ParkingValidation_DictsMoreExercises_Dim

namespace _00.Practice
{
    using System;
    using System.Collections.Generic;
    using System.Text.RegularExpressions;

    public class Program
    {
        public static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var userLicense = new Dictionary<string, string>();

            for (int i = 0; i < n; i++)
            {
                var input = Console.ReadLine().Split(' ');
                var command = input[0];
                var username = input[1];

                switch (command)
                {
                    case "register":

                        var license = input[2];

                        if (!userLicense.ContainsKey(username))
                        {
                            if (!userLicense.ContainsValue(license))
                            {

                                bool licenseIsValid = IsValid(license);

                                if (!licenseIsValid)
                                {
                                    Console.WriteLine($"ERROR: invalid license plate {license}");
                                    continue;
                                }

                                userLicense[username] = license;
                                Console.WriteLine($"{username} registered {license} successfully");
                            }
                            else
                            {
                                Console.WriteLine($"ERROR: license plate {license} is busy");
                            }
                        }
                        else
                        {
                            Console.WriteLine($"ERROR: already registered with plate number {userLicense[username]}");
                        }

                        break;

                    case "unregister":
                        if (!userLicense.ContainsKey(username))
                        {
                            Console.WriteLine($"ERROR: user {username} not found");
                        }
                        else
                        {
                            userLicense.Remove(username);
                            Console.WriteLine($"user {username} unregistered successfully");
                        }

                        break;
                }
            }

            foreach (var pair in userLicense)
            {
                Console.WriteLine($"{pair.Key} => {pair.Value}");
            }
        }

        private static bool IsValid(string license)
        {
            string pattern = "([A-Z]{2})([0-9]{4})([A-Z]{2})";
            Regex regex = new Regex(pattern);
            Match match = regex.Match(license);
            return match.Success;
        }
    }
}