В процессе

PuferFishContracts/PuferFishContracts/DataModels/BuyerDataModel.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Text.RegularExpressions;
+using System.Threading.Tasks;
+using PuferFishContracts.Extensions;
+using PuferFishContracts.Exceptions;
+using PuferFishContracts.Infrastructure;
+
+namespace PuferFishContracts.DataModels
+{
+    public class BuyerDataModel(string id, string fio, string phoneNumber, double points) : IValidation
+    {
+        public string Id { get; private set; } = id;
+        public string FIO { get; private set; } = fio;
+        public string PhoneNumber { get; private set; } = phoneNumber;
+        public double Points { get; private set; } = points;
+
+        public void Validate()
+        {
+            if (Id.IsEmpty())
+                throw new ValidationException("Field Id is empty");
+
+            if (!Id.IsGuid())
+                throw new ValidationException("The value in the field Id is not a unique identifier");
+
+            if (FIO.IsEmpty())
+                throw new ValidationException("Field FIO is empty");
+
+            if (PhoneNumber.IsEmpty())
+                throw new ValidationException("Field PhoneNumber is empty");
+
+            if (!Regex.IsMatch(PhoneNumber, @"^((8|\+7)[\- ]?)?(\(?\d{3}\)?[\- ]?)?[\d\- ]{7,10}$"))
+                throw new ValidationException("Field PhoneNumber is not a phone number");
+        }
+    }
+}

PuferFishContracts/PuferFishContracts/DataModels/PostDataModel.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace PuferFishContracts.DataModels
+{
+    internal class PostDataModel
+    {
+    }
+}

PuferFishContracts/PuferFishContracts/Enums/PostType.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace PuferFishContracts.Enums
+{
+    public enum PostType
+    {
+        None = 0,
+        Cashier = 1,
+        chef = 2,
+        Packer = 3
+    }
+}

PuferFishContracts/PuferFishContracts/Exceptions/ValidationException.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace PuferFishContracts.Exceptions;
+
+public class ValidationException(string message) : Exception(message)
+{
+}

PuferFishContracts/PuferFishContracts/Extensions/StringExtensions.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace PuferFishContracts.Extensions
+{
+    public static class StringExtensions
+    {
+        public static bool IsEmpty(this string str)
+        {
+            return string.IsNullOrWhiteSpace(str);
+        }
+
+        public static bool IsGuid(this string str)
+        {
+            return Guid.TryParse(str, out var _);
+        }
+    }
+}

PuferFishContracts/PuferFishContracts/Infrastructure/IValidation.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace PuferFishContracts.Infrastructure
+{
+    public interface IValidation
+    {
+        void Validate();
+    }
+}