/**
 * Some utils for manipulating dates
 *
 * **WARNING** experimental
 */

/**
 * Return the date to local ISO date, like YYYY-mm-dd
 *
 * The date is valid for the same timezone as the date's locale
 *
 * Do not take time into account
 *
 */
export const dateToISO = (date: Date|null): string|null => {
    if (null === date) {
        return null;
    }

    return [
        date.getFullYear(),
        (date.getMonth() + 1).toString().padStart(2, '0'),
        date.getDate().toString().padStart(2, '0')
    ].join('-');
};

/**
 * Return a date object from iso string formatted as YYYY-mm-dd
 *
 * **Experimental**
 */
export const ISOToDate = (str: string|null): Date|null => {
    if (null === str) {
        return null;
    }
    if ("" === str.trim()) {
        return null;
    }

    let
        [year, month, day] = str.split('-').map(p => parseInt(p));

    return new Date(year, month-1, day, 0, 0, 0, 0);
}

/**
 * Return a date object from iso string formatted as YYYY-mm-dd:HH:MM:ss+01:00
 *
 */
export const ISOToDatetime = (str: string|null): Date|null => {
    if (null === str) {
        return null;
    }

    let
        [cal, times] = str.split('T'),
        [year, month, date] = cal.split('-').map(s => parseInt(s)),
        [time, timezone] = times.split(times.charAt(8)),
        [hours, minutes, seconds] = time.split(':').map(s => parseInt(s));
    ;

    if ('0000' === timezone) {
        return new Date(Date.UTC(year, month-1, date, hours, minutes, seconds));
    }

    return new Date(year, month-1, date, hours, minutes, seconds);
}

/**
 * Convert a date to ISO8601, valid for usage in api
 *
 */
export const datetimeToISO = (date: Date): string => {
    let cal, time, offset;
    cal = [
        date.getFullYear(),
        (date.getMonth() + 1).toString().padStart(2, '0'),
        date.getDate().toString().padStart(2, '0')
    ].join('-');

    time = [
        date.getHours().toString().padStart(2, '0'),
        date.getMinutes().toString().padStart(2, '0'),
        date.getSeconds().toString().padStart(2, '0')
    ].join(':');

    offset = [
        date.getTimezoneOffset() <= 0 ? '+' : '-',
        Math.abs(Math.floor(date.getTimezoneOffset() / 60)).toString().padStart(2, '0'),
        ':',
        Math.abs(date.getTimezoneOffset() % 60).toString().padStart(2, '0'),
    ].join('');

    let x = cal + 'T' + time + offset;

    return x;
};

export const intervalDaysToISO = (days: number|string|null): string => {
    if (null === days) {
        return 'P0D';
    }

    return `P${days}D`;
}

export const intervalISOToDays = (str: string|null): number|null => {
    if (null === str) {
        return null
    }

    if ("" === str.trim()) {
        return null;
    }

    let days = 0;
    let isDate = true;
    let vstring = "";
    for (let i = 0; i < str.length; i = i + 1) {
        if (!isDate) {
            continue;
        }
        switch (str.charAt(i)) {
            case 'P':
                isDate = true;
                break;
            case 'T':
                isDate = false;
                break;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                vstring = vstring + str.charAt(i);
                break;
            case 'Y':
                days = days + Number.parseInt(vstring) * 365;
                vstring = "";
                break;
            case 'M':
                days = days + Number.parseInt(vstring) * 30;
                vstring = "";
                break;
            case 'D':
                days = days + Number.parseInt(vstring);
                vstring = "";
                break;
            default:
                throw Error("this character should not appears: " + str.charAt(i));
        }
    }

    return days;
}