I am resurrecting this post because today I had to find a way to exclude not only Saturday and Sunday weekdays but also holidays. More specifically, I needed to handle various sets of possible holidays, including:
- country-invariant holidays (at least for the Western countries - such as January, 01).
- calculated holidays (such as Easter and Easter monday).
- country-specific holidays (such as the Italian liberation day or the United States ID4).
- town-specific holidays (such as the Rome St. Patron Day).
- any other custom-made holiday (such as "tomorrow our office wil be closed").
Eventually, I came out with the following set of helper/extensions classes: although they aren't blatantly elegant, as they do make a massive use of unefficient loops, they are decent enough to solve my issues for good. I'm dropping the whole source code here in this post, hoping it will be useful to someone else as well.
Source code
/// <summary>
/// Helper/extension class for manipulating date and time values.
/// </summary>
public static class DateTimeExtensions
{
/// <summary>
/// Calculates the absolute year difference between two dates.
/// </summary>
/// <param name="dt1"></param>
/// <param name="dt2"></param>
/// <returns>A whole number representing the number of full years between the specified dates.</returns>
public static int Years(DateTime dt1,DateTime dt2)
{
return Months(dt1,dt2)/12;
//if (dt2<dt1)
//{
// DateTime dt0=dt1;
// dt1=dt2;
// dt2=dt0;
//}
//int diff=dt2.Year-dt1.Year;
//int m1=dt1.Month;
//int m2=dt2.Month;
//if (m2>m1) return diff;
//if (m2==m1 && dt2.Day>=dt1.Day) return diff;
//return (diff-1);
}
/// <summary>
/// Calculates the absolute year difference between two dates.
/// Alternative, stand-alone version (without other DateTimeUtil dependency nesting required)
/// </summary>
/// <param name="start"></param>
/// <param name="end"></param>
/// <returns></returns>
public static int Years2(DateTime start, DateTime end)
{
return (end.Year - start.Year - 1) +
(((end.Month > start.Month) ||
((end.Month == start.Month) && (end.Day >= start.Day))) ? 1 : 0);
}
/// <summary>
/// Calculates the absolute month difference between two dates.
/// </summary>
/// <param name="dt1"></param>
/// <param name="dt2"></param>
/// <returns>A whole number representing the number of full months between the specified dates.</returns>
public static int Months(DateTime dt1,DateTime dt2)
{
if (dt2<dt1)
{
DateTime dt0=dt1;
dt1=dt2;
dt2=dt0;
}
dt2=dt2.AddDays(-(dt1.Day-1));
return (dt2.Year-dt1.Year)*12+(dt2.Month-dt1.Month);
}
/// <summary>
/// Returns the higher of the two date time values.
/// </summary>
/// <param name="dt1">The first of the two <c>DateTime</c> values to compare.</param>
/// <param name="dt2">The second of the two <c>DateTime</c> values to compare.</param>
/// <returns><c>dt1</c> or <c>dt2</c>, whichever is higher.</returns>
public static DateTime Max(DateTime dt1,DateTime dt2)
{
return (dt2>dt1?dt2:dt1);
}
/// <summary>
/// Returns the lower of the two date time values.
/// </summary>
/// <param name="dt1">The first of the two <c>DateTime</c> values to compare.</param>
/// <param name="dt2">The second of the two <c>DateTime</c> values to compare.</param>
/// <returns><c>dt1</c> or <c>dt2</c>, whichever is lower.</returns>
public static DateTime Min(DateTime dt1,DateTime dt2)
{
return (dt2<dt1?dt2:dt1);
}
/// <summary>
/// Adds the given number of business days to the <see cref="DateTime"/>.
/// </summary>
/// <param name="current">The date to be changed.</param>
/// <param name="days">Number of business days to be added.</param>
/// <param name="holidays">An optional list of holiday (non-business) days to consider.</param>
/// <returns>A <see cref="DateTime"/> increased by a given number of business days.</returns>
public static DateTime AddBusinessDays(
this DateTime current,
int days,
IEnumerable<DateTime> holidays = null)
{
var sign = Math.Sign(days);
var unsignedDays = Math.Abs(days);
for (var i = 0; i < unsignedDays; i++)
{
do
{
current = current.AddDays(sign);
}
while (current.DayOfWeek == DayOfWeek.Saturday
|| current.DayOfWeek == DayOfWeek.Sunday
|| (holidays != null && holidays.Contains(current.Date))
);
}
return current;
}
/// <summary>
/// Subtracts the given number of business days to the <see cref="DateTime"/>.
