Regex to replace all \n in a String, but no those inside [code] [/code] tag

I need help to replace all \n (new line) caracters for
in a String, but not those \n inside [code][/code] tags. My brain is burning, I can't solve this by my own :(

Example:

test test test
test test test
test
test

[code]some
test
code
[/code]

more text

Should be:

test test test<br />
test test test<br />
test<br />
test<br />
<br />
[code]some
test
code
[/code]<br />
<br />
more text<br />

Thanks for your time. Best regards.