ChocolateBoiler.cs

namespace SingletonPattern;

public class ChocolateBoiler
{
    private static readonly Lazy<ChocolateBoiler> Lazy = new(() => new ChocolateBoiler());

    public static ChocolateBoiler Instance => Lazy.Value;

    private ChocolateBoiler()
    {
        Empty = true;
        Boiled = false;
    }

    private bool Empty { get; set; }
    private bool Boiled { get; set; }

    public void Fill()
    {
        if (!Empty)
        {
            Console.WriteLine();
            return;
        }
        Empty = false;
        Boiled = false;
        Console.WriteLine("Fill the boiler with a milk/chocolate mixture.");
    }

    public void Drain()
    {
        if (Empty || !Boiled)
        {
            Console.WriteLine();
            return;
        }
        Console.WriteLine("Drain the boiled milk and chocolate.");
        Empty = true;
    }

    public void Boil()
    {
        if (Empty || Boiled)
        {
            Console.WriteLine();
            return;
        }
        Console.WriteLine("Bring the contents to a boil.");
        Boiled = true;
    }
}