How the Spotify Currently Playing Widget Works

let cachedAccessToken: string | null = null;
let tokenExpiresAt = 0;

async function getAccessToken(): Promise<string> {
  if (cachedAccessToken && Date.now() < tokenExpiresAt - 60000) {
    return cachedAccessToken;
  }

  const basic = Buffer.from(`${clientId}:${clientSecret}`).toString("base64");
  const response = await fetch("https://accounts.spotify.com/api/token", {
    method: "POST",
    headers: {
      Authorization: `Basic ${basic}`,
      "Content-Type": "application/x-www-form-urlencoded",
    },
    body: new URLSearchParams({
      grant_type: "refresh_token",
      refresh_token: refreshToken,
    }),
    cache: "no-store",
  });

  const data = await response.json();
  cachedAccessToken = data.access_token;
  tokenExpiresAt = Date.now() + data.expires_in * 1000;
  return data.access_token;
}

// Credentials remain isolated on the server. The token is reused across client requests until expiry.

export async function getCurrentlyPlaying(): Promise<SpotifyResponse> {
  if (cachedPlayingData && Date.now() < playingDataExpiresAt) {
    return cachedPlayingData;
  }

  try {
    const accessToken = await getAccessToken();
    const response = await fetch("https://api.spotify.com/v1/me/player/currently-playing", {
      headers: { Authorization: `Bearer ${accessToken}` },
      cache: "no-store",
    });

    if (response.status === 204 || response.status === 404) {
      const result = { isConfigured: true, isPlaying: false, track: null, timestamp: Date.now() };
      cachedPlayingData = result;
      playingDataExpiresAt = Date.now() + 15000;
      return result;
    }
    // Parse track payload & cache for 15s
  } catch (error) {
    return { isConfigured: true, isPlaying: false, track: null, timestamp: Date.now(), error: "connection-error" };
  }
}

// In-memory caching guarantees that client polling (every 15s) never exceeds Spotify API quota thresholds.