import crypto from "crypto"

// Signed OAuth `state` (HMAC-SHA256) — carries the initiating owner + provider
// and is tamper-proof, so the callback can't be forged/CSRF'd.
const SECRET = process.env.BETTER_AUTH_SECRET ?? "dev-secret"

export function signState(data: { ownerId: string; provider: string }): string {
  const payload = Buffer.from(JSON.stringify(data)).toString("base64url")
  const sig = crypto.createHmac("sha256", SECRET).update(payload).digest("base64url")
  return `${payload}.${sig}`
}

export function verifyState(state: string): { ownerId: string; provider: string } | null {
  const [payload, sig] = state.split(".")
  if (!payload || !sig) return null
  const expect = crypto.createHmac("sha256", SECRET).update(payload).digest("base64url")
  if (sig.length !== expect.length || !crypto.timingSafeEqual(Buffer.from(sig), Buffer.from(expect))) return null
  try {
    return JSON.parse(Buffer.from(payload, "base64url").toString("utf8"))
  } catch {
    return null
  }
}