telegram-bot/modules/UrlLimitations/MessageExtension.cs

using System;
using System.Linq;
using System.Threading.Tasks;
using Telegram.Bot;
using Telegram.Bot.Types;
using Telegram.Bot.Types.Enums;

namespace Kruzya.TelegramBot.UrlLimitations;

public static class MessageExtension
{
    public static async Task<bool> HasUnknownMention(this Message message, ITelegramBotClient bot)
    {
        foreach (var mention in message.Entities.Where(e =>
                     e.Type == MessageEntityType.Mention || e.Type == MessageEntityType.TextMention))
        {
            long userId = 0;
            if (mention.Type == MessageEntityType.TextMention)
            {
                userId = mention.User.Id;
            }
            else
            {
                try
                {
                    var chat = await bot.GetChatAsync(
                        new ChatId(message.Text.Substring(mention.Offset, mention.Length)));

                    if (chat != null)
                    {
                        if (chat.Type != ChatType.Private)
                        {
                            return true;
                        }

                        userId = Convert.ToInt64(chat.Id);
                    }
                }
                catch (Exception)
                {
                    return true;
                }
            }

            var status = (await bot.GetChatMemberAsync(message.Chat, userId)).Status;

            if ((new ChatMemberStatus[]
                {
                    ChatMemberStatus.Administrator, ChatMemberStatus.Creator, ChatMemberStatus.Member,
                    ChatMemberStatus.Restricted

                    // i'm not sure about "Restricted"
                    // maybe leaved members with some restrictions also can be "Restricted".
                }).Any(e => e == status) == false)
            {
                return true;
            }
        }

        return false;
    }
}