import { Dayjs } from 'dayjs';

/**
 * Converts a Dayjs picker value to a UTC ISO timestamp anchored at the user's
 * LOCAL day boundary.
 *
 * Used by date-range filter bars where the BE expects a full ISO timestamp
 * boundary — `OccurredFrom` is start-of-local-day, `OccurredTo` is
 * end-of-local-day so the filter is inclusive of the user's calendar day
 * regardless of their timezone.
 *
 * Critical: hardcoding `T00:00:00.000Z` on the formatted date treats the picker
 * value as UTC, which shifts the boundary by the user's offset (e.g. a user in
 * Europe/London during BST loses the first hour of their local day).
 * `startOf("day")` / `endOf("day")` give the local boundary; `.toISOString()`
 * then converts to UTC for the wire.
 *
 * Lives behind the `@ethisyscore/core-utils/date/dayjs` sub-path so the core
 * entry stays free of the optional `dayjs` peer dependency.
 *
 * @param value - The Dayjs picker value (or null when the user cleared the field)
 * @param endOfDay - When true, returns the end-of-local-day boundary
 * @returns ISO timestamp string in UTC, or undefined when the value is null/invalid
 */
declare function dayjsToIsoDayBoundary(value: Dayjs | null | undefined, endOfDay?: boolean): string | undefined;

export { dayjsToIsoDayBoundary };