private static bool SearchByUsernames(string text, int position, out string searchText)
        {
            if (text.Length == 0)
            {
                searchText = string.Empty;
                return false;
            }

            var found = false;
            var index = -1;
            var length = 0;

            for (int i = position - 1; i >= 0; i--)
            {
                if (text[i] == '@')
                {
                    found = true;
                    index = i;
                    break;
                }
            }

            if (found)
            {
                for (int i = index + 1; i < position; i++)
                {
                    if (IsValidUsernameSymbol(text[i]))
                    {
                        length++;
                    }
                    else
                    {
                        found = false;
                        break;
                    }
                }
            }

            if (found)
            {
                searchText = text.Substring(index + 1, length);
            }
            else
            {
                searchText = string.Empty;
            }

            return found;
        }