Looks like that he parses the log with the hook and then stores the json output in ~/.git-stats (git-stats --record), my guess is that he then generates the cal

Looks like that he parses the log with the hook and then stores the json output in ~/.git-stats (git-stats --record), my guess is that he then generates the calendar only from that data so that he doesn't have to parse the whole history all over again. I'm a bit worried about the size of that file though...