15 years later the app was close to half milion lines long of huge bowl of spaghetti code. Only comments in whole codebase were timestamps. I don't know why he dated his code, but I find it fascinating: he never deleted basically anything so you can find different timeframes of when he discovered various concepts. There is use-exception-instead-of-if period, there is time when he discovered design patterns, there is time before he learnt SQL so all the database queries was done by iterating over whole tables and such. I am sure I will find commented Hello world somewhere in the code someday.
I am working on this codebase for 10 years. Code quality improved and major issues get fixed, but there is not enough budget to actually rewrote whole system, so after all it is more or less huge spaghetti monster and I get used to it.
Company did tried to migrate to other software few times, but the software is just too specific for given industry and legislation of small country that the companies who tried to create similar software usually went bankrupt soon.
A spaghetti monster which solves a real business problem can be improved, chunked into pieces, gradually rewritten, whatever improves maintenance. If need be, there will be funds and time for doing so.
By contract, an impeccably architectured, layered, no-design-patterns-omitted, product which solves no business problem .. oh, the horror.
The company is quite fascinating, they started around 1945 and during the years they've became small conglomerate. There are three or even four generations workign together and once they like you as a person they will find something for you to do.
The basic was so old it only had two (yes two) character variables - the Fortran code made liberal uses of Arithmetic IF staements !!!!
An example of one is IF (S12 - 1.0) 13, 13, 12
As pointed out elsewhere, this is definitely solving a real problem, the longevity of the app is the proof.
Instead of rewriting, can you replace it with newer idioms? A MVP/PoC for a newer way of solving a problem (AR may be here) that the software solves with some tangible gains, the latter is more important, can lead to approval of a mini budget for that MVP and who knows what that can lead to.
App consist of maybe 20 different codebases that generate around 30 executables, kind of randomly, fetching source files from different codebases as programmer find a fit + random "fixes" of system modules/component make it all very very hard to do much groundbreaking work.
I would say that rewrite would cost about 2 millions of euros. Which is really big price tag for company that use this system as a backoffice tool.