Mood x Moody: Qual a diferença

I think a lot o people have this same doubt, the difference between MOOD and MOODY and when we can use both.

I saw at a movie couple days ago I guy inviting another one to play poker, so he said:\
- Hey, let`s play some poker.

The other guy said:
- No thanks, I`m not in a ________(mood or moody).

That`s my doubt ! When do I use Mood or moody and what exactly these two words mean?

Thanks for while.