using System;

public class Program

{

    public static void Main()

    {

        /*

        var dog = new Dog();

        var bird = new Bird();

        Console.WriteLine(dog.GetNumberOfLegs());

        Console.WriteLine(bird.GetNumberOfLegs());

        */

        IAnimals dogObject = AnimalFactory.ChooseAnimal("Dog");

        Console.WriteLine(dogObject.GetNumberOfLegs());

        IAnimals birdObject = AnimalFactory.ChooseAnimal("Bird");

        Console.WriteLine(birdObject.GetNumberOfLegs());

        IAnimals invalidAnimalObject = AnimalFactory.ChooseAnimal("Plane");

        Console.WriteLine(invalidAnimalObject.GetNumberOfLegs());

    }

    public static class AnimalFactory

    {

        private static IAnimals theAnimal;

        public static IAnimals ChooseAnimal(string animal)

        {

            switch(animal)

            {

                case "Dog":

                    theAnimal = new Dog();

                    break;

                case "Bird":

                    theAnimal = new Bird();

                    break;

                default:

                    theAnimal = new InvalidAnimal();

                        break;

            }

            return theAnimal;

        }

    }

    public interface IAnimals

    {

        string GetNumberOfLegs();

    }

    public class InvalidAnimal : IAnimals

    {

        public string GetNumberOfLegs()

        {

            return "Specified Animal does not exist or not available";

        }

    }

    public class Dog : IAnimals

    {

        public Dog()

        {

        }

        public string GetNumberOfLegs()

        {

            return "Dog has 4 legs";

        }

    }

    public class Bird : IAnimals

    {

        public Bird()

        {           

        }

        public string GetNumberOfLegs()

        {

            return "Bird has 2 legs";

        }

    }

}