SolveCaptcha.cs

//Solves Captcha on the NZ Government's "Hand in firearms" form https://forms.police.govt.nz/forms/firearms-hand-in
//Probably can be adapted to break captchas for other shitty Math Based captchas.

using NCalc;
using System;
using System.Collections.Generic;
using Flurl.Http;
using HtmlAgilityPack;

namespace CaptchaBreaker
{
    class Program
    {

        static Dictionary<String, String> NumberStrings = new Dictionary<String, String>
        {
            { "zero", "0" },
            { "one", "1" },
            { "two", "2" },
            { "three", "3" },
            { "four", "4" },
            { "five", "5" },
            { "six", "6" },
            { "seven", "7" },
            { "eight", "8" },
            { "nine", "9" },
            { "ten", "10" },
            { "eleven", "11" },
            { "twelve", "12" },
            { "thirteen", "13" },
            { "fourteen", "14" },
            { "fifteen", "15" },
            { "plus", "+" },
            { "minus", "-" },
            { "times", "*" },
            { "equals", "=" },
            { "devide", "/" }
        };


        static string FindNeededValue(String Equation)
        {
            string[] Components = Equation.Split(' ');

            int i = 0;
            foreach (String Component in Components)
            {
                if (Component == "=")
                {
                    return Components[i + 1];
                }
                i++;
            }
            return "0";
        }

        static int FindX(String Equation)
        {
            int i = 0;

            int NeededValue = int.Parse(FindNeededValue(Equation));
            String FinalEquation = Equation.Substring(0, Equation.IndexOf('='));

            while (true)
            {
                string Try = FinalEquation.Replace("X", i.ToString());
                Expression e = new Expression(Try);
                if ((int)e.Evaluate() == NeededValue)
                {
                    return i;
                }

                i++;
            }
        }

        static int SolveEquation(string Equation)
        {
            String[] Components = Equation.Split(' ');

            List<String> Reconstructed = new List<String>();

            foreach(String Component in Components)
            {
                try
                {
                    int.Parse(Component);
                    Reconstructed.Add(Component);
                }
                catch(Exception)
                {
                    if (Component == "X")
                    {
                        Reconstructed.Add("X");
                    }
                    if (NumberStrings.ContainsKey(Component))
                    {
                        Reconstructed.Add(NumberStrings[Component]);
                    }

                }
            }


            String FinalEquation = String.Join(" ", Reconstructed.ToArray());

            if(FinalEquation.Contains("X"))
            {
                return FindX(FinalEquation);
            }

            try
            {
                FinalEquation = FinalEquation.Substring(0, FinalEquation.IndexOf('='));
            }
            catch (Exception) { };


            Expression e = new Expression(FinalEquation);
            return (int)e.Evaluate();
        }

        static void Main(string[] args)
        {
            while(true)
            {
                var Request = "https://forms.police.govt.nz/forms/firearms-hand-in".GetStringAsync();
                Request.Wait();
                String PageHtml = Request.Result;

                var doc = new HtmlDocument();
                doc.LoadHtml(PageHtml);

                var Node = doc.DocumentNode.SelectSingleNode("//*[@id=\"webform-client-form-155\"]/div/fieldset/div/div[2]/span[1]");
                var Node2 = doc.DocumentNode.SelectSingleNode("//*[@id=\"webform-client-form-155\"]/div/fieldset/div/div[2]/span[2]");

                String FullEquation;

                String Eq1 = Node.InnerText;
                String Eq2 = "";

                if (Node2 != null)
                {
                    Eq2 = Node2.InnerText;
                    FullEquation = Eq1 + "X" + Eq2;
                }
                else if (Eq1.StartsWith(" "))
                {
                    FullEquation = "X" + Eq1;
                }
                else
                {
                    FullEquation = Eq1;
                }


                Console.WriteLine(FullEquation);
                Console.WriteLine(SolveEquation(FullEquation));
            }
        }
    }
}