SearchIndex.cs

using System.Text.RegularExpressions;

namespace ShellDocs.Core;

/* An in-memory search index built from the navigation graph. Each entry
 represents one searchable thing — a page, or a heading within a page.
 Page entries carry a trimmed plain-text body so client-side match can
 find hits that aren't in the title/description surface. */
public sealed class SearchIndex
{
 public IReadOnlyList<SearchEntry> Entries { get; }

 public SearchIndex(IReadOnlyList<SearchEntry> entries) => Entries = entries;

 public static SearchIndex FromGraph(NavigationGraph graph)
 {
 var entries = new List<SearchEntry>();
 Walk(graph.Root, section: null, entries);
 return new SearchIndex(entries);
 }

 private static void Walk(NavigationNode node, string? section, List<SearchEntry> acc)
 {
 if (node.Kind == NodeKind.Page && !string.IsNullOrEmpty(node.Url))
 {
 acc.Add(new SearchEntry(
 Url: node.Url,
 Title: node.Title,
 Description: node.Description,
 Section: section,
 Kind: SearchEntryKind.Page,
 Body: ExtractBodyFromFile(node.Path)));

 // Prefer headings already extracted at render time; otherwise pull
 // them from the source markdown ourselves so the index isn't blank
 // at startup (headings normally populate only when a page renders).
 var headings = node.Headings.Count > 0
 ? node.Headings
 : ExtractHeadingsFromFile(node.Path);
 foreach (var h in headings.Where(h => h.Level == 2 || h.Level == 3))
 {
 acc.Add(new SearchEntry(
 Url: node.Url + "#" + h.Id,
 Title: h.Text,
 Description: null,
 Section: node.Title,
 Kind: SearchEntryKind.Heading));
 }
 }

 var nextSection = node.Kind == NodeKind.Section && !string.IsNullOrEmpty(node.Title)
 ? node.Title
 : section;
 foreach (var child in node.Children)
 {
 Walk(child, nextSection, acc);
 }
 }

 private static readonly Regex FencedBlock = new(@"^```[\s\S]*?^```", RegexOptions.Multiline | RegexOptions.Compiled);
 private static readonly Regex HeadingLine = new(@"^(#{2,3})\s+(.+?)\s*$", RegexOptions.Multiline | RegexOptions.Compiled);

 private static IReadOnlyList<Heading> ExtractHeadingsFromFile(string? path)
 {
 if (string.IsNullOrEmpty(path) || !File.Exists(path)) return Array.Empty<Heading>();
 var text = File.ReadAllText(path);
 // Strip fenced code blocks so # inside code doesn't parse as a heading.
 text = FencedBlock.Replace(text, "");
 var list = new List<Heading>();
 foreach (Match m in HeadingLine.Matches(text))
 {
 var level = m.Groups[1].Value.Length;
 var raw = m.Groups[2].Value.Trim();
 list.Add(new Heading(level, raw, Slugify(raw)));
 }
 return list;
 }

 private static string? ExtractBodyFromFile(string? path)
 {
 if (string.IsNullOrEmpty(path) || !File.Exists(path)) return null;
 return MarkdownPlainText.Extract(File.ReadAllText(path));
 }

 private static string Slugify(string text)
 {
 var lowered = text.ToLowerInvariant();
 var sb = new System.Text.StringBuilder(lowered.Length);
 var lastDash = false;
 foreach (var ch in lowered)
 {
 if (char.IsLetterOrDigit(ch)) { sb.Append(ch); lastDash = false; }
 else if ((ch == ' ' || ch == '-' || ch == '_') && !lastDash)
 {
 sb.Append('-'); lastDash = true;
 }
 }
 return sb.ToString().Trim('-');
 }
}

public record SearchEntry(
 string Url,
 string Title,
 string? Description,
 string? Section,
 SearchEntryKind Kind,
 string? Body = null);

public enum SearchEntryKind { Page, Heading }