openchamber/packages/ui/src/hooks/useDurationTicker.ts

// Shared wall-clock ticker for live duration readouts (tool runtimes, session
// activity counters). Subscribers of the same interval share one timer and one
// `now`, so N live rows cost one interval rather than N.

import React from 'react';

type Subscriber = (now: number) => void;

type TickerChannel = {
    subscribers: Set<Subscriber>;
    timerId: number | null;
};

const tickerChannels = new Map<number, TickerChannel>();

const getTickerChannel = (intervalMs: number): TickerChannel => {
    const existing = tickerChannels.get(intervalMs);
    if (existing) {
        return existing;
    }

    const created: TickerChannel = {
        subscribers: new Set<Subscriber>(),
        timerId: null,
    };
    tickerChannels.set(intervalMs, created);
    return created;
};

const subscribeToTicker = (intervalMs: number, subscriber: Subscriber): (() => void) => {
    const channel = getTickerChannel(intervalMs);
    channel.subscribers.add(subscriber);
    subscriber(Date.now());

    if (channel.timerId === null && typeof window !== 'undefined') {
        channel.timerId = window.setInterval(() => {
            const now = Date.now();
            channel.subscribers.forEach((listener) => {
                listener(now);
            });
        }, intervalMs);
    }

    return () => {
        const tracked = tickerChannels.get(intervalMs);
        if (!tracked) {
            return;
        }

        tracked.subscribers.delete(subscriber);
        if (tracked.subscribers.size > 0) {
            return;
        }

        if (tracked.timerId !== null && typeof window !== 'undefined') {
            window.clearInterval(tracked.timerId);
        }
        tickerChannels.delete(intervalMs);
    };
};

export const useDurationTickerNow = (active: boolean, intervalMs: number = 250): number => {
    const [now, setNow] = React.useState(() => Date.now());

    React.useEffect(() => {
        if (!active) {
            return;
        }

        return subscribeToTicker(intervalMs, setNow);
    }, [active, intervalMs]);

    return now;
};