NuclearWaffle

So I was given this as it was found in my friends new house and he didn't want it. I was wondering what would be the bare minimum i'd need to get to give it a hope of giving it life again? I've not done anything techy and I'm coming back to airsoft after a fair few years hiatus so may not be too clued up anymore. Thanks in advance So I'm thinking a new upper receiver, new hop unit/barrel. I'm yet to charge the battery to check the gearbox function.