Programmatically set default column values based on folder in SharePoint Online

I'm working on enhancing metadata in our SharePoint online (O365) environment. Since a portion of my user base is used to foldering (explorer style), I've started using default column values to automatically set values on any files added to that specific folder (we have content organized categorically by folder currently). An example is our HR documents library - we have separate folders for recruiting, payroll, personnel files, etc. that automatically categorize files added to that folder with the same categories (recruiting, payroll, personnel, etc.). This supports both "search" and "click" users and makes adoption WAY easier while getting important metadata.

I want to implement this in a larger, more dynamic fashion, so manually setting default column values on each folder is not going to be scalable.

How can I reference the top level folder within the library (or even the current folder) for each newly added file and populate the "category" field for that new file with that folder name? I can do some very basic C# or Java code copy/paste, but bonus points for non-coding solutions =)

I was actually able to use MS Flow to accomplish this in a pretty simple and straightforward fashion without managing custom views per team. The concept at a high level was:

1. (Trigger) When a new document is created in a folder in the library
2. Get the link of the parent folder of the newly added document
3. Create a variable (or just code it out in the Flow step) to parse out the name of the parent folder from the parent folder link (should be all text to the right of the last "/")
4. Set the category field as the variable

I'm sure that you could do the same right in a SharePoint designer workflow, but I prefer flow due to the visual aspect of it and being far easier to troubleshoot.