import type { Temporal } from "@js-temporal/polyfill";
/**
 * Return the start of the specified date-time `unit` for a `Temporal.PlainDateTime`.
 *
 * - Always uses Monday as the week start (consistent with roundDateTime semantics).
 * - Date units (year, month, week) reset the time to midnight.
 * - Does NOT validate the unit — caller ensures it is a DateTimeUnit.
 *
 * @param source Temporal.PlainDateTime to round
 * @param unit DateTimeUnit to specify the unit for the start
 * @returns Temporal.PlainDateTime at the start of the specified unit
 */
export declare function getStartOfDateTimeUnit(source: Temporal.PlainDateTime, unit: string): Temporal.PlainDateTime;
/**
 * Add `amount` units of the specified date-time `unit` to a `Temporal.PlainDateTime`.
 *
 * - Only year, month, and week are meaningful for the manual rounding path.
 * - Day and time units return the input unchanged (they are handled by
 *   `Temporal.PlainDateTime.round()` in the callers).
 * - Does NOT validate the unit — caller ensures it is a DateTimeUnit.
 *
 * @param date Temporal.PlainDateTime to advance
 * @param unit DateTimeUnit to add
 * @param amount number of units to add
 * @returns new Temporal.PlainDateTime advanced by the specified amount
 */
export declare function addDateTimeUnit(date: Temporal.PlainDateTime, unit: string, amount: number): Temporal.PlainDateTime;