ln.http/ln.http.helpers/HttpCaptcha.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using ln.http.route;
using ln.json;
using ln.json.mapping;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Drawing;
using SixLabors.ImageSharp.Drawing.Processing;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;

namespace ln.http.helpers
{

    public class HttpCaptcha : HttpRoute
    {
        private Dictionary<Guid, CaptchaInstance> _captchaInstances = new Dictionary<Guid, CaptchaInstance>();
        private CaptchaEndpoints _captchaEndpoints;
        
        public HtmlColor[] CaptchaColors { get; } = new HtmlColor[]
        {
            HtmlColor.Red, HtmlColor.Green, HtmlColor.Blue, HtmlColor.Yellow, HtmlColor.Violett, HtmlColor.turquoise
        };

        public Random _random = new Random(Environment.TickCount + Thread.CurrentThread.GetHashCode());

        public TimeSpan Timeout { get; set; } = TimeSpan.FromMinutes(10);
        public int SolutionLength { get; set; }
        public int GroupLength { get; set; }

        public HttpCaptcha(HttpRouter httpRouter, string mapPath)
        :this(httpRouter, mapPath, 25, 5)
        {}
        public HttpCaptcha(HttpRouter httpRouter, string mapPath, int groupLength, int solutionLength)
            : base(HttpMethod.ANY, mapPath)
        {
            _captchaEndpoints = new CaptchaEndpoints(this);
            _routerDelegate = _captchaEndpoints.RouteRequest;
            
            GroupLength = groupLength;
            SolutionLength = solutionLength;
            
            httpRouter.Map(this);
        }

        public CaptchaInstance CreateInstance() => new CaptchaInstance(this);

        public bool Authorize(HttpRequest httpRequest)
        {
            return false;
        }
        
        class CaptchaEndpoints : HttpEndpointController
        {
            private HttpCaptcha _httpCaptcha;

            public CaptchaEndpoints(HttpCaptcha httpCaptcha)
            {
                _httpCaptcha = httpCaptcha;
            }

            [Map(HttpMethod.GET,"")]
            public HttpResponse GetCaptcha()
            {
                return HttpResponse
                    .OK()
                    .Content(
                        _httpCaptcha
                            .CreateInstance()
                            .Json()
                        );
            }
            
            [Map(HttpMethod.GET, "/:instance/:combination")]
            public HttpResponse DrawCombination(Guid instance, int combination)
            {
                int imageSize = 48;
                
                if (!_httpCaptcha._captchaInstances.TryGetValue(instance, out CaptchaInstance captchaInstance) ||
                    ((combination < 0) || (combination >= captchaInstance.Combinations.Length)))
                    return HttpResponse.NotFound();

                CaptchaCombination captchaCombination = captchaInstance.Combinations[combination];

                Image<Rgb24> combinationImage = new Image<Rgb24>(imageSize, imageSize, new Rgb24(255,255,255));
                IPath combinationPath = null;
                
                switch (captchaCombination.Form)
                {
                    case CaptchaForm.Stern:
                        combinationPath = new Star((float)(imageSize / 2.0),
                            (float)(imageSize / 2.0), captchaCombination.Corners,
                                (float)(imageSize / 6.0), (float)(imageSize / 2.3));
                        break;
                    case CaptchaForm.Vieleck:
                        combinationPath = new RegularPolygon((float)(imageSize / 2.0),
                            (float)(imageSize / 2.0), captchaCombination.Corners,
                            (float)(imageSize / 2.3));
                        break;
                    default:
                        return HttpResponse.InternalServerError();
                }
                
                combinationImage.Mutate(x => x.Fill(captchaCombination.Color, combinationPath.RotateDegree(_httpCaptcha._random.Next(360))));
                
                StreamedContent streamedContent = new StreamedContent("image/png");
                combinationImage.SaveAsPng(streamedContent.ContentStream);
                
                HttpResponse httpResponse = HttpResponse.OK().Content(streamedContent);
                return httpResponse;
            }

            [Map(HttpMethod.POST, "/:instance")]
            public HttpResponse Solve(Guid instance, [HttpArgumentSource(HttpArgumentSource.CONTENT)] JSONValue body)
            {
                if (!_httpCaptcha._captchaInstances.TryGetValue(instance, out CaptchaInstance captchaInstance))
                    return HttpResponse.NotFound();

                if (body is JSONArray jsonSolution)
                {
                    int[] solution = JSONMapper.DefaultMapper.FromJson<int[]>(jsonSolution);

                    if (captchaInstance.Solve(solution))
                    {
                        return HttpResponse.NoContent();
                    }
                    return HttpResponse.Forbidden();   
                }
                else
                {
                    return HttpResponse.BadRequest();
                }
            }
        }

        public class CaptchaInstance : IDisposable
        {
            public Guid Guid { get; }

            public CaptchaCombination[] Combinations { get; private set; }
            public int[] Solution { get; private set; }


            private HttpCaptcha _httpCaptcha;
            private Timer _timer;

            public CaptchaInstance(HttpCaptcha httpCaptcha)
            {
                _httpCaptcha = httpCaptcha;
                Guid = Guid.NewGuid();

