доделаны классы, потом проверю

Confectionery/ConfectioneryFileImplement/DataFileSingleton.cs

@@ -5,6 +5,7 @@ using System.Text;
 using System.Threading.Tasks;
 using ConfectioneryFileImplement.Models;
 using System.Xml.Linq;
+using ConfectioneryDatabaseImplement;
 
 namespace ConfectioneryFileImplement
 {
@@ -16,11 +17,13 @@ namespace ConfectioneryFileImplement
         private readonly string PastryFileName = "Pastry.xml";
         private readonly string ClientFileName = "Client.xml";
 		private readonly string ImplementerFileName = "Implementer.xml";
+		private readonly string MessageInfoFileName = "MessageInfo.xml";
 		public List<Component> Components { get; private set; }
         public List<Order> Orders { get; private set; }
         public List<Pastry> Pastrys { get; private set; }
         public List<Client> Clients { get; private set; }
 		public List<Implementer> Implementers { get; private set; }
+		public List<MessageInfo> Messages { get; private set; }
 		public static DataFileSingleton GetInstance()
         {
             if (instance == null)
@@ -39,6 +42,8 @@ namespace ConfectioneryFileImplement
         "Clients", x => x.GetXElement);
 		public void SaveImplementers() => SaveData(Implementers, ImplementerFileName, 
         "Implementers", x => x.GetXElement);
+		public void SaveMessages() => SaveData(Orders, ImplementerFileName, 
+        "Messages", x => x.GetXElement);
 		private DataFileSingleton()
         {
             Components = LoadData(ComponentFileName, "Component", x => Component.Create(x)!)!;
@@ -46,6 +51,7 @@ namespace ConfectioneryFileImplement
             Orders = LoadData(OrderFileName, "Order", x => Order.Create(x)!)!;
             Clients = LoadData(ClientFileName, "Client", x => Client.Create(x)!)!;
 			Implementers = LoadData(ImplementerFileName, "Implementer", x => Implementer.Create(x)!)!;
+			Messages = LoadData(MessageInfoFileName, "MessageInfo", x => MessageInfo.Create(x)!)!;
 		}
         private static List<T>? LoadData<T>(string filename, string xmlNodeName, Func<XElement, T> selectFunction)
         {

Confectionery/ConfectioneryFileImplement/MessageInfoStorage.cs

@@ -0,0 +1,58 @@
+using ConfectioneryContracts.BindingModels;
+using ConfectioneryContracts.SearchModels;
+using ConfectioneryContracts.StoragesContracts;
+using ConfectioneryContracts.ViewModels;
+using ConfectioneryDatabaseImplement;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace ConfectioneryFileImplement
+{
+	public class MessageInfoStorage : IMessageInfoStorage
+	{
+		private readonly DataFileSingleton _source;
+		public MessageInfoStorage()
+		{
+			_source = DataFileSingleton.GetInstance();
+		}
+
+		public MessageInfoViewModel? GetElement(MessageInfoSearchModel model)
+		{
+			if (model.MessageId != null)
+			{
+				return _source.Messages.FirstOrDefault(x => x.MessageId == model.MessageId)?.GetViewModel;
+			}
+			return null;
+		}
+
+		public List<MessageInfoViewModel> GetFilteredList(MessageInfoSearchModel model)
+		{
+			return _source.Messages
+				.Where(x => x.ClientId == model.ClientId)
+				.Select(x => x.GetViewModel)
+				.ToList();
+		}
+
+		public List<MessageInfoViewModel> GetFullList()
+		{
+			return _source.Messages
+				.Select(x => x.GetViewModel)
+				.ToList();
+		}
+
+		public MessageInfoViewModel? Insert(MessageInfoBindingModel model)
+		{
+			var newMessage = MessageInfo.Create(model);
+			if (newMessage == null)
+			{
+				return null;
+			}
+			_source.Messages.Add(newMessage);
+			_source.SaveMessages();
+			return newMessage.GetViewModel;
+		}
+	}
+}

