TocBlockParser.cs

using Markdig.Helpers;
using Markdig.Parsers;
using Markdig.Syntax;

using System;

namespace Leisn.MarkdigToc
{
    public class TocBlockParser : BlockParser, IAttributesParseable
    {
        public TocOptions Options { get; }
        public TryParseAttributesDelegate? TryParseAttributes { get; set; }

        public TocBlockParser(TocOptions options)
        {
            Options = options ?? throw new ArgumentNullException(nameof(options));
            OpeningCharacters = new[] { '[' };
        }

        readonly string[] TOCTags = { "[toc]", "[[_toc_]]" };
        public override BlockState TryOpen(BlockProcessor processor)
        {
            if (processor.IsCodeIndent)
                return BlockState.None;
            var line = processor.Line;
            var column = processor.Column;
            var sourcePosition = line.Start;

            foreach (var toc in TOCTags)
            {
                var match = line.MatchLowercase(toc);
                if (!match)
                    continue;

                var c = line.CurrentChar;
                for (int i = 0; i < toc.Length; i++)
                    c = processor.NextChar();

                StringSlice trivia = StringSlice.Empty;
                if (processor.TrackTrivia && c.IsSpaceOrTab())
                {
                    trivia = new StringSlice(processor.Line.Text, processor.Start, processor.Start);
                    processor.NextChar();
                }

                var block = new TocBlock(this)
                {
                    Column = column,
                    Span = { Start = sourcePosition },
                    TriviaAfterAtxHeaderChar = trivia,
                    TriviaBefore = processor.UseTrivia(sourcePosition - 1),
                    LinesBefore = processor.LinesBefore,
                    NewLine = processor.Line.NewLine,
                };
                processor.LinesBefore = null;

                processor.NewBlocks.Push(block);
                if (!processor.TrackTrivia)
                {
                    processor.GoToColumn(column + toc.Length + 1);
                }

                TryParseAttributes?.Invoke(processor, ref processor.Line, block);

                block.Span.End = processor.Line.End;

                if (processor.TrackTrivia)
                {
                    var wsa = new StringSlice(processor.Line.Text, processor.Line.End + 1, processor.Line.End);
                    block.TriviaAfter = wsa;
                    if (wsa.Overlaps(block.TriviaAfterAtxHeaderChar))
                        block.TriviaAfter = StringSlice.Empty;
                }

                return BlockState.Break;
            }

            return BlockState.None;
        }

        public override bool Close(BlockProcessor processor, Block block)
        {
            if (!processor.TrackTrivia)
            {
                (block as TocBlock)?.Lines.Trim();
            }
            return true;
        }
    }
}