import crypto from "crypto"

// Signed OAuth `state` for the e-sign connect flow — carries the initiating
// owner + provider + a random nonce (bound to a cookie by the connect route),
// plus an issued-at so a leaked state can't be replayed. Mirrors the hardened
// accounting OAuth state; fails closed if BETTER_AUTH_SECRET is missing.

const STATE_TTL_MS = 10 * 60 * 1000 // 10 minutes

export const ESIGN_NONCE_COOKIE = "esign_oauth_nonce"

function secret(): string {
  const s = process.env.BETTER_AUTH_SECRET
  if (!s) throw new Error("BETTER_AUTH_SECRET is not set — required to sign OAuth state")
  return s
}

export type EsignOAuthState = { ownerId: string; provider: string; nonce: string }

export function signState(data: EsignOAuthState): string {
  const payload = Buffer.from(JSON.stringify({ ...data, iat: Date.now() })).toString("base64url")
  const sig = crypto.createHmac("sha256", secret()).update(payload).digest("base64url")
  return `${payload}.${sig}`
}

export function verifyState(state: string): EsignOAuthState | 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 {
    const obj = JSON.parse(Buffer.from(payload, "base64url").toString("utf8")) as EsignOAuthState & { iat?: number }
    if (!obj.iat || Date.now() - obj.iat > STATE_TTL_MS) return null
    if (!obj.ownerId || !obj.provider || !obj.nonce) return null
    return { ownerId: obj.ownerId, provider: obj.provider, nonce: obj.nonce }
  } catch {
    return null
  }
}