Confectionery/ConfectioneryListImplement/DataListSingleton.cs

@@ -15,6 +15,7 @@ namespace ConfectioneryListImplement
         public List<Pastry> Pastrys { get; set; }
         public List<Client> Clients { get; set; }
 		public List<Implementer> Implementers { get; set; }
+		public List<MessageInfo> Messages { get; set; }
 		private DataListSingleton()
         {
             Components = new List<Component>();
@@ -22,6 +23,7 @@ namespace ConfectioneryListImplement
             Pastrys = new List<Pastry>();
             Clients = new List<Client>();
 			Implementers = new List<Implementer>();
+			Messages = new List<MessageInfo>();
 		}
         public static DataListSingleton GetInstance()
         {

Confectionery/ConfectioneryListImplement/MessageInfo.cs

@@ -0,0 +1,53 @@
+using ConfectioneryContracts.BindingModels;
+using ConfectioneryContracts.ViewModels;
+using ConfectioneryDataModels.Models;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace ConfectioneryListImplement.Models
+{
+	public class MessageInfo : IMessageInfoModel
+	{
+		public string MessageId { get; private set; } = string.Empty;
+
+		public int? ClientId { get; private set; }
+
+		public string SenderName { get; private set; } = string.Empty;
+
+		public DateTime DateDelivery { get; private set; } = DateTime.Now;
+
+		public string Subject { get; private set; } = string.Empty;
+
+		public string Body { get; private set; } = string.Empty;
+
+		public static MessageInfo? Create(MessageInfoBindingModel model)
+		{
+			if (model == null)
+			{
+				return null;
+			}
+			return new()
+			{
+				Body = model.Body,
+				Subject = model.Subject,
+				ClientId = model.ClientId,
+				MessageId = model.MessageId,
+				SenderName = model.SenderName,
+				DateDelivery = model.DateDelivery,
+			};
+		}
+
+		public MessageInfoViewModel GetViewModel => new()
+		{
+			Body = Body,
+			Subject = Subject,
+			ClientId = ClientId,
+			MessageId = MessageId,
+			SenderName = SenderName,
+			DateDelivery = DateDelivery,
+		};
+	}
+}

Confectionery/ConfectioneryListImplement/MessageInfoStorage.cs

@@ -0,0 +1,68 @@
+using ConfectioneryContracts.BindingModels;
+using ConfectioneryContracts.SearchModels;
+using ConfectioneryContracts.StoragesContracts;
+using ConfectioneryContracts.ViewModels;
+using ConfectioneryListImplement.Models;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace ConfectioneryListImplement.Implements
+{
+	public class MessageInfoStorage : IMessageInfoStorage
+	{
+		private readonly DataListSingleton _source;
+		public MessageInfoStorage()
+		{
+			_source = DataListSingleton.GetInstance();
+		}
+
+		public List<MessageInfoViewModel> GetFullList()
+		{
+			List<MessageInfoViewModel> result = new();
+			foreach (var item in _source.Messages)
+			{
+				result.Add(item.GetViewModel);
+			}
+			return result;
+		}
+
+		public List<MessageInfoViewModel> GetFilteredList(MessageInfoSearchModel model)
+		{
+			List<MessageInfoViewModel> result = new();
+			foreach (var item in _source.Messages)
+			{
+				if (item.ClientId.HasValue && item.ClientId == model.ClientId)
+				{
+					result.Add(item.GetViewModel);
+				}
+			}
+			return result;
+		}
+
+		public MessageInfoViewModel? GetElement(MessageInfoSearchModel model)
+		{
+			foreach (var message in _source.Messages)
+			{
+				if (model.MessageId != null && model.MessageId.Equals(message.MessageId))
+				{
+					return message.GetViewModel;
+				}
+			}
+			return null;
+		}
+
+		public MessageInfoViewModel? Insert(MessageInfoBindingModel model)
+		{
+			var newMessage = MessageInfo.Create(model);
+			if (newMessage == null)
+			{
+				return null;
+			}
+			_source.Messages.Add(newMessage);
+			return newMessage.GetViewModel;
+		}
+	}
+}