/// </summary>
/// <param name="current">The date to be changed.</param>
/// <param name="days">Number of business days to be subtracted.</param>
/// <param name="holidays">An optional list of holiday (non-business) days to consider.</param>
/// <returns>A <see cref="DateTime"/> increased by a given number of business days.</returns>
public static DateTime SubtractBusinessDays(
this DateTime current,
int days,
IEnumerable<DateTime> holidays)
{
return AddBusinessDays(current, -days, holidays);
}
/// <summary>
/// Retrieves the number of business days from two dates
/// </summary>
/// <param name="startDate">The inclusive start date</param>
/// <param name="endDate">The inclusive end date</param>
/// <param name="holidays">An optional list of holiday (non-business) days to consider.</param>
/// <returns></returns>
public static int GetBusinessDays(
this DateTime startDate,
DateTime endDate,
IEnumerable<DateTime> holidays)
{
if (startDate > endDate)
throw new NotSupportedException("ERROR: [startDate] cannot be greater than [endDate].");
int cnt = 0;
for (var current = startDate; current < endDate; current = current.AddDays(1))
{
if (current.DayOfWeek == DayOfWeek.Saturday
|| current.DayOfWeek == DayOfWeek.Sunday
|| (holidays != null && holidays.Contains(current.Date))
)
{
// skip holiday
}
else cnt++;
}
return cnt;
}
/// <summary>
/// Calculate Easter Sunday for any given year.
/// src.: https://stackoverflow.com/a/2510411/1233379
/// </summary>
/// <param name="year">The year to calcolate Easter against.</param>
/// <returns>a DateTime object containing the Easter month and day for the given year</returns>
public static DateTime GetEasterSunday(int year)
{
int day = 0;
int month = 0;
int g = year % 19;
int c = year / 100;
int h = (c - (int)(c / 4) - (int)((8 * c + 13) / 25) + 19 * g + 15) % 30;
int i = h - (int)(h / 28) * (1 - (int)(h / 28) * (int)(29 / (h + 1)) * (int)((21 - g) / 11));
day = i - ((year + (int)(year / 4) + i + 2 - c + (int)(c / 4)) % 7) + 28;
month = 3;
if (day > 31)
{
month++;
day -= 31;
}
return new DateTime(year, month, day);
}
/// <summary>
/// Retrieve holidays for given years
/// </summary>
/// <param name="years">an array of years to retrieve the holidays</param>
/// <param name="countryCode">a country two letter ISO (ex.: "IT") to add the holidays specific for that country</param>
/// <param name="cityName">a city name to add the holidays specific for that city</param>
/// <returns></returns>
public static IEnumerable<DateTime> GetHolidays(IEnumerable<int> years, string countryCode = null, string cityName = null)
{
var lst = new List<DateTime>();
foreach (var year in years.Distinct())
{
lst.AddRange(new[] {
new DateTime(year, 1, 1), // 1 gennaio (capodanno)
new DateTime(year, 1, 6), // 6 gennaio (epifania)
new DateTime(year, 5, 1), // 1 maggio (lavoro)
new DateTime(year, 8, 15), // 15 agosto (ferragosto)
new DateTime(year, 11, 1), // 1 novembre (ognissanti)
new DateTime(year, 12, 8), // 8 dicembre (immacolata concezione)
new DateTime(year, 12, 25), // 25 dicembre (natale)
new DateTime(year, 12, 26) // 26 dicembre (s. stefano)
});
// add easter sunday (pasqua) and monday (pasquetta)
var easterDate = GetEasterSunday(year);
lst.Add(easterDate);
lst.Add(easterDate.AddDays(1));
// country-specific holidays
if (!String.IsNullOrEmpty(countryCode))
{
switch (countryCode.ToUpper())
{
case "IT":
lst.Add(new DateTime(year, 4, 25)); // 25 aprile (liberazione)
break;
case "US":
lst.Add(new DateTime(year, 7, 4)); // 4 luglio (Independence Day)
break;
// todo: add other countries
case default:
// unsupported country: do nothing
break;
}
}
// city-specific holidays
if (!String.IsNullOrEmpty(cityName))
{
switch (cityName)
{
case "Rome":
case "Roma":
lst.Add(new DateTime(year, 6, 29)); // 29 giugno (s. pietro e paolo)
break;
case "Milano":
case "Milan":
lst.Add(new DateTime(year, 12, 7)); // 7 dicembre (s. ambrogio)
break;
// todo: add other cities
default:
// unsupported city: do nothing
break;
}
}
}
return lst;
}
}
Usage info
The code is quite self-explanatory, however here's a couple examples to explain how you can use it.
Add 10 business days (skipping only saturday and sunday week days)
var dtResult = DateTimeUtil.AddBusinessDays(srcDate, 10);
Add 10 business days (skipping saturday, sunday and all country-invariant holidays for 2019)
var dtResult = DateTimeUtil.AddBusinessDays(srcDate, 10, GetHolidays(2019));
Add 10 business days (skipping saturday, sunday and all italian holidays for 2019)
var dtResult = DateTimeUtil.AddBusinessDays(srcDate, 10, GetHolidays(2019, "IT"));
Add 10 business days (skipping saturday, sunday, all italian holidays and the Rome-specific holidays for 2019)
var dtResult = DateTimeUtil.AddBusinessDays(srcDate, 10, GetHolidays(2019, "IT", "Rome"));
The above functions and code examples are further explained in this post of my blog.
