const [url, roundsText = "100", concurrencyText = "32"] = process.argv.slice(2);

if (!url) {
  console.error("usage: websocket_churn.mjs URL [ROUNDS] [CONCURRENCY]");
  process.exit(2);
}

const rounds = Number.parseInt(roundsText, 10);
const concurrency = Number.parseInt(concurrencyText, 10);

if (!Number.isSafeInteger(rounds) || rounds < 1 ||
    !Number.isSafeInteger(concurrency) || concurrency < 1) {
  console.error("rounds and concurrency must be positive integers");
  process.exit(2);
}

function connectOnce() {
  return new Promise((resolve, reject) => {
    const socket = new WebSocket(url);
    const timeout = setTimeout(() => {
      socket.close();
      reject(new Error("websocket close timed out"));
    }, 5000);

    socket.addEventListener("open", () => socket.close(), { once: true });
    socket.addEventListener("close", () => {
      clearTimeout(timeout);
      resolve();
    }, { once: true });
    socket.addEventListener("error", () => {
      clearTimeout(timeout);
      reject(new Error("websocket connection failed"));
    }, { once: true });
  });
}

// Long-lived cursored subscribers must not exhaust the bounded backfill
// slots: each slot is released once the subscriber catches up to live, so
// more held connections than slots all handshake successfully.
function connectAndHold(cursorUrl, sockets) {
  return new Promise((resolve, reject) => {
    const socket = new WebSocket(cursorUrl);
    socket.binaryType = "arraybuffer";
    sockets.push(socket);
    const timeout = setTimeout(() => reject(new Error("held websocket open timed out")), 5000);
    socket.addEventListener("open", () => {
      clearTimeout(timeout);
      setTimeout(resolve, 300);
    }, { once: true });
    socket.addEventListener("error", () => {
      clearTimeout(timeout);
      reject(new Error("held cursored websocket rejected"));
    }, { once: true });
  });
}

const heldText = process.argv[5];
if (heldText) {
  const held = Number.parseInt(heldText, 10);
  const sockets = [];
  const cursorUrl = `${url}${url.includes("?") ? "&" : "?"}cursor=0`;
  for (let i = 0; i < held; i += 1) {
    await connectAndHold(cursorUrl, sockets);
  }
  for (const socket of sockets) socket.close();
} else {
  for (let round = 0; round < rounds; round += 1) {
    await Promise.all(Array.from({ length: concurrency }, connectOnce));
  }
}