Google Pay

<div id="container"></div>
<script async
  src="https://pay.google.com/gp/p/js/pay.js"
  onload="onGooglePayLoaded()"></script>

<script>
/**
 * Define the version of the Google Pay API referenced when creating your
 * configuration
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#PaymentDataRequest|apiVersion in PaymentDataRequest}
 */
const baseRequest = {
  apiVersion: 2,
  apiVersionMinor: 0
};

/**
 * Card networks supported by your site and your gateway
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#CardParameters|CardParameters}
 * @todo confirm card networks supported by your site and gateway
 */
const allowedCardNetworks = ["AMEX", "DISCOVER", "INTERAC", "JCB", "MASTERCARD", "VISA"];

/**
 * Card authentication methods supported by your site and your gateway
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#CardParameters|CardParameters}
 * @todo confirm your processor supports Android device tokens for your
 * supported card networks
 */
const allowedCardAuthMethods = ["PAN_ONLY", "CRYPTOGRAM_3DS"];

/**
 * Identify your gateway and your site's gateway merchant identifier
 *
 * The Google Pay API response will return an encrypted payment method capable
 * of being charged by a supported gateway after payer authorization
 *
 * @todo check with your gateway on the parameters to pass
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#gateway|PaymentMethodTokenizationSpecification}
 */
const tokenizationSpecification = {
  type: 'PAYMENT_GATEWAY',
  parameters: {
    'gateway': 'example',
    'gatewayMerchantId': 'exampleGatewayMerchantId'
  }
};

/**
 * Describe your site's support for the CARD payment method and its required
 * fields
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#CardParameters|CardParameters}
 */
const baseCardPaymentMethod = {
  type: 'CARD',
  parameters: {
    allowedAuthMethods: allowedCardAuthMethods,
    allowedCardNetworks: allowedCardNetworks
  }
};

/**
 * Describe your site's support for the CARD payment method including optional
 * fields
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#CardParameters|CardParameters}
 */
const cardPaymentMethod = Object.assign(
  {},
  baseCardPaymentMethod,
  {
    tokenizationSpecification: tokenizationSpecification
  }
);

/**
 * An initialized google.payments.api.PaymentsClient object or null if not yet set
 *
 * @see {@link getGooglePaymentsClient}
 */
let paymentsClient = null;

/**
 * Configure your site's support for payment methods supported by the Google Pay
 * API.
 *
 * Each member of allowedPaymentMethods should contain only the required fields,
 * allowing reuse of this base request when determining a viewer's ability
 * to pay and later requesting a supported payment method
 *
 * @returns {object} Google Pay API version, payment methods supported by the site
 */
function getGoogleIsReadyToPayRequest() {
  return Object.assign(
      {},
      baseRequest,
      {
        allowedPaymentMethods: [baseCardPaymentMethod]
      }
  );
}

/**
 * Configure support for the Google Pay API
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#PaymentDataRequest|PaymentDataRequest}
 * @returns {object} PaymentDataRequest fields
 */
function getGooglePaymentDataRequest() {
  const paymentDataRequest = Object.assign({}, baseRequest);
  paymentDataRequest.allowedPaymentMethods = [cardPaymentMethod];
  paymentDataRequest.transactionInfo = getGoogleTransactionInfo();
  paymentDataRequest.merchantInfo = {
    // @todo a merchant ID is available for a production environment after approval by Google
    // See {@link https://developers.google.com/pay/api/web/guides/test-and-deploy/integration-checklist|Integration checklist}
    // merchantId: '01234567890123456789',
    merchantName: 'Example Merchant'
  };

  paymentDataRequest.callbackIntents = ["PAYMENT_AUTHORIZATION"];

  return paymentDataRequest;
}

/**
 * Return an active PaymentsClient or initialize
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/client#PaymentsClient|PaymentsClient constructor}
 * @returns {google.payments.api.PaymentsClient} Google Pay API client
 */
function getGooglePaymentsClient() {
  if ( paymentsClient === null ) {
    paymentsClient = new google.payments.api.PaymentsClient({
        environment: 'TEST',
      paymentDataCallbacks: {
        onPaymentAuthorized: onPaymentAuthorized
      }
    });
  }
  return paymentsClient;
}

