using Markdig;
using Markdig.Extensions.Yaml;
using Markdig.Syntax;

namespace Elternbeirat.Web.Services;

/// <summary>
/// Reads simple <c>key: value</c> pairs from a Markdown file's YAML front
/// matter. Kept deliberately minimal (one value per line, no nesting) — this is
/// enough for titles and dates. YamlDotNet will take over once we need
/// structured metadata. Front-matter keys stay German because the Markdown
/// files are edited by German-speaking editors.
/// </summary>
public static class FrontMatter
{
    /// <summary>
    /// Returns the value of the given front-matter key, or <c>null</c> if the
    /// file has no front matter or the key is missing. The key match is
    /// case-insensitive; surrounding quotes on the value are removed.
    /// </summary>
    public static string? Read(string key, MarkdownDocument document, string source)
    {
        var block = document.Descendants<YamlFrontMatterBlock>().FirstOrDefault();
        if (block is null)
        {
            return null;
        }

        var prefix = key + ":";
        var frontMatter = source.Substring(block.Span.Start, block.Span.Length);
        foreach (var line in frontMatter.Split('\n'))
        {
            var trimmed = line.Trim();
            if (trimmed.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
            {
                return trimmed[prefix.Length..].Trim().Trim('"');
            }
        }

        return null;
    }
}