import { type AllDurations } from './duration.js';
import { DurationUnit } from './units/duration-unit.js';
/**
 * Select a set of duration units to use in {@link DurationBySelection}.
 *
 * @category Internal
 * @example
 *
 * ```ts
 * import {type DurationUnitSelection} from 'date-vir';
 *
 * const select: DurationUnitSelection = {
 *     days: true,
 *     months: true,
 * };
 * ```
 */
export type DurationUnitSelection = Partial<Record<DurationUnit, boolean | undefined>>;
/**
 * Reduce a {@link DurationUnitSelection} object into an array of the selected units, in order from
 * smallest unit (at index 0) to largest.
 *
 * @category Internal
 */
export declare function flattenUnitSelection(units: Readonly<DurationUnitSelection>): DurationUnit[];
/**
 * Pick a subset of {@link Duration} keys by a {@link DurationUnitSelection} input.
 *
 * @category Internal
 * @example
 *
 * ```ts
 * import {type DurationBySelection} from 'date-vir';
 *
 * type MySelection = DurationBySelection<{days: true; months: true}>; // `{days: number, months: number}`
 * ```
 */
export type DurationBySelection<SelectedUnits extends Readonly<DurationUnitSelection> | undefined> = undefined extends SelectedUnits ? AllDurations : {
    [Unit in keyof AllDurations as Unit extends keyof SelectedUnits ? SelectedUnits[Unit] extends true ? Unit : never : never]: AllDurations[Unit];
};
/**
 * An {@link DurationUnitSelection} instance that sets all duration units to `true`.
 *
 * @category Util
 */
export declare const selectAllDurationUnits: {
    readonly years: true;
    readonly quarters: true;
    readonly months: true;
    readonly weeks: true;
    readonly days: true;
    readonly hours: true;
    readonly minutes: true;
    readonly seconds: true;
    readonly milliseconds: true;
};