Free Comment System, BUT...

Hi Folks,

I'm looking for some free comment code (to create a comment system) for the website I'm building. There's lots of good options out there, but I'm looking for one that does two things.

1) I want to have authority/access over the comment database (or however the comments are being stored, I'm not particular.) I'm not keen on having it on someone else's server/database on a different site, as I want to make sure it doesn't disappear or get edited without my permission. I know this might seem a little odd, but hopefully not so odd no one has done it before. If I can't do that, at least some serious assurance that my saved comments aren't messed with.

2) (And this is the essential one) I want to have access to the comment program code so I can make changes. This is more than simple CSS style "I want to change the font!" changes. I want to be able to influence whether or not a comment gets posted, return information on the length of the comment to other areas of the site to run other programs ect... I need to access to the guts somehow.

3) Comment system needs to not have a limitation on comments posted (part of the reason for #1, and wanting it on the same sever as my webpage.)

I've found several possibilities while googling, but instead of messing with them all one-by-one or building my own (and the rather large time sink that would be) I thought I would ask around first in case anyone knew one off the top of their head, or had any suggestions! I'm new to comment systems for sites, so if it's newbie friendly that's a plus. But I'm more than willing to suss it out myself if need be (and it's shorter than learning to code my own, lol!)

Thanks!