@burglekitt/gmt/dist/plain/interval/intervalFromDurationDateTime.js

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

import { Temporal } from "@js-temporal/polyfill";
import { isValidDuration } from "../../duration/validate/index.js";
import { resolveOverflow } from "../../internal/index.js";
import { isValidDateTime } from "../validate/index.js";
/**
 * Construct a datetime interval from a single point plus an ISO 8601 duration, anchored at either end.
 *
 * - `anchor: "start"` treats `value` as the interval start and adds `duration` to get the end.
 * - `anchor: "end"` treats `value` as the interval end and subtracts `duration` to get the start.
 * - Uses `Temporal.PlainDateTime.prototype.add`/`.subtract`, so calendar units (years/months/weeks)
 *   resolve against `value` itself — no separate `relativeTo` is needed, unlike `addDuration`.
 * - A negative `duration` (e.g. `"-P1D"`) can invert the computed span; returns null when that
 *   happens, mirroring `intervalIntersectionDateTime`'s `start > end` rejection.
 * - `overflow` ("constrain" (default) | "reject") controls out-of-range results, e.g. adding 1 month
 *   to Jan 31: "constrain" clamps to Feb 29/28, "reject" returns null.
 * - Returns null on invalid input (unparseable `value`, invalid `duration`, or an `anchor` other
 *   than `"start"`/`"end"`).
 *
 * @param value ISO PlainDateTime string
 * @param duration ISO 8601 duration string
 * @param anchor "start" | "end" — which endpoint `value` represents
 * @param options optional: overflow ("constrain" | "reject")
 * @returns `{ start, end }` with the constructed span, or null on invalid input
 *
 * @example intervalFromDurationDateTime("2024-01-01T00:00:00", "P1DT2H", "start") // { start: "2024-01-01T00:00:00", end: "2024-01-02T02:00:00" }
 * @example intervalFromDurationDateTime("2024-01-02T02:00:00", "P1DT2H", "end") // { start: "2024-01-01T00:00:00", end: "2024-01-02T02:00:00" }
 * @example intervalFromDurationDateTime("2024-01-31T12:00:00", "P1M", "start", { overflow: "reject" }) // null
 * @example intervalFromDurationDateTime("2024-01-05T00:00:00", "-P10D", "start") // null (inverted span)
 * @example intervalFromDurationDateTime("invalid", "P1D", "start") // null
 */
export function intervalFromDurationDateTime(value, duration, anchor, options) {
    if (typeof value !== "string" || !isValidDateTime(value)) {
        return null;
    }
    if (!isValidDuration(duration)) {
        return null;
    }
    if (anchor !== "start" && anchor !== "end") {
        return null;
    }
    try {
        const point = Temporal.PlainDateTime.from(value);
        const dur = Temporal.Duration.from(duration);
        const overflow = resolveOverflow(options?.overflow);
        const other = anchor === "start"
            ? point.add(dur, { overflow })
            : point.subtract(dur, { overflow });
        const start = anchor === "start" ? point : other;
        const end = anchor === "start" ? other : point;
        if (Temporal.PlainDateTime.compare(start, end) > 0) {
            return null;
        }
        return { start: start.toString(), end: end.toString() };
    }
    catch {
        return null;
    }
}