agent-wiki-ui/Gui/MarkdownView.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Controls.Documents;
using Avalonia.Input;
using Avalonia.Input.Platform;
using Avalonia.Layout;
using Avalonia.Media;
using Markdig;
using Markdig.Extensions.Tables;
using Markdig.Syntax;
using Markdig.Syntax.Inlines;

namespace AgentWikiUi.Gui;

/// <summary>Mostra markdown come controlli Avalonia (nessun HTML): il testo è Markdig, il rendering è qui.</summary>
class MarkdownView : Decorator
{
    public static readonly StyledProperty<string?> SourceProperty = AvaloniaProperty.Register<MarkdownView, string?>(nameof(Source));
    static readonly MarkdownPipeline Pipeline = new MarkdownPipelineBuilder().UseAdvancedExtensions().DisableHtml().Build();
    static readonly FontFamily Mono = new("Cascadia Code, Consolas, DejaVu Sans Mono, Liberation Mono, monospace");

    public string? Source { get => GetValue(SourceProperty); set => SetValue(SourceProperty, value); }

    public MarkdownView()
    {
        // i colori si risolvono in fase di rendering: al cambio di tema si ricostruisce
        ActualThemeVariantChanged += (_, _) => Rebuild();
    }

    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
    {
        base.OnPropertyChanged(change);
        if (change.Property == SourceProperty) Rebuild();
    }

    void Rebuild() => Child = string.IsNullOrEmpty(Source) ? null : RenderBlocks(Markdig.Markdown.Parse(Source, Pipeline), 10);

    IBrush Brush(string key) => this.TryFindResource(key, ActualThemeVariant, out var v) && v is IBrush b ? b : Brushes.Gray;

    Control RenderBlocks(IEnumerable<Block> blocks, double spacing)
    {
        var panel = new StackPanel { Spacing = spacing };
        foreach (var b in blocks) panel.Children.Add(RenderBlock(b));
        return panel;
    }

    Control RenderBlock(Block block) => block switch
    {
        HeadingBlock h => Text(h.Inline, bold: true, size: h.Level switch { 1 => 24, 2 => 20, 3 => 18, 4 => 16, _ => 15.5 }),
        ParagraphBlock p => Text(p.Inline),
        FencedCodeBlock or CodeBlock => Code(string.Join('\n', ((LeafBlock)block).Lines.Lines.Take(((LeafBlock)block).Lines.Count).Select(l => l.ToString()))),
        QuoteBlock q => new Border { BorderBrush = Brush("Border"), BorderThickness = new(3, 0, 0, 0), Padding = new(12, 0, 0, 0), Child = RenderBlocks(q, 8) },
        ListBlock l => List(l),
        Table t => TableOf(t),
        ThematicBreakBlock => new Border { Height = 1, Background = Brush("Border"), Margin = new(0, 6) },
        LeafBlock leaf => Text(leaf.Inline),
        ContainerBlock c => RenderBlocks(c, 8),
        _ => new Panel(),
    };

    Control List(ListBlock list)
    {
        var panel = new StackPanel { Spacing = 4 };
        var n = int.TryParse(list.OrderedStart, out var start) ? start : 1;
        foreach (var item in list.OfType<ListItemBlock>())
        {
            var row = new Grid { ColumnDefinitions = new("Auto,*") };
            var marker = new TextBlock { Text = list.IsOrdered ? $"{n++}." : "•", Foreground = Brush("FgMuted"), Margin = new(0, 0, 8, 0), MinWidth = 18, TextAlignment = TextAlignment.Right };
            var body = RenderBlocks(item, 4);
            Grid.SetColumn(body, 1);
            row.Children.Add(marker);
            row.Children.Add(body);
            panel.Children.Add(row);
        }
        return panel;
    }

    Control Code(string code)
    {
        var text = new SelectableTextBlock { Text = code, FontFamily = Mono, FontSize = 13.5, Padding = new(14, 12, 64, 12) };
        var copy = new Button { Content = "Copia", Classes = { "mini" }, HorizontalAlignment = HorizontalAlignment.Right, VerticalAlignment = VerticalAlignment.Top, Margin = new(0, 6, 6, 0) };
        copy.Click += async (_, _) =>
        {
            if (TopLevel.GetTopLevel(this)?.Clipboard is { } cb) await cb.SetTextAsync(code);
            copy.Content = "Copiato";
            await Task.Delay(1400);
            copy.Content = "Copia";
        };
        return new Border
        {
            Background = Brush("Muted"), BorderBrush = Brush("Border"), BorderThickness = new(1), CornerRadius = new(10),
            Child = new Grid { Children = { new ScrollViewer { HorizontalScrollBarVisibility = Avalonia.Controls.Primitives.ScrollBarVisibility.Auto, Content = text }, copy } },
        };
    }

