perf(slideshow): cache global settings to cut /state DB reads (PR #646 review)

Each /state poll fired ~10 getAppSetting reads to resolve the watermark/fit; a leaked link x N tabs amplified that linearly (review concern 2). Add a 5s-TTL cached bundle (utils/slideshowGlobals) for the global slideshow_* + branding-logo settings, invalidated on PUT /admin/settings/slideshow so admin live-edit stays instant. slideshowSettings now does ~2 reads per poll (event row + photo count) on a cache hit. Also documents the frontend optimistic-default nit.
2026-06-21 02:53:34 +02:00
parent e36b3309ca
commit a995131f42
5 changed files with 90 additions and 24 deletions
@@ -0,0 +1,58 @@
+/**
+ * Cached read of the global Live-Slideshow settings (Settings → Slideshow) +
+ * the branding logo URLs the watermark resolves against.
+ *
+ * Why: a running projector polls `/show/:token/state` every ~3s, and each poll
+ * resolved the watermark/fit by firing ~7–10 individual `getAppSetting` reads.
+ * A leaked link × N tabs amplifies that linearly (PR #646 review, concern 2).
+ * These globals change only via `PUT /admin/settings/slideshow`, so we cache
+ * the whole bundle with a short TTL and invalidate on write — admin live-edit
+ * stays effectively instant, and steady-state polls drop to ~0 settings reads.
+ */
+const { getAppSetting } = require('./appSettings');
+
+const TTL_MS = 5000;
+let cache = null; // { at, val }
+
+async function getSlideshowGlobals() {
+  const now = Date.now();
+  if (cache && now - cache.at < TTL_MS) return cache.val;
+
+  const [
+    enabled, source, position, opacity, style, size, fit,
+    logo, logoDark, favicon,
+  ] = await Promise.all([
+    getAppSetting('slideshow_watermark_enabled', false),
+    getAppSetting('slideshow_watermark_source', 'logo'),
+    getAppSetting('slideshow_watermark_position', 'bottom-right'),
+    getAppSetting('slideshow_watermark_opacity', 60),
+    getAppSetting('slideshow_watermark_style', 'white'),
+    getAppSetting('slideshow_watermark_size', 12),
+    getAppSetting('slideshow_fit', 'cover'),
+    getAppSetting('branding_logo_url', null),
+    getAppSetting('branding_logo_url_dark', null),
+    getAppSetting('branding_favicon_url', null),
+  ]);
+
+  const val = {
+    watermark_enabled: enabled === true,
+    watermark_source: source || 'logo',
+    watermark_position: position || 'bottom-right',
+    watermark_opacity: opacity ?? 60,
+    watermark_style: style || 'white',
+    watermark_size: size ?? 12,
+    fit: fit === 'contain' ? 'contain' : 'cover',
+    branding_logo_url: logo || null,
+    branding_logo_url_dark: logoDark || null,
+    branding_favicon_url: favicon || null,
+  };
+  cache = { at: now, val };
+  return val;
+}
+
+/** Clear the cache — call after any write to the slideshow_* / branding logo settings. */
+function invalidateSlideshowGlobals() {
+  cache = null;
+}
+
+module.exports = { getSlideshowGlobals, invalidateSlideshowGlobals };