WorkerBot.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Telegram.Bot;
using Telegram.Bot.Extensions.Polling;
using Telegram.Bot.Types;
using Telegram.Bot.Exceptions;
using System.Threading;

namespace TelegramBot
{
    internal class WorkerBot
    {
        public static async Task HandleUpdateAsync(ITelegramBotClient botClient, Update update, CancellationToken cancellationToken)
        {
            // Некоторые действия
            Console.WriteLine(Newtonsoft.Json.JsonConvert.SerializeObject(update));
            if (update.Type == Telegram.Bot.Types.Enums.UpdateType.Message)
            {
                var message = update.Message;
                var link = ParserLink.AngleSharp(message.Text);

                if (message.Text.ToLower() == "/start")
                {
                    await botClient.SendTextMessageAsync(message.Chat, $"Добро пожаловать, {message.Chat.Username}");
                    return;
                }
                if (message.Text.ToLower().Contains("https"))
                {
                    await botClient.SendPhotoAsync(message.Chat, link[0]);
                    return;
                }
                await botClient.SendTextMessageAsync(message.Chat, "Привет!");
            }
        }

        public static async Task HandleErrorAsync(ITelegramBotClient botClient, Exception exception, CancellationToken cancellationToken)
        {
            // Некоторые действия
            Console.WriteLine(Newtonsoft.Json.JsonConvert.SerializeObject(exception));
        }
    }
}