telegram-bot/Core/Extensions/BotExtension.cs

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

namespace Kruzya.TelegramBot.Core.Extensions
{
    public static class BotExtension
    {
        public static async Task<bool> CanPunishMember(this ITelegramBotClient bot, Chat chat, User user, User victim = null)
        {
            var canUse = await IsUserAdminAsync(bot, chat, user);

            if (victim != null && canUse)
            {
                var victimMember = await bot.GetChatMemberAsync(chat, victim.Id);
                canUse = victimMember is not ChatMemberOwner && victimMember is not ChatMemberAdministrator && !victim.IsBot;
            }

            return canUse;
        }

        public static async Task<bool> IsUserAdminAsync(this ITelegramBotClient bot, Chat chat, User user)
        {
            var callerMember = await bot.GetChatMemberAsync(chat, user.Id);
            var isAdmin = callerMember is ChatMemberOwner;

            if (callerMember is ChatMemberAdministrator callerAdmin)
            {
                isAdmin = callerAdmin.CanRestrictMembers;
            }

            return isAdmin;
        }

        public static async Task<bool> CanDeleteMessagesAsync(this ITelegramBotClient bot, Chat chat)
        {
            return await CanDeleteMessagesAsync(bot, chat, await bot.GetMeAsync());
        }

        public static async Task<bool> CanDeleteMessagesAsync(this ITelegramBotClient bot, Chat chat, User user)
        {
            return await bot.GetChatMemberAsync(chat.Id, user.Id) is ChatMemberOwner 
                or ChatMemberAdministrator {CanRestrictMembers: true};
        }
    }
}