refactor: migrate aris-data-source-tfl to aris-source-tfl

Migrates TFL package from old DataSource interface to new FeedSource
interface for use with FeedEngine.

Changes:
- Rename package from @aris/data-source-tfl to @aris/source-tfl
- Replace TflDataSource class with TflSource implementing FeedSource
- Add dependency on @aris/source-location for LocationKey
- Use normalized priority values (0-1) instead of arbitrary numbers
- Update tests for FeedSource interface
- Update README.md with new package name

Co-authored-by: Ona <no-reply@ona.com>

packages/aris-source-tfl/src/tfl-api.ts

@@ -0,0 +1,172 @@
+import { type } from "arktype"
+
+import type { StationLocation, TflAlertSeverity, TflLineStatus } from "./types.ts"
+
+const TFL_API_BASE = "https://api.tfl.gov.uk"
+
+const ALL_LINE_IDS: TflLineId[] = [
+	"bakerloo",
+	"central",
+	"circle",
+	"district",
+	"hammersmith-city",
+	"jubilee",
+	"metropolitan",
+	"northern",
+	"piccadilly",
+	"victoria",
+	"waterloo-city",
+	"lioness",
+	"mildmay",
+	"windrush",
+	"weaver",
+	"suffragette",
+	"liberty",
+	"elizabeth",
+]
+
+// TfL severity codes: https://api.tfl.gov.uk/Line/Meta/Severity
+// 0 = Special Service, 1 = Closed, 6 = Severe Delays, 9 = Minor Delays, 10 = Good Service
+const SEVERITY_MAP: Record<number, TflAlertSeverity | null> = {
+	1: "closure",
+	2: "closure", // Suspended
+	3: "closure", // Part Suspended
+	4: "closure", // Planned Closure
+	5: "closure", // Part Closure
+	6: "major-delays", // Severe Delays
+	7: "major-delays", // Reduced Service
+	8: "major-delays", // Bus Service
+	9: "minor-delays", // Minor Delays
+	10: null, // Good Service
+	11: null, // Part Closed
+	12: null, // Exit Only
+	13: null, // No Step Free Access
+	14: null, // Change of frequency
+	15: null, // Diverted
+	16: null, // Not Running
+	17: null, // Issues Reported
+	18: null, // No Issues
+	19: null, // Information
+	20: null, // Service Closed
+}
+
+export class TflApi {
+	private apiKey: string
+	private stationsCache: StationLocation[] | null = null
+
+	constructor(apiKey: string) {
+		this.apiKey = apiKey
+	}
+
+	private async fetch<T>(path: string): Promise<T> {
+		const url = new URL(path, TFL_API_BASE)
+		url.searchParams.set("app_key", this.apiKey)
+		const response = await fetch(url.toString())
+		if (!response.ok) {
+			throw new Error(`TfL API error: ${response.status} ${response.statusText}`)
+		}
+		return response.json() as Promise<T>
+	}
+
+	async fetchLineStatuses(lines?: TflLineId[]): Promise<TflLineStatus[]> {
+		const lineIds = lines ?? ALL_LINE_IDS
+		const data = await this.fetch<unknown>(`/Line/${lineIds.join(",")}/Status`)
+
+		const parsed = lineResponseArray(data)
+		if (parsed instanceof type.errors) {
+			throw new Error(`Invalid TfL API response: ${parsed.summary}`)
+		}
+
+		const statuses: TflLineStatus[] = []
+
+		for (const line of parsed) {
+			for (const status of line.lineStatuses) {
+				const severity = SEVERITY_MAP[status.statusSeverity]
+				if (severity) {
+					statuses.push({
+						lineId: line.id,
+						lineName: line.name,
+						severity,
+						description: status.reason ?? status.statusSeverityDescription,
+					})
+				}
+			}
+		}
+
+		return statuses
+	}
+
+	async fetchStations(): Promise<StationLocation[]> {
+		if (this.stationsCache) {
+			return this.stationsCache
+		}
+
+		// Fetch stations for all lines in parallel
+		const responses = await Promise.all(
+			ALL_LINE_IDS.map(async (id) => {
+				const data = await this.fetch<unknown>(`/Line/${id}/StopPoints`)
+				const parsed = lineStopPointsArray(data)
+				if (parsed instanceof type.errors) {
+					throw new Error(`Invalid TfL API response for line ${id}: ${parsed.summary}`)
+				}
+				return { lineId: id, stops: parsed }
+			}),
+		)
+
+		// Merge stations, combining lines for shared stations
+		const stationMap = new Map<string, StationLocation>()
+
+		for (const { lineId: currentLineId, stops } of responses) {
+			for (const stop of stops) {
+				const existing = stationMap.get(stop.naptanId)
+				if (existing) {
+					if (!existing.lines.includes(currentLineId)) {
+						existing.lines.push(currentLineId)
+					}
+				} else {
+					stationMap.set(stop.naptanId, {
+						id: stop.naptanId,
+						name: stop.commonName,
+						lat: stop.lat,
+						lng: stop.lon,
+						lines: [currentLineId],
+					})
+				}
+			}
+		}
+
+		this.stationsCache = Array.from(stationMap.values())
+		return this.stationsCache
+	}
+}
+
+// Schemas
+
+const lineId = type(
+	"'bakerloo' | 'central' | 'circle' | 'district' | 'hammersmith-city' | 'jubilee' | 'metropolitan' | 'northern' | 'piccadilly' | 'victoria' | 'waterloo-city' | 'lioness' | 'mildmay' | 'windrush' | 'weaver' | 'suffragette' | 'liberty' | 'elizabeth'",
+)
+
+export type TflLineId = typeof lineId.infer
+
+const lineStatus = type({
+	statusSeverity: "number",
+	statusSeverityDescription: "string",
+	"reason?": "string",
+})
+
+const lineResponse = type({
+	id: lineId,
+	name: "string",
+	lineStatuses: lineStatus.array(),
+})
+
+const lineResponseArray = lineResponse.array()
+
+const lineStopPoint = type({
+	naptanId: "string",
+	commonName: "string",
+	lat: "number",
+	lon: "number",
+})
+
+const lineStopPointsArray = lineStopPoint.array()