Log usage and time spent on a file.

I'm just experimenting at the moment, and want to have an applescript that would run from boot up prety much, that will log the ;

appilcation in use

the current file.

time spent on file, before that file closes,

then log the next file and so on and adding a time stamp,

Early days for what I want to get from it, but i a nut shell a productivity log.