import mongoose from "mongoose";

/** Cached connection for Next.js hot reload (global is preserved across HMR). */
const globalForMongoose = globalThis as typeof globalThis & {
  mongooseConn?: typeof mongoose;
};

export default async function connectDB(): Promise<typeof mongoose> {
  const uri = process.env.MONGODB_URI;
  if (!uri) {
    throw new Error("MONGODB_URI is not set. Add it to .env (e.g. mongodb://localhost:27017/ipv6_summit).");
  }

  if (globalForMongoose.mongooseConn?.connection?.readyState === 1) {
    return globalForMongoose.mongooseConn;
  }

  const conn = await mongoose.connect(uri);
  globalForMongoose.mongooseConn = conn;
  return conn;
}