Post-processing an uploaded (txt) file

I’d like to know what is the best way of going about this.

After a user uploads a specific kind of file (.txt), I want to do some automatic post-processing. I’d like to read the file in a delimited format and then update a mysql table with the values read.

Where should this post-processing be done?

I know how to do the file reading and outputting to mysql, I just don’t know where this code should go logistically. PHP/WP beginner here.