@burglekitt/gmt/dist/plain/format/formatRelativeDateTime.js

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

import { Temporal } from "@js-temporal/polyfill";
import { normalizeDateTime, resolveRelativeRounding } from "../../internal/index.js";
import { isValidDateTime } from "../validate/index.js";
const AUTO_UNITS = [
    { unit: "second", maxSeconds: 60 },
    { unit: "minute", maxSeconds: 3_600 },
    { unit: "hour", maxSeconds: 86_400 },
    { unit: "day", maxSeconds: Infinity },
];
/**
 * Format the relative time between a plain date-time and a reference date-time.
 *
 * - Auto-picks the display unit (second through year) based on the distance, unless
 *   `largestUnit` forces one.
 * - `roundingMethod` controls how the distance rounds to the display unit.
 *
 * @param value ISO date-time string to format
 * @param locale optional: BCP 47 locale tag
 * @param options optional: { style, numeric, largestUnit, roundingMethod, reference }
 * @returns the formatted relative-time string, or "" on invalid input
 *
 * @example formatRelativeDateTime("2026-03-17T09:00:00", "en-GB", { style: "long" }) // "in 3 hours"
 * @example formatRelativeDateTime(value, "en-US", { roundingMethod: "floor" }) // rounds toward the earlier boundary
 * @example formatRelativeDateTime("not-a-date") // ""
 */
export function formatRelativeDateTime(value, locale, options = {}) {
    if (!isValidDateTime(value))
        return "";
    if (options.reference !== undefined && !isValidDateTime(options.reference))
        return "";
    try {
        const target = Temporal.PlainDateTime.from(value);
        const reference = options.reference
            ? Temporal.PlainDateTime.from(options.reference)
            : Temporal.Now.plainDateTimeISO();
        const diff = target.since(reference);
        const absSeconds = Math.abs(diff.total("second"));
        const unit = options.largestUnit ??
            AUTO_UNITS.find((t) => absSeconds < t.maxSeconds)?.unit ??
            "day";
        let amount;
        try {
            amount = resolveRelativeRounding(diff.total(unit), options.roundingMethod);
        }
        catch {
            // month/year are calendrical — relativeTo needs a PlainDate
            amount = resolveRelativeRounding(diff.total({ unit, relativeTo: reference.toPlainDate() }), options.roundingMethod);
        }
        return normalizeDateTime(new Intl.RelativeTimeFormat(locale, {
            numeric: options.numeric ?? "auto",
            style: options.style ?? "long",
        }).format(amount, unit));
    }
    catch {
        return "";
    }
}