How to parse through Mobile USSD Parameters passed as http GET requests

Question

Am trying to build a web api that will process data supplied by a USSD server from the mobile network operator (MNO). Below is a snippet of how this kind of interaction operates with the External System being My App.

For each request, I have to determine at what level the user is and respond with the appropriate menu. The MNO will send me something like http://my_app_url?*123*#. Since there is nothing between the last * and the #, I determine that this is a root menu request and I can respond with a menu to the user e.g. 1. Register, 2. Check Balance, 3. Request PIN. Assuming the user wants to Check Balance, they will select Menu 2 on their mobile phone and the MNO will send to me http://my_app_url?*123*2#. I respond with 1. Enter Account Number, 2. Request call back. The user opts to enter the account number and the MNO will send http://my_app_url?*123*2*1# which will tell me where the user is at.

While the whole menu is not long, it can get confusing to maintain as I can have the following combination. http://my_app_url?*123*1*2*3*1# or http://my_app_url?*123*1*1*3# or http://my_app_url?*123*2*1*3*1# etc etc

Some more info:

1. Each request sent from the MNO comes with the mobile number of the user, a USSD session ID created by the MNO which will remain until the USSD session is over and the USSD Parameters i.e. the from the first * to the # in the examples above.

2. I have stored the Menus for the USSD App in a database (sql fiddle) so depending on the level a user is at, I can know what menu to serve them e.g. if its root request, I can serve the user with all the menus whose parent_menu is 1. If its a check balance request, I will respond with all the menu's whose parent menu is 2 etc etc

My current approach to determine what request the user is making is to write multiple if else statements but in the middle am loosing track and its getting complicated. Deep down I feel there must be a more elegant way to parse through the requests sent by the user and determine what level the request is at and know what to serve them. Can you provide a better approach? Better yet, do you have experience in building this type of app and could you share you logic of traversing the menus?

Answer 1

I had a similar problem some months ago. To me I used Regular expressions to process the USSD string i.e the *123*3*3#. But you will still need the if else statements. Depending on your system you will need to divide your code into classes.

Example way of processing using Regex is:

ussd_string=123*2
if bool(re.match(r"^(\d+)[*]2",self.ussd_string)):
     #this will match 123*2 so process here

Answer 2

You can create extra columns for the ussd users table to track the current level of the user and use something like progress .If you are still in need of this i would be glad to inform you more.