public static DateTime GetRelativeDate(DateTime date, int delta, TimeUnit unit)
{
switch (unit)
{
case TimeUnit.Day:
return(date.Add(new TimeSpan(1 * delta, 0, 0, 0)));
case TimeUnit.Week:
return(date.Add(new TimeSpan(7 * delta, 0, 0, 0)));
case TimeUnit.Month:
int monthIndex0 = date.Month - 1;
monthIndex0 += delta;
int year = date.Year;
//Ensure within 0-11 range, and in/decrement year accordingly
while (monthIndex0 < 0)
{
--year;
monthIndex0 += 12;
}
while (monthIndex0 > 11)
{
++year;
monthIndex0 -= 12;
}
//Add one to year to get back to range 1-12
return(new DateTime(year, monthIndex0 + 1, date.Day));
case TimeUnit.Year:
return(new DateTime(date.Year + delta, date.Month, date.Day));
default:
throw new ArgumentOutOfRangeException("Cannot get relative date for this type of time unit: " + unit.Humanize());
}
}