add: table of contents

YaeBlog.Core/Services/TableOfContentService.cs

@@ -0,0 +1,20 @@
+using System.Collections.Concurrent;
+using YaeBlog.Core.Abstractions;
+using YaeBlog.Core.Models;
+
+namespace YaeBlog.Core.Services;
+
+public class TableOfContentService : ITableOfContentService
+{
+    private readonly ConcurrentDictionary<string, BlogHeadline> _headlines = [];
+
+    public IReadOnlyDictionary<string, BlogHeadline> Headlines => _headlines;
+
+    public void AddHeadline(string filename, BlogHeadline headline)
+    {
+        if (!_headlines.TryAdd(filename, headline))
+        {
+            throw new InvalidOperationException();
+        }
+    }
+}