FrontmatterParser.cs

using YamlDotNet.Serialization;

namespace ShellDocs.Core;

public static class FrontmatterParser
{
 private static readonly string[] LineSeparators = new[] { "\r\n", "\n" };
 private static readonly IDeserializer YamlDeserializer = new DeserializerBuilder().Build();

 public static ParsedDocument Parse(string source)
 {
 if (string.IsNullOrEmpty(source))
 {
 return new ParsedDocument(new Dictionary<string, object?>(), source ?? "");
 }

 var lines = source.Split(LineSeparators, StringSplitOptions.None);
 if (lines.Length < 2 || lines[0].TrimEnd() != "---")
 {
 return new ParsedDocument(new Dictionary<string, object?>(), source);
 }

 var closingIndex = -1;
 for (var i = 1; i < lines.Length; i++)
 {
 if (lines[i].TrimEnd() == "---")
 {
 closingIndex = i;
 break;
 }
 }
 if (closingIndex == -1)
 {
 return new ParsedDocument(new Dictionary<string, object?>(), source);
 }

 var yaml = string.Join("\n", lines[1..closingIndex]);
 var body = string.Join("\n", lines[(closingIndex + 1)..]);

 Dictionary<string, object?> frontmatter;
 try
 {
 frontmatter = YamlDeserializer.Deserialize<Dictionary<string, object?>>(yaml)
 ?? new Dictionary<string, object?>();
 }
 catch (YamlDotNet.Core.YamlException)
 {
 frontmatter = new Dictionary<string, object?>();
 }

 return new ParsedDocument(frontmatter, body);
 }

 public static T? GetValue<T>(this IReadOnlyDictionary<string, object?> frontmatter, string key)
 {
 if (!frontmatter.TryGetValue(key, out var raw) || raw is null) return default;
 if (raw is T typed) return typed;
 try
 {
 return (T)Convert.ChangeType(raw, typeof(T));
 }
 catch
 {
 return default;
 }
 }
}

public record ParsedDocument(IReadOnlyDictionary<string, object?> Frontmatter, string Body);