PIbd-23_Leonteva_V._A._LawFirm/LawFirm/LawFirmFileImplement/DataFileSingleton.cs

using LawFirmFileImplement.Models;
using System.Xml.Linq;

namespace LawFirmFileImplement
{
    public class DataFileSingleton
    {
        private static DataFileSingleton? instance;
        private readonly string BlankFileName = "Blank.xml";
        private readonly string OrderFileName = "Order.xml";
        private readonly string DocumentFileName = "Document.xml";
		private readonly string ClientFileName = "Client.xml";
		public List<Blank> Blanks { get; private set; }
        public List<Order> Orders { get; private set; }
        public List<Document> Documents { get; private set; }
		public List<Client> Clients { get; private set; }
		public static DataFileSingleton GetInstance()
        {
            if (instance == null)
            {
                instance = new DataFileSingleton();
            }
            return instance;
        }
        public void SaveBlanks() => SaveData(Blanks, BlankFileName, "Blanks", x => x.GetXElement);
        public void SaveDocuments() => SaveData(Documents, DocumentFileName, "Documents", x => x.GetXElement);
        public void SaveOrders() => SaveData(Orders, OrderFileName, "Orders", x => x.GetXElement);
		public void SaveClients() => SaveData(Clients, OrderFileName, "Clients", x => x.GetXElement);
		private DataFileSingleton()
        {
            Blanks = LoadData(BlankFileName, "Blank", x => Blank.Create(x)!)!;
            Documents = LoadData(DocumentFileName, "Document", x => Document.Create(x)!)!;
			Orders = LoadData(OrderFileName, "Order", x => Order.Create(x)!)!;
			Clients = LoadData(ClientFileName, "Client", x => Client.Create(x)!)!;
		}
		private static List<T>? LoadData<T>(string filename, string xmlNodeName,
            Func<XElement, T> selectFunction)
        {
            if (File.Exists(filename))
            {
                return XDocument.Load(filename)?.
                    Root?.
                    Elements(xmlNodeName)?.
                    Select(selectFunction)?.
                    ToList();
            }
            return new List<T>();
        }
        private static void SaveData<T>(List<T> data, string filename,
            string xmlNodeName, Func<T, XElement> selectFunction)
        {
            if (data != null)
            {
                new XDocument(new XElement(xmlNodeName,
                data.Select(selectFunction).ToArray())).Save(filename);
            }
        }
    }
}