RocketChat/Rocket.Chat

import moment from 'moment-timezone';

import { settings } from '../../../settings/server';

const padOffset = (offset: string | number): string => {
    const numberOffset = Number(offset);
    const absOffset = Math.abs(numberOffset);
    const isNegative = !(numberOffset === absOffset);

    return `${isNegative ? '-' : '+'}${absOffset < 10 ? `0${absOffset}` : absOffset}:00`;
};

const guessTimezoneFromOffset = (offset?: string | number): string => {
    if (!offset) {
        return moment.tz.guess();
    }

    return moment.tz.names().find((tz) => padOffset(offset) === moment.tz(tz).format('Z').toString()) || moment.tz.guess();
};

export const getTimezone = (user?: { utcOffset?: string | number } | null): string => {
    const timezone = settings.get('Default_Timezone_For_Reporting');

    switch (timezone) {
        case 'custom':
            return settings.get<string>('Default_Custom_Timezone');
        case 'user':
            return guessTimezoneFromOffset(user?.utcOffset);
        default:
            return moment.tz.guess();
    }
};