LehrerApp/LehrerApp.Desktop/ViewModels/Groups/ExamEvaluationViewModels.cs

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using LehrerApp.Core.Interfaces;
using LehrerApp.Core.Models;
using LehrerApp.Core.Services;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Text;

namespace LehrerApp.Desktop.ViewModels.Groups;

// ── Klausurauswertung (1.5) ───────────────────────────────────────────────────

public partial class ExamEvaluationDialogViewModel : ObservableObject
{
    private readonly IExamRepository _exams;
    private readonly IExamResultRepository _results;
    private readonly GradingService _grading;
    private readonly Exam _exam;
    private readonly GradingSystem _gradingSystem;
    private readonly double _examMaxPoints;
    private List<ExamResult> _gradedResults = [];

    public string ExamTitle => _exam.Title;
    public string ExamDateLabel => _exam.Date.ToString("dd.MM.yyyy");
    public string NiveauLabel => _exam.Niveau.HasValue ? NiveauDisplay.ToName(_exam.Niveau) : "";

    [ObservableProperty] private int _gradedCount;
    [ObservableProperty] private int _absentCount;
    [ObservableProperty] private string _averageDisplay = "–";
    [ObservableProperty] private string _medianDisplay = "–";
    [ObservableProperty] private string _belowThresholdLabel1 = "";
    [ObservableProperty] private string _belowThresholdDisplay1 = "";
    [ObservableProperty] private string _belowThresholdLabel2 = "";
    [ObservableProperty] private string _belowThresholdDisplay2 = "";
    [ObservableProperty] private string _gradingKeyValidation = "";
    [ObservableProperty] private string _gradingKeyStatus = "";

    public ObservableCollection<GradeBarItem> GradeDistribution { get; } = [];
    public ObservableCollection<TaskAnalysisItem> TaskAnalysis { get; } = [];
    public ObservableCollection<GradingKeyEntryEditItem> GradingKeyEntries { get; } = [];

    public ExamEvaluationDialogViewModel(IExamRepository exams, IExamResultRepository results,
        GradingService grading, Exam exam, GradingSystem gradingSystem)
    {
        _exams = exams; _results = results; _grading = grading; _exam = exam;
        _gradingSystem = gradingSystem;
        _examMaxPoints = exam.Tasks.Sum(t => t.MaxPoints);

        foreach (var e in exam.GradingKey.OrderByDescending(e => e.MinPercent))
            AddGradingKeyRowInternal(e.Grade, e.MinPercent);

        LoadResults();
    }

    private void LoadResults()
    {
        var all = _results.GetByExam(_exam.Id);
        AbsentCount = all.Count(r => r.Absent);
        _gradedResults = all.Where(r => !r.Absent).ToList();
        GradedCount = _gradedResults.Count;
        Recompute();
    }

    // ── Notenschlüssel-Editor (1.5.3) ────────────────────────────────────────

    [RelayCommand]
    private void AddGradingKeyRow() => AddGradingKeyRowInternal("", 0);

    private void AddGradingKeyRowInternal(string grade, double minPercent)
    {
        var item = new GradingKeyEntryEditItem
        {
            Grade = grade,
            MinPercent = minPercent,
            OnChanged = OnGradingKeyRowChanged,
            OnRemove = RemoveGradingKeyRow,
        };
        GradingKeyEntries.Add(item);
        RecomputeGradingKeyAbsolutes();
    }

    private void OnGradingKeyRowChanged()
    {
        RecomputeGradingKeyAbsolutes();
        Recompute();
    }

    private void RemoveGradingKeyRow(GradingKeyEntryEditItem item)
    {
        GradingKeyEntries.Remove(item);
        RecomputeGradingKeyAbsolutes();
        Recompute();
    }

    private void RecomputeGradingKeyAbsolutes()
    {
        foreach (var e in GradingKeyEntries)
            e.AbsolutePointsDisplay = _examMaxPoints <= 0
                ? "–"
                : $"ab {(e.MinPercent / 100.0 * _examMaxPoints).ToString("0.##", CultureInfo.InvariantCulture)} " +
                  $"von {_examMaxPoints.ToString("0.##", CultureInfo.InvariantCulture)} Punkten";
    }

    private List<GradingKeyEntry> BuildCurrentGradingKey() => GradingKeyEntries
        .Select(e => new GradingKeyEntry { Grade = e.Grade.Trim(), MinPercent = e.MinPercent })
        .OrderByDescending(e => e.MinPercent)
        .ToList();

    [RelayCommand]
    private void ApplyGradingKey()
    {
        var key = BuildCurrentGradingKey();
        var error = _grading.ValidateGradingKey(key);
        if (error is not null) { GradingKeyValidation = error; GradingKeyStatus = ""; return; }
        GradingKeyValidation = "";
        _exam.GradingKey = key;
        _exams.Save(_exam);
        GradingKeyStatus = "Notenschlüssel für diese Klausur übernommen.";
    }

    // ── Auswertung neu berechnen ──────────────────────────────────────────────

    private void Recompute()
    {
        var currentKey = BuildCurrentGradingKey();
        GradingKeyValidation = _grading.ValidateGradingKey(currentKey) ?? "";

        var grades = _gradedResults
            .Select(r => _grading.CalculateGrade(r.TotalPoints, _examMaxPoints, currentKey))
            .ToList();

        GradeDistribution.Clear();
        var counts = grades.GroupBy(g => g).ToDictionary(g => g.Key, g => g.Count());
        var maxCount = counts.Count == 0 ? 0 : counts.Values.Max();
        foreach (var entry in currentKey.OrderByDescending(e => e.MinPercent))
        {
            counts.TryGetValue(entry.Grade, out var count);
            GradeDistribution.Add(new GradeBarItem(entry.Grade, count, grades.Count, maxCount));
        }

