import mitt from 'mitt';
import type { AppEvents } from './events.registry';

// ─── Singleton Event Bus ────────────────────────────────────────

/**
 * Application-wide event bus — a strictly typed `mitt` instance.
 *
 * Prefer the `publish` / `subscribe` helper functions or the React
 * hooks (`useAppEvent`, `usePublishEvent`) over using this directly.
 * Direct access is provided for edge cases like middleware or testing.
 *
 * @example
 * ```ts
 * import { eventBus } from '@repo/core-events';
 * eventBus.on('APP:ERROR', (e) => console.error(e.message));
 * ```
 */
export const eventBus = mitt<AppEvents>();

// ─── Type-Safe Helpers ──────────────────────────────────────────

/**
 * Emit (publish) a typed event to all subscribers.
 *
 * @param type  - The event name from `AppEvents`.
 * @param event - The payload matching that event's type.
 *
 * @example
 * ```ts
 * publish('AUTH:PROFILE_UPDATED', { id: '1', name: 'Firman', ... });
 * ```
 */
export function publish<K extends keyof AppEvents>(
  type: K,
  event: AppEvents[K],
): void {
  eventBus.emit(type, event);
}

/**
 * Subscribe to a typed event.
 *
 * Returns an `unsubscribe` function — call it to remove the handler.
 * For React components, prefer `useAppEvent` which handles cleanup
 * automatically on unmount.
 *
 * @param type    - The event name from `AppEvents`.
 * @param handler - Callback receiving the typed payload.
 * @returns A function that removes this subscription.
 *
 * @example
 * ```ts
 * const unsub = subscribe('WS:STOCK_UPDATE', (data) => {
 *   console.log(data.price); // fully typed
 * });
 * // Later:
 * unsub();
 * ```
 */
export function subscribe<K extends keyof AppEvents>(
  type: K,
  handler: (event: AppEvents[K]) => void,
): () => void {
  eventBus.on(type, handler);
  return () => eventBus.off(type, handler);
}