import { Temporal } from "@js-temporal/polyfill";
import type { FractionalDigit } from "../../types/index.js";
/**
 * Round a UTC datetime string to the specified unit.
 *
 * - Converts to Instant, rounds, converts back to UTC Instant string.
 * - Supports: "hour", "minute", "second", "millisecond", "microsecond", "nanosecond".
 * - Date units ("year", "month", "week", "day") are not supported by the Temporal polyfill's Instant.round() — they return "".
 * - Wraps all Temporal calls in try-catch; returns "" on any error.
 *
 * @param value ISO UTC datetime string
 * @param options Rounding options: smallestUnit, optional roundingIncrement, roundingMode, fractionalSecondDigits
 * @returns Rounded ISO UTC Instant string, or "" on invalid input
 *
 * @example roundUtc("2024-06-15T12:34:56Z", { smallestUnit: "hour" }) // "2024-06-15T13:00:00Z"
 * @example roundUtc("2024-06-15T12:34:56Z", { smallestUnit: "minute", roundingIncrement: 15 }) // "2024-06-15T12:45:00Z"
 * @example roundUtc("2024-06-15T12:34:56Z", { smallestUnit: "second", roundingMode: "floor" }) // "2024-06-15T12:34:56Z"
 * @example roundUtc("invalid", { smallestUnit: "hour" }) // ""
 * @example roundUtc("", { smallestUnit: "hour" }) // ""
 */
export declare function roundUtc(value: string, options: {
    smallestUnit: Temporal.SmallestUnit<"hour" | "minute" | "second" | "millisecond" | "microsecond" | "nanosecond">;
    roundingIncrement?: number;
    roundingMode?: Temporal.RoundingMode;
    fractionalSecondDigits?: FractionalDigit;
}): string;