import { OtpTarget } from "../otp/otp.service";

/**
 * Mask an OTP target for echoing back to the caller: `+251911234567` ->
 * `+251•••••4567`; `ab@x.com` -> `a•@x.com`. Never return an unmasked target to
 * a caller who has not yet proven possession of the channel.
 */
export function maskOtpTarget(target: OtpTarget): string {
  if (target.email) {
    const [local, domain] = target.email.split("@");
    const head = local.slice(0, 1);
    return `${head}${"•".repeat(Math.max(local.length - 1, 1))}@${domain}`;
  }
  const phone = target.phone ?? "";
  return `${phone.slice(0, 4)}${"•".repeat(Math.max(phone.length - 8, 1))}${phone.slice(-4)}`;
}