Strong exclamatory agreement, often to an unusually concise or precise statement or proposed course of action.
This is the correct spelling - beware the overformal 'fucking a', taking time to pronounce the g is a profanity faux pas and de-emphasizes the strong expression of agreement - you might as well say "jolly good show", queerbait.
Also beware dropping the apostrophe for the omitted g, just because we're using profanity doesn't mean we need to do it like an illiterate.
Ripley - "I say we take off, and nuke the entire site from orbit. It's the only way to be sure"
Hudson - "Fuckin' A..."