EPPlus/FormulaParsing/Excel/Functions/DateTime/Workdays/AdditionalHolidayDays.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using OfficeOpenXml.Utils;

namespace OfficeOpenXml.FormulaParsing.Excel.Functions.DateTime.Workdays
{
    public class AdditionalHolidayDays
    {
        private readonly FunctionArgument _holidayArg;
        private readonly List<System.DateTime> _holidayDates = new List<System.DateTime>(); 

        public AdditionalHolidayDays(FunctionArgument holidayArg)
        {
            _holidayArg = holidayArg;
            Initialize();
        }

        public IEnumerable<System.DateTime> AdditionalDates => _holidayDates;

        private void Initialize()
        {
            var holidays = _holidayArg.Value as IEnumerable<FunctionArgument>;
            if (holidays != null)
            {
                foreach (var holidayDate in from arg in holidays where ConvertUtil.IsNumeric(arg.Value) select ConvertUtil.GetValueDouble(arg.Value) into dateSerial select System.DateTime.FromOADate(dateSerial))
                {
                    _holidayDates.Add(holidayDate);
                }
            }
            var range = _holidayArg.Value as ExcelDataProvider.IRangeInfo;
            if (range != null)
            {
                foreach (var holidayDate in from cell in range where ConvertUtil.IsNumeric(cell.Value) select ConvertUtil.GetValueDouble(cell.Value) into dateSerial select System.DateTime.FromOADate(dateSerial))
                {
                    _holidayDates.Add(holidayDate);
                }
            }
            if (ConvertUtil.IsNumeric(_holidayArg.Value))
            {
                _holidayDates.Add(System.DateTime.FromOADate(ConvertUtil.GetValueDouble(_holidayArg.Value)));
            }
        }
    }
}