// Keypad keys and how one press changes a field value.
export type KeypadKey = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | "clear" | "back";

/** Applies one key press to a field value. Digits stop at `max` characters. */
export function applyKey(value: string, key: KeypadKey, max = 64): string {
  if (key === "clear") return "";
  if (key === "back") return value.slice(0, -1);
  return value.length >= max ? value : value + key;
}