telegram-bot/modules/ChatManagement/Handler/Greet.cs

using System.Linq;
using System.Threading.Tasks;
using BotFramework;
using BotFramework.Attributes;
using BotFramework.Enums;
using BotFramework.Utils;
using Kruzya.TelegramBot.Core.Extensions;
using Telegram.Bot;
using Telegram.Bot.Types.Enums;
using West.TelegramBot.ChatManagement.Service;

namespace West.TelegramBot.ChatManagement.Handler;

public class Greet : BotEventHandler
{
    private readonly RulesService _rulesService;

    public Greet(RulesService rulesService)
    {
        _rulesService = rulesService;
    }

    [InChat(InChat.Public)]
    [Message(MessageFlag.HasNewChatMembers)]
    public async Task HandleNewChatMembers()
    {
        var message = RawUpdate.Message!;
        var members = message.NewChatMembers!;
        var reply = new HtmlString();
        string membersHtml;
        if (members.Length > 1)
        {
            reply.Code("Приветствуем новых участников!");
            membersHtml = string.Join(", ", members.Select(u => u.ToHtml()));
        }
        else
        {
            reply.Code("Приветствуем нового участника!");
            membersHtml = members.First().ToHtml();
        }

        reply.Br().TextBr("{0}");

        if (await _rulesService.HasRulesAsync(Chat))
        {
            reply.Text("Пожалуйста, ознакомьтесь с правилами. /rules");
        }

        await Bot.SendMessage(Chat.Id, string.Format(reply.ToString(), membersHtml), 
            parseMode: ParseMode.Html, replyParameters: message.MessageId);
    }
}