    Control TableOf(Table table)
    {
        var grid = new Grid();
        var rows = table.OfType<TableRow>().ToList();
        var cols = rows.Max(r => r.Count);
        for (var c = 0; c < cols; c++) grid.ColumnDefinitions.Add(new ColumnDefinition(GridLength.Star));
        for (var r = 0; r < rows.Count; r++)
        {
            grid.RowDefinitions.Add(new RowDefinition(GridLength.Auto));
            var cells = rows[r].OfType<TableCell>().ToList();
            for (var c = 0; c < cells.Count; c++)
            {
                var cell = RenderBlocks(cells[c], 4);
                if (cell is StackPanel { Children: [SelectableTextBlock tb] }) // intestazione in grassetto
                    if (rows[r].IsHeader) tb.FontWeight = FontWeight.SemiBold;
                var align = c < table.ColumnDefinitions.Count ? table.ColumnDefinitions[c].Alignment : null;
                cell.HorizontalAlignment = align switch { TableColumnAlign.Center => HorizontalAlignment.Center, TableColumnAlign.Right => HorizontalAlignment.Right, _ => HorizontalAlignment.Left };
                var box = new Border
                {
                    BorderBrush = Brush("Border"), BorderThickness = new(0.5), Padding = new(10, 6),
                    Background = rows[r].IsHeader ? Brush("Muted") : null, Child = cell,
                };
                Grid.SetRow(box, r); Grid.SetColumn(box, c);
                grid.Children.Add(box);
            }
        }
        return new Border { BorderBrush = Brush("Border"), BorderThickness = new(0.5), CornerRadius = new(6), ClipToBounds = true, Child = grid };
    }

    // Testo con inline; i link sono Run colorati e il clic si risolve con l'hit-test sul testo.
    SelectableTextBlock Text(ContainerInline? inline, bool bold = false, double size = 0)
    {
        var tb = new SelectableTextBlock { TextWrapping = TextWrapping.Wrap };
        if (size > 0) tb.FontSize = size;
        if (bold) tb.FontWeight = FontWeight.SemiBold;
        var links = new List<(int Start, int End, string Url)>();
        var pos = 0;
        AddInlines(tb.Inlines!, inline, new(), links, ref pos);
        if (links.Count > 0) WireLinks(tb, links);
        return tb;
    }

    record struct Style(bool Bold, bool Italic, bool Strike, bool Link);

    void AddInlines(InlineCollection target, ContainerInline? container, Style st, List<(int, int, string)> links, ref int pos)
    {
        if (container is null) return;
        foreach (var node in container)
        {
            switch (node)
            {
                case LiteralInline lit: Add(target, lit.Content.ToString(), st, ref pos); break;
                case LineBreakInline br: Add(target, br.IsHard ? "\n" : " ", st, ref pos); break;
                case CodeInline code:
                    target.Add(new Run(code.Content) { FontFamily = Mono, FontSize = 13.5, Background = Brush("Muted") });
                    pos += code.Content.Length;
                    break;
                case EmphasisInline em:
                    var inner = em.DelimiterChar == '~' ? st with { Strike = true }
                        : em.DelimiterCount >= 2 ? st with { Bold = true } : st with { Italic = true };
                    AddInlines(target, em, inner, links, ref pos);
                    break;
                case LinkInline { IsImage: true } img:
                    Add(target, "[" + string.Concat(img.OfType<LiteralInline>().Select(l => l.Content.ToString())) + "]", st, ref pos);
                    break;
                case LinkInline link:
                    var start = pos;
                    AddInlines(target, link, st with { Link = true }, links, ref pos);
                    if (link.Url is { } url) links.Add((start, pos, url));
                    break;
                case AutolinkInline auto:
                    var s = pos;
                    Add(target, auto.Url, st with { Link = true }, ref pos);
                    links.Add((s, pos, auto.Url));
                    break;
                case ContainerInline c: AddInlines(target, c, st, links, ref pos); break;
                default: break;
            }
        }
    }

    void Add(InlineCollection target, string text, Style st, ref int pos)
    {
        var run = new Run(text);
        if (st.Bold) run.FontWeight = FontWeight.Bold;
        if (st.Italic) run.FontStyle = FontStyle.Italic;
        if (st.Strike) run.TextDecorations = TextDecorations.Strikethrough;
        if (st.Link) { run.Foreground = Brush("Accent"); run.TextDecorations = TextDecorations.Underline; }
        target.Add(run);
        pos += text.Length;
    }

    void WireLinks(SelectableTextBlock tb, List<(int Start, int End, string Url)> links)
    {
        string? UrlAt(Point p)
        {
            var i = tb.TextLayout.HitTestPoint(p).TextPosition;
            foreach (var (s, e, url) in links) if (i >= s && i < e) return url;
            return null;
        }
        tb.PointerMoved += (_, e) => tb.Cursor = UrlAt(e.GetPosition(tb)) is null ? null : new Cursor(StandardCursorType.Hand);
        tb.PointerReleased += async (_, e) =>
        {
            if (tb.SelectionStart != tb.SelectionEnd) return; // era una selezione, non un clic
            if (UrlAt(e.GetPosition(tb)) is { } url && Uri.TryCreate(url, UriKind.Absolute, out var uri) && uri.Scheme is "http" or "https")
                if (TopLevel.GetTopLevel(this)?.Launcher is { } l) await l.LaunchUriAsync(uri);
        };
    }
}