export type AppEvent = {
  id?: string;
  type: string;
  invoiceId?: string;
  status?: string | null;
  updatedAt?: string | null;
  createdAt?: string | null;
};

type SubscribeAppEventsOptions = {
  accessToken: string;
  onEvent: (event: AppEvent) => void;
  onError?: (error: unknown) => void;
};

function parseSseMessage(message: string): AppEvent | null {
  const dataLines = message
    .split(/\r?\n/)
    .filter((line) => line.startsWith("data:"))
    .map((line) => line.slice("data:".length).trimStart());

  if (!dataLines.length) {
    return null;
  }

  try {
    return JSON.parse(dataLines.join("\n")) as AppEvent;
  } catch {
    return null;
  }
}

export function subscribeAppEvents(options: SubscribeAppEventsOptions) {
  const controller = new AbortController();

  void (async () => {
    try {
      const response = await fetch("/api/events", {
        method: "GET",
        credentials: "include",
        headers: {
          authorization: `Bearer ${options.accessToken}`,
          accept: "text/event-stream",
        },
        signal: controller.signal,
      });

      if (!response.ok || !response.body) {
        throw new Error(`events_stream_unavailable:${response.status}`);
      }

      const reader = response.body.getReader();
      const decoder = new TextDecoder();
      let buffer = "";

      while (!controller.signal.aborted) {
        const { done, value } = await reader.read();
        if (done) {
          break;
        }

        buffer += decoder.decode(value, { stream: true });
        const chunks = buffer.split(/\r?\n\r?\n/);
        buffer = chunks.pop() ?? "";

        for (const chunk of chunks) {
          const event = parseSseMessage(chunk);
          if (event) {
            options.onEvent(event);
          }
        }
      }
    } catch (error) {
      if (!controller.signal.aborted) {
        options.onError?.(error);
      }
    }
  })();

  return () => controller.abort();
}