[cm] greet new members & refactor rules

modules/ChatManagement/Service/RulesService.cs

@@ -0,0 +1,50 @@
+#nullable enable
+
+using System.Threading.Tasks;
+using Kruzya.TelegramBot.Core.Data;
+using Kruzya.TelegramBot.Core.Extensions;
+using Telegram.Bot.Types;
+
+namespace West.TelegramBot.ChatManagement.Service;
+
+public class RulesService
+{
+    private readonly CoreContext _db;
+
+    public RulesService(CoreContext db)
+    {
+        _db = db;
+    }
+
+    public async Task<BotUserValue?> GetRulesOptionAsync(Chat chat)
+    {
+        return await _db.UserValues.FindOption(chat.Id, "rulesMsgId");
+    }
+
+    public async Task<int?> GetRulesMessageIdAsync(Chat chat)
+    {
+        return (await GetRulesOptionAsync(chat))?.GetValue<int>();
+    }
+
+    public async Task<bool> HasRulesAsync(Chat chat)
+    {
+        return await GetRulesMessageIdAsync(chat) != null;
+    }
+
+    public async Task SetRulesAsync(Chat chat, int messageId)
+    {
+        var option = await GetRulesOptionAsync(chat) ?? _db.UserValues.Create();
+        option.SetValue(messageId);
+        _db.AddOrUpdate(option);
+    }
+
+    public async Task RemoveChatRulesAsync(Chat chat)
+    {
+        var option = await GetRulesOptionAsync(chat);
+        if (option == null)
+        {
+            return;
+        }
+        _db.Remove(option);
+    }
+}