAgencyID will lock onto whichever agency was set first, and later stops' alerts get namespaced under the wrong agency ID. Worth flagging now since it'll be harder to fix once a second caller depends on it.
Requesting changes primarily on #1 and #2 — the rest are good candidates for a follow-up commit or PR.
# Conflicts: # internal/restapi/arrivals_and_departures_for_stop_handler.go
The extraction in refactor/extract-arrivals-core predates main's GTFS frequency work, so merging main in silently dropped frequency data from arrivals-and-departures-for-stop: BuildTripStatus's freqMap parameter had nothing feeding it. Batch-fetch frequencies alongside routes and trips in batchArrivalEntities, thread the map through arrivalInput, and apply it in a small applyFrequency helper kept separate from buildArrival to avoid pushing its cognitive complexity back over the SonarCloud limit. This also gives the location endpoint frequency support for free, since it shares the same core.
A hard 500 here means a single failed batch stop lookup takes down an otherwise complete arrivals response. Match the treatment already given to the sibling route lookup: log and continue with an incomplete references.stops rather than failing the whole request.
The prior wording read as if any caller could rely on this field to namespace alerts. It is only ever read by the single-stop handler; a multi-stop caller must pass a per-stop agency ID directly to situations.add instead. Reword to state that plainly rather than scoping the field, since it is genuinely single-caller today.
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Both blockers fixed, branch is up to date with Commits: Merged 1. Frequency — fixed. Re-ported into 2. 3 & 4. 5. Reference helpers — I don't think these are safe swaps:
Same call as the 6. Singular handler duplication — agreed, separate PR. 7.
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Inline comments:
In `@internal/restapi/arrivals_core.go`:
- Line 229: Update the day-0 error path in activeStopTimesForWindow to return a
wrapped error from GetStopTimesForStopInWindow instead of nil, nil, while
preserving best-effort handling for spillover days; ensure callers route
non-sql.ErrNoRows database errors through serverErrorResponse as HTTP 500.
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| api.Logger.Warn("failed to query stop times in window", | ||
| slog.String("stopID", in.StopCode), | ||
| slog.Any("error", err)) | ||
| return nil, nil |
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🗄️ Data Integrity & Integration | 🟠 Major | ⚡ Quick win
Return the current-day stop-time query error.
When GetStopTimesForStopInWindow fails for day 0, this returns an empty successful result. The handler then treats the failure as no arrivals and can send a 200 response with missing arrivals. Return a wrapped error here. activeStopTimesForWindow already preserves best-effort handling for spillover days.
Proposed fix
- return nil, nil
+ return nil, fmt.Errorf("query stop times for %s: %w", serviceDateStr, err)As per coding guidelines, route database lookup errors other than sql.ErrNoRows through serverErrorResponse as 500.
📝 Committable suggestion
‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
| return nil, nil | |
| return nil, fmt.Errorf("query stop times for %s: %w", serviceDateStr, err) |
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In `@internal/restapi/arrivals_core.go` at line 229, Update the day-0 error path
in activeStopTimesForWindow to return a wrapped error from
GetStopTimesForStopInWindow instead of nil, nil, while preserving best-effort
handling for spillover days; ensure callers route non-sql.ErrNoRows database
errors through serverErrorResponse as HTTP 500.
Source: Coding guidelines
2 participants
Summary
Pure refactor. Moves the arrivals pipeline out of the
arrivals-and-departures-for-stophandler into functions a second endpoint can call. No behavior change — the test suite passes untouched.What changed
internal/restapi/arrivals_core.goholdingarrivalsForStopandbuildArrivalsReferences.arrivals_and_departures_for_stop_handler.godrops from 744 to 235 lines and now just parses, calls the core, and builds the envelope.arrivalsAccumulatorgathers the routes, trips, stops and situations that arrivals reference. This is what makes the code reusable across stops: a caller loops over many stops sharing one accumulator and gets a single deduplicated references block.Why
The pipeline — the ±1 day service window scan, batch route/trip resolution, per-row arrival construction, reference assembly — was entirely inline and not callable from anywhere. Implementing
arrivals-and-departures-for-locationwithout this means duplicating all of it.Two things worth a look
BuildTripStatusnow receives the vehicle the caller already looked up instead ofnil. Not a fix — it falls back to the sameGetVehicleForTripcall when handednil, so the result is identical. It just drops one redundant lookup per arrival row.buildStopModel. That helper defaultsCodeto the stop ID whenstops.codeis NULL, where this endpoint emits an empty string, so adopting it would be a response change rather than a refactor. Happy to switch it in a follow-up if thebuildStopModelbehavior is the intended one.Testing
make testpasses with zero test file changes — that is the whole correctness argument for this PR.Summary by CodeRabbit
Bug Fixes
Performance