I am making a driver to calculate various holidays in a given time span. So, I need to find the Gregorian dates of all the Chinese Holidays (Chinese New Year, QingMing Festival, Dragon Boat Festival, etc). I used the famous 'Easter algorithm' for Good Friday, Easter Monday, Ascension Day, and Whit Monday calculations; however, I don't understand it well enough to adapt it for the Chinese calendar.
I have found similar questions, but they often go from Gregorian to Chinese:
Calculating lunar/lunisolar holidays in python
http://www.herongyang.com/year/program.html
http://www.hermetic.ch/cal_stud/ch_year.htm
The last link was exremely helpful but I'm still not sure how to implement that algorithm in a way that can help me. Any advice or code would be greatly appreciated!
Here is my Good Friday Algorithm:
private void GetGoodFridayOccurances(DateTime startDate, DateTime endDate, List<ObservedHoliday> observedHolidays, StandardHoliday holiday)
{
for (DateTime date = startDate; date <= endDate; date = date.AddYears(1))
{
#region Finding the Day of Easter Algorithm
int day, month;
int firstTwo = date.Year / 100;
int remainderMod = date.Year % 19;
int pfmDate = (firstTwo - 15) / 2 + 202 - 11 * remainderMod;
#region switches
switch (firstTwo)
{
case 21:
case 24:
case 25:
case 27:
case 28:
case 29:
case 30:
case 31:
case 32:
case 34:
case 35:
case 38:
pfmDate = pfmDate - 1;
break;
case 33:
case 36:
case 37:
case 39:
case 40:
pfmDate = pfmDate - 2;
break;
}
#endregion
pfmDate = pfmDate % 30;
int tA = pfmDate + 21;
if (pfmDate == 29)
tA = tA - 1;
if (pfmDate == 29 && remainderMod > 10)
tA = tA - 1;
//Find next sunday
int tB = (tA - 19) % 7;
int tC = (40 - firstTwo) % 4;
if (tC == 3 || tC > 1)
tC = tC + 1;
pfmDate = date.Year % 100;
int tD = (pfmDate + pfmDate / 4) % 7;
int tE = ((20 - tB - tC - tD) % 7) + 1;
day = tA + tE;
if (day > 31)
{
day = day - 31;
month = 4;
}
else
{
month = 3;
}
#endregion
DateTime observed = new DateTime(date.Year, month, day).AddDays(-2);
ObservedHoliday obsdate = new ObservedHoliday(holiday);
if (startDate == endDate && startDate.Day == observed.Day)
{
obsdate.DateObserved = observed;
observedHolidays.Add(obsdate);
}
else if (startDate != endDate && observed >= startDate)
{
obsdate.DateObserved = observed;
observedHolidays.Add(obsdate);
}
}
For Chinese New Year, I think this would work:
using System;
using System.Globalization;
public static ( Int32 year, Int32 month, Int32 day ) GetDateOfChineseNewYear()
{
ChineseLunisolarCalendar chinese = new ChineseLunisolarCalendar();
GregorianCalendar gregorian = new GregorianCalendar();
DateTime utcNow = DateTime.UtcNow;
// Get Chinese New Year of current UTC date/time
DateTime chineseNewYear = chinese.ToDateTime( utcNow.Year, 1, 1, 0, 0, 0, 0 );
// Convert back to Gregorian (you could just query properties of `chineseNewYear` directly, but I prefer to use `GregorianCalendar` for consistency:
Int32 year = gregorian.GetYear( chineseNewYear );
Int32 month = gregorian.GetMonth( chineseNewYear );
Int32 day = gregorian.GetDayOfMonth( chineseNewYear );
return ( year, month, day );
}
Now that .NET 6 (finally) has the DateOnly type (after we've been asking for it for 20 years now...), this works:
(Unfortunately .NET 6's Calendar class hasn't yet been updated to support DateOnly, but it's straightforward to handle manually):
private static readonly ChineseLunisolarCalendar _chineseCal = new ChineseLunisolarCalendar();
private static readonly GregorianCalendar _gregorianCal = new GregorianCalendar();
public static DateOnly GetGregorianDateOfChineseNewYear()
{
return GetGregorianDateOfChineseNewYear( DateTime.UtcNow.Year );
}
public static DateOnly GetGregorianDateOfChineseNewYear( Int32 gregorianYear )
{
// Get Chinese New Year of current UTC date/time
DateTime chineseNewYear = _chineseCal.ToDateTime( year: gregorianYear, month: 1, day: 1, /*hms:*/ 0, 0, 0, 0 );
// Convert back to Gregorian (you could just query properties of `chineseNewYear` directly, but I prefer to use `GregorianCalendar` for consistency:
Int32 year = _gregorianCal.GetYear( chineseNewYear );
Int32 month = _gregorianCal.GetMonth( chineseNewYear );
Int32 day = _gregorianCal.GetDayOfMonth( chineseNewYear );
return new DateOnly( year, month, day, _gregorianCal );
}
So running this...
Console.WriteLine( "Gregorian year: {0}, Chinese New Year: {1:ddd} {1}", 2021, GetGregorianDateOfChineseNewYear( 2021 ) );
Console.WriteLine();
Console.WriteLine( "Next 10 years:" );
for( Int32 i = 2022; i < 2030; i++ )
{
Console.WriteLine( "Gregorian year: {0}, Chinese New Year: {1:ddd} {1}", i, GetGregorianDateOfChineseNewYear( i ) );
}
...gives me this output:
Gregorian year: 2021, Chinese New Year: Sat 2021-02-12 Next 10 years: Gregorian year: 2022, Chinese New Year: Tue 2022-02-01 Gregorian year: 2023, Chinese New Year: Sun 2023-01-22 Gregorian year: 2024, Chinese New Year: Sat 2024-02-10 Gregorian year: 2025, Chinese New Year: Wed 2025-01-29 Gregorian year: 2026, Chinese New Year: Tue 2026-02-17 Gregorian year: 2027, Chinese New Year: Sat 2027-02-06 Gregorian year: 2028, Chinese New Year: Wed 2028-01-26 Gregorian year: 2029, Chinese New Year: Tue 2029-02-13 Gregorian year: 2030, Chinese New Year: Sun 2030-02-03 Gregorian year: 2031, Chinese New Year: Thu 2031-01-23