using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Message("filename", 1, "Dog"));

        Console.WriteLine(Message("filename", 2, "Dog", "Cat"));

        Console.WriteLine(Message("filename", 3, "Dog", "Cat", "Mouse"));

        Console.WriteLine(Message("filename", 4, "Dog", "Cat", "Mouse", "Spider"));

        Console.WriteLine(Message("filename", 5, "Dog", "Cat", "Mouse", "Spider", "Mongoose"));

    }

    public static string Message(string filename, int rowNumber, string field, params string[] otherFields) 

        => Message3(filename, rowNumber, field, otherFields);

    public static string Message1(string filename, int rowNumber, string field, params string[] otherFields)

    {

        string fields;

        switch (otherFields.Length)

        {

            case 0:

                fields = field;

                break;

            case 1:

                fields = $"one of {field} or {otherFields[0]}";

                break;

            default:

                fields = $"one of {field}, {string.Join(", ", otherFields.Take(otherFields.Length - 1))} or {otherFields.Last()}";

                break;

        }

        return $"In the file {filename} it is mandatory to have {fields}.  This happened on row {rowNumber}";

    }

    public static string Message2(string filename, int rowNumber, string field, params string[] otherFields)

    {

        var fields = (otherFields.Length == 0) 

            ? field 

            : "one of " + string.Join(", ", otherFields.Prepend(field).Take(otherFields.Length)) + " or " + otherFields.Last();

        return $"In the file {filename} it is mandatory to have {fields}.  This happened on row {rowNumber}";

    }

    public static string Message3(string filename, int rowNumber, string field, params string[] otherFields)

    {

        string fields = (otherFields.Length == 0)

            ? field

            : (otherFields.Length == 1)

                ? $"one of {field} or {otherFields[0]}"

                : $"one of {field}, {string.Join(", ", otherFields.Take(otherFields.Length - 1))} or {otherFields.Last()}";

        return $"In the file {filename} it is mandatory to have {fields}.  This happened on row {rowNumber}";

    }

}