[GNC] Cash Accounting with Automated GST

[flywire]

TLDR; Automate GST for cash accounting by preprocessing transactions to
enrich with GST and import as a multisplit file

GST effectively doubles the number of transactions so you'll want automated
gst calculations. Automated gst has been arbitrarily restricted to business
finances in GnuCash which enforces accrual accounting. Additionally, the
associated A/R and A/P appear to be a big overhead that's not really
compatible with the simpler personal finances cash accounting workflow.

GST accounts are the same regardless of which system is used - see
https://www.gnucash.org/viewdoc.phtml?rev=4&lang=C&doc=guide and
https://lists.gnucash.org/pipermail/gnucash-user/2021-July/097083.html

Transaction data can be preprocessed to add gst splits before loading it
into GnuCash as a multisplit csv (or qif equivalent). I normally
pre-process transactions in a spreadsheet using the 80:20 rule to classify
most (90%) transactions then fix the remaining ones within GnuCash. The
most important thing is to try and distinguish gst from non-gst
transactions.

Multisplit csv files are more complex, transactions require a line for each
split and don't support specifying an account for the opposing split for
the whole file like importing normal csv files. After adding accounts to
transactions you'll want another process to prepare the splits based on the
account gst attribute. For me, that's a python program and I use GnuCash
preferences, Import, clear Use bayesian matching.

Multisplit csv files - see
https://lists.gnucash.org/pipermail/gnucash-user/2021-August/097442.html