Function createEventHub

src/services/events.ts:28–87

(eventName: string)

type Listener<T> = (payload: T) => void;

function createEventHub<T>(eventName: string) {
  const listeners = new Set<Listener<T>>();
  let unlisten: Unsubscribe | null = null;
  let listenPromise: Promise<Unsubscribe> | null = null;

  const start = (options?: SubscriptionOptions) => {
    if (unlisten || listenPromise) {
      return;
    }
    listenPromise = listen<T>(eventName, (event) => {
      for (const listener of listeners) {
        try {
          listener(event.payload);
        } catch (error) {
          console.error(`[events] ${eventName} listener failed`, error);
        }
      }
    });
    listenPromise
      .then((handler) => {
        listenPromise = null;
        if (listeners.size === 0) {
          handler();
          return;
        }
        unlisten = handler;
      })
      .catch((error) => {
        listenPromise = null;
        options?.onError?.(error);
      });
  };

  const stop = () => {
    if (unlisten) {
      try {
        unlisten();
      } catch {
        // Ignore double-unlisten when tearing down.
      }
      unlisten = null;
    }
  };

  const subscribe = (
    onEvent: Listener<T>,
    options?: SubscriptionOptions,
  ): Unsubscribe => {
    listeners.add(onEvent);
    start(options);
    return () => {
      listeners.delete(onEvent);
      if (listeners.size === 0) {
        stop();
      }
    };
  };