import { ENV_CONSTANT } from '@/constants/secrect.constant';

export type SseEventHandler<T = unknown> = (
  data: T,
  event: MessageEvent,
) => void;

export type SseEventMap<TEvents extends Record<string, unknown>> = {
  [EventName in keyof TEvents]: SseEventHandler<TEvents[EventName]>;
};

export interface SseConnection {
  source: EventSource;
  close: () => void;
}

function getSseUrl(path: string) {
  if (/^https?:\/\//i.test(path)) return path;

  const baseUrl = ENV_CONSTANT.BASE_API_URL ?? '';
  const normalizedBase = baseUrl.endsWith('/') ? baseUrl.slice(0, -1) : baseUrl;
  const normalizedPath = path.startsWith('/') ? path : `/${path}`;

  return `${normalizedBase}${normalizedPath}`;
}

function parseEventData(event: MessageEvent) {
  if (!event.data) return null;

  try {
    return JSON.parse(event.data);
  } catch {
    return event.data;
  }
}

export const sseService = {
  connect: <TEvents extends Record<string, unknown>>(
    path: string,
    events: SseEventMap<TEvents>,
  ): SseConnection => {
    const source = new EventSource(getSseUrl(path));
    const cleanups: Array<() => void> = [];

    Object.entries(events).forEach(([eventName, handler]) => {
      const listener = (event: Event) => {
        const messageEvent = event as MessageEvent;
        (handler as SseEventHandler)(
          parseEventData(messageEvent),
          messageEvent,
        );
      };

      source.addEventListener(eventName, listener);
      cleanups.push(() => source.removeEventListener(eventName, listener));
    });

    return {
      source,
      close: () => {
        cleanups.forEach((cleanup) => cleanup());
        source.close();
      },
    };
  },
};