LehrerApp/LehrerApp.Desktop/Views/Groups/ExamGradingDialog.axaml.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Controls.Templates;
using Avalonia.Data;
using Avalonia.Input;
using Avalonia.Interactivity;
using Avalonia.Layout;
using Avalonia.Media;
using Avalonia.Threading;
using Avalonia.VisualTree;
using LehrerApp.Desktop.ViewModels.Groups;
using System.Collections;
using System.Globalization;

namespace LehrerApp.Desktop.Views.Groups;

public partial class ExamGradingDialog : Window
{
    private static readonly IBrush InvalidBackground = new SolidColorBrush(Color.Parse("#FFCDD2"));

    public ExamGradingDialog() => InitializeComponent();

    protected override void OnOpened(EventArgs e)
    {
        base.OnOpened(e);
        if (DataContext is ExamGradingDialogViewModel vm) BuildColumns(vm);
    }

    private void BuildColumns(ExamGradingDialogViewModel vm)
    {
        var grid = this.FindControl<DataGrid>("ResultGrid");
        if (grid is null) return;

        grid.Columns.Clear();

        grid.Columns.Add(new DataGridTextColumn
        {
            Header  = "Schüler",
            Binding = new Binding("Name"),
            IsReadOnly = true,
            Width   = new DataGridLength(170, DataGridLengthUnitType.Pixel),
        });

        for (var i = 0; i < vm.Tasks.Count; i++)
        {
            var task = vm.Tasks[i];
            grid.Columns.Add(new DataGridTemplateColumn
            {
                Header       = string.IsNullOrWhiteSpace(task.Title) ? $"Aufg. {task.Nr}" : $"{task.Nr}. {task.Title}",
                Width        = new DataGridLength(1, DataGridLengthUnitType.Star),
                CellTemplate = BuildPointsCellTemplate(i, grid, vm.Tasks.Count),
            });
        }

        grid.Columns.Add(new DataGridTextColumn
        {
            Header = "Summe", Binding = new Binding("TotalPointsDisplay"), IsReadOnly = true,
            Width = new DataGridLength(70, DataGridLengthUnitType.Pixel),
        });
        grid.Columns.Add(new DataGridTextColumn
        {
            Header = "Note", Binding = new Binding("GradeDisplay"), IsReadOnly = true,
            Width = new DataGridLength(70, DataGridLengthUnitType.Pixel),
        });
        grid.Columns.Add(new DataGridTemplateColumn
        {
            Header = "Abw.", Width = new DataGridLength(50, DataGridLengthUnitType.Pixel),
            CellTemplate = BuildAbsentCellTemplate(),
        });
        grid.Columns.Add(new DataGridTemplateColumn
        {
            Header = "Kommentar", Width = new DataGridLength(180, DataGridLengthUnitType.Pixel),
            CellTemplate = BuildCommentCellTemplate(grid),
        });
    }

    private IDataTemplate BuildPointsCellTemplate(int taskIndex, DataGrid grid, int taskCount)
    {
        var cellName = $"Pts_{taskIndex}";
        return new FuncDataTemplate<ExamResultRow>((row, _) =>
        {
            if (row is null) return new TextBlock();
            var cell = row.Cells.ElementAtOrDefault(taskIndex);
            if (cell is null) return new TextBlock();

            var tb = new TextBox
            {
                Name = cellName,
                Text = FormatPoints(cell.Value),
                BorderThickness = new Thickness(0),
                Background = Brushes.Transparent,
                Padding = new Thickness(6, 4),
                HorizontalContentAlignment = HorizontalAlignment.Center,
            };
            ToolTip.SetTip(tb, $"max. {FormatPoints(cell.MaxPoints)} Punkte");
            UpdateInvalidVisual(tb, cell.IsInvalid);

            cell.PropertyChanged += (_, pe) =>
            {
                if (pe.PropertyName == nameof(PointsCell.IsInvalid))
                    UpdateInvalidVisual(tb, cell.IsInvalid);
            };

            tb.LostFocus += (_, _) => CommitPointsCell(tb, cell);
            tb.KeyDown += (_, e) => HandlePointsCellKeyDown(e, grid, row, taskIndex, taskCount);

            return tb;
        });
    }

    private static void CommitPointsCell(TextBox tb, PointsCell cell)
    {
        var text = tb.Text?.Trim().Replace(',', '.');
        double? parsed = string.IsNullOrEmpty(text)
            ? null
            : double.TryParse(text, NumberStyles.Any, CultureInfo.InvariantCulture, out var v) ? v : cell.Value;
        cell.TrySetValue(parsed);
        tb.Text = FormatPoints(cell.Value);
    }

    private static void UpdateInvalidVisual(TextBox tb, bool invalid) =>
        tb.Background = invalid ? InvalidBackground : Brushes.Transparent;

    private static string FormatPoints(double? value) =>
        value?.ToString("0.##", CultureInfo.InvariantCulture) ?? "";

    private IDataTemplate BuildAbsentCellTemplate()
    {
        return new FuncDataTemplate<ExamResultRow>((row, _) =>
        {
            if (row is null) return new TextBlock();
            var cb = new CheckBox { IsChecked = row.Absent, HorizontalAlignment = HorizontalAlignment.Center };
            cb.IsCheckedChanged += (_, _) => row.Absent = cb.IsChecked == true;
            return cb;
        });
    }

    private IDataTemplate BuildCommentCellTemplate(DataGrid grid)
    {
        const string cellName = "Comment";
        return new FuncDataTemplate<ExamResultRow>((row, _) =>
        {
            if (row is null) return new TextBlock();
            var tb = new TextBox
            {
                Name = cellName,
                Text = row.Comment,
                BorderThickness = new Thickness(0),
                Background = Brushes.Transparent,
                Padding = new Thickness(6, 4),
            };
            tb.LostFocus += (_, _) => row.Comment = tb.Text ?? "";
            tb.KeyDown += (_, e) => HandleCommentCellKeyDown(e, grid, row, cellName);
            return tb;
        });
    }

