deepKey.ts

type ValidValues = string | number | Record<string, any> | Array<any> | undefined | null;

type DeepKey<T extends Record<string, any>, K extends string = string> = K extends keyof T
  ? T[K] extends ValidValues
    ? K
    : never
  : K extends `${infer TKey}.${infer Rest}`
  ? T[TKey] extends ValidValues
    ? DeepKey<Exclude<T[TKey], undefined>, Rest> extends never
      ? never
      : K
    : never
  : never;