import java.util.Scanner;

public class Mod10Slide26 {

    public static void main(String[] args) {

        Scanner k = new Scanner(System.in);
        ArrayList<String> calls = new ArrayList<String>();

        int option;
        String input = "";

        System.out.println("Call Center System\n\n");
        System.out.println("1) Add a number");
        System.out.println("2) Retrieve next number");
        System.out.println("3) Show all numbers waiting for callback");
        System.out.println("4) Exit");
        System.out.print("Enter your option: ");
        option = Integer.parseInt(k.nextLine());

        while (option != 4) {
            switch (option) {
                case 1:
                    System.out.printf("Enter callback #: ");
                    input = k.nextLine();
                    calls.add(input);
                    break;
                case 2:
                    String nextCall = calls.get(0);
                    calls.remove(0);
                    System.out.printf("Next phone number to call: %s\n", nextCall);
                    break;
                case 3:
                    System.out.println("Callback list\n");
                    System.out.printf("%8s %12s\n", "Position", "Number");

                    for (int i = 0; i < calls.size(); i++) {
                        System.out.printf("%-8d %12s\n", i + 1, calls.get(i));
                    }
                    System.out.println();
                    break;
            }
            System.out.println("Call Center System\n\n");
            System.out.println("1) Add a number");
            System.out.println("2) Retrieve next number");
            System.out.println("3) Show all numbers waiting for callback");
            System.out.println("4) Exit");
            System.out.print("Enter your option: ");
            option = Integer.parseInt(k.nextLine());
        }
    }
}