perf(website): cache GitHub release metadata in KV

packages/website/src/github-cache.ts

@@ -0,0 +1,68 @@
+import { env, waitUntil } from "cloudflare:workers";
+
+export const GITHUB_CACHE_TTL_MS = 5 * 60 * 1000;
+
+interface CachedValue<T> {
+  fetchedAt: number;
+  value: T;
+}
+
+type Validator<T> = (value: unknown) => value is T;
+
+function getWebsiteCache(): KVNamespace | null {
+  return (env as { WEBSITE_CACHE?: KVNamespace }).WEBSITE_CACHE ?? null;
+}
+
+function isCachedValue<T>(value: unknown, isValue: Validator<T>): value is CachedValue<T> {
+  if (typeof value !== "object" || value === null) return false;
+  const record = value as Record<string, unknown>;
+  return typeof record.fetchedAt === "number" && isValue(record.value);
+}
+
+async function readCachedValue<T>(
+  key: string,
+  isValue: Validator<T>,
+): Promise<CachedValue<T> | null> {
+  const cache = getWebsiteCache();
+  if (!cache) return null;
+  const cached = await cache.get(key, { cacheTtl: 60, type: "json" });
+  return isCachedValue(cached, isValue) ? cached : null;
+}
+
+async function writeCachedValue<T>(key: string, value: T): Promise<void> {
+  const cache = getWebsiteCache();
+  if (!cache) return;
+  await cache.put(
+    key,
+    JSON.stringify({
+      fetchedAt: Date.now(),
+      value,
+    }),
+  );
+}
+
+export async function getBlockingColdCache<T>({
+  key,
+  isValue,
+  fetchFresh,
+}: {
+  key: string;
+  isValue: Validator<T>;
+  fetchFresh: () => Promise<T>;
+}): Promise<T> {
+  const cached = await readCachedValue(key, isValue);
+  if (cached) {
+    if (Date.now() - cached.fetchedAt > GITHUB_CACHE_TTL_MS) {
+      waitUntil(
+        fetchFresh()
+          .then((fresh) => writeCachedValue(key, fresh))
+          .catch(() => undefined),
+      );
+    }
+    return cached.value;
+  }
+
+  const fresh = await fetchFresh();
+  await writeCachedValue(key, fresh);
+  return fresh;
+}