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95 Workday - tidy-up time calculation to make it more readable

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Steve Bosman
2022-01-31 16:52:55 +00:00
parent cd35451992
commit 84615c1a75
1 changed files with 17 additions and 3 deletions
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20
95_Weekday/javascript/weekday.js
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@@ -119,6 +119,18 @@ function isLeapYear(year) {
return true;
}
/**
* Determine the day of the week.
* This calculation returns a number between 1 and 7 where Sunday=1, Monday=2, ..., Saturday=7.
* First it calculates a known date near the start of the century (defined as a year ending "00").
* January 1st in "00" years is always one of: Saturday (years divisible by 400), Friday, Wednesday, or Monday.
* This is a combination of years being 52 weeks and either 1 (non-leap years) or 2 (leap years) days,
* and years ending "00" only being leap years if they are also divisible by 400.
* @param year
* @param month
* @param day
* @returns {number} Value between 1 and 7 representing Sunday to Saturday.
*/
function getDayOfWeek(year, month, day) {
const centuriesSince1500 = Math.floor((year - 1500) / 100);
let centuryOffset = centuriesSince1500 * 5 + (centuriesSince1500 + 3) / 4;
@@ -127,12 +139,14 @@ function getDayOfWeek(year, month, day) {
const yearInCentury = year % 100;
const yearInCenturyOffsets = yearInCentury / 4 + yearInCentury;
const a = yearInCenturyOffsets + day + COMMON_YEAR_MONTH_OFFSET[month-1] + centuryOffset;
let dayOfWeek = Math.floor(a % 7) + 1;
let dayOfWeek = centuryOffset + yearInCenturyOffsets + day + COMMON_YEAR_MONTH_OFFSET[month-1];
dayOfWeek = Math.floor(dayOfWeek % 7) + 1;
if (month <= 2 && isLeapYear(year)) {
dayOfWeek--;
}
if (dayOfWeek === 0) {
dayOfWeek = 7;
}
return dayOfWeek;
}