@burglekitt/gmt/dist/plain/calculate/startOfDate.js

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

import { Temporal } from "@js-temporal/polyfill";
import { isValidDate } from "../validate/index.js";
const supported = ["year", "month", "week"];
/**
 * Return the start of the specified date `unit` for a given ISO 8601 date string.
 *
 * - Returns "" for invalid inputs.
 *
 * @param value ISO 8601 date string
 * @param unit Temporal.DateUnit to specify the unit for the start
 * @param optionsArg optional: weekStartsOn ("monday" | "sunday")
 * @returns ISO 8601 string representing the start of the specified unit, or "" on invalid input
 *
 * @example startOfDate("2024-02-29", "month") // "2024-02-01"
 * @example startOfDate("invalid-date", "month") // ""
 */
export function startOfDate(value, unit, optionsArg) {
    const weekStartsOn = optionsArg?.weekStartsOn ?? "monday";
    if (!isValidDate(value) || !supported.includes(unit))
        return "";
    try {
        const source = Temporal.PlainDate.from(value);
        let result;
        switch (unit) {
            case "year":
                result = source.with({ month: 1, day: 1 });
                break;
            case "month":
                result = source.with({ day: 1 });
                break;
            case "week": {
                // Week start: compute how many days to subtract to reach Monday.
                // Temporal: 1 (Mon) to 7 (Sun)
                // If Monday start: Monday(1) subtracts 0, Sunday(7) subtracts 6.
                // If Sunday start: Sunday(7) subtracts 0, Monday(1) subtracts 1.
                const daysToSubtract = weekStartsOn === "monday"
                    ? source.dayOfWeek - 1
                    : source.dayOfWeek % 7;
                result = source.subtract({ days: daysToSubtract });
                break;
            }
            default:
                return "";
        }
        return result.toString();
    }
    catch {
        return "";
    }
}