Improve caching and error handling in hooks.server.js

src/hooks.server.js

@@ -1,47 +1,72 @@
 import oba from '$lib/obaSdk.js';
 
 let routesCache = null;
+let cacheTimestamp = null;
+const CACHE_EXPIRATION_MS = 5 * 60 * 1000; // Cache expires every 5 minutes
 
+/**
+ * Fetches routes data from the OneBusAway (OBA) SDK.
+ * Retrieves all agencies and their corresponding routes.
+ * Caches the results to optimize performance.
+ */
 async function fetchRoutesData() {
 	try {
 		const agenciesResponse = await oba.agenciesWithCoverage.list();
 		const agencies = agenciesResponse.data.list;
 
+		// Fetch routes for each agency concurrently
 		const routesPromises = agencies.map(async (agency) => {
 			const routesResponse = await oba.routesForAgency.list(agency.agencyId);
 			const routes = routesResponse.data.list;
 			const references = routesResponse.data.references;
 
+			// Create a map of agency references for quick lookups
 			const agencyReferenceMap = new Map(references.agencies.map((agency) => [agency.id, agency]));
 
+			// Attach agency info to each route
 			routes.forEach((route) => {
 				route.agencyInfo = agencyReferenceMap.get(route.agencyId);
 			});
 
 			return routes;
 		});
 
-		const routes = await Promise.all(routesPromises);
-		return routes.flat();
+		// Wait for all routes to be fetched and flatten the results
+		const routes = (await Promise.all(routesPromises)).flat();
+
+		// Update cache and timestamp
+		routesCache = routes;
+		cacheTimestamp = Date.now();
+
+		return routes;
 	} catch (error) {
 		console.error('Error fetching routes:', error);
 		return null;
 	}
 }
 
+/**
+ * Ensures the routes data is loaded and cached.
+ * Refreshes the cache if it is expired.
+ */
 async function preloadRoutesData() {
-	if (!routesCache) {
-		routesCache = await fetchRoutesData();
+	const isCacheExpired = !cacheTimestamp || (Date.now() - cacheTimestamp > CACHE_EXPIRATION_MS);
+	if (!routesCache || isCacheExpired) {
+		await fetchRoutesData();
 	}
 }
 
-preloadRoutesData();
-
+/**
+ * Middleware hook that ensures routes data is available before handling the request.
+ */
 export async function handle({ event, resolve }) {
 	await preloadRoutesData();
 	return resolve(event);
 }
 
+/**
+ * Returns the cached routes data.
+ */
 export function getRoutesCache() {
 	return routesCache;
 }