pod 'Braintree/ApplePay'

var braintreeClient: BTAPIClient?

// BTAPIClient can be initialized in a couple different ways, here's one example:
braintreeClient = BTAPIClient(authorization: CLIENT_AUTHORIZATION)

func applePayButton() -> UIButton {
    let button = PKPaymentButton(type: PKPaymentButtonType.buy, style: PKPaymentButtonStyle.black)

    button?.addTarget(self, action: #selector(tappedApplePay), for: UIControlEvents.touchUpInside)

    return button!
}

import PassKit
// Add BraintreeApplePay.h to bridging header

class MyCheckoutViewController: UIViewController, PKPaymentAuthorizationViewControllerDelegate {
  // ...

  override func viewDidLoad() {
    super.viewDidLoad()

    // Conditionally show Apple Pay button based on device availability
    if PKPaymentAuthorizationViewController.canMakePayments(usingNetworks: [PKPaymentNetwork.visa, PKPaymentNetwork.masterCard, PKPaymentNetwork.amex, PKPaymentNetwork.discover]) {
      let button = self.applePayButton()
      // TODO: Set button constraints/frame...
      self.view.addSubview(button)
    }
  }

  // ...
}

let dropIn = BTDropInController(authorization: clientTokenOrTokenizationKey, request: request) {
	 (controller, result, error) in
	 	if (result?.paymentMethodType == .applePay) {
	 		// Display PKPaymentButton
	 		let button = self.applePayButton()

	 		// TODO: Set button constraints/frame...
	 		// self.view.addSubview(button)
	 	}
}

func setupPaymentRequest(completion: @escaping (PKPaymentRequest?, Error?) -> Void) {
    let applePayClient = BTApplePayClient(apiClient: self.braintreeApiClient)
    // You can use the following helper method to create a PKPaymentRequest which will set the 'countryCode',
    // 'currencyCode', 'merchantIdentifier', and 'supportedNetworks' properties.
    // You can also create the PKPaymentRequest manually. Be aware that you'll need to keep these in
    // sync with the gateway settings if you go this route.
    applePayClient.paymentRequest { (paymentRequest, error) in
        guard let paymentRequest = paymentRequest else {
            completion(nil, error)
            return
        }

        // We recommend collecting billing address information, at minimum
        // billing postal code, and passing that billing postal code with all
        // Apple Pay transactions as a best practice.
        paymentRequest.requiredBillingContactFields = [.postalAddress]

        // Set other PKPaymentRequest properties here
        paymentRequest.merchantCapabilities = .capability3DS
        paymentRequest.paymentSummaryItems =
        [
            PKPaymentSummaryItem(label: "<#ITEM_NAME#>", amount: NSDecimalNumber(string: "<#PRICE#>")),
            // Add add'l payment summary items...
            PKPaymentSummaryItem(label: "<#COMPANY NAME#>", amount: NSDecimalNumber(string: "<#GRAND TOTAL#>")),
        ]
        completion(paymentRequest, nil)
    }
}

func tappedApplePay() {
    self.setupPaymentRequest { (paymentRequest, error)
        guard error == nil else {
           // Handle error
           return
        }

        // Example: Promote PKPaymentAuthorizationViewController to optional so that we can verify
        // that our paymentRequest is valid. Otherwise, an invalid paymentRequest would crash our app.
        if let vc = PKPaymentAuthorizationViewController(paymentRequest: paymentRequest)
            as PKPaymentAuthorizationViewController?
        {
            vc.delegate = self
            present(vc, animated: true, completion: nil)
        } else {
            print("Error: Payment request is invalid.")
        }
    }
}

func paymentAuthorizationViewController(_ controller: PKPaymentAuthorizationViewController,
                         didAuthorizePayment payment: PKPayment,
                                  handler completion: @escaping (PKPaymentAuthorizationResult) -> Void) {

    // Tokenize the Apple Pay payment
    braintree!.tokenizeApplePay(payment) { (nonce, error) in
        if error != nil {
            // Received an error from Braintree.
            // Indicate failure via the completion callback.
            completion(PKPaymentAuthorizationResult(status: .failure, errors: nil)
            return
        }

        // TODO: On success, send nonce to your server for processing.
        // If requested, address information is accessible in 'payment' and may
        // also be sent to your server.

        // Then indicate success or failure based on the server side result of Transaction.sale
        // via the completion callback.
        // e.g. If the Transaction.sale was successful
        completion(PKPaymentAuthorizationResult(status: .success, errors: nil))
    }
}

func paymentAuthorizationViewControllerDidFinish(_ controller: PKPaymentAuthorizationViewController) {
    // Apple Payment finished
    dismiss(animated: true)
}