using ConfectioneryFileImplement.Models;
using System.Xml.Linq;
namespace ConfectioneryFileImplement
{
    internal class DataFileSingleton
    {
        private static DataFileSingleton? instance;
        private readonly string ComponentFileName = "Component.xml";
        private readonly string OrderFileName = "Order.xml";
        private readonly string PastryFileName = "Pastry.xml";
        public List<Component> Components { get; private set; }
        public List<Order> Orders { get; private set; }
        public List<Pastry> Pastries { 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 SavePastries() => SaveData(Pastries, PastryFileName,
            "Pastries", x => x.GetXElement);
        public void SaveOrders() => SaveData(Orders, OrderFileName, "Orders",
            x => x.GetXElement);
        private DataFileSingleton()
        {
            Components = LoadData(ComponentFileName, "Component",
                x => Component.Create(x)!)!;
            Pastries = LoadData(PastryFileName, "Pastry",
                x => Pastry.Create(x)!)!;
            Orders = LoadData(OrderFileName, "Order",
                x => Order.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);
            }
        }
    }
}