bitspire/apps/machine/electron/lnurl-withdraw.ts

/**
 * LNURL-withdraw executor (LUD-03) — the ATM as the *withdrawing* party.
 *
 * Bolt Card tap-to-pay for the cash-out flow: a Bolt Card presents an
 * `lnurlw://…?p=…&c=…` voucher (NTAG424 SUN — fresh p/c per tap). The ATM has
 * already generated its cash-out BOLT11; here it asks the card's wallet to pay
 * that invoice:
 *   1. GET the lnurlw URL → a `withdrawRequest` (callback, k1, max/min).
 *   2. GET `callback?k1=…&pr=<our bolt11>` → the card's wallet pays it.
 * Settlement itself is observed elsewhere (the existing invoice watcher over
 * nostr), so a returned `{ ok: true }` means "the card accepted the pull", not
 * "cash dispensed" — the state machine still waits for PAYMENT_RECEIVED.
 *
 * Runs in the MAIN process (Node fetch) to avoid renderer CORS: LNURL
 * endpoints don't send CORS headers, so a renderer fetch to the card's host
 * would be blocked.
 */

export interface LnurlWithdrawResult {
  ok: boolean
  /** Human-readable reason when ok is false (safe to surface on-screen). */
  reason?: string
}

/** LUD-03 withdrawRequest (subset we consume) + LUD-06 error shape. */
interface WithdrawRequest {
  tag?: string
  callback?: string
  k1?: string
  minWithdrawable?: number
  maxWithdrawable?: number
  defaultDescription?: string
  status?: string
  reason?: string
}

type FetchLike = typeof fetch

export interface ExecuteLnurlWithdrawOptions {
  /** Injected for tests; defaults to global fetch. */
  fetchImpl?: FetchLike
  /**
   * Our invoice amount in millisats. When set, we reject early if it exceeds
   * the voucher's maxWithdrawable (defensive; the callback would reject anyway).
   */
  amountMsat?: number
  /** Per-request timeout (default 15s). */
  timeoutMs?: number
}

/**
 * Normalize a Bolt Card / LNURL-withdraw pointer to an https URL.
 * Bolt Cards emit `lnurlw://host/path?query`; we also accept `lnurl://` and a
 * bare `https://`. Bech32 `LNURL1…` is intentionally unsupported (Bolt Cards
 * never use it) and rejected with a clear reason.
 */
export function lnurlwToHttps(raw: string): string | null {
  let s = raw.trim()
  if (!s) return null
  if (s.toLowerCase().startsWith('lightning:')) s = s.slice('lightning:'.length)
  const lower = s.toLowerCase()
  if (lower.startsWith('lnurlw://')) return 'https://' + s.slice('lnurlw://'.length)
  if (lower.startsWith('lnurl://')) return 'https://' + s.slice('lnurl://'.length)
  if (lower.startsWith('https://')) return s
  // Reject http:// (must be TLS) and bech32 lnurl1… (not a Bolt Card).
  return null
}

function appendQuery(url: string, params: Record<string, string>): string {
  const u = new URL(url)
  for (const [k, v] of Object.entries(params)) u.searchParams.set(k, v)
  return u.toString()
}

function errMsg(e: unknown): string {
  if (e instanceof Error) return e.name === 'TimeoutError' || e.name === 'AbortError' ? 'timed out' : e.message
  return String(e)
}

export async function executeLnurlWithdraw(
  lnurlw: string,
  bolt11: string,
  opts: ExecuteLnurlWithdrawOptions = {}
): Promise<LnurlWithdrawResult> {
  const doFetch = opts.fetchImpl ?? fetch
  const timeoutMs = opts.timeoutMs ?? 15_000

  const paramsUrl = lnurlwToHttps(lnurlw)
  if (!paramsUrl) return { ok: false, reason: 'not a valid Bolt Card (lnurlw) tag' }
  if (!bolt11 || !/^ln[a-z0-9]/i.test(bolt11.trim())) {
    return { ok: false, reason: 'no invoice to charge' }
  }

  // 1) Fetch the withdraw request.
  let params: WithdrawRequest
  try {
    const res = await doFetch(paramsUrl, { signal: AbortSignal.timeout(timeoutMs) })
    params = (await res.json()) as WithdrawRequest
  } catch (e) {
    return { ok: false, reason: `could not reach the card: ${errMsg(e)}` }
  }
  if (params.status === 'ERROR') {
    return { ok: false, reason: params.reason || 'card rejected the tap' }
  }
  if (params.tag !== 'withdrawRequest' || !params.callback || !params.k1) {
    return { ok: false, reason: 'card did not return a withdraw voucher' }
  }
  if (
    opts.amountMsat != null &&
    typeof params.maxWithdrawable === 'number' &&
    opts.amountMsat > params.maxWithdrawable
  ) {
    return { ok: false, reason: 'card limit is below this amount' }
  }

  // 2) Hand our invoice to the callback — the card's wallet pays it.
  const cbUrl = appendQuery(params.callback, { k1: params.k1, pr: bolt11.trim() })
  let cb: { status?: string; reason?: string }
  try {
    const res = await doFetch(cbUrl, { signal: AbortSignal.timeout(timeoutMs) })
    cb = (await res.json()) as { status?: string; reason?: string }
  } catch (e) {
    return { ok: false, reason: `card payment failed: ${errMsg(e)}` }
  }
  if (cb.status === 'OK') return { ok: true }
  return { ok: false, reason: cb.reason || 'card declined the payment' }
}