A Script To Close All Bbcode Tags In Php can you help me write one?

ok, ive got a chat that I made from scratch in flash. Its actually pretty damn cool! I just coded it so bbcode is allowed, but ive got a sligt problem. if sobody dosnt close a tag, then the tag stays active for the following messges. , so i thout, why not add the end of every tag, at the end of every message
example:

[/b][/u][/i][/url][/color]

but then i relized, flash's html encoding is very propor, and all tags must be closed in the order that they were opened!

[b][u]text[/u][/b] << works[b][u]text[/b][/u] << dosn't work

AND if sombody opens the same tag twice, the tag must be closed twice!

[b][b]text[/b][/b] << works[b][b]text[/b] << dosn't work

I need a php script that can take a string, and add close tags to every line, in the same order they were opend. I was thinking of how to approach this, but i just can't come up with a script. Any ideas?

Thanks!

edit: put code in code tags
Edited July 15, 2006 by qwertyiscool (see edit history)

This post was offering hosting credits for helping me write the code, but i have recently found out that you must be hosted to transfer hosting credits. But i still really need this code or anything that can help me!Any input would help as well!!!Thanks!!

Edited July 18, 2006 by qwertyiscool (see edit history)