import { useEffect, useRef, useCallback } from 'react';
import type { AppEvents } from './events.registry';
import { eventBus, publish as busPublish } from './event-bus';

// ─── useAppEvent ────────────────────────────────────────────────

/**
 * Subscribe to an application event with automatic cleanup on unmount.
 *
 * The handler is stored in a ref so that:
 * 1. The subscription is stable — re-renders don't cause unsubscribe/resubscribe churn.
 * 2. The handler always sees the latest closure values (no stale closures).
 * 3. The parent component's render cycle is never triggered by the subscription itself.
 *
 * @param type    - The event name from `AppEvents`.
 * @param handler - Callback receiving the typed payload. May be updated on re-render.
 *
 * @example
 * ```tsx
 * useAppEvent('AUTH:PROFILE_UPDATED', (profile) => {
 *   console.log(profile.name); // fully typed, auto-cleaned on unmount
 * });
 * ```
 */
export function useAppEvent<K extends keyof AppEvents>(type: K, handler: (event: AppEvents[K]) => void): void {
  // Always keep the latest handler in a ref to avoid stale closures
  // and prevent re-subscription on every render.
  const handlerRef = useRef(handler);
  handlerRef.current = handler;

  useEffect(() => {
    // Create a stable delegate that forwards to the latest handler ref
    const delegate = (event: AppEvents[K]) => {
      handlerRef.current(event);
    };

    eventBus.on(type, delegate);

    // Cleanup: unsubscribe when the component unmounts or `type` changes.
    // This is the critical memory-leak prevention mechanism.
    return () => {
      eventBus.off(type, delegate);
    };
  }, [type]);
}

// ─── usePublishEvent ────────────────────────────────────────────

/**
 * Returns a strictly typed `publish` function.
 *
 * The returned function is referentially stable (memoized) so it
 * can be safely passed as a prop or used in dependency arrays
 * without causing unnecessary re-renders.
 *
 * @example
 * ```tsx
 * const publish = usePublishEvent();
 *
 * const handleClick = () => {
 *   publish('DEVICE:PRINT_RECEIPT', {
 *     receiptId: '001',
 *     items: [{ name: 'Widget', qty: 2, price: 9.99 }],
 *     total: 19.98,
 *     cashierName: 'Firman',
 *     timestamp: Date.now(),
 *   });
 * };
 * ```
 */
export function usePublishEvent(): typeof busPublish {
  return useCallback(busPublish, []);
}