import { Temporal } from "@js-temporal/polyfill";
import type { DateTimeDurationUnit, RoundingOptions } from "../../types/index.js";
/**
 * Return the difference between two PlainDateTime values in the requested unit.
 *
 * - Returns `null` for invalid inputs (negative diffs are valid).
 * - Uses Temporal.PlainDateTime.until and extracts the requested unit.
 *
 * `smallestUnit`, `roundingIncrement`, and `roundingMode` control optional rounding of the result,
 * per Temporal's DifferenceOptions — e.g. `{ smallestUnit: "hour", roundingMode: "halfExpand" }`
 * rounds the difference to the nearest hour before extracting the requested unit.
 * - When `units` is an array, `smallestUnit` must not be coarser than the largest unit in the
 *   array (e.g. `["day", "hour"]` with `smallestUnit: "week"`) — this combination is rejected by
 *   Temporal and returns null, same as other invalid input.
 *
 * @param dateTime1 ISO PlainDateTime string for the start
 * @param dateTime2 ISO PlainDateTime string for the end
 * @param units DateTimeDurationUnit | DateTimeDurationUnit[] to measure the difference
 * @param options optional: smallestUnit, roundingIncrement, roundingMode (Temporal.DifferenceOptions rounding controls)
 * @returns numeric difference in the requested unit, or null on invalid input
 *
 * @example diffDateTime("2024-03-10T12:00:00", "2024-03-15T12:00:00", "day") // 5
 * @example diffDateTime("invalid", "2024-03-15T12:00:00", "day") // null
 */
export declare function diffDateTime(dateTime1: string, dateTime2: string, units: DateTimeDurationUnit | DateTimeDurationUnit[], options?: RoundingOptions<Temporal.DateTimeUnit>): number | Record<DateTimeDurationUnit, number> | null;