Add hours to datetime but exclude weekends and should be between working hours

Question

I am trying to add hours to a date but want the new date to exclude weekends and only be between 9.00 to 17.00.

example:

first scenario:

if my date is 23/02/2012 16:00:00.
if I add 4 hours to that my new date should be 24/02/2012 12:00:00 (which will be within working hours)

second scenario:

if my date is 24/02/2012 09:00:00 (which is a friday)
if I add 24 hours then the new date should be 27/02/2012 09:00:00 (which would be monday next week at 9am)

so far I got this but am stuck as this will not count for any date that is in past say date passed was 10/02/2012(Friday last week) :

   private static void ExcludeWeekend(Datetime dt)
    {
        DateTime todaysDate = DateTime.Today;
        DateTime dueDate = null;

                if (dueDate.DayOfWeek == DayOfWeek.Friday)
                {
                    dueDate.AddHours(48);
                }
                else if (dueDate.DayOfWeek == DayOfWeek.Saturday)
                {
                    dueDate.AddHours(72);
                }
    }

Answer 1

@BlueMonkMN 's answer is great. However, I rectified a couple of issues there and now it worked perfectly for me.

Function SLARespondBy(start As DateTime, SLA As Integer) As String
    Const hoursPerDay As Integer = 12
    Const startHour As Integer = 7

    Dim isWholeDayNeeded As Boolean = True
    If start.AddMinutes(SLA).TimeOfDay = TimeSpan.FromHours(19) Then
        isWholeDayNeeded = False
    End If

    Dim offset As TimeSpan = TimeSpan.FromMinutes(SLA)

    ' Don't start counting hours until start time is during working hours
    If start.TimeOfDay.TotalHours > startHour + hoursPerDay Then
        start = start.Date.AddDays(1).AddHours(startHour)
    End If
    If start.TimeOfDay.TotalHours < startHour Then
        start = start.Date.AddHours(startHour)
    End If
    If start.DayOfWeek = DayOfWeek.Saturday Then
        start = start.AddDays(2) ' Move to Monday
        start = New DateTime(start.Year, start.Month, start.Day, 7, 0, 0) ' Set time to 7:00 AM
    ElseIf start.DayOfWeek = DayOfWeek.Sunday Then
        start = start.AddDays(1) ' Move to Monday
        start = New DateTime(start.Year, start.Month, start.Day, 7, 0, 0) ' Set time to 7:00 AM
    End If

    ' Calculate how much working time already passed on the first day
    Dim firstDayOffset As TimeSpan = start.TimeOfDay.Subtract(TimeSpan.FromHours(startHour))

    ' Calculate number of whole days to add
    Dim wholeDays As Integer = 0
    If isWholeDayNeeded Then
        wholeDays = CInt(Math.Truncate(offset.Add(firstDayOffset).TotalHours / hoursPerDay))
    End If

    ' How many hours off the specified offset does this many whole days consume?
    Dim wholeDaysHours As TimeSpan = TimeSpan.FromHours(wholeDays * hoursPerDay)

    ' Calculate the final time of day based on the number of whole days spanned and the specified offset
    Dim remainder As TimeSpan = offset - wholeDaysHours

    ' How far into the week is the starting date?
    Dim weekOffset As Integer = ((CInt(start.DayOfWeek) + 7) - CInt(DayOfWeek.Monday)) Mod 7

    ' How many weekends are spanned?
    Dim weekends As Integer = CInt(Math.Truncate((wholeDays + weekOffset) / 5))

    ' Calculate the final result using all the above calculated values
    Dim finalDateTime As DateTime = start.AddDays(wholeDays + weekends * 2).Add(remainder)
    '
    Return finalDateTime.ToString("MM/dd/yyyy h:mm tt")
End Function

Answer 2

Not an elegant solution but it seems to work.

DateTime AddHoursIgnoreWeekend(DateTime startDate, int hours)
{
    DateTime endDate = startDate;

    for (int i = 0; i < hours; i++) {

        endDate = endDate.AddHours(1);

        if (endDate.DayOfWeek == DayOfWeek.Saturday || endDate.DayOfWeek == DayOfWeek.Sunday) 
        {
            i--;
        }
    }

