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

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

import { Temporal } from "@js-temporal/polyfill";
import { isValidDateTime, isValidDateTimeUnit } from "../validate/index.js";
/**
 * Return the start of the specified date-time `unit` for a given ISO 8601 datetime string.
 *
 * - Returns "" for invalid inputs.
 *
 * @param value ISO 8601 datetime string
 * @param unit Temporal.DateUnit|Temporal.TimeUnit to specify the unit for the start
 * @param optionsArg optional: weekStartsOn ("monday" | "sunday"), fractionalSecondDigits (number)
 * @returns ISO 8601 string representing the start of the specified unit, or "" on invalid input
 *
 * @example startOfDateTime("2024-02-29T12:34:56", "month") // "2024-02-01T00:00:00"
 * @example startOfDateTime("invalid-datetime", "month") // ""
 */
export function startOfDateTime(value, unit, optionsArg) {
    const weekStartsOn = optionsArg?.weekStartsOn ?? "monday";
    const fractionalSecondDigits = optionsArg?.fractionalSecondDigits;
    if (!isValidDateTime(value) || !isValidDateTimeUnit(unit))
        return "";
    try {
        const source = Temporal.PlainDateTime.from(value);
        let result;
        switch (unit) {
            case "year":
                result = source.with({ month: 1, day: 1 }).withPlainTime();
                break;
            case "month":
                result = source.with({ day: 1 }).withPlainTime();
                break;
            case "week": {
                const daysToSubtract = weekStartsOn === "monday"
                    ? source.dayOfWeek - 1
                    : source.dayOfWeek % 7;
                result = source.subtract({ days: daysToSubtract }).withPlainTime();
                break;
            }
            case "day":
                result = source.withPlainTime();
                break;
            case "hour":
                result = source.with({
                    minute: 0,
                    second: 0,
                    millisecond: 0,
                    microsecond: 0,
                    nanosecond: 0,
                });
                break;
            case "minute":
                result = source.with({
                    second: 0,
                    millisecond: 0,
                    microsecond: 0,
                    nanosecond: 0,
                });
                break;
            case "second":
                result = source.with({ millisecond: 0, microsecond: 0, nanosecond: 0 });
                break;
            case "millisecond":
                result = source.with({ microsecond: 0, nanosecond: 0 });
                break;
            case "microsecond":
                result = source.with({ nanosecond: 0 });
                break;
            case "nanosecond":
                result = source; // Smallest unit, nothing to reset
                break;
            default:
                return "";
        }
        // Handle default precision: 0 for > sec, 3 for ms, 6 for µs, 9 for ns
        const precisionMap = {
            millisecond: 3,
            microsecond: 6,
            nanosecond: 9,
        };
        const fractionalDigits = fractionalSecondDigits ?? (precisionMap[unit] || 0);
        return result.toString({ fractionalSecondDigits: fractionalDigits });
    }
    catch {
        return "";
    }
}