In case you are wondering how core Moodle really is - I tried to calculate it. To get the "real" number of LOC I've excluded external libraries, build and lang directories and I ended up with about 800k for PHP code and 90k for JS. Those are non-empty and non-comment lines - see lines of code for Moodle 2.6 to 3.4 for more details..
Add in a few plugins and we can boast it's a million. Or perhaps in the words of Dr Evil a Meeeeeeeeelion.