import type { DateTimeDurationUnit, Overflow } from "../../types/index.js";
/**
 * Add a temporal amount to a Unix epoch value and return the resulting epoch.
 *
 * - Converts to ZonedDateTime, adds the duration, then converts back to epoch.
 * - Validates duration units and values.
 * - Returns null for invalid input.
 *
 * `overflow` ("constrain" (default) | "reject") controls out-of-range results, e.g. adding 1 month
 * to Jan 31: "constrain" clamps to Feb 29/28, "reject" throws (resulting in null).
 *
 * @param value Unix timestamp (number)
 * @param units Partial<Record<DateTimeDurationUnit, number>> object specifying units to add
 * @param options optional: epochUnit ("seconds" | "milliseconds"), timeZone (IANA), overflow ("constrain" | "reject")
 * @returns Unix epoch number after addition, or null on invalid input
 *
 * @example addUnix(1706659200000, { days: 1 }) // 1706745600000
 * @example addUnix(1706659200, { days: 1 }, { epochUnit: "seconds" }) // 1706745600
 * @example addUnix(-86400000, { days: 1 }) // 0 (Dec 31 1969 + 1 day = Jan 1 1970)
 */
export declare function addUnix(value: number, units: Partial<Record<DateTimeDurationUnit, number>>, options?: {
    epochUnit?: "seconds" | "milliseconds";
    timeZone?: string;
    overflow?: Overflow;
}): number | null;