public static void main(String[] args) {

        try {

            if (System.getSecurityManager() == null) {
                System.setSecurityManager(new SecurityManager());
            }

            Client client = new Client();
            //System.out.println(client.serverInterface().Login());
            System.out.println("Pinging Server...." + client.serverInterface().Ping());

            int logged_in = 0;
            int exit_flag = 0;

            do {
                //not logged in
                if (logged_in == 0) {
                    Scanner scanner = new Scanner(System.in);
                    System.out.println("" +
                            "1 - Register.\n" +
                            "2 - Login.\n" +
                            "3 - Exit.");
                    try {
                        switch (Integer.parseInt(scanner.nextLine())) {
                            //Register
                            case 1:
                                int register_flag = 0;
                                do {
                                    String username;
                                    String name;
                                    String email;
                                    String password;
                                    String re_password;

                                    System.out.println("###### Register Menu #######");
                                    System.out.println("Please enter you USERNAME ");
                                    username = scanner.nextLine();
                                    System.out.println("Please enter you NAME: ");
                                    name = scanner.nextLine();
                                    System.out.println("Please enter you email (Required for login)");
                                    email = scanner.nextLine();

                                    int password_flag = 0;
                                    try {
                                        MessageDigest hash_function = MessageDigest.getInstance("SHA-256");

                                        do {

                                            System.out.println("Please enter you password: (Required for login)");
                                            hash_function.update(scanner.nextLine().getBytes());
                                            password = new String(hash_function.digest());
                                            System.out.println("Please re-enter your password: ");
                                            hash_function.update(scanner.nextLine().getBytes());
                                            re_password = new String(hash_function.digest());

                                            if (password.equals(re_password)) {
                                                password_flag = 1;
                                            } else System.out.println("Passwords do NOT match! Try again.");


                                        } while (password_flag == 0);

                                    } catch (NoSuchAlgorithmException nsa) {
                                        nsa.printStackTrace();
                                        break;
                                    }
                                    System.out.println("Is the following information correct?");
                                    System.out.println("Username ----> " + username);
                                    System.out.println("Name     ----> " + name);
                                    System.out.println("Email    ----> " + email);
                                    System.out.println("Yes(Y) / No(N)");
                                    String inf_correct = scanner.nextLine();
                                    if (inf_correct.equals("Y") || inf_correct.equals("y")) {
                                        register_flag = 1;
                                        try {
                                            client.serverInterface().Ping();

                                            if (client.serverInterface().RegisterUser(username, name, email, new String(Base64.getEncoder().encode(password.getBytes())))) {
                                                System.out.println("User registration Successful.");
                                            } else
                                                System.out.println("User could not be registered. Please try again.");

                                        } catch (RemoteException re) {
                                            System.out.println("Server is no longer reachable. Please try again later.");
                                            break;
                                        }
                                    }

                                } while (register_flag == 0);

                                break;

                            //login
                            case 2:

                                try {
                                    MessageDigest hash_function = MessageDigest.getInstance("SHA-256");

                                    System.out.println("###### Login Menu #######");
                                    System.out.println("Please enter your email:");
                                    String email = scanner.nextLine();
                                    System.out.println("Please enter your password: ");
                                    hash_function.update(scanner.nextLine().getBytes());
                                    String hashed_password = new String(hash_function.digest());
                                    SecureRandom random = new SecureRandom();
                                    int port = Math.abs(random.nextInt()%65000+1109);
                                    Remote remote = client.serverInterface().Login(email, Base64.getEncoder().encodeToString(hashed_password.getBytes()), port);
                                    client.rmiServerLoggedInInterface = (ServerLoggedInInterface) remote;
                                    System.out.println("EMAIL" + client.rmiServerLoggedInInterface.getEmail());

                                    logged_in = 1;

                                } catch (RemoteException re) {
                                    System.out.println("Login credentials are incorrect. Please Try Again.");
                                } catch (NoSuchAlgorithmException nsa) {
                                    System.out.println("Could not satisfy minimum security requirements. Aborting");
                                    System.exit(5);
                                }
                                break;

