D365: Add business day(s) to specific date considering weekends and public holidays

/// <summary>
/// Get Next working date 
/// </summary>
/// <param name="service">Organisation Service</param>
/// <param name="serviceCalenderId">GUID of service calendar</param>
/// <param name="specificDate">Date to which days need to be added</param>
/// <param name="workingDaysToAdd">Number of days to be added</param>
/// <returns>Next Working Date</returns>
public static DateTime GetNextWorkingDay(IOrganizationService service, Guid serviceCalenderId, DateTime specificDate, int workingDaysToAdd)
{
	var currentDate = specificDate;
	var businessClosures = GetBusinessClosureCalendarRules(service, serviceCalenderId);

	// Calculate the working days by taking out the weekends(Fridays and Saturdays)
	int completeWeeks = workingDaysToAdd / 5;
	DateTime date = specificDate.AddDays(completeWeeks * 7);
	workingDaysToAdd = workingDaysToAdd % 5;
	for (int i = 0; i < workingDaysToAdd; i++)
	{
		date = date.AddDays(1);
		while (!IsWorkingDayOfWeek(date))
		{
			date = date.AddDays(1);
		}
	}

	// Calculate the working days by taking out public holidays
	for (var i = currentDate; i <= date; i = i.AddDays(1))
	{
		if (i.DayOfWeek == DayOfWeek.Friday || i.DayOfWeek == DayOfWeek.Saturday)
			continue;

		foreach (var closure in businessClosures)
		{
			var startDate = (DateTime)closure["effectiveintervalstart"];
			var endDate = (DateTime)closure["effectiveintervalend"];
			var range = new DateRange(startDate, endDate);

			if (range.Includes(i))
			{
				date = date.AddDays(1);
                                while (!IsWorkingDayOfWeek(date))
                                {
                                        date = date.AddDays(1);
                                }
				if (date.DayOfWeek == DayOfWeek.Friday)
				{
					date = date.AddDays(2);
                                        while (!IsWorkingDayOfWeek(date))
                                        {
                                                date = date.AddDays(1);
                                        }
					i = i.AddDays(1);
				}
				else if (date.DayOfWeek == DayOfWeek.Saturday)
				{
					date = date.AddDays(1);
                                        while (!IsWorkingDayOfWeek(date))
                                        {
                                                date = date.AddDays(1);
                                        }
				}
			}
		}
	}
	return date;
}

private static IEnumerable<Entity> GetBusinessClosureCalendarRules(IOrganizationService service, Guid serviceCalendarId)
{
	var query = new QueryExpression("calendar")
	{
		ColumnSet = new ColumnSet(true),
		Criteria = new FilterExpression()
	};

	// Add condition to get Get Calander where CalanderId is equal to Organization's businessclosurecalendarid
	query.Criteria.AddCondition(new ConditionExpression("calendarid", ConditionOperator.Equal, serviceCalendarId.ToString()));

	// Get Calendar
	var businessClosureCalendar = service.RetrieveMultiple(query).Entities[0];
	var holidaySchedule = service.Retrieve(businessClosureCalendar.GetAttributeValue<EntityReference>("holidayschedulecalendarid").LogicalName, businessClosureCalendar.GetAttributeValue<EntityReference>("holidayschedulecalendarid").Id, new ColumnSet(true));

	// Return the Calendar rules
	return businessClosureCalendar != null ? holidaySchedule.GetAttributeValue<EntityCollection>("calendarrules").Entities : null;
}

private static bool IsWorkingDayOfWeek(DateTime date)
{
	var day = date.DayOfWeek;
	return day != DayOfWeek.Friday && day != DayOfWeek.Saturday;
}

public interface IRange<T>
{
	T Start { get; }
	T End { get; }
	bool Includes(T value);
}

public class DateRange : IRange<DateTime>
{
	public DateRange(DateTime start, DateTime end)
	{
		Start = start;
		End = end;
	}

	public DateTime Start { get; private set; }
	public DateTime End { get; private set; }

	public bool Includes(DateTime value)
	{
		return (Start <= value) && (value < End);
	}
}