Add Lesson 4 Task 3

Lesson_4/Task_3/IWorkingWithFile.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LiskovSubstitution
+{
+    public interface IWorkingWithFile
+    {
+        public string ReadFromFile(string filename);
+        public void WriteToFile(string filename);
+        public void DeleteFile(string filename);
+        public void DownloadFile(string filename);
+        public void CopyFile(string filename);
+        public void GetDataFromFile(string filename);
+        public void CheckFile(string filename);
+        public void SaveToFile(string filename);
+        public Guid CheckRole(Guid role);
+        public Guid CheckUser(Guid user);
+    }
+}

Lesson_4/Task_3/Program.cs

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+using LiskovSubstitution;
+
+(new User()).SaveToFile("test");
+
+(new Administrator()).SaveToFile("test");

Lesson_4/Task_3/Task_3.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

Lesson_4/Task_3/WorkingWithFile.cs

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+namespace LiskovSubstitution
+{
+    public class User : IWorkingWithFile
+    {
+        public virtual Guid Role { get; } = new Guid("a65d9c1d-b8a9-4f4f-be9b-ab03856f33f4");
+
+        public string ReadFromFile(string filename)
+        {
+            return filename;
+        }
+
+        public void WriteToFile(string filename)
+        {
+            Console.WriteLine("Access denied.");
+        }
+
+        public void DeleteFile(string filename)
+        {
+            Console.WriteLine("Access denied.");
+        }
+        
+        public void DownloadFile(string filename)
+        {
+            Console.WriteLine("Downloaded the file.");
+        }
+
+        public void CopyFile(string filename)
+        {
+            Console.WriteLine("Access denied.");
+        }
+        
+        public void GetDataFromFile(string filename)
+        {
+            Console.WriteLine("Got data from the file.");
+        }
+        
+        public void CheckFile(string filename)
+        {
+            Console.WriteLine("Checked the file.");
+        }
+
+        public void SaveToFile(string filename)
+        {
+            Console.WriteLine("Access denied.");
+        }
+
+        public Guid CheckRole(Guid role)
+        {
+            return new Guid("00000000-0000-0000-0000-000000000000");
+        }
+        
+        public Guid CheckUser(Guid user)
+        {
+            return new Guid("00000000-0000-0000-0000-000000000000");
+        }
+    }
+
+    public class Administrator : User
+    {
+        public override Guid Role { get; } = new Guid("c1cfcc4a-e49e-4585-9ccb-265c35321b11");
+
+        public new void WriteToFile(string filename)
+        {
+            Console.WriteLine("Written to the file.");
+        }
+        
+        public new void DeleteFile(string filename)
+        {
+            Console.WriteLine("Deleted the file.");
+        }
+
+        public new void CopyFile(string filename)
+        {
+            Console.WriteLine("Copied the file.");
+        }
+
+        public new void SaveToFile(string filename)
+        {
+            Console.WriteLine("Saved to the file.");
+        }
+    }
+
+    public class Owner : User
+    {
+        public override Guid Role { get; } = new Guid("a157c9cf-c996-46d7-9905-4cd1319a451d");
+
+        public new Guid CheckRole(Guid role)
+        {
+            return role;
+        }
+        
+        public new Guid CheckUser(Guid user)
+        {
+            return user;
+        }
+    }
+}