telegram-bot/modules/CombotAntiSpam/UserJoinHandler.cs

using System.Text;
using System.Threading.Tasks;
using BotFramework;
using BotFramework.Attributes;
using BotFramework.Enums;
using Kruzya.TelegramBot.CombotAntiSpam.Combot;
using Kruzya.TelegramBot.Core.Extensions;
using Telegram.Bot;
using Telegram.Bot.Types.Enums;

namespace Kruzya.TelegramBot.CombotAntiSpam;

public class UserJoinHandler : BotEventHandler
{
    private readonly ICombotClient _combotClient;

    public UserJoinHandler(ICombotClient combotClient)
    {
        _combotClient = combotClient;
    }

    [InChat(InChat.Public)]
    [Message(MessageFlag.HasNewChatMembers)]
    public async Task OnUserJoined()
    {
        var canKickMembers = await Bot.IsUserAdminAsync(Chat, await Bot.GetMe());

        foreach (var member in RawUpdate.Message!.NewChatMembers!)
        {
            if (!(await _combotClient.IsSpammerAsync(member)))
            {
                continue;
            }
                
            var messageText = new StringBuilder();
            messageText.Append("⚠️ <b>Combot Anti-Spam</b>\n\n");
            messageText.Append($"User {member.ToHtml(true)} is spammer.\n");
            messageText.Append(
                $"More details you can find on <a href=\"https://cas.chat/query?u={member.Id}\">CAS site</a>.");
                
            await Bot.SendMessage(Chat, messageText.ToString(), parseMode: ParseMode.Html);
                
            if (canKickMembers)
            {
                await Bot.BanChatMember(Chat, member.Id);
            }
        }
    }
}