///**
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// * collection of mathematical function for calculation of date/time
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// * information
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// * */
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/**
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* checks if a year is a leap year.
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* @param year {number} a valid year in gregorian calendar
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* @return {boolean} true for a leaf year, false otherwise
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* */
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export function isLeapYear(year) {
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let leapYear = (year % 4 === 0);
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leapYear = leapYear && (year % 100 !== 0);
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leapYear = leapYear || (year % 400 === 0);
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return leapYear;
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}
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/**
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* finds a weekday of a given date by a tuple of (day, month, year)
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*
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* @param {number} day of month (first day in a month is always 1)
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* @param {number} month (1 for January and 12 for December)
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* @param {number} year (a year in Gregorian calendar)
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*
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* @return {number} a number from 0 (Sunday) to 6 (Saturday)
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*
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* */
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export function weekDayOfDate(day, month, year) {
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let y0 = year - ((14-month)/12 | 0);
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let x = y0 + ((y0/4)|0) - ((y0/100)|0) + ((y0/400)|0);
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let m0 = month + 12 * ((14-month)/12 |0) - 2;
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return (day + x + ( (31*m0)/12) | 0 ) % 7;
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}
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/**
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* counts how many days in a month of a year.
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* @param {number} month a number between 1 (for January) and 12 (for December)
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* @param {number} year a valid year respected Gregorian calendar system.
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*
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* @return {number} number of day in the given month of the year (28|29|30|31).
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*
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* */
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export function countDaysOfMonth(month, year) {
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const daysInMonth = [undefined,
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31, 28, 31, 30,
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31, 30, 31, 31,
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30, 31, 30, 31];
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if (month === 2 && isLeapYear(year)) {
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return 29;
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}
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return daysInMonth[month];
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}
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