LehrerApp/LehrerApp.Desktop/ViewModels/Groups/ExamGradingViewModels.cs

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

namespace LehrerApp.Desktop.ViewModels.Groups;

// ── Punkteeingabe & Korrektur (1.4) ──────────────────────────────────────────

public partial class ExamGradingDialogViewModel : ObservableObject
{
    private readonly IExamResultRepository _results;
    private readonly GradingService _grading;
    private readonly Exam _exam;
    private readonly double _examMaxPoints;

    public string ExamTitle => _exam.Title;
    public string ExamDateLabel => _exam.Date.ToString("dd.MM.yyyy");
    public string NiveauLabel => _exam.Niveau.HasValue ? NiveauDisplay.ToName(_exam.Niveau) : "";
    public List<ExamTask> Tasks { get; }

    public ObservableCollection<ExamResultRow> Rows { get; } = [];

    public ExamGradingDialogViewModel(IExamResultRepository results, IStudentRepository students,
        IGroupMembershipRepository memberships, GradingService grading, Exam exam, Guid groupId)
    {
        _results = results; _grading = grading; _exam = exam;
        Tasks = exam.Tasks.OrderBy(t => t.Nr).ToList();
        _examMaxPoints = Tasks.Sum(t => t.MaxPoints);

        var enrolled = students.GetByGroup(groupId);
        var membershipList = memberships.GetByGroup(groupId);
        var existing = results.GetByExam(exam.Id).ToDictionary(r => r.StudentId);

        foreach (var s in enrolled.OrderBy(s => s.LastName).ThenBy(s => s.FirstName))
        {
            var membership = membershipList.FirstOrDefault(e => e.StudentId == s.Id);
            if (membership is not null && !IsMemberAtDate(membership, exam.Date)) continue;

            // Niveau-Klausur: nur Schüler mit passendem Niveau zeigen. Klausuren ohne
            // Niveau-Zuordnung gelten weiterhin für die ganze Gruppe.
            if (exam.Niveau.HasValue && membership?.Niveau != exam.Niveau) continue;

            existing.TryGetValue(s.Id, out var result);
            var row = new ExamResultRow(s.Id, s.FullName, Tasks, result, _exam.GradingKey, _examMaxPoints, _grading);
            row.OnChanged = SaveRow;
            Rows.Add(row);
        }
    }

    private void SaveRow(ExamResultRow row) => _results.Save(row.ToModel(_exam.Id));

    private static bool IsMemberAtDate(GroupMembership membership, DateOnly date) => membership.Period switch
    {
        MembershipPeriod.H1Only => date.Month >= 8 || date.Month <= 1,
        MembershipPeriod.H2Only => date.Month >= 2 && date.Month <= 7,
        MembershipPeriod.Custom => (membership.JoinedAt is null || date >= membership.JoinedAt.Value)
                                && (membership.LeftAt  is null || date <= membership.LeftAt.Value),
        _                       => true,
    };
}

// ── Zeile im Punkteraster ──────────────────────────────────────────────────

public partial class ExamResultRow : ObservableObject
{
    private readonly Guid _resultId;
    private readonly List<GradingKeyEntry> _gradingKey;
    private readonly double _examMaxPoints;
    private readonly GradingService _grading;

    public Guid StudentId { get; }
    public string Name { get; }

    public ObservableCollection<PointsCell> Cells { get; } = [];

    [ObservableProperty] private bool _absent;
    [ObservableProperty] private string _comment = "";
    [ObservableProperty] private double _totalPoints;
    [ObservableProperty] private string _gradeDisplay = "";

    public string TotalPointsDisplay => TotalPoints.ToString("0.##", CultureInfo.InvariantCulture);

    public Action<ExamResultRow>? OnChanged { get; set; }

    public ExamResultRow(Guid studentId, string name, List<ExamTask> tasks, ExamResult? existing,
        List<GradingKeyEntry> gradingKey, double examMaxPoints, GradingService grading)
    {
        StudentId = studentId; Name = name;
        _gradingKey = gradingKey; _examMaxPoints = examMaxPoints; _grading = grading;
        _resultId = existing?.Id ?? Guid.NewGuid();
        _absent = existing?.Absent ?? false;
        _comment = existing?.Comment ?? "";

        for (var i = 0; i < tasks.Count; i++)
        {
            double? pts = existing is not null && i < existing.Points.Count ? existing.Points[i] : null;
            var cell = new PointsCell(tasks[i].MaxPoints, pts);
            cell.OnChanged = () => { RecomputeTotals(); OnChanged?.Invoke(this); };
            Cells.Add(cell);
        }
        RecomputeTotals();
    }

    partial void OnAbsentChanged(bool value)
    {
        RecomputeTotals();
        OnChanged?.Invoke(this);
    }

    partial void OnCommentChanged(string value) => OnChanged?.Invoke(this);

    private void RecomputeTotals()
    {
        TotalPoints = Cells.Sum(c => c.IsInvalid ? 0 : (c.Value ?? 0));
        OnPropertyChanged(nameof(TotalPointsDisplay));
        GradeDisplay = Absent ? "abwesend" : _grading.CalculateGrade(TotalPoints, _examMaxPoints, _gradingKey);
    }

    public ExamResult ToModel(Guid examId) => new()
    {
        Id = _resultId,
        ExamId = examId,
        StudentId = StudentId,
        Points = Cells.Select(c => c.Value ?? 0).ToList(),
        TotalPoints = TotalPoints,
        Grade = Absent ? null : GradeDisplay,
        Absent = Absent,
        Comment = string.IsNullOrWhiteSpace(Comment) ? null : Comment.Trim(),
    };
}

// ── Eine Punktezelle ─────────────────────────────────────────────────────────

public partial class PointsCell : ObservableObject
{
    public double MaxPoints { get; }
    [ObservableProperty] private double? _value;
    [ObservableProperty] private bool _isInvalid;

    public Action? OnChanged { get; set; }

    public PointsCell(double maxPoints, double? value)
    {
        MaxPoints = maxPoints;
        _value = value;
        _isInvalid = IsOutOfRange(value);
    }

    /// Setzt den Wert; bei Punkten außerhalb 0..Maximalpunkte wird nur rot markiert,
    /// aber nicht gespeichert (1.4.5) — OnChanged (und damit Autosave) wird dann nicht ausgelöst.
    public void TrySetValue(double? value)
    {
        Value = value;
        IsInvalid = IsOutOfRange(value);
        if (!IsInvalid) OnChanged?.Invoke();
    }

    private bool IsOutOfRange(double? value) =>
        value.HasValue && (value.Value < 0 || value.Value > MaxPoints + 0.0001);
}