        AverageDisplay = grades.Count == 0
            ? "–"
            : _grading.WeightedAverage(grades.Select(g => (Grade: g, Weight: 1.0)).ToList())
                       .ToString("0.00", CultureInfo.InvariantCulture);

        var numeric = grades.Select(g => int.TryParse(g, out var n) ? (int?)n : null)
                             .Where(n => n.HasValue).Select(n => n!.Value)
                             .OrderBy(n => n).ToList();
        MedianDisplay = numeric.Count == 0 ? "–" : ComputeMedian(numeric).ToString("0.##", CultureInfo.InvariantCulture);

        if (_gradingSystem == GradingSystem.Points0To15)
        {
            BelowThresholdLabel1   = "Anteil < 5 Punkte";
            BelowThresholdDisplay1 = Percent(numeric.Count(n => n < 5), numeric.Count);
            BelowThresholdLabel2   = "Anteil < 4 Punkte";
            BelowThresholdDisplay2 = Percent(numeric.Count(n => n < 4), numeric.Count);
        }
        else
        {
            BelowThresholdLabel1   = "Anteil nicht ausreichend (Note 5/6)";
            BelowThresholdDisplay1 = Percent(numeric.Count(n => n >= 5), numeric.Count);
            BelowThresholdLabel2   = "";
            BelowThresholdDisplay2 = "";
        }

        RecomputeTaskAnalysis();
    }

    private void RecomputeTaskAnalysis()
    {
        TaskAnalysis.Clear();
        var tasks = _exam.Tasks.OrderBy(t => t.Nr).ToList();
        for (var i = 0; i < tasks.Count; i++)
        {
            var task = tasks[i];
            var achieved = _gradedResults.Where(r => i < r.Points.Count).Select(r => r.Points[i]).ToList();
            var avgPercent = task.MaxPoints <= 0 || achieved.Count == 0
                ? 0
                : achieved.Average() / task.MaxPoints * 100.0;
            TaskAnalysis.Add(new TaskAnalysisItem(task.Nr, task.Title, avgPercent));
        }
    }

    private static double ComputeMedian(List<int> sorted)
    {
        var n = sorted.Count;
        return n % 2 == 1 ? sorted[n / 2] : (sorted[n / 2 - 1] + sorted[n / 2]) / 2.0;
    }

    private static string Percent(int count, int total) =>
        total == 0 ? "–" : $"{(count * 100.0 / total).ToString("0.#", CultureInfo.InvariantCulture)} %";

    // ── Export (1.5.4) ────────────────────────────────────────────────────────

    public string ExportCsv()
    {
        var sb = new StringBuilder();
        sb.AppendLine($"Klausur;{_exam.Title}");
        sb.AppendLine($"Datum;{_exam.Date:dd.MM.yyyy}");
        sb.AppendLine();
        sb.AppendLine("Notenspiegel");
        sb.AppendLine("Note;Anzahl;Anteil");
        foreach (var g in GradeDistribution)
            sb.AppendLine($"{g.Grade};{g.Count};{Percent(g.Count, GradedCount)}");
        sb.AppendLine();
        sb.AppendLine($"Durchschnitt;{AverageDisplay}");
        sb.AppendLine($"Median;{MedianDisplay}");
        if (!string.IsNullOrEmpty(BelowThresholdLabel1)) sb.AppendLine($"{BelowThresholdLabel1};{BelowThresholdDisplay1}");
        if (!string.IsNullOrEmpty(BelowThresholdLabel2)) sb.AppendLine($"{BelowThresholdLabel2};{BelowThresholdDisplay2}");
        sb.AppendLine($"Bewertet;{GradedCount}");
        sb.AppendLine($"Abwesend;{AbsentCount}");
        sb.AppendLine();
        sb.AppendLine("Aufgabenanalyse");
        sb.AppendLine("Aufgabe;Ø Erfüllungsgrad;Auffällig schwach");
        foreach (var t in TaskAnalysis)
            sb.AppendLine($"{t.Label};{t.AvgPercentDisplay};{(t.IsWeak ? "ja" : "")}");
        return sb.ToString();
    }
}

// ── Notenspiegel-Balken ────────────────────────────────────────────────────

public class GradeBarItem
{
    public string Grade { get; }
    public int Count { get; }
    public string CountDisplay { get; }
    public double BarWidth { get; }

    public GradeBarItem(string grade, int count, int totalGraded, int maxCount)
    {
        Grade = grade;
        Count = count;
        var percent = totalGraded == 0 ? 0 : count * 100.0 / totalGraded;
        CountDisplay = $"{count}  ({percent.ToString("0.#", CultureInfo.InvariantCulture)} %)";
        BarWidth = maxCount <= 0 ? 0 : count * 200.0 / maxCount;
    }
}

// ── Aufgabenanalyse-Zeile ──────────────────────────────────────────────────

public class TaskAnalysisItem
{
    public string Label { get; }
    public double AvgPercent { get; }
    public string AvgPercentDisplay { get; }
    public bool IsWeak { get; }
    public double BarWidth { get; }

    public TaskAnalysisItem(int nr, string? title, double avgPercent)
    {
        Label = string.IsNullOrWhiteSpace(title) ? $"Aufgabe {nr}" : $"{nr}. {title}";
        AvgPercent = avgPercent;
        AvgPercentDisplay = $"{avgPercent.ToString("0.#", CultureInfo.InvariantCulture)} %";
        IsWeak = avgPercent < 50.0;
        BarWidth = Math.Clamp(avgPercent, 0, 100) * 2.0;
    }
}