Combination Lock using the Iteration State Machine

CombinationLockIterationStateMachine.cs

/*
 * REVISITING THE COMBINATION LOCK
 * - We can make our machine non-deterministic
 */

using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        UnlockUsingCorrectCombination();
    }
    
    public static void UnlockUsingCorrectCombination()
    {
        var combinationLock = new CombinationLock();
        combinationLock.Start();
        Console.WriteLine(string.Format("Starting State: {0}", combinationLock.CurrentState));

        combinationLock.EnterNumber(7);
        Console.WriteLine(combinationLock.CurrentState);

        combinationLock.EnterNumber(1);
        Console.WriteLine(combinationLock.CurrentState);

        combinationLock.EnterNumber(3);
        Console.WriteLine(combinationLock.CurrentState);

        Console.WriteLine(string.Format("Ending State: {0}", combinationLock.CurrentState));
    }
}

public enum CombinationLockState
{
    NoneRight,
    OneRight,
    TwoRight,
    Open
}

public class CombinationLock : IteratorStateMachine<CombinationLockState>
{
    private int? firstNumber;
    private int? secondNumber;
    private int? thirdNumber;

    public void EnterNumber(int number)
    {
        this.SetNumber(number);

        Console.WriteLine(string.Format("Entered {0}...", number));
        this.Trigger();
    }
    
    protected override IEnumerable<CombinationLockState> States()
    {
        /*
         * Of course, nobody in their right mind would build a system that confirms
         * each value after input as our example is doing. Doing so reduces the
         * number of attempts required to crack the code from a maximum of 1000 to
         * just 30!
         */

        while (true)
        {
            if (this.firstNumber == 7 && this.secondNumber == 1 && this.thirdNumber == 3)
            {
                yield return CombinationLockState.Open;
            }
            else if (this.firstNumber == 7 && this.secondNumber == 1 && this.thirdNumber != 3)
            {
                yield return CombinationLockState.TwoRight;
            }
            else if (this.firstNumber == 7 && this.secondNumber != 1)
            {
                yield return CombinationLockState.OneRight;
            }
            else
            {
                yield return CombinationLockState.NoneRight;
            }
        }
    }

    private void SetNumber(int number)
    {
        if (this.firstNumber == null)
        {
            this.firstNumber = number;
        }
        else if (this.secondNumber == null)
        {
            this.secondNumber = number;
        }
        else if (this.thirdNumber == null)
        {
            this.thirdNumber = number;
        }
        else
        {
            this.firstNumber = number;
            this.secondNumber = null;
            this.thirdNumber = null;
        }
    }
}

public abstract class IteratorStateMachine<TState>
{
    private IEnumerator<TState> enumerator;

    public TState CurrentState
    {
        get
        {
            return this.enumerator.Current;
        }
    }

    public void Start()
    {
        this.enumerator = this.States().GetEnumerator();
        this.enumerator.MoveNext();
    }

    protected abstract IEnumerable<TState> States();

    protected void Trigger()
    {
        this.enumerator.MoveNext();
    }
}