Generates the barcode of a bank slip (pt-br: Boleto bancário) from typeful line (linha digitável)

generateBankSlipBarCode.cs

        /// <summary>
        /// Calculates the bar code.
        /// </summary>
        private string CalculateBarCode(string typefulLine)
        {
            var line = Regex.Replace(typefulLine, "[^0-9]", "");

            if (line.Length < 47)
            {
                line = line + new string('0', 47 - line.Length);
            }

            return line.Substring(0, 4)
                       + line.Substring(32, 15)
                       + line.Substring(4, 5)
                       + line.Substring(10, 10)
                       + line.Substring(21, 10);
        }