@burglekitt/gmt/dist/zoned/calculate/subtractZoned.js

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

import { Temporal } from "@js-temporal/polyfill";
import { calendarSystemOfZonedValue, formatZonedInCalendar, isValidAmount, parseCalendarZonedValue, resolveOverflow, } from "../../internal/index.js";
import { isValidDateTimeDurationUnit } from "../../plain/validate/index.js";
import { isValidCalendarZonedDateTime } from "../validate/index.js";
/**
 * Subtract a temporal amount from a zoned ISO 8601 datetime string and return a zoned ISO 8601 string.
 *
 * - Uses Temporal.ZonedDateTime.subtract to subtract duration.
 * - Validates duration units and values.
 * - Accepts a GMT calendar-annotated zoned string (as produced by `convertZonedToCalendar`, e.g.
 *   `"5784-07-15T14:30:00-04:00[u-ca=hebrew][America/New_York]"`), not just a bare ISO string —
 *   E7 (issue #152). Calendar-unit arithmetic ("subtract 1 month") resolves against that calendar
 *   (a Hebrew leap month, an Ethiopic Pagumen, a Japanese era change) **and** the DST rules of the
 *   zone, in one operation. The calendar tag, the era, the wall time and the UTC offset are all
 *   re-derived from the result, never copied from the input. A bare ISO string is unaffected —
 *   always treated as, and always returns, `"gregorian"`.
 * - `disambiguation` controls DST resolution ONLY when the arithmetic result lands on an ambiguous
 *   local time from a fall-back (DST-end) overlap: "compatible" (default), "earlier", "later", or
 *   "reject" (throws, resulting in ""). Has no effect when the result lands in a spring-forward
 *   (DST-start) gap — Temporal's arithmetic always resolves gap landings unambiguously (by advancing
 *   past the gap) before disambiguation is ever evaluated.
 * - `offset` ("prefer" | "use" | "ignore" (default) | "reject") is accepted for API consistency with
 *   sibling zoned-construction functions (see `startOfZoned`, `endOfZoned`, etc.) but has **no effect
 *   here**: the internal rebuild step reconstructs from a plain datetime string with no UTC offset
 *   embedded, so there is never a stored offset for `offset` to prefer/use/ignore/reject against.
 *   `disambiguation` is the only option that affects this function's output.
 * - `overflow` ("constrain" (default) | "reject") controls out-of-range results, e.g. subtracting
 *   1 month from Mar 31: "constrain" clamps to Feb 29/28, "reject" throws (resulting in "").
 * - Returns "" for invalid input.
 *
 * @param value ISO 8601 zoned datetime string, optionally calendar-annotated
 * @param units Partial<Record<DateTimeDurationUnit, number>> object specifying units to subtract
 * @param optionsArg optional: disambiguation ("compatible" | "earlier" | "later" | "reject"), offset ("prefer" | "use" | "ignore" | "reject" — accepted but inert, see above), overflow ("constrain" | "reject")
 * @returns zoned ISO 8601 string on success, or "" on invalid input
 *
 * @example subtractZoned("2024-03-10T12:00:00-04:00[America/New_York]", { days: 5 }) // "2024-03-05T12:00:00-05:00[America/New_York]"
 * @example subtractZoned("invalid", { days: 5 }) // ""
 * @example subtractZoned("2024-11-04T01:30:00-05:00[America/New_York]", { days: 1 }, { disambiguation: "later" }) // "2024-11-03T01:30:00-05:00[America/New_York]" (fall-back overlap resolved; default "compatible" would return the -04:00 instant instead)
 * @example subtractZoned("2024-11-04T01:30:00-05:00[America/New_York]", { days: 1 }, { disambiguation: "reject" }) // "" (fall-back overlap rejected)
 * @example subtractZoned("2024-03-11T03:30:00-04:00[America/New_York]", { days: 1 }, { disambiguation: "reject" }) // "2024-03-10T03:30:00-04:00[America/New_York]" (spring-forward gap — disambiguation has no effect, arithmetic already advanced past it, so "reject" does not throw here)
 * @example subtractZoned("2024-03-31T12:00:00-04:00[America/New_York]", { months: 1 }, { overflow: "reject" }) // ""
 * @example subtractZoned("5784-07-15T14:30:00-04:00[u-ca=hebrew][America/New_York]", { months: 1 }) // "5784-06-15T14:30:00-05:00[u-ca=hebrew][America/New_York]" (Adar -> Adar I, EDT -> EST in one call)
 * @example subtractZoned("0001-05-01T12:00:00+09:00[u-ca=japanese;era=reiwa][Asia/Tokyo]", { days: 1 }) // "0031-04-30T12:00:00+09:00[u-ca=japanese;era=heisei][Asia/Tokyo]" (era re-derived, not copied)
 * @example subtractZoned("2024-03-10T14:30:00-04:00[America/New_York][u-ca=hebrew]", { days: 1 }) // "" (Temporal's segment ordering is not GMT's grammar)
 */
export function subtractZoned(value, units, optionsArg) {
    const validZonedDateTime = isValidCalendarZonedDateTime(value);
    const validUnits = Object.keys(units).every(isValidDateTimeDurationUnit);
    const validAmounts = Object.values(units).every(isValidAmount);
    if (!validZonedDateTime || !validUnits || !validAmounts) {
        return "";
    }
    const disambiguation = optionsArg?.disambiguation ?? "compatible";
    const offset = optionsArg?.offset ?? "ignore";
    const overflow = resolveOverflow(optionsArg?.overflow);
    try {
        const calendar = calendarSystemOfZonedValue(value);
        if (!calendar) {
            return "";
        }
        const zoned = parseCalendarZonedValue(value);
        const subtracted = zoned.subtract(units, { overflow });
        if (disambiguation === "compatible") {
            return formatZonedInCalendar(subtracted, calendar);
        }
        // The calendar MUST be stripped before this rebuild string is composed (E7 risk R1) — see
        // `addZoned`'s equivalent comment for the full reasoning. In short: a calendared
        // `.toPlainDateTime().toString()` already carries Temporal's own `[u-ca=...]` annotation, so
        // appending `[${timeZoneId}]` produces GMT's forbidden segment ordering and
        // `Temporal.ZonedDateTime.from` rejects it, silently degrading every non-"compatible"
        // disambiguation to "".
        const plainDateTime = subtracted
            .withCalendar("iso8601")
            .toPlainDateTime()
            .toString();
        const resolved = Temporal.ZonedDateTime.from(`${plainDateTime}[${subtracted.timeZoneId}]`, { disambiguation, offset }).withCalendar(subtracted.calendarId);
        return formatZonedInCalendar(resolved, calendar);
    }
    catch {
        return "";
    }
}