/*
 * @author Usman Naeem
 */
async function load_timezones(select_id, selected_time_zone, select_local_for_unselected, preferred_check) {
    try {
        const prefferedTimezonesOnlyElement = preferred_check ? getElement("preferred_timezones_only") : "undefined";
        if (!Intl.supportedValuesOf || (prefferedTimezonesOnlyElement && prefferedTimezonesOnlyElement.checked)) {
            const timeZones = ['Australia/Sydney', 'Asia/Tokyo', 'Asia/Hong_Kong', 'Asia/Singapore', 'Asia/Karachi', 'Asia/Dubai', 'Europe/London', 'America/New_York'];
            if (!selected_time_zone) {
                selected_time_zone = 'America/New_York';
            }
            if (Intl.supportedValuesOf) {
                if (!selected_time_zone && select_local_for_unselected) {
                    selected_time_zone = localTimezone;
                }
                if (!timeZones.includes(selected_time_zone)) {
                    timeZones.push(selected_time_zone);
                }
                const localTimezone = Intl.DateTimeFormat().resolvedOptions().timeZone;
                if (!timeZones.includes(localTimezone)) {
                    timeZones.push(localTimezone);
                }
            }
            await add_timezone_options(select_id, timeZones, selected_time_zone).catch((error) => {
                throw new Error("Failed to load timezones");
            });
        } else {
            const localTimezone = Intl.DateTimeFormat().resolvedOptions().timeZone;
            if (!selected_time_zone) {
                selected_time_zone = select_local_for_unselected ? localTimezone : 'America/New_York';
            }
            const allTimeZones = Intl.supportedValuesOf('timeZone');
            await add_timezone_options(select_id, allTimeZones, selected_time_zone);
        }
    } catch (error) {
        throw new Error("Failed to load timezones");
    }
}

async function add_timezone_options(select_id, timeZones, selectedTimezone) {
    const timezoneElement = getElement(select_id);
    timezoneElement.innerHTML = "";
    const zoneCityoneMap = new Map();
    const cities = [];
    timeZones.forEach(timeZone => {
        const city = timeZone.substring(timeZone.indexOf("/") + 1).replaceAll("_", " ");
        cities.push(city);
        zoneCityoneMap.set(city, timeZone);
    });
    cities.sort();
    if (!selectedTimezone) {
        selectedTimezone = zoneCityoneMap.get(timeZones[0]);
    }
    cities.forEach(city => {
        var optionElement = document.createElement('option');
        const timeZone = zoneCityoneMap.get(city);
        optionElement.value = timeZone;
        optionElement.innerHTML = city;
        if (selectedTimezone === timeZone) {
            optionElement.selected = true;
        }
        timezoneElement.appendChild(optionElement);
    });
}