/**
 * Fetches TikTok follower count using the official TikTok API v2.
 *
 * Required env vars:
 * - TIKTOK_CLIENT_KEY
 * - TIKTOK_CLIENT_SECRET
 * - TIKTOK_REFRESH_TOKEN (obtained via one-time OAuth flow at /api/auth/tiktok)
 */

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

async function getAccessToken(): Promise<string | null> {
  // Return cached token if still valid (with 5 min buffer)
  if (cachedAccessToken && Date.now() < tokenExpiresAt - 300_000) {
    return cachedAccessToken;
  }

  const clientKey = process.env.TIKTOK_CLIENT_KEY;
  const clientSecret = process.env.TIKTOK_CLIENT_SECRET;
  const refreshToken = process.env.TIKTOK_REFRESH_TOKEN;

  if (!clientKey || !clientSecret || !refreshToken) return null;

  try {
    const res = await fetch("https://open.tiktokapis.com/v2/oauth/token/", {
      method: "POST",
      headers: { "Content-Type": "application/x-www-form-urlencoded" },
      body: new URLSearchParams({
        client_key: clientKey,
        client_secret: clientSecret,
        grant_type: "refresh_token",
        refresh_token: refreshToken,
      }),
      signal: AbortSignal.timeout(5000),
    });

    if (!res.ok) return null;

    const data = await res.json();
    if (data.access_token) {
      cachedAccessToken = data.access_token;
      tokenExpiresAt = Date.now() + (data.expires_in ?? 7200) * 1000;
      return cachedAccessToken;
    }

    return null;
  } catch {
    return null;
  }
}

export interface TiktokProfile {
  followerCount: number | null;
  displayName: string | null;
  username: string | null;
  avatarUrl: string | null;
}

export async function getTiktokProfile(): Promise<TiktokProfile> {
  const empty: TiktokProfile = {
    followerCount: null,
    displayName: null,
    username: null,
    avatarUrl: null,
  };

  const accessToken = await getAccessToken();
  if (!accessToken) return empty;

  try {
    const res = await fetch(
      "https://open.tiktokapis.com/v2/user/info/?fields=follower_count,display_name,username,avatar_url",
      {
        headers: { Authorization: `Bearer ${accessToken}` },
        next: { revalidate: 3600 },
        signal: AbortSignal.timeout(5000),
      }
    );

    if (!res.ok) return empty;

    const data = await res.json();
    const user = data.data?.user;
    if (!user) return empty;

    return {
      followerCount: user.follower_count != null ? Number(user.follower_count) : null,
      displayName: user.display_name ?? null,
      username: user.username ?? null,
      avatarUrl: user.avatar_url ?? null,
    };
  } catch {
    return empty;
  }
}

/** Convenience wrapper that just returns the follower count */
export async function getTiktokFollowerCount(): Promise<number | null> {
  const profile = await getTiktokProfile();
  return profile.followerCount;
}