                _httpCaptcha._captchaInstances.Add(Guid, this);
                _timer = new Timer((state) => Dispose(), null, _httpCaptcha.Timeout, TimeSpan.Zero);

                Initialize();
            }

            private void Initialize()
            {
                HashSet<CaptchaCombination> hashSet = new HashSet<CaptchaCombination>();
                while (hashSet.Count < _httpCaptcha.GroupLength)
                    hashSet.Add(new CaptchaCombination(this._httpCaptcha));

                List<CaptchaCombination> combinationPool = hashSet.ToList();

                Combinations = new CaptchaCombination[combinationPool.Count];
                for (int n = 0; n < Combinations.Length; n++)
                {
                    Combinations[n] = combinationPool[_httpCaptcha._random.Next(combinationPool.Count)];
                    combinationPool.Remove(Combinations[n]);
                }

                hashSet.Clear();

                while (hashSet.Count < _httpCaptcha.SolutionLength)
                    hashSet.Add(Combinations[_httpCaptcha._random.Next(Combinations.Length)]);

                Solution = hashSet.Select(cs => Array.IndexOf(Combinations, cs)).ToArray();
                Console.WriteLine(String.Join('-', Solution));
                Array.Sort(Solution);
                Console.WriteLine(String.Join('-', Solution));
            }

            public bool Solve(int[] possibleSolution)
            {
                lock (this)
                {
                    try
                    {
                        possibleSolution = possibleSolution.Distinct().ToArray();
                        Array.Sort(possibleSolution);

                        return Solution.SequenceEqual(possibleSolution);
                    }
                    finally
                    {
                        Dispose();
                    }
                }
            }
            
            public JSONObject Json()
            {
                JSONObject json = new JSONObject()
                    .Add("uuid", Guid)
                    .Add("questions", Solution.Select(n => Combinations[n].ToString()).ToArray())
                    .Add("group", Combinations.Length);
                    ;
                return json;
            }


            public void Dispose()
            {
                lock (this)
                {
                    _timer.Dispose();
                    _httpCaptcha?._captchaInstances.Remove(Guid);
                }
            }

            public override string ToString() => String.Join(", ", Solution.Select(n => Combinations[n].ToString()));
        }

        public class CaptchaCombination
        {
            public HtmlColor Color { get; }
            public int Corners { get; }
            public CaptchaForm Form { get; }

            public CaptchaCombination(HttpCaptcha httpCaptcha)
            {
                Color = httpCaptcha.CaptchaColors[httpCaptcha._random.Next(httpCaptcha.CaptchaColors.Length)];
                Corners = 4 + httpCaptcha._random.Next(4);

                CaptchaForm[] captchaForms = Enum.GetValues<CaptchaForm>();
                Form = captchaForms[httpCaptcha._random.Next(captchaForms.Length)];
            }

            public override bool Equals(object? obj) => obj is CaptchaCombination other && Color.Equals(other.Color) &&
                                                        Corners.Equals(other.Corners) && Form.Equals(other.Form);

            public override int GetHashCode() => Color.GetHashCode() ^ Corners ^ Form.GetHashCode();

            public override string ToString() => $"ein {Form} mit {Corners} {(Form == CaptchaForm.Stern ? "Strahlen" : "Ecken")} in {Color.Name}";
        }

        public enum CaptchaForm
        {
            Stern,
            Vieleck
        }

        public class HtmlColor
        {
            public static readonly HtmlColor Red = new HtmlColor(255, 0, 0, "Rot");
            public static readonly HtmlColor Green = new HtmlColor(0, 255, 0, "Grün");
            public static readonly HtmlColor Blue = new HtmlColor(0, 0, 255, "Blau");
            public static readonly HtmlColor Yellow = new HtmlColor(240, 240, 0, "Gelb");
            public static readonly HtmlColor Violett = new HtmlColor(255, 0, 255, "Lila");
            public static readonly HtmlColor turquoise = new HtmlColor(0, 255, 255, "Türkis");


            public byte R { get; }
            public byte G { get; }
            public byte B { get; }

            public string Name { get; }
            
            public HtmlColor(byte r, byte g, byte b) : this(r, g, b, null)
            {
            }

            public HtmlColor(byte r, byte g, byte b, string name)
            {
                R = r;
                G = g;
                B = b;
                Name = name;
            }

            public override string ToString() => $"#{Red:X2}{Green:X2}{Blue:X2}";

            public static implicit operator Color(HtmlColor htmlColor) =>
                new Rgb24(htmlColor.R, htmlColor.G, htmlColor.B);
        }

    }
}