/**
 * Handles authorize payments callback intents.
 *
 * @param {object} paymentData response from Google Pay API after a payer approves payment through user gesture.
 * @see {@link https://developers.google.com/pay/api/web/reference/response-objects#PaymentData object reference}
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/response-objects#PaymentAuthorizationResult}
 * @returns Promise<{object}> Promise of PaymentAuthorizationResult object to acknowledge the payment authorization status.
 */
function onPaymentAuthorized(paymentData) {
  return new Promise(function(resolve, reject){
    // handle the response
    processPayment(paymentData)
      .then(function() {
        resolve({transactionState: 'SUCCESS'});
      })
      .catch(function() {
        resolve({
          transactionState: 'ERROR',
          error: {
            intent: 'PAYMENT_AUTHORIZATION',
            message: 'Insufficient funds, try again. Next attempt should work.',
            reason: 'PAYMENT_DATA_INVALID'
          }
        });
	    });
  });
}

/**
 * Initialize Google PaymentsClient after Google-hosted JavaScript has loaded
 *
 * Display a Google Pay payment button after confirmation of the viewer's
 * ability to pay.
 */
function onGooglePayLoaded() {
  const paymentsClient = getGooglePaymentsClient();
  paymentsClient.isReadyToPay(getGoogleIsReadyToPayRequest())
    .then(function(response) {
      if (response.result) {
        addGooglePayButton();
      }
    })
    .catch(function(err) {
      // show error in developer console for debugging
      console.error(err);
    });
}

/**
 * Add a Google Pay purchase button alongside an existing checkout button
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#ButtonOptions|Button options}
 * @see {@link https://developers.google.com/pay/api/web/guides/brand-guidelines|Google Pay brand guidelines}
 */
function addGooglePayButton() {
  const paymentsClient = getGooglePaymentsClient();
  const button =
      paymentsClient.createButton({onClick: onGooglePaymentButtonClicked});
  document.getElementById('container').appendChild(button);
}

/**
 * Provide Google Pay API with a payment amount, currency, and amount status
 *
 * @see {@link https://developers.google.com/pay/api/web/reference/request-objects#TransactionInfo|TransactionInfo}
 * @returns {object} transaction info, suitable for use as transactionInfo property of PaymentDataRequest
 */
function getGoogleTransactionInfo() {
  return {
        displayItems: [
        {
          label: "Subtotal",
          type: "SUBTOTAL",
          price: "11.00",
        },
      {
          label: "Tax",
          type: "TAX",
          price: "1.00",
        }
    ],
    countryCode: 'US',
    currencyCode: "USD",
    totalPriceStatus: "FINAL",
    totalPrice: "12.00",
    totalPriceLabel: "Total"
  };
}


/**
 * Show Google Pay payment sheet when Google Pay payment button is clicked
 */
function onGooglePaymentButtonClicked() {
  const paymentDataRequest = getGooglePaymentDataRequest();
  paymentDataRequest.transactionInfo = getGoogleTransactionInfo();

  const paymentsClient = getGooglePaymentsClient();
  paymentsClient.loadPaymentData(paymentDataRequest);
}

let attempts = 0;
/**
 * Process payment data returned by the Google Pay API
 *
 * @param {object} paymentData response from Google Pay API after user approves payment
 * @see {@link https://developers.google.com/pay/api/web/reference/response-objects#PaymentData|PaymentData object reference}
 */
function processPayment(paymentData) {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      // @todo pass payment token to your gateway to process payment
      paymentToken = paymentData.paymentMethodData.tokenizationData.token;

			if (attempts++ % 2 == 0) {
	      reject(new Error('Every other attempt fails, next one should succeed'));      
      } else {
	      resolve({});      
      }
    }, 500);
  });
}
</script>