Just enter the positions inside the yaml data block of your invoice template and generate it. There you have your finished invoice with:
- due date (in days and resolved to actual date)
- with tax, without tax, etc.
- versioned as markdown/yaml files
Use pandoc!
You need the advdate.sty package.
See create-invoice.sh for reference or run it by
$ sh create-invoice.sh example # example is the filename of invoices/This will create a pdf file archive/example.pdf