    /// Zwei Korrektur-Workflows (Nutzer-Feedback): "Arbeit für Arbeit" (ein Schüler komplett,
    /// dann der nächste) und "Aufgabe für Aufgabe" (eine Aufgabe für alle Schüler, dann die
    /// nächste) — beide bewusst ohne Moduswechsel über zwei verschiedene Tasten, weil sich beide
    /// Reihenfolgen ohnehin schon auf die Tabelle abbilden (Zeile vs. Spalte). Enter läuft
    /// zeilenweise (am Zeilenende zurück zu Aufgabe 1 der nächsten Zeile), Pfeil-hoch/-runter
    /// spaltenweise (am Spaltenende weiter zur Nachbaraufgabe) — beides bricht am Tabellenende
    /// einfach ab, kein Rundlauf zurück zum Anfang.
    private void HandlePointsCellKeyDown(KeyEventArgs e, DataGrid grid, ExamResultRow row, int taskIndex, int taskCount)
    {
        if (e.Key is not (Key.Down or Key.Up or Key.Enter)) return;
        e.Handled = true;

        if (grid.ItemsSource is not IList items) return;
        var rowIdx = items.IndexOf(row);
        if (rowIdx < 0) return;

        int targetRowIdx;
        int targetTaskIndex;

        if (e.Key == Key.Enter)
        {
            targetTaskIndex = taskIndex + 1;
            targetRowIdx = rowIdx;
            if (targetTaskIndex >= taskCount) { targetTaskIndex = 0; targetRowIdx = rowIdx + 1; }
        }
        else
        {
            targetTaskIndex = taskIndex;
            targetRowIdx = e.Key == Key.Up ? rowIdx - 1 : rowIdx + 1;
            if (targetRowIdx < 0) { targetRowIdx = items.Count - 1; targetTaskIndex = taskIndex - 1; }
            else if (targetRowIdx >= items.Count) { targetRowIdx = 0; targetTaskIndex = taskIndex + 1; }
        }

        if (targetTaskIndex < 0 || targetTaskIndex >= taskCount
            || targetRowIdx < 0 || targetRowIdx >= items.Count) return;

        FocusPointsCell(grid, items[targetRowIdx]!, targetTaskIndex);
    }

    /// Enter/Pfeil-Hoch/Pfeil-Runter springen im Kommentarfeld zur gleichen Spalte in der
    /// Nachbarzeile (Tab funktioniert bereits über die normale Fokus-Reihenfolge).
    private void HandleCommentCellKeyDown(KeyEventArgs e, DataGrid grid, object rowItem, string cellName)
    {
        if (e.Key is not (Key.Down or Key.Up or Key.Enter)) return;
        e.Handled = true;

        if (grid.ItemsSource is not IList items) return;
        var idx = items.IndexOf(rowItem);
        if (idx < 0) return;
        var targetIdx = e.Key == Key.Up ? idx - 1 : idx + 1;
        if (targetIdx < 0 || targetIdx >= items.Count) return;

        var targetItem = items[targetIdx]!;
        grid.ScrollIntoView(targetItem, grid.CurrentColumn);

        Dispatcher.UIThread.Post(() =>
        {
            var targetTb = grid.GetVisualDescendants().OfType<TextBox>()
                .FirstOrDefault(t => t.DataContext == targetItem && t.Name == cellName);
            if (targetTb is null) return;
            targetTb.Focus();
            targetTb.SelectAll();
        }, DispatcherPriority.Loaded);
    }

    /// Spalte 0 ist "Schüler", danach folgen die Aufgaben-Spalten in Reihenfolge — daher der
    /// Offset von 1 beim Auflösen des Spaltenobjekts für ScrollIntoView (muss auch horizontal
    /// zur Nachbaraufgabe scrollen, nicht nur vertikal zur Nachbarzeile).
    private void FocusPointsCell(DataGrid grid, object targetItem, int targetTaskIndex)
    {
        var targetColumn = grid.Columns.ElementAtOrDefault(1 + targetTaskIndex);
        if (targetColumn is null) return;
        grid.ScrollIntoView(targetItem, targetColumn);

        var cellName = $"Pts_{targetTaskIndex}";
        Dispatcher.UIThread.Post(() =>
        {
            var targetTb = grid.GetVisualDescendants().OfType<TextBox>()
                .FirstOrDefault(t => t.DataContext == targetItem && t.Name == cellName);
            if (targetTb is null) return;
            targetTb.Focus();
            targetTb.SelectAll();
        }, DispatcherPriority.Loaded);
    }

    private void OnClose(object? sender, RoutedEventArgs e) => Close();
}