Authorisation

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace RoleBasedAuthorizationWithAttributes
{
    // Define User and Role classes
    public class User
    {
        public string Username { get; set; }
        public string Password { get; set; } // Simplified for example purposes
        public List<string> Roles { get; set; } = new List<string>();
    }

    public class Role
    {
        public string RoleName { get; set; }
    }

    // User store with predefined users and roles
    public static class UserStore
    {
        public static List<User> Users = new List<User>
        {
            new User { Username = "admin", Password = "admin", Roles = new List<string> { "Admin" } },
            new User { Username = "editor", Password = "editor", Roles = new List<string> { "Editor" } },
            new User { Username = "viewer", Password = "viewer", Roles = new List<string> { "Viewer" } }
        };

        public static User Authenticate(string username, string password)
        {
            return Users.FirstOrDefault(u => u.Username == username && u.Password == password);
        }
    }

    // Define custom attribute for role-based access control
    [AttributeUsage(AttributeTargets.Method, Inherited = false, AllowMultiple = false)]
    sealed class RequiresRoleAttribute : Attribute
    {
        public string Role { get; }

        public RequiresRoleAttribute(string role) => Role = role;
    }

    // CRUD Operations class with role-based attributes
    public class CrudOperations
    {
        [RequiresRole("Admin")]
        public void Create(User user)
        {
            Console.WriteLine("Create operation successful.");
        }

        [RequiresRole("Viewer")]
        public void Read(User user)
        {
            Console.WriteLine("Read operation successful.");
        }

        [RequiresRole("Editor")]
        public void Update(User user)
        {
            Console.WriteLine("Update operation successful.");
        }

        [RequiresRole("Admin")]
        public void Delete(User user)
        {
            Console.WriteLine("Delete operation successful.");
        }
    }

    // Authorization logic to check role attributes
    public static class Authorization
    {
        public static bool HasRequiredRole(User user, MethodInfo method)
        {
            var attribute = method.GetCustomAttribute<RequiresRoleAttribute>();
            if (attribute == null) return true; // No attribute means no restriction
            return user.Roles.Contains(attribute.Role);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Enter username:");
            var username = Console.ReadLine();
            Console.WriteLine("Enter password:");
            var password = Console.ReadLine();

            var user = UserStore.Authenticate(username, password);

            if (user == null)
            {
                Console.WriteLine("Authentication failed. Exiting...");
                return;
            }

            Console.WriteLine($"Welcome {user.Username}! Your roles: {string.Join(", ", user.Roles)}");

            var operations = new CrudOperations();

            while (true)
            {
                Console.WriteLine("\nSelect operation: 1-Create, 2-Read, 3-Update, 4-Delete, 5-Exit");
                var choice = Console.ReadLine();

                switch (choice)
                {
                    case "1":
                        ExecuteOperation(operations, nameof(CrudOperations.Create), user);
                        break;
                    case "2":
                        ExecuteOperation(operations, nameof(CrudOperations.Read), user);
                        break;
                    case "3":
                        ExecuteOperation(operations, nameof(CrudOperations.Update), user);
                        break;
                    case "4":
                        ExecuteOperation(operations, nameof(CrudOperations.Delete), user);
                        break;
                    case "5":
                        return;
                    default:
                        Console.WriteLine("Invalid choice. Please try again.");
                        break;
                }
            }
        }

        static void ExecuteOperation(object operations, string methodName, User user)
        {
            var method = operations.GetType().GetMethod(methodName);
            if (method != null && Authorization.HasRequiredRole(user, method))
            {
                method.Invoke(operations, new object[] { user });
            }
            else
            {
                Console.WriteLine("Access denied. You do not have the required role for this operation.");
            }
        }
    }
}