Announcements/client/public/display-sw.js

/* Announcements signage app-shell worker.
 *
 * Scope is deliberately narrow: this worker makes the /display application
 * shell available for a future offline start. Slide bytes are NOT its job —
 * those are owned explicitly by the display asset manager in Cache Storage, so
 * the two caches never compete for the same responsibility.
 */
const SHELL_CACHE = "announcements-display-shell-v1";
const SHELL_FALLBACK = "/display";
// A kiosk must reach its slides quickly. When a usable shell is already
// cached, a slow or dead origin is never allowed to delay startup: a reverse
// proxy whose backend is down can otherwise hold a navigation open for its
// full connect timeout, leaving the screen blank the whole time.
const SHELL_NETWORK_TIMEOUT_MS = 3_000;

// Paths the worker must never handle. Media is the asset manager's; the API and
// socket are live server state and must never be answered from a cache.
const BYPASS_PREFIXES = ["/api/", "/socket.io/", "/media/", "/health"];

function isBypassed(url) {
  return BYPASS_PREFIXES.some(
    (prefix) => url.pathname === prefix.replace(/\/$/, "") || url.pathname.startsWith(prefix),
  );
}

self.addEventListener("install", (event) => {
  event.waitUntil(
    (async () => {
      const cache = await caches.open(SHELL_CACHE);
      try {
        await cache.add(new Request(SHELL_FALLBACK, { cache: "reload" }));
      } catch {
        // A first install while the network is unavailable still succeeds; the
        // shell is captured on the next successful navigation instead.
      }
      // A kiosk must never be trapped on a stale application version.
      await self.skipWaiting();
    })(),
  );
});

self.addEventListener("activate", (event) => {
  event.waitUntil(
    (async () => {
      for (const name of await caches.keys()) {
        // Only this worker's own shell generations are removed. The display
        // asset cache is left strictly alone.
        if (name.startsWith("announcements-display-shell-") && name !== SHELL_CACHE) {
          await caches.delete(name);
        }
      }
      await self.clients.claim();
    })(),
  );
});

async function networkFirst(request) {
  const cache = await caches.open(SHELL_CACHE);
  const cached =
    (await cache.match(SHELL_FALLBACK)) || (await cache.match("/index.html"));

  // Without a cached shell there is nothing to fall back to, so wait normally.
  if (!cached) {
    const response = await fetch(request);
    if (response && response.ok) await cache.put(SHELL_FALLBACK, response.clone());
    return response;
  }

  const abort = new AbortController();
  const timer = setTimeout(() => abort.abort(), SHELL_NETWORK_TIMEOUT_MS);
  try {
    const response = await fetch(request, { signal: abort.signal });
    clearTimeout(timer);
    if (response && response.ok) {
      // Keep the shell fresh so an online kiosk always updates.
      await cache.put(SHELL_FALLBACK, response.clone());
      return response;
    }
    // A production kiosk reaches this origin through a reverse proxy, so an
    // outage behind it arrives as 502/503/504 rather than a refused
    // connection. That is still an outage: serve the cached shell.
    return cached;
  } catch {
    clearTimeout(timer);
    return cached;
  }
}

async function cacheFirst(request) {
  const cache = await caches.open(SHELL_CACHE);
  const cached = await cache.match(request);
  if (cached) return cached;
  const response = await fetch(request);
  if (response && response.ok) await cache.put(request, response.clone());
  return response;
}

self.addEventListener("fetch", (event) => {
  const { request } = event;
  if (request.method !== "GET") return;
  const url = new URL(request.url);
  if (url.origin !== self.location.origin) return;
  if (isBypassed(url)) return;

  if (request.mode === "navigate") {
    // Online kiosks always get the newest application; offline ones get the
    // last known good shell.
    event.respondWith(networkFirst(request));
    return;
  }

  // Vite emits content-hashed asset filenames, so these are safely immutable.
  if (url.pathname.startsWith("/assets/")) {
    event.respondWith(cacheFirst(request));
  }
});