import type { CustomOptions, CustomValidate } from "../custom/index.ts";
/**
 * @credits
 * [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) time with seconds regex.
 * [Valibot](https://github.com/fabian-hiller/valibot/blob/c3de9371c2cfa4e126734ddf0e2ab1de98e8a6ef/library/src/regex.ts#L102)
 */
export declare const ISO_TIME_SECOND_REGEX: RegExp;
/**
 * Determines if the input is an ISO time with seconds string.
 *
 * @param input The value to check.
 * @param validate Additional validation to run against the input if it is an ISO time with seconds string. Default is `undefined`.
 * @returns `true` if the input is an ISO time with seconds string, `false` otherwise.
 */
export declare function isIsoTimeSecond(input: unknown, validate?: CustomValidate<string>): input is string;
export type IsoTimeSecondOptions = Omit<CustomOptions<string>, "typecheck">;
/**
 * Verifies that the input is an ISO time with seconds string, and returns it.
 * If the input is not an ISO time with seconds string, the fallback value is returned.
 *
 * @param input The value to check.
 * @param fallback The value to return if the input is not an ISO time with seconds string. Default is `null`.
 * @returns The ISO time with seconds string value of the input, or the fallback if the input is not an ISO time with seconds string.
 */
export declare function isoTimeSecond(input: unknown, fallback: string, options?: IsoTimeSecondOptions): string;
export declare function isoTimeSecond(input: unknown, fallback?: string | null | undefined, options?: IsoTimeSecondOptions): string | null;