using FileImplements.Models;
using System.Xml.Linq;

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

		private readonly string KeyFileName = "Key.xml";
		private readonly string CertFileName = "Cert.xml";
		public List<Key> Keys { get; private set; }
		public List<Cert> Certs { get; private set; }
		public static DataFileSingleton GetInstance()
		{
			if (instance == null)
			{
				instance = new DataFileSingleton();
			}
			return instance;
		}
		public void SaveKeys() => SaveData(Keys, KeyFileName, "Keys", x => x.GetXElement);
		public void SaveCerts() => SaveData(Certs, CertFileName, "Certs", x => x.GetXElement);
		private DataFileSingleton()
		{
			Keys = LoadData(KeyFileName, "Keys", x => Key.Create(x)!)!;
			Certs = LoadData(CertFileName, "Certs", x => Cert.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);
			}
		}
	}
}