                            //Exit
                            case 3:
                                exit_flag = 1;
                                break;
                            //unknow option
                            default:
                                System.out.println("Unknown option. Try Again.");
                                break;
                        }
                    } catch (NumberFormatException nfe) {
                        System.out.println("Unexpected token received. Check your answer.");
                    }
                }
                //logged in
                else {
                    System.out.println("#### Hello, " + client.serverLoggedInInterface().getEmail());
                    System.out.println("### Main Menu ###");
                    System.out.println("1 - Ver os meus exericios submetidos.");
                    System.out.println("2 - Ver as minhas soluções submetidas.");
                    System.out.println("3 - Submeter novo exercicio.");
                    System.out.println("4 - Apagar exercicio.");
                    System.out.println("5 - Propor solução.");
                    System.out.println("6 - Inserir UC.");
                    System.out.println("7 - Consultar UCs.");
                    System.out.println("8 - Consultar exercicios em aberto por UC.");
                    System.out.println("9 - Consultar exercicios encerrados por UC.");
                    System.out.println("10 - Procurar exercicio.");
                    System.out.println("11 - Logout.");

                    try {
                        Scanner scanner = new Scanner(System.in);
                        switch (Integer.parseInt(scanner.nextLine())){

                            //Ver os meus exercicios submetidos.
                            case 1:
                                System.out.println(client.serverLoggedInInterface().getExercisesSubmitedByAuthor());
                                break;

                            //ver as minhas soluções submetidas
                            case 2:
                                System.out.println(client.serverLoggedInInterface().getSolutionsSubmittedByAuthor());
                                break;
                            // Submeter novo exercicio.
                            case 3:
                                System.out.println("### New Exercise Menu ###");
                                System.out.println("Introduza o nome da UC: ");
                                String uc_name = scanner.nextLine();
                                System.out.println("Introduza o nome do exercicio: ");
                                String ex_name = scanner.nextLine();
                                System.out.println("Introduza uma descricao do exercicio: (Opcional)");
                                String ex_description = scanner.nextLine();
                                System.out.println("Introduza o contéudo do exercicio: ");
                                String exercice_contents = scanner.nextLine();

                                if (client.serverLoggedInInterface().submitNewExercise(uc_name, ex_name, ex_description, exercice_contents)){
                                    System.out.println("Exercicio adicionado com sucesso!");
                                } else System.out.println("Erro ao inserir exercicio. Tente Novemente.");

                                break;

                            //Apagar exercicio.
                            case 4:
                                break;

                            //Propor solução.
                            case 5:
                                System.out.println("### Inserir Solucao ###");
                                System.out.println("Introduza o nome da UC: ");
                                String ucname = scanner.nextLine();
                                System.out.println("Introduza o ID do exercicio:");
                                int ex_id = Integer.parseInt(scanner.nextLine());
                                System.out.println("Introduza a sua solucao: ");
                                String solution = scanner.nextLine();

                                if (client.serverLoggedInInterface().submitNewSolution(solution, ex_id, ucname))
                                    System.out.println("A solução foi correctamente inserida.");
                                else System.out.println("Houve um erro ao inserir a solucao ao exercicio.");

                                break;
                            //Inserir UC.
                            case 6:
                                System.out.println("### Inserir UC ###");
                                System.out.println("Introduza o nome da UC: ");
                                String nome_uc = scanner.nextLine();
                                System.out.println("Introduza uma descricao da cadeira: (opcional)");
                                String descricao_uc = scanner.nextLine();

                                if (descricao_uc == null) descricao_uc = "";

                                if (client.serverLoggedInInterface().createNewUC(nome_uc, descricao_uc)){
                                    System.out.println("UC criada com sucesso!");
                                } else System.out.println("Ocorreu um erro na criação da UC.");

                                break;
                            //Consultar UCS com exercicios.
                            case 7:
                                String uc_with_ex = client.serverLoggedInInterface().ucWithExercises();
                                if (uc_with_ex.equals("")){
                                    System.out.println("Não existem UCs com exercicios.");
                                } else System.out.println(uc_with_ex);
                                break;

                            //Consultar exercicios em abertos por UC.
                            case 8:
                                //pedir o nome da UC, devolver exercicios em aberto.
                                System.out.println("### Consultar exercicios em aberto por UC");
                                String uc = scanner.nextLine();
                                client.serverLoggedInInterface().getOpenExercises(uc);
                                break;

                            //Consultar exercicios encerrados por UC.
                            case 9:
                                //pedir o nome da UC, devolver exercicios encerrados.
                                break;

                            //Procurar exercicio.
                            case 10:
                                break;

                            case 11:
                                System.out.println("Please comeback soon! Bye!");
                                client.serverLoggedInInterface().logOut();
                                logged_in = 0;
                                exit_flag = 1;
                                break;

                            default:
                                break;

                        }

                    }catch (NumberFormatException nfe){
                        System.out.println("Wrong input given. Try again.");
                    }


                }
            } while (exit_flag == 0);

        } catch (ConnectException cn) {
            System.out.println("Could not connect to server. Aborting!");
            cn.printStackTrace();
            System.exit(1);
        } catch (RemoteException rm) {
            rm.printStackTrace();