Single IAP in Swift 2

import StoreKit

class ViewController: UIViewController, SKProductsRequestDelegate, SKPaymentTransactionObserver {

var product_id: NSString?

override func viewDidLoad() {
    
    
    product_id = "YOUR_PRODUCT_ID"
    super.viewDidLoad()
    SKPaymentQueue.defaultQueue().addTransactionObserver(self)

   //Check if product is purchased
   if (NSUserDefaults.standardUserDefaults().boolForKey("purchased")){
   
       // Hide ads
       adView.hidden = true
        
   } else {
       print("Should show ads...")
        
   }

}

@IBAction func unlockAction(sender: AnyObject) {
    
   print("About to fetch the product...")

// Can make payments
if (SKPaymentQueue.canMakePayments())
    {
        let productID:NSSet = NSSet(object: self.product_id!);
        let productsRequest:SKProductsRequest = SKProductsRequest(productIdentifiers: productID as! Set<NSString>);
        productsRequest.delegate = self;
        productsRequest.start();
        println("Fetching Products");
    }else{
        print("Can't make purchases");
    }

}

func buyProduct(product: SKProduct){
    println("Sending the Payment Request to Apple");
    let payment = SKPayment(product: product)
    SKPaymentQueue.defaultQueue().addPayment(payment);
    
 }

func productsRequest (request: SKProductsRequest, didReceiveResponse response: SKProductsResponse) {

    let count : Int = response.products.count
    if (count>0) {
        var validProduct: SKProduct = response.products[0] as SKProduct
        if (validProduct.productIdentifier == self.product_id) {
            print(validProduct.localizedTitle)
            print(validProduct.localizedDescription)
            print(validProduct.price)
            buyProduct(validProduct);
        } else {
            print(validProduct.productIdentifier)
        }
    } else {
        print("nothing")
    }
}

func request(request: SKRequest!, didFailWithError error: NSError!) {
    print("Error Fetching product information");
}

    func paymentQueue(_ queue: SKPaymentQueue,
updatedTransactions transactions: [SKPaymentTransaction])

{
    print("Received Payment Transaction Response from Apple");
    
    for transaction:AnyObject in transactions {
        if let trans:SKPaymentTransaction = transaction as? SKPaymentTransaction{
            switch trans.transactionState {
            case .Purchased:
                print("Product Purchased");
                SKPaymentQueue.defaultQueue().finishTransaction(transaction as! SKPaymentTransaction)
                // Handle the purchase
                NSUserDefaults.standardUserDefaults().setBool(true , forKey: "purchased")
                adView.hidden = true
                break;
            case .Failed:
                print("Purchased Failed");
                SKPaymentQueue.defaultQueue().finishTransaction(transaction as! SKPaymentTransaction)
                break;
                
        

            case .Restored:
                print("Already Purchased");
               SKPaymentQueue.defaultQueue().restoreCompletedTransactions()

// Handle the purchase
   NSUserDefaults.standardUserDefaults().setBool(true , forKey: "purchased")
   adView.hidden = true
   break;
default:
break;
}
}
}

}

if (SKPaymentQueue.canMakePayments()) {
  SKPaymentQueue.defaultQueue().restoreCompletedTransactions()
}