Auto-renewable subscriptions transaction observer

Example.swift

extension IAPManager: SKPaymentTransactionObserver {
    
    public func paymentQueue(_ queue: SKPaymentQueue, updatedTransactions transactions: [SKPaymentTransaction]) {
        for transaction in transactions {
            switch (transaction.transactionState) {
            case .purchased:
                SKPaymentQueue.default().finishTransaction(transaction)
                notifyIsPurchased(transaction: transaction)
                break
            case .failed:
                SKPaymentQueue.default().finishTransaction(transaction)
                print("purchase error : \(transaction.error?.localizedDescription ?? "")")
                self.failureBlock?(transaction.error)
                cleanUp()
                break
            case .restored:
                SKPaymentQueue.default().finishTransaction(transaction)
                notifyIsPurchased(transaction: transaction)
                break
            case .deferred, .purchasing:
                break
            default:
                break
            }
        }
    }
    
    private func notifyIsPurchased(transaction: SKPaymentTransaction) {
        refreshSubscriptionsStatus(callback: { 
            self.successBlock?()
            self.cleanUp()
        }) { (error) in            
            // couldn't verify receipt
            self.failureBlock?(error)
            self.cleanUp()
        }
    }
    
    func cleanUp(){
        self.successBlock = nil
        self.failureBlock = nil
    }
}