import type { Args, Fn } from "../HKT";
import type { SDigit } from "../Num";
import type { AssertBool } from "../helpers";

/**
 * Check if a string is a digit (i.e. 0-9).
 *
 * Sig: `(s: string) => boolean`
 */
export type IsDigit<S extends string> = AssertBool<
  string extends S ? boolean
  : S extends `${infer C}` ?
    C extends SDigit ?
      true
    : false
  : false
>;

/**
 * [Fn] Check if a string is a digit (i.e. 0-9).
 *
 * Sig: `(s: string) => boolean`
 */
export default interface IsDigitFn extends Fn<[string], boolean> {
  def: ([s]: Args<this>) => IsDigit<typeof s>;
}