Shadowmeld, Vanish, Stealth

Not a dps macro but wondering…

Can I have a macro (one button) that will Stealth if available… else in combat it will vanish, else it will shadowmeld to stealth.

Does that make sense

It looks like this will make me stealth and then shadowmeld, if stealth is on cooldown…

/cast [nostealth]!Shadowmeld; !Stealth