/**
 * Simple pub/sub event bus.
 * on(evt, cb) - subscribe
 * emit(evt, data) - publish
 */
const Bus = (() => {
  const listeners = new Map();

  return {
    on(evt, cb) {
      if (!listeners.has(evt)) listeners.set(evt, new Set());
      listeners.get(evt).add(cb);
      return () => this.off(evt, cb);
    },

    off(evt, cb) {
      const set = listeners.get(evt);
      if (set) {
        set.delete(cb);
        if (set.size === 0) listeners.delete(evt);
      }
    },

    emit(evt, data) {
      const set = listeners.get(evt);
      if (set) {
        for (const cb of set) {
          try { cb(data); } catch (e) { console.error(`Bus emit error (${evt}):`, e); }
        }
      }
    }
  };
})();

export default Bus;
export { Bus };