1
import { useSyncExternalStore } from "react";
2
 
3
const listeners = new Set<() => void>();
4
let lastTick = Date.now();
5
let intervalId: ReturnType<typeof setInterval> | null = null;
6
 
7
function ensureClock() {
8
  if (intervalId != null || typeof window === "undefined") return;
9
  intervalId = setInterval(() => {
10
    lastTick = Date.now();
11
    for (const fn of listeners) fn();
12
  }, 30_000);
13
}
14
 
15
function subscribe(fn: () => void) {
16
  ensureClock();
17
  listeners.add(fn);
18
  return () => {
19
    listeners.delete(fn);
20
    if (listeners.size === 0 && intervalId != null) {
21
      clearInterval(intervalId);
22
      intervalId = null;
23
    }
24
  };
25
}
26
 
27
function snapshot() {
28
  return lastTick;
29
}
30
 
31
function serverSnapshot() {
32
  return 0;
33
}
34
 
35
/** Returns a timestamp that ticks once every 30 seconds — safe for "is expired"
36
 *  badges and relative-time labels without making the render impure. */
37
export function useNow(): number {
38
  return useSyncExternalStore(subscribe, snapshot, serverSnapshot);
39
}