PIbd-21_Yaruskin_S.A_MotorPlant/MotorPlant/MotorPlantFileImplement/DataFileSingleton.cs

using MotorPlantFileImplement.Models;
using System.Xml.Linq;

namespace MotorPlantFileImplement
{
    public class DataFileSingleton
    {
        private static DataFileSingleton? instance;

        private readonly string ComponentFileName = "Component.xml";

        private readonly string OrderFileName = "Order.xml";

        private readonly string EngineFileName = "Engine.xml";

		private readonly string ClientFileName = "Client.xml";

		public List<Component> Components { get; private set; }

        public List<Order> Orders { get; private set; }

        public List<Engine> Engines { get; private set; }

		public List<Client> Clients { get; private set; }

		public static DataFileSingleton GetInstance()
        {
            if (instance == null)
            {
                instance = new DataFileSingleton();
            }
            return instance;
        }
        public void SaveComponents() => SaveData(Components, ComponentFileName, "Components", x => x.GetXElement);

        public void SaveEngines() => SaveData(Engines, EngineFileName, "Engines", x => x.GetXElement);

        public void SaveOrders() => SaveData(Orders, OrderFileName, "Orders", x => x.GetXElement);

		public void SaveClients() => SaveData(Clients, ClientFileName, "Clients", x => x.GetXElement);

		private DataFileSingleton()
        {
            Components = LoadData(ComponentFileName, "Component", x => Component.Create(x)!)!;
            Engines = LoadData(EngineFileName, "Engine", x => Engine.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);
            }
        }
    }
}