    return endDate;
 }

Answer 3

 static DateTime AddWithinWorkingHours(DateTime start, TimeSpan offset)
 {
    const int hoursPerDay = 8;
    const int startHour = 9;
    // Don't start counting hours until start time is during working hours
    if (start.TimeOfDay.TotalHours > startHour + hoursPerDay)
       start = start.Date.AddDays(1).AddHours(startHour);
    if (start.TimeOfDay.TotalHours < startHour)
       start = start.Date.AddHours(startHour);
    if (start.DayOfWeek == DayOfWeek.Saturday)
       start.AddDays(2);
    else if (start.DayOfWeek == DayOfWeek.Sunday)
       start.AddDays(1);
    // Calculate how much working time already passed on the first day
    TimeSpan firstDayOffset = start.TimeOfDay.Subtract(TimeSpan.FromHours(startHour));
    // Calculate number of whole days to add
    int wholeDays = (int)(offset.Add(firstDayOffset).TotalHours / hoursPerDay);
    // How many hours off the specified offset does this many whole days consume?
    TimeSpan wholeDaysHours = TimeSpan.FromHours(wholeDays * hoursPerDay);
    // Calculate the final time of day based on the number of whole days spanned and the specified offset
    TimeSpan remainder = offset - wholeDaysHours;
    // How far into the week is the starting date?
    int weekOffset = ((int)(start.DayOfWeek + 7) - (int)DayOfWeek.Monday) % 7;
    // How many weekends are spanned?
    int weekends = (int)((wholeDays + weekOffset) / 5);
    // Calculate the final result using all the above calculated values
    return start.AddDays(wholeDays + weekends * 2).Add(remainder);
 }

Answer 4

You can use the class CalendarDateAdd from the Time Period Library for .NET:

// ----------------------------------------------------------------------
public void CalendarDateAddSample()
{
  CalendarDateAdd calendarDateAdd = new CalendarDateAdd();
  // use only weekdays
  calendarDateAdd.AddWorkingWeekDays();
  // setup working hours
  calendarDateAdd.WorkingHours.Add( new HourRange( new Time( 09 ), new Time( 17 ) ) );

  DateTime start = new DateTime( 2012, 2, 23 ); // start date
  TimeSpan offset = new TimeSpan( 4, 0, 0 ); // 4 hours

  DateTime? end = calendarDateAdd.Add( start, offset ); // end date

  Console.WriteLine( "start: {0}", start );
  Console.WriteLine( "offset: {0}", offset );
  Console.WriteLine( "end: {0}", end );
} // CalendarDateAddSample

Answer 5

    var d1 = DateTime.Now;
    var ts = TimeSpan.FromHours(40);
    var d2 = d1 + ts;
    if(d2.DayOfWeek == DayOfWeek.Saturday) {
        d2 = d2.AddDays(2);
    }else if(d2.DayOfWeek == DayOfWeek.Sunday){
        d2 = d2.AddDays(1);
    }

If you really want to make it an extension:

var d2 = DateTime.Now.AddSkipWeekend(TimeSpan.FromHours(40));

static class DateExtensions { 
    public static DateTime AddSkipWeekend(this DateTime date1, TimeSpan ts){
        DateTime d2 = date1 + ts;
        if(d2.DayOfWeek == DayOfWeek.Saturday) {
            d2 = d2.AddDays(2);
        } else if(d2.DayOfWeek == DayOfWeek.Sunday) {
            d2 = d2.AddDays(1);
        }
        return d2;
    }
}

Edit: Just realized your non-working-hours requirement:

var d2 = DateTime.Now.AddSkipWeekend(TimeSpan.FromHours(50),TimeSpan.FromHours(9),TimeSpan.FromHours(17));

public static DateTime AddSkipWeekend(this DateTime date1, TimeSpan addTime, TimeSpan workStart, TimeSpan workEnd)
{
    DateTime d2 = date1 + addTime;
    if(d2.TimeOfDay < workStart) {
        d2 = d2.Add(workStart - d2.TimeOfDay);
    } else if(d2.TimeOfDay > workEnd) {
        d2 = d2.Add(TimeSpan.FromHours(12) - d2.TimeOfDay);
    }
    if(d2.DayOfWeek == DayOfWeek.Saturday) {
        d2 = d2.AddDays(2);
    } else if(d2.DayOfWeek == DayOfWeek.Sunday) {
        d2 = d2.AddDays(1);
    }
    return d2;
}

Answer 6

Try this:

public static DateTime Add(DateTime dt, TimeSpan t)
{
    while (true)
    {
        dt = Max(dt, dt.Date.AddHours(9));
        DateTime x = Min(dt + t, dt.Date.AddHours(17));
        // Console.WriteLine("{0} -> {1} ({2})", dt, x, x - dt);
        t -= x - dt;
        dt = x;
        if (t == TimeSpan.Zero) { return dt; }
        do { dt = dt.Date.AddDays(1); } while (dt.IsWeekendDay());
    }
}

Helper methods from here.

Example 1:

var result = Add(DateTime.Parse("23/02/2012 16:00:00"), TimeSpan.FromHours(4));
// result == {24/02/2012 12:00:00}

23/02/2012 16:00:00 -> 23/02/2012 17:00:00 (01:00:00)
24/02/2012 09:00:00 -> 24/02/2012 12:00:00 (03:00:00)

Example 2:

var result = Add(DateTime.Parse("24/02/2012 09:00:00"), TimeSpan.FromHours(24));
// result == {28/02/2012 17:00:00}

24/02/2012 09:00:00 -> 24/02/2012 17:00:00 (08:00:00)
27/02/2012 09:00:00 -> 27/02/2012 17:00:00 (08:00:00)
28/02/2012 09:00:00 -> 28/02/2012 17:00:00 (08:00:00)