function checkLeapYear(year) {
    return (
        year % 400 == 0 ||
        (year % 4 == 0 && year % 100 != 0));
}

function getMonthDays(month, year) {
    const leapYear = checkLeapYear(year);
    if ((month <= 7 && month % 2 == 1) || (month >= 8 && month % 2 == 0)) return 31;
    if (month == 2 && leapYear) return 29;
    if (month == 2 && !leapYear) return 28;
    return 30;
}

function getNextMonthDays(month, year) {
    const leapYear = checkLeapYear(year);
    if (month == 1 && leapYear) return 29;
    if (month == 1 && !leapYear) return 28;
    if (month == 12) return 31;
    if ((month <= 7 && month % 2 == 1) || (month >= 8 && month % 2 == 0)) return 30;
    return 31;
}

function getPrevMonthDays(month, year) {
    const leapYear = checkLeapYear(year);
    if (month == 3 && leapYear) return 29;
    if (month == 3 && !leapYear) return 28;
    if (month == 1) return 31;
    if ((month <= 7 && month % 2 == 1) || (month >= 8 && month % 2 == 0)) return 30;
    return 31;
}

export function getCalendarLayout(dateObject, highlight) {
    if (!dateObject) dateObject = new Date();
    const weekday = (dateObject.getDay() + 6) % 7; // MONDAY IS THE FIRST DAY OF THE WEEK
    const day = dateObject.getDate();
    const month = dateObject.getMonth() + 1;
    const year = dateObject.getFullYear();
    const weekdayOfMonthFirst = (weekday + 35 - (day - 1)) % 7;
    const daysInMonth = getMonthDays(month, year);
    const daysInNextMonth = getNextMonthDays(month, year);
    const daysInPrevMonth = getPrevMonthDays(month, year);

    // Fill
    var monthDiff = (weekdayOfMonthFirst == 0 ? 0 : -1);
    var toFill, dim;
    if(weekdayOfMonthFirst == 0) {
        toFill = 1;
        dim = daysInMonth;
    }
    else {
        toFill = (daysInPrevMonth - (weekdayOfMonthFirst - 1));
        dim = daysInPrevMonth;
    }
    var calendar = [...Array(6)].map(() => Array(7));
    var i = 0, j = 0;
    while (i < 6 && j < 7) {
        calendar[i][j] = {
            "day": toFill,
            "today": ((toFill == day && monthDiff == 0 && highlight) ? 1 : (
                monthDiff == 0 ? 0 :
                    -1
            ))
        };
        // Increment
        toFill++;
        if (toFill > dim) { // Next month?
            monthDiff++;
            if (monthDiff == 0)
                dim = daysInMonth;
            else if (monthDiff == 1)
                dim = daysInNextMonth;
            toFill = 1;
        }
        // Next tile
        j++;
        if (j == 7) {
            j = 0;
            i++;
        }

    }
    return calendar;
}