Состояние (State)

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Linq;
using System.Threading.Tasks;

class Program
{
   static void Main(string[] args)
   {
    Water water = new Water(new LiquidWaterState());

    water.Head();
    water.Frost();
    water.Frost();

    Console.ReadLine();
   }
}

class Water
{
    public IWaterState State {get; set;}

    public Water(IWaterState ws)
    {
        this.State = ws;
    }

    public void Head()
    {
        State.Head(this);
    }

    public void Frost()
    {
        State.Frost(this);
    }
}

interface IWaterState
{
    void Head(Water water);
    void Frost(Water water);
}

class SolidWaterState : IWaterState
{
    public void Head(Water water)
    {
        Console.WriteLine("Превращаем лёд в воду");
        water.State = new LiquidWaterState();
    }

    public void Frost(Water water)
    {
        Console.WriteLine("Продолжаем заморозку льда");
    }
}

class LiquidWaterState : IWaterState
{
    public void Head(Water water)
    {
        Console.WriteLine("Превращаем жидкость в пар");
        water.State = new GasWaterState();
    }

    public void Frost(Water water)
    {
        Console.WriteLine("Превращаем жидкость в лёд");
        water.State = new SolidWaterState();
    }
}

class GasWaterState : IWaterState
{
    public void Head(Water water)
    {
        Console.WriteLine("Продолжаем нагревать газ");
    }

    public void Frost(Water water)
    {
        Console.WriteLine("Превращаем пар в жидкость");
        water.State = new LiquidWaterState();
    }
}