public static StatisticResponse GetResponse(DateTime startDate, DateTime endDate)
        {
            StatisticResponse response = null;

            var suitableResponse = Items.Where(row => row.StartDate <= startDate && row.EndDate >= endDate).FirstOrDefault();

            if (suitableResponse != null)
            {
                if (suitableResponse.StartDate == startDate && suitableResponse.EndDate == endDate)
                {
                    response = suitableResponse;
                }
                else
                {
                    var items = suitableResponse.Items.Where(row => row.Date >= startDate && row.Date <= endDate).ToList();
                    response = new StatisticResponse(startDate, endDate, items);
                }
            }

            return response;
        }
 public static void AddResponse(StatisticResponse response)
 {
     Items.Add(response);
 }