feat(backend): add TfL disruptions API with Gemini AI shortening

- Add TfL Unified API integration for real-time transport disruptions
- Implement batch AI shortening using Gemini 2.5 Flash-Lite
- Add in-memory caching with 1-hour TTL
- Support Tube, Overground, DLR, Elizabeth Line, and Tram
- Sort disruptions by severity with regex-based line name cleanup

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

apps/backend/src/tfl/index.ts

@@ -0,0 +1,195 @@
+import { Hono } from "hono"
+import { shortenMultipleDisruptions } from "./gemini"
+
+const tfl = new Hono()
+
+interface TflLineStatus {
+	$type: string
+	id: number
+	lineId?: string
+	statusSeverity: number
+	statusSeverityDescription: string
+	reason?: string
+	created: string
+	validityPeriods: {
+		$type: string
+		fromDate: string
+		toDate: string
+		isNow: boolean
+	}[]
+	disruption?: {
+		$type: string
+		category: string
+		categoryDescription: string
+		description: string
+		affectedRoutes: unknown[]
+		affectedStops: unknown[]
+		closureText: string
+	}
+}
+
+interface TflLine {
+	$type: string
+	id: string
+	name: string
+	modeName: string
+	disruptions: unknown[]
+	created: string
+	modified: string
+	lineStatuses: TflLineStatus[]
+	routeSections: unknown[]
+	serviceTypes: {
+		$type: string
+		name: string
+		uri: string
+	}[]
+	crowding: {
+		$type: string
+	}
+}
+
+interface DisruptionSummary {
+	lineId: string
+	lineName: string
+	mode: string
+	status: string
+	statusSeverity: number
+	reason?: string
+	validFrom?: string
+	validTo?: string
+}
+
+interface DisruptionsResponse {
+	lastUpdated: string
+	disruptions: DisruptionSummary[]
+	goodService: string[]
+	totalLines: number
+	disruptedLines: number
+}
+
+// Get current disruptions across all London transport modes
+tfl.get("/disruptions", async (c) => {
+	try {
+		// Fetch status for all major transport modes
+		const modes = ["tube", "overground", "dlr", "elizabeth-line", "tram"]
+		const url = `https://api.tfl.gov.uk/Line/Mode/${modes.join(",")}/Status`
+
+		const response = await fetch(url)
+
+		if (!response.ok) {
+			return new Response(
+				JSON.stringify({
+					error: "Failed to fetch TfL data",
+					status: response.status,
+				}),
+				{
+					status: response.status,
+					headers: { "Content-Type": "application/json" },
+				},
+			)
+		}
+
+		const data = (await response.json()) as TflLine[]
+
+		const disruptions: DisruptionSummary[] = []
+		const goodService: string[] = []
+
+		for (const line of data) {
+			// Get the most severe status for this line
+			const status = line.lineStatuses[0]
+
+			if (!status) continue
+
+			// statusSeverity: 10 = Good Service, anything less is a disruption
+			if (status.statusSeverity === 10) {
+				goodService.push(line.name)
+			} else {
+				const validPeriod = status.validityPeriods.find((p) => p.isNow)
+
+				disruptions.push({
+					lineId: line.id,
+					lineName: line.name,
+					mode: line.modeName,
+					status: status.statusSeverityDescription,
+					statusSeverity: status.statusSeverity,
+					reason: status.reason,
+					validFrom: validPeriod?.fromDate,
+					validTo: validPeriod?.toDate,
+				})
+			}
+		}
+
+		// Sort disruptions by severity (lower number = more severe)
+		disruptions.sort((a, b) => a.statusSeverity - b.statusSeverity)
+
+		// Shorten all disruption reasons in a single Gemini API call
+		const disruptionsToShorten = disruptions
+			.filter(d => d.reason)
+			.map(d => ({
+				lineName: d.lineName,
+				status: d.status,
+				reason: d.reason!,
+			}))
+
+		if (disruptionsToShorten.length > 0) {
+			const shortenedMap = await shortenMultipleDisruptions(disruptionsToShorten)
+			
+			// Apply shortened reasons back to disruptions
+			for (const disruption of disruptions) {
+				const shortened = shortenedMap.get(disruption.lineName)
+				if (shortened) {
+					disruption.reason = shortened
+				}
+			}
+		}
+
+		const summary: DisruptionsResponse = {
+			lastUpdated: new Date().toISOString(),
+			disruptions,
+			goodService: goodService.sort(),
+			totalLines: data.length,
+			disruptedLines: disruptions.length,
+		}
+
+		return c.json(summary)
+	} catch (error) {
+		return c.json(
+			{ error: "Internal server error", message: String(error) },
+			500
+		)
+	}
+})
+
+// Get status for specific line(s)
+tfl.get("/line/:lineIds", async (c) => {
+	try {
+		const lineIds = c.req.param("lineIds")
+
+		const url = `https://api.tfl.gov.uk/Line/${lineIds}/Status`
+
+		const response = await fetch(url)
+
+		if (!response.ok) {
+			return new Response(
+				JSON.stringify({
+					error: "Failed to fetch TfL line data",
+					status: response.status,
+				}),
+				{
+					status: response.status,
+					headers: { "Content-Type": "application/json" },
+				},
+			)
+		}
+
+		const data = await response.json()
+		return c.json(data)
+	} catch (error) {
+		return c.json(
+			{ error: "Internal server error", message: String(error) },
+			500
+		)
+	}
+})
+
+export default tfl