🚧 Anti-spam system based on entities

Core/Extensions/StartupExtension.cs

@@ -1,4 +1,5 @@
 using System.Collections.Concurrent;
+using Kruzya.TelegramBot.Core.Cache;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Kruzya.TelegramBot.Core.Extensions
@@ -7,5 +8,8 @@ namespace Kruzya.TelegramBot.Core.Extensions
     {
         public static IServiceCollection AddQueue<T>(this IServiceCollection collection)
             => collection.AddSingleton<ConcurrentQueue<T>>();
+
+        public static IServiceCollection AddMemoryCache<TKey, TValue>(this IServiceCollection collection)
+            => collection.AddSingleton<MemoryCache<TKey, TValue>>();
     }
 }

Core/Extensions/UserExtension.cs

@@ -8,7 +8,7 @@ namespace Kruzya.TelegramBot.Core.Extensions
         public static string ToHtml(this User user)
         {
             var text = new StringBuilder();
-            text.Append("<a href=\"tg://user?id={member.Id}\">");
+            text.Append($"<a href=\"tg://user?id={user.Id}\">");
             if (!string.IsNullOrWhiteSpace(user.Username))
                 text.Append(user.Username);
             else