import { NextRequest } from "next/server";
import config from "@payload-config";
import { getPayload } from "payload";
import { type SSEEventClient, subscribe, unsubscribe } from "@/lib/realtime/bus";
import { getPresence } from "@/lib/realtime/presence";

export const dynamic = "force-dynamic";
export const runtime = "nodejs";

export async function GET(req: NextRequest) {
  const payload = await getPayload({ config: await config });
  const { user } = await payload.auth({ headers: req.headers, canSetHeaders: false });
  const encoder = new TextEncoder();
  const channel = req.nextUrl.searchParams.get("channel");

  let client: SSEEventClient | null = null;
  let heartbeat: ReturnType<typeof setInterval> | null = null;

  const cleanup = () => {
    if (heartbeat) clearInterval(heartbeat);
    if (client) unsubscribe(client);
    client = null;
    heartbeat = null;
  };

  const stream = new ReadableStream({
    start(controller) {
      client = {
        send: (data) => controller.enqueue(encoder.encode(data)),
        userId: user ? Number(user.id) : undefined,
        events: channel ? new Set(["presence"]) : undefined,
      };
      subscribe(client);

      controller.enqueue(encoder.encode(": connected\n\n"));
      if (channel) {
        controller.enqueue(encoder.encode(`event: presence\ndata: ${JSON.stringify({ channel, action: "snapshot", participants: getPresence(channel) })}\n\n`));
      }

      heartbeat = setInterval(() => {
        try {
          controller.enqueue(encoder.encode(": keepalive\n\n"));
        } catch {
          cleanup();
        }
      }, 25_000);

      req.signal.addEventListener("abort", cleanup);
    },
    cancel() {
      cleanup();
    },
  });

  return new Response(stream, {
    headers: {
      "Content-Type": "text/event-stream",
      "Cache-Control": "no-cache, no-transform",
      Connection: "keep-alive",
    },
  });
}