Build a live tennis scoreboard

const URL = "https://api.citoapi.com/api/v1/tennis/live/stream";
const board = new Map();          // match id -> latest row

async function follow() {
  const res = await fetch(URL, { headers: { "x-api-key": process.env.CITO_API_KEY, accept: "text/event-stream" } });
  if (!res.ok) throw new Error(`stream refused: ${res.status} ${await res.text()}`);
  const decoder = new TextDecoder();
  let buf = "";
  for await (const chunk of res.body) {
    buf += decoder.decode(chunk, { stream: true });
    let cut;
    while ((cut = buf.indexOf("\n\n")) >= 0) {
      const block = buf.slice(0, cut); buf = buf.slice(cut + 2);
      const event = /^event: (.*)$/m.exec(block)?.[1];
      const data = JSON.parse(/^data: (.*)$/m.exec(block)?.[1] ?? "null");
      handle(event, data);
    }
  }
}

function handle(event, data) {
  if (event === "snapshot") { board.clear(); for (const m of data.items) board.set(m.id, m); }
  if (event === "match_start" || event === "match_update") board.set(data.id, data);
  if (event === "match_end") board.delete(data.match_id);   // fetch data.final for the result if you show it
}

(async function run() {
  for (;;) {
    try { await follow(); } catch (e) { console.error(e.message); }
    await new Promise((r) => setTimeout(r, 3000));          // reconnect; the next snapshot resets the board
  }
})();

function line(m) {
  const side = (p) => `${p.is_serving ? "• " : "  "}${p.name.padEnd(24)} ${p.sets_won}  ${p.current_game_score ?? ""}`;
  return [`${m.tour} ${m.tournament_name}, ${m.round_name}, set ${m.current_set}`, side(m.player1), side(m.player2)].join("\n");
}

// ATP Taipei CH, Final, set 2
// • Yosuke Watanuki         1  40
//   Jan Kumstat             0  30