I was in your position 10 years ago. We had a Makefile for generating tar.gz, srpm, rpm. Another target for generating RPMs from snapshots. It grows up every month. At the end we had huge Makefile splitted into several files, which was pain to maintain.
That was the time when Tito project was born: https://github.com/dgoodwin/tito
Just drop .spec file in that git directory and use Tito for RPM building. You can use just fraction of its features. And you can learn the more powerful features later.
You do not need to care about changelog bumping. Checking if your collegues pushed git-tag. Inventing how to bump up release for developers build etc.