import { useEffect, useRef } from 'react';
import type { GameState } from '@shared/types';
import type { TurnResult } from '@shared/protocol';

interface SseHandlers {
  onState?: (state: GameState) => void;
  onTurn?: (state: GameState, result: TurnResult) => void;
  /**
   * Fired for a server-sent NAMED `event: error` (a MessageEvent with a JSON
   * body `{ message }`) — e.g. the game was deleted or no longer exists. Pure
   * connection errors (no data) are ignored and EventSource auto-reconnects.
   */
  onError?: (message: string) => void;
}

/**
 * Subscribe to a game's SSE stream. The server sends a `state` event on connect
 * and a `turn` event after every turn; EventSource auto-reconnects on drop, so a
 * reload always resyncs to the persisted server state.
 *
 * Handlers are kept in a ref so the (id-keyed) effect always invokes the latest
 * callbacks without re-subscribing on every render.
 */
export function useSse(id: string | null, handlers: SseHandlers): void {
  const handlersRef = useRef(handlers);
  handlersRef.current = handlers;

  useEffect(() => {
    if (!id) return;
    const es = new EventSource(`/sse/${id}`);
    const onState = (e: MessageEvent) => {
      try {
        handlersRef.current.onState?.(JSON.parse(e.data).state as GameState);
      } catch {
        /* ignore malformed */
      }
    };
    const onTurn = (e: MessageEvent) => {
      try {
        const d = JSON.parse(e.data) as { state: GameState; result: TurnResult };
        handlersRef.current.onTurn?.(d.state, d.result);
      } catch {
        /* ignore malformed */
      }
    };
    const onError = (e: Event) => {
      if (e instanceof MessageEvent && e.data) {
        try {
          const d = JSON.parse(e.data) as { message?: string };
          if (d.message) handlersRef.current.onError?.(d.message);
        } catch {
          /* ignore malformed */
        }
      }
    };
    es.addEventListener('state', onState);
    es.addEventListener('turn', onTurn);
    es.addEventListener('error', onError);
    return () => es.close();
  }, [id]);
}