// Minimal shared-password auth. Enabled ONLY when LYRA_PASSWORD is set; otherwise the
// app stays open (unchanged behavior) — see README "Security". The auth cookie holds a
// token derived from the password via HMAC-SHA256 keyed by LYRA_SECRET_KEY, so it can't
// be forged without the secret and the plaintext password is never stored client-side.
// Edge-safe: uses global Web Crypto + btoa (no node:crypto / Buffer), so the same code
// runs in middleware (Edge runtime) and in the API route (Node runtime).

export const AUTH_COOKIE = "lyra_auth";

function toB64(bytes: Uint8Array): string {
  let s = "";
  for (const b of bytes) s += String.fromCharCode(b);
  return btoa(s);
}

/** The token a valid session cookie must carry, or "" when auth is disabled (no password). */
export async function expectedToken(): Promise<string> {
  const password = process.env.LYRA_PASSWORD;
  if (!password) return "";
  const secret = process.env.LYRA_SECRET_KEY ?? "lyra";
  const enc = new TextEncoder();
  const key = await crypto.subtle.importKey(
    "raw",
    enc.encode(secret),
    { name: "HMAC", hash: "SHA-256" },
    false,
    ["sign"],
  );
  const sig = await crypto.subtle.sign("HMAC", key, enc.encode(password));
  return toB64(new Uint8Array(sig));
}

/** Constant-time string compare (both operands are our own derived tokens). */
export function safeEqual(a: string, b: string): boolean {
  if (a.length !== b.length) return false;
  let diff = 0;
  for (let i = 0; i < a.length; i++) diff |= a.charCodeAt(i) ^ b.charCodeAt(i);
  return diff === 0;
}