feat(events): stream Redis invalidations over SSE

lib/events/refresh.ts

@@ -0,0 +1,58 @@
+import type { InvalidationEvent } from "./invalidation";
+
+export interface RefreshScheduler {
+  connected(): void;
+  notified(event: InvalidationEvent): void;
+  dispose(): void;
+}
+
+export interface RefreshSchedulerOptions {
+  delayMs?: number;
+  duplicateWindowMs?: number;
+  now?: () => number;
+}
+
+export function createRefreshScheduler(
+  refresh: () => void,
+  options: RefreshSchedulerOptions = {},
+): RefreshScheduler {
+  const delayMs = options.delayMs ?? 75;
+  const duplicateWindowMs = options.duplicateWindowMs ?? 2_000;
+  const now = options.now ?? Date.now;
+  let pending: ReturnType<typeof setTimeout> | undefined;
+  let lastEventKey: string | undefined;
+  let lastEventAt = 0;
+
+  const schedule = (event?: InvalidationEvent) => {
+    if (event) {
+      const key = `${event.type}:${event.id}:${event.version}`;
+      const timestamp = now();
+      if (
+        key === lastEventKey &&
+        timestamp - lastEventAt < duplicateWindowMs
+      ) {
+        return;
+      }
+      lastEventKey = key;
+      lastEventAt = timestamp;
+    }
+    if (pending) return;
+    pending = setTimeout(() => {
+      pending = undefined;
+      refresh();
+    }, delayMs);
+  };
+
+  return {
+    connected() {
+      schedule();
+    },
+    notified(event) {
+      schedule(event);
+    },
+    dispose() {
+      if (pending) clearTimeout(pending);
+      pending = undefined;
+    },
+  };
+}