SIPSorcery.SIP.SIPUserField.ParseSIPUserField C# (CSharp) Method

        public static SIPUserField ParseSIPUserField(string userFieldStr)
        {
            if (userFieldStr.IsNullOrBlank())
            {
                throw new ArgumentException("A SIPUserField cannot be parsed from an empty string.");
            }

            SIPUserField userField = new SIPUserField();
            string trimUserField = userFieldStr.Trim();

            int position = trimUserField.IndexOf('<');

            if (position == -1)
            {
                // Treat the field as a URI only, except that all parameters are Header parameters and not URI parameters
                // (RFC3261 section 20.39 which refers to 20.10 for parsing rules).
                string uriStr = trimUserField;
                int paramDelimPosn = trimUserField.IndexOf(PARAM_TAG_DELIMITER);

                if (paramDelimPosn != -1)
                {
                    string paramStr = trimUserField.Substring(paramDelimPosn + 1).Trim();
                    userField.Parameters = new SIPParameters(paramStr, PARAM_TAG_DELIMITER);
                    uriStr = trimUserField.Substring(0, paramDelimPosn);
                }

                userField.URI = SIPURI.ParseSIPURI(uriStr);
            }
            else
            {
                if (position > 0)
                {
                    userField.Name = trimUserField.Substring(0, position).Trim().Trim('"');
                    trimUserField = trimUserField.Substring(position, trimUserField.Length - position);
                }

                int addrSpecLen = trimUserField.Length;
                position = trimUserField.IndexOf('>');
                if (position != -1)
                {
                    addrSpecLen = trimUserField.Length - 1;
                    if (position != -1)
                    {
                        addrSpecLen = position - 1;

                        string paramStr = trimUserField.Substring(position + 1).Trim();
                        userField.Parameters = new SIPParameters(paramStr, PARAM_TAG_DELIMITER);
                    }

                    string addrSpec = trimUserField.Substring(1, addrSpecLen);

                    userField.URI = SIPURI.ParseSIPURI(addrSpec);
                }
                else
                {
                    throw new SIPValidationException(SIPValidationFieldsEnum.ContactHeader, "A SIPUserField was missing the right quote, " + userFieldStr + ".");
                }
            }

            return userField;
        }