@burglekitt/gmt/dist/internal/intervalCountHelpers.js

Temporal-based date and time utilities with timezone support and polyfill integration

/**
 * Singular DateTimeUnit to its `Temporal.Duration` field name.
 *
 * Example lookups:
 * - DURATION_FIELD_BY_UNIT.day => "days"
 * - DURATION_FIELD_BY_UNIT.nanosecond => "nanoseconds"
 */
const DURATION_FIELD_BY_UNIT = {
    year: "years",
    month: "months",
    week: "weeks",
    day: "days",
    hour: "hours",
    minute: "minutes",
    second: "seconds",
    millisecond: "milliseconds",
    microsecond: "microseconds",
    nanosecond: "nanoseconds",
};
/**
 * Return the start of the specified date-time `unit` for a `Temporal.ZonedDateTime`.
 *
 * - Always uses Monday as the week start (consistent with `startOfZoned` semantics).
 * - Day-and-below units truncate by instant via `round({ roundingMode: "trunc" })`, which
 *   resolves DST correctly — a local day whose midnight is skipped starts at 01:00.
 * - Does NOT validate the unit — caller ensures it is a DateTimeUnit.
 *
 * @param source Temporal.ZonedDateTime to truncate
 * @param unit DateTimeUnit to truncate to
 * @returns Temporal.ZonedDateTime at the start of the specified unit
 */
export function getStartOfZonedUnit(source, unit) {
    switch (unit) {
        case "year":
            return source
                .with({ month: 1, day: 1 })
                .round({ smallestUnit: "day", roundingMode: "trunc" });
        case "month":
            return source
                .with({ day: 1 })
                .round({ smallestUnit: "day", roundingMode: "trunc" });
        case "week":
            return source
                .subtract({ days: source.dayOfWeek - 1 })
                .round({ smallestUnit: "day", roundingMode: "trunc" });
        default:
            return source.round({ smallestUnit: unit, roundingMode: "trunc" });
    }
}
/**
 * Extract the whole-unit span from a `Temporal.Duration` measured with `largestUnit: unit`.
 *
 * - Floors the field so a partial trailing amount never inflates a boundary count.
 * - Does NOT validate the unit — caller ensures the duration was measured in it.
 *
 * @param duration Temporal.Duration produced by `until({ largestUnit: unit })`
 * @param unit DateTimeUnit the duration was measured in
 * @returns whole number of units spanned
 */
export function getUnitSpan(duration, unit) {
    return Math.floor(duration[DURATION_FIELD_BY_UNIT[unit]]);
}