what type of sentence

Please explain to me this sentence: Hey! What do you think you're doing?

Is this a simple sentence? (Is the whole thing an independent clause or what? )
What about "Hey!"?

Thank you so much.

[Ouisch]

"Hey" is an interjection - a word used to express emotion or to get attention. "What do you think you're doing" is usually not translated literally, that is, we're not actually asking someone to interpret his thoughts. It is usually used in the context that someone is doing something that is obviously suspect, like trespassing, or stealing something right in front of you.