what Arrch said 
also: I did not test it. it should work in principle, but it probably wont as I am a horrible coder (I am sloppy with the details, so chances are high there are more little bugs in there.) also. I never tested it.
so the principle is correct. but you need to work on the details ... and in order to do that, you need to understand the principle... so in the end... its still down to you to write your code
also, you want to understand it, so you can edit it later.
I just found it easyer to do it, than to explain how to do it.