OfficeOpenXml.Table.PivotTable.ExcelPivotTableField.AddDateGrouping C# (CSharp) Method

        private void AddDateGrouping(eDateGroupBy groupBy, DateTime startDate, DateTime endDate, int groupInterval)
        {
            if (groupInterval < 1 || groupInterval >= Int16.MaxValue)
            {
                throw (new ArgumentOutOfRangeException("Group interval is out of range"));
            }
            if (groupInterval > 1 && groupBy != eDateGroupBy.Days)
            {
                throw (new ArgumentException("Group interval is can only be used when groupBy is Days"));
            }
            ValidateGrouping();

            bool firstField = true;
            List<ExcelPivotTableField> fields=new List<ExcelPivotTableField>();
            //Seconds
            if ((groupBy & eDateGroupBy.Seconds) == eDateGroupBy.Seconds)
            {
                fields.Add(AddField(eDateGroupBy.Seconds, startDate, endDate, ref firstField));
            }
            //Minutes
            if ((groupBy & eDateGroupBy.Minutes) == eDateGroupBy.Minutes)
            {
                fields.Add(AddField(eDateGroupBy.Minutes, startDate, endDate, ref firstField));
            }
            //Hours
            if ((groupBy & eDateGroupBy.Hours) == eDateGroupBy.Hours)
            {
                fields.Add(AddField(eDateGroupBy.Hours, startDate, endDate, ref firstField));
            }
            //Days
            if ((groupBy & eDateGroupBy.Days) == eDateGroupBy.Days)
            {
                fields.Add(AddField(eDateGroupBy.Days, startDate, endDate, ref firstField, groupInterval));
            }
            //Month
            if ((groupBy & eDateGroupBy.Months) == eDateGroupBy.Months)
            {
                fields.Add(AddField(eDateGroupBy.Months, startDate, endDate, ref firstField));
            }
            //Quarters
            if ((groupBy & eDateGroupBy.Quarters) == eDateGroupBy.Quarters)
            {
                fields.Add(AddField(eDateGroupBy.Quarters, startDate, endDate, ref firstField));
            }
            //Years
            if ((groupBy & eDateGroupBy.Years) == eDateGroupBy.Years)
            {
                fields.Add(AddField(eDateGroupBy.Years, startDate, endDate, ref firstField));
            }

            if (fields.Count > 1) _cacheFieldHelper.SetXmlNodeString("d:fieldGroup/@par", (_table.Fields.Count - 1).ToString());
            if (groupInterval != 1)
            {
                _cacheFieldHelper.SetXmlNodeString("d:fieldGroup/d:rangePr/@groupInterval", groupInterval.ToString());
            }
            else
            {
                _cacheFieldHelper.DeleteNode("d:fieldGroup/d:rangePr/@groupInterval");
            }
            _items = null;
        }