/**
 * Briven Auth M2M (machine-to-machine) — server only.
 * SuperTokens-style client_credentials via briven-engine.
 * @see https://supertokens.com/docs/authentication/m2m/client-credentials
 * @see Briven docs/HANDOFF-AUTH-M2M-FOR-ALL-PROJECTS.md
 *
 * Never import this from client components. Never put m2ms_ secrets in NEXT_PUBLIC_*.
 */

type M2mTokenCache = { accessToken: string; expiresAtMs: number };

let cache: M2mTokenCache | null = null;

function apiOrigin(): string {
  return (
    process.env.BRIVEN_API_ORIGIN?.trim() ||
    process.env.NEXT_PUBLIC_BRIVEN_API_ORIGIN?.trim() ||
    "https://api.briven.tech"
  );
}

export function isM2mConfigured(): boolean {
  const id = process.env.BRIVEN_M2M_CLIENT_ID?.trim() ?? "";
  const secret = process.env.BRIVEN_M2M_CLIENT_SECRET?.trim() ?? "";
  return id.startsWith("m2m_") && secret.startsWith("m2ms_");
}

/**
 * Mint (or reuse cached) M2M access token.
 * Token TTL is ~3600s; refresh 60s early.
 */
export async function getBrivenM2mToken(): Promise<string> {
  if (!isM2mConfigured()) {
    throw new Error(
      "M2M not configured. Create a machine client in Briven Auth → Keys, then set BRIVEN_M2M_CLIENT_ID + BRIVEN_M2M_CLIENT_SECRET.",
    );
  }

  const now = Date.now();
  if (cache && cache.expiresAtMs > now + 60_000) {
    return cache.accessToken;
  }

  const res = await fetch(`${apiOrigin()}/v1/auth-core/oauth/token`, {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({
      grant_type: "client_credentials",
      client_id: process.env.BRIVEN_M2M_CLIENT_ID,
      client_secret: process.env.BRIVEN_M2M_CLIENT_SECRET,
    }),
    cache: "no-store",
  });

  if (!res.ok) {
    const text = await res.text();
    throw new Error(`m2m token failed: ${res.status} ${text.slice(0, 200)}`);
  }

  const data = (await res.json()) as {
    access_token: string;
    expires_in: number;
    project_id?: string;
    role?: string;
  };

  cache = {
    accessToken: data.access_token,
    expiresAtMs: now + (data.expires_in ?? 3600) * 1000,
  };
  return cache.accessToken;
}

/** Example: call project info with M2M bearer. */
export async function brivenProjectInfoWithM2m(): Promise<unknown> {
  const token = await getBrivenM2mToken();
  const projectId =
    process.env.BRIVEN_PROJECT_ID?.trim() ||
    process.env.NEXT_PUBLIC_BRIVEN_PROJECT_ID?.trim();
  if (!projectId) throw new Error("BRIVEN_PROJECT_ID missing");

  const res = await fetch(`${apiOrigin()}/v1/projects/${projectId}/info`, {
    headers: { authorization: `Bearer ${token}` },
    cache: "no-store",
  });
  if (!res.ok) {
    throw new Error(`project info ${res.status}: ${(await res.text()).slice(0, 200)}`);
  }
  return res.json();
}