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.