EinmaleinsTrainer/ViewModels/QuizViewModel.cs

using ReactiveUI;
using System;
using System.Collections.Generic;
using System.Reactive;
using System.Reactive.Concurrency;
using System.Reactive.Linq;
using System.Reactive.Subjects;
using EinmaleinsTrainer.Models;

namespace EinmaleinsTrainer.ViewModels;

public class QuizViewModel : ViewModelBase
{
    // =========================
    // Basisdaten
    // =========================

    private QuizModel _model = new();

    private List<Question> _questions = new();
    public List<Question> Questions
    {
        get => _questions;
        private set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                this.RaiseAndSetIfChanged(ref _questions, value);
                this.RaisePropertyChanged(nameof(Total));

                // Wenn sich Questions ändern → Index resetten
                Index = 0;
            });
        }
    }

    public int Total => Questions.Count;

    private int _index;
    public int Index
    {
        get => _index;
        private set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                bool changed = _index == value;
                this.RaiseAndSetIfChanged(ref _index, value);
                if (!changed)
                {
                    this.RaisePropertyChanged();
                }
                UpdateDerivedProperties();
            });
        }
    }

    // =========================
    // Abgeleitete Properties
    // =========================

    private Question _currentQuestion = new() { A = 0, B = 0 };
    public Question CurrentQuestion
    {
        get => _currentQuestion;
        private set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                this.RaiseAndSetIfChanged(ref _currentQuestion, value);
            });
        }
    }

    private int _questionNumber;
    public int QuestionNumber
    {
        get => _questionNumber;
        private set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                this.RaiseAndSetIfChanged(ref _questionNumber, value);
            });
        }
    }

    private string _currentQuestionText = "0 × 0";
    public string CurrentQuestionText
    {
        get => _currentQuestionText;
        private set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                this.RaiseAndSetIfChanged(ref _currentQuestionText, value);
            });
        }
    }

    // =========================
    // User Input / Status
    // =========================

    private string _userAnswer = "";
    public string UserAnswer
    {
        get => _userAnswer;
        set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                this.RaiseAndSetIfChanged(ref _userAnswer, value);
            });
        }
    }

    private int _remaining;
    public int RemainingSeconds
    {
        get => _remaining;
        private set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                this.RaiseAndSetIfChanged(ref _remaining, value);
                if (value > 0)
                    RedrawRequired?.Invoke(this, new());
            });
        }
    }

    private int _score;
    public int Score
    {
        get => _score;
        private set
        {
            RxApp.MainThreadScheduler.Schedule(() =>
            {
                this.RaiseAndSetIfChanged(ref _score, value);
            });
        }
    }

    public bool UseTimer { get; private set; }

    private TimeSpan TimeRequired = TimeSpan.Zero;
    private DateTime Started = DateTime.MinValue;

    // =========================
    // Commands / Events
    // =========================

    public ReactiveCommand<Unit, Unit> SubmitCommand { get; }

    private readonly Subject<ResultModel> _finished = new();
    public IObservable<ResultModel> Finished => _finished.AsObservable();

    public event EventHandler? RedrawRequired;

    private IDisposable? _timerSub;

    // =========================
    // ctor
    // =========================

    public QuizViewModel()
    {
        SubmitCommand = ReactiveCommand.Create(
            Submit,
            outputScheduler: RxApp.MainThreadScheduler
        );
    }

    // =========================
    // Init
    // =========================

    public void Init(QuizModel model)
    {
        _timerSub?.Dispose();
        _model = model;

        TimeRequired = TimeSpan.Zero;
        Questions = new List<Question>(model.Questions);

        Score = 0;
        UserAnswer = "";
        UseTimer = model.UseTimer && model.Seconds > 1;

        RemainingSeconds = UseTimer ? model.Seconds : 0;

        // Abgeleitete Properties initial setzen
        UpdateDerivedProperties();

        if (UseTimer)
            StartTimer(model.Seconds);
    }

    // =========================
    // Ableitungen zentral
    // =========================

    private void UpdateDerivedProperties()
    {
        if (Questions.Count == 0 || Index < 0 || Index >= Questions.Count)
        {
            CurrentQuestion = new Question { A = 0, B = 0 };
            QuestionNumber = 0;
            CurrentQuestionText = "0 × 0";
            return;
        }

        var q = Questions[Index];
        CurrentQuestion = q;  // Direkt zuweisen
        QuestionNumber = Index + 1;
        CurrentQuestionText = $"{q.A} × {q.B}";
    }

    // =========================
    // Timer
    // =========================

    private void StartTimer(int seconds)
    {
        Started = DateTime.Now;
        RemainingSeconds = seconds;

        _timerSub?.Dispose();
        _timerSub = Observable
            .Interval(TimeSpan.FromSeconds(1), RxApp.MainThreadScheduler)
            .Select(i => seconds - (int)i - 1)
            .TakeWhile(s => s >= 0)
            .Subscribe(s =>
            {
                RemainingSeconds = s;

                if (s == 0)
                    SubmitInternal(false);
            });
    }

    // =========================
    // Submit
    // =========================

    private void Submit()
    {
        bool correct =
            int.TryParse(UserAnswer, out int a) &&
            a == CurrentQuestion.CorrectAnswer;

        SubmitInternal(correct);
    }

    private void SubmitInternal(bool correct)
    {
        if (correct)
            RxApp.MainThreadScheduler.Schedule(() => Score++);

        _timerSub?.Dispose();
        if (UseTimer)
            TimeRequired += DateTime.Now - Started;

        RxApp.MainThreadScheduler.Schedule(() => 
        {
            Index++;

            if (Index >= Questions.Count)
            {
                _finished.OnNext(new ResultModel
                {
                    Score = Score,
                    Total = Total,
                    TimeRequired = UseTimer ? TimeRequired : null
                });
                return;
            }

            // UserAnswer zurücksetzen
            UserAnswer = "";

            // Update der abgeleiteten Properties (CurrentQuestionText, QuestionNumber)
            UpdateDerivedProperties();

            RedrawRequired?.Invoke(this, new());
        });

        if (UseTimer && Index < Questions.Count)
            StartTimer(_model.Seconds);
    }
}