Initial implementation of Markdown Component for QuestPDF

MarkdownComponent.cs

using Markdig;
using Markdig.Syntax;
using Markdig.Syntax.Inlines;
using QuestPDF.Fluent;
using QuestPDF.Helpers;
using QuestPDF.Infrastructure;

namespace PdfExperiments;

public record MarkdownBlockStyle(Func<IContainer, IContainer>? ItemStyle, 
    TextStyle BlockDefaultTextStyle)
{
    public MarkdownBlockStyle(Func<IContainer, IContainer>? itemStyle) : this(itemStyle, TextStyle.Default)
    {
    }

    public static MarkdownBlockStyle Identity => new(c => c, TextStyle.Default);
}

public enum BlockType
{
    Heading1,
    Heading2,
    Heading3,
    Heading4,
    Heading5,
    Heading,
    Paragraph,
    BlockQuote,
    BlockQuoteLine,
}

public class MarkdownComponent : IComponent
{
    private readonly Dictionary<BlockType, MarkdownBlockStyle> _customStyles;
    private readonly MarkdownDocument _parsed;

    private static readonly Dictionary<BlockType, MarkdownBlockStyle> DefaultStyles = new()
    {
        [BlockType.Heading1] =
            new MarkdownBlockStyle(c => c.PaddingBottom(10).BorderBottom(1).PaddingBottom(4),
                new TextStyle().FontFamily(Fonts.TimesNewRoman).FontSize(24).Bold()),
        [BlockType.Heading2] =
            new MarkdownBlockStyle(c => c.PaddingBottom(6).BorderBottom(1).BorderColor(Colors.Grey.Medium).PaddingBottom(2),
                new TextStyle().FontFamily(Fonts.TimesNewRoman).FontSize(21).Bold()),
        [BlockType.Heading3] =
            new MarkdownBlockStyle(c => c, new TextStyle().FontFamily(Fonts.TimesNewRoman).FontSize(18).Bold()),
        [BlockType.Heading4] =
            new MarkdownBlockStyle(c => c, new TextStyle().FontSize(16).Bold()),
        [BlockType.Heading5] =
            new MarkdownBlockStyle(c => c, new TextStyle().FontSize(14).Bold()),
        [BlockType.Heading] =
            new MarkdownBlockStyle(c => c, new TextStyle().FontFamily(Fonts.TimesNewRoman).FontSize(12).Bold()),
        [BlockType.BlockQuote] =
            new MarkdownBlockStyle(c => 
                c.PaddingHorizontal(36).PaddingVertical(18)
                    .BorderLeft(4).BorderColor(Colors.Green.Medium).PaddingBottom(-18).PaddingLeft(18)),
        [BlockType.BlockQuoteLine] =
            new MarkdownBlockStyle(c => c.PaddingBottom(18), new TextStyle().FontFamily(Fonts.TimesNewRoman).Italic().FontSize(14)),
        [BlockType.Paragraph] =
            new MarkdownBlockStyle(c => c.PaddingBottom(9))
    };

    public MarkdownComponent(string markdown, Dictionary<BlockType, MarkdownBlockStyle>? customStyles = null)
    {
        _customStyles = customStyles ?? new Dictionary<BlockType, MarkdownBlockStyle>();
        _parsed = Markdown.Parse(markdown);
    }

    private MarkdownBlockStyle GetStyler(BlockType blockType)
    =>
        _customStyles.TryGetValue(blockType, out var styler)
            ? styler
            : DefaultStyles.TryGetValue(blockType, out var defaultStyler)
                ? defaultStyler
                : MarkdownBlockStyle.Identity;

    public void Compose(IContainer container)
    {
        container.Column(columnDescriptor =>
        {
            foreach (var block in _parsed)
            {
                RenderBlock(columnDescriptor, block);
            }
        });
    }

    private void RenderBlock(ColumnDescriptor columnDescriptor, Block? block, 
        MarkdownBlockStyle? subStyle = null)
    {
        if (block is null) return;
        
        switch (block)
        {
            case HeadingBlock heading:
            {
                if (heading.Inline is null) break;

                var style = heading.Level switch
                {
                    1 => BlockType.Heading1,
                    2 => BlockType.Heading2,
                    3 => BlockType.Heading3,
                    4 => BlockType.Heading4,
                    5 => BlockType.Heading5,
                    _ => BlockType.Heading
                };

                var headingStyler = GetStyler(style);

                var textStyle = headingStyler.BlockDefaultTextStyle;
                var item = columnDescriptor.Item();
                headingStyler.ItemStyle(item).Text(t => RenderInline(t, heading.Inline, textStyle));
                break;
            }
            case ParagraphBlock paragraph:
            {
                if (paragraph.Inline is null) break;
                var paragraphStyler = subStyle ?? GetStyler(BlockType.Paragraph);
                var blockItem = columnDescriptor.Item();
                blockItem = paragraphStyler.ItemStyle.Invoke(blockItem);
                
                blockItem.Text(textDescriptor =>
                {
                    foreach (var item in paragraph.Inline)
                        RenderInline(textDescriptor, item, paragraphStyler.BlockDefaultTextStyle);
                });
                break;
            }
            case QuoteBlock quote:
                var blockQuoteStyler = GetStyler(BlockType.BlockQuote);
                var blockQuoteTextStyle = blockQuoteStyler.BlockDefaultTextStyle;
                        
                var blockQuoteItem = blockQuoteStyler.ItemStyle(columnDescriptor.Item());
                blockQuoteItem.Column(column =>
                {
                    foreach (var quoteLine in quote)
                        RenderBlock(column, quoteLine, GetStyler(BlockType.BlockQuoteLine));
                });
                break;
            default:
                Console.WriteLine(block.GetType().Name);
                break;
        }
    }

    private static void RenderParagraph(TextDescriptor text, ParagraphBlock paragraph)
    {
        if (paragraph.Inline is null) return;

        var textStyle = new TextStyle();

        foreach (var item in paragraph.Inline)
        {
            RenderInline(text, item, textStyle);
        }
    }

    private static void RenderInline(TextDescriptor text, Inline inline, TextStyle textStyle)
    {
        switch (inline)
        {
            case LiteralInline literal:
                text.Span(literal.Content.ToString()).Style(textStyle);
                break;
            case EmphasisInline emphasis when emphasis.Any():
            {
                foreach (var child in emphasis)
                {
                    switch (emphasis.DelimiterCount)
                    {
                        case 1:
                            RenderInline(text, child, textStyle.Italic());
                            break;
                        case 2:
                            RenderInline(text, child, textStyle.Bold());
                            break;
                        default:
                            RenderInline(text, child, textStyle);
                            break;
                    }
                }

                break;
            }
            case ContainerInline container:
                foreach (var item in container)
                {
                    RenderInline(text, item, textStyle);
                }

                break;
        }
    }
}