Paypal express checkout and drupal

paypal_example.paypal_example:
  path: '/paypal_example/form'
  defaults:
    _form: '\Drupal\paypal_example\Form\PaypalExample'
    _title: 'PaypalExample'
  requirements:
    _permission: 'access content'

<?php
 
namespace Drupal\paypal_example\Form;
 
use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Url;
use PayPal\Api\Amount;
use PayPal\Api\Details;
use PayPal\Api\Item;
use PayPal\Api\ItemList;
use PayPal\Api\Payer;
use PayPal\Api\Payment;
use PayPal\Api\RedirectUrls;
use PayPal\Api\Transaction;
use Drupal\Core\Routing\TrustedRedirectResponse;
use Paypal\Exception\PayPalConnectionException;
 
/**
 * Class PaypalExample.
 */
class PaypalExample extends FormBase {
 
 
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'paypal_example';
  }
 
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['amount'] = [
      '#type' => 'number',
      '#title' => $this->t('Amount'),
      '#description' => $this->t('The amount in store currency'),
      '#weight' => '0',
    ];
    $form['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Pay with paypal'),
    ];
 
    return $form;
  }
 
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    $amount = $form_state->getValue('amount');
    if (!$amount) {
      $form_state->setErrorByName('amount', t('Amount must be a valid value'));
      return;
    }
 
 
  }
 
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    /**
     * will update code from here
     */
    $storeCurrency = 'AUD';// set currency to pass
    if ($form_state->getValue('amount')) {
      // call our paypal express request passing the required vals
      $this->paypalExpressCheckoutRequest($form_state, $storeCurrency);
    }
 
 
 
  }
 
  /**
   * Request to paypal with our payment object
   */
 
  protected function paypalExpressCheckoutRequest(FormStateInterface $formState, $storeCurrency){
    // fill in our Test App credentials as created here
    // https://developer.paypal.com/developer/applications/
    $clientId = '';//Your own app
    $clientSecret = '';//Your own app
    $apiContext = new \PayPal\Rest\ApiContext(
      new \PayPal\Auth\OAuthTokenCredential(
        $clientId,
        $clientSecret
      )
    );
 
    $product_sku = 'test product 01';
    $product = $product_sku;
    $price = (float)$formState->getValue('amount');
    $shipping = 0.50;
    $total = $price + $shipping;
 
    // Create and fill in our payment object
    $payer = new Payer();
    $payer->setPaymentMethod('paypal');
 
    $item = new Item();
    $item->setName($product)
      ->setCurrency($storeCurrency)
      ->setQuantity(1)
      ->setPrice($price);
 
    $itemList = new ItemList();
    $itemList->setItems([$item]);
 
    $details =new Details();
    $details->setShipping($shipping)
      ->setSubtotal($price);
 
    $amount = new Amount();
    $amount->setCurrency($storeCurrency)
      ->setTotal($total)
      ->setDetails($details);
 
    $transaction = new Transaction();
    $transaction->setAmount($amount)
      ->setItemList($itemList)
      ->setDescription($product_sku)
      ->setInvoiceNumber(uniqid($product_sku));
 
    /**
     * define our route for paypal redirects first
     *  we will generate a url string from this current
     * route where the user is accessing the form, which is
     * also the route we defined in our routing.yml
     */
    $current_url = Url::fromRoute('paypal_example.paypal_example', [], ['absolute' => 'TRUE']);
    $urlString = $current_url->toString();
 
    $redirectUrls = new RedirectUrls();
    $redirectUrls->setReturnUrl($urlString. "/?success=true") // TODO, attach security token to url
      ->setCancelUrl($urlString. "/?success=false'");
 
    $payment = new Payment();
    $payment->setIntent('sale')
      ->setPayer($payer)
      ->setRedirectUrls($redirectUrls)
      ->setTransactions([$transaction]);
 
 
    try {
      $payment->create($apiContext);
 
    } catch (\Exception $exception) {
      die('Request failed '.$exception); //incase of error, output to user
    }
 
    $approvalUrl = $payment->getApprovalLink(); // Url to this payment
    $response = new TrustedRedirectResponse($approvalUrl); // redirect to external url
    $formState->setResponse($response);
 
    return;
  }
 
}

#paypal_example.services.yml
services:
  paypal_example.paypal_listener:
    class: Drupal\paypal_example\PaypalListener
    arguments: []
    tags:
      - { name: event_subscriber }

<?php
/**
 * PaypalListener
 */
 
namespace Drupal\paypal_example;
 
 
use Drupal\Core\Url;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;
use PayPal\Api\Payment;
use PayPal\Api\PaymentExecution;
use PayPal\Rest\ApiContext;
use PayPal\Auth\OAuthTokenCredential;
 
class PaypalListener implements EventSubscriberInterface {
 
 
  public function paypalResponseEvent(GetResponseEvent $event){
    $request = $event->getRequest();
    /**
     * Check from the request if the route name matches what we
     * defined in our routing.yml, is for continue to process
     * the request
     */
    if ($request->attributes->get('_route') === 'paypal_example.paypal_example') {
 
      // get current route for use in redirects
      $current_url = Url::fromRoute('paypal_example.paypal_example', [], ['absolute' => 'TRUE']);
      $urlString = $current_url->toString();
 
      if ($request->query->get('success') && $request->query->get('paymentId') && $request->query->get('PayerID')) {
        $paypalSuccessResponse = $request->query->get('success');
        if ($paypalSuccessResponse === 'false') {
          // clear the temporary values in the Url by redirect the user
          $response = new RedirectResponse($urlString);#same page
          $response->send();
          \Drupal::messenger()->addMessage('Failed to authorize charge/payment');
 
          return;
        }
 
        if ($paypalSuccessResponse === 'true') {
 
          $paymentId = $request->query->get('paymentId');
          $payerId = $request->query->get('PayerID');
 
          // fill in our Test App credentials as created here
          // https://developer.paypal.com/developer/applications/
          $clientId = '';//Your own app
          $clientSecret = '';// Your own app
          $apiContext = new ApiContext(
            new OAuthTokenCredential(
              $clientId,
              $clientSecret
            )
          );
 
          /**
           * create our payment object to send to paypal
           * if success, we will use it's data
           */
          $payment = Payment::get($paymentId, $apiContext);
          $execute = new PaymentExecution();
          $execute->setPayerId($payerId);
 
 
          try {
 
            $payment->execute($execute, $apiContext);
 
          } catch (\Exception $exception) {
            // maybe log errors here and choose what to pass on to display to user
 
            // if we have an error display message and return
            // we should still clear the values in the url here
            // but to avoid code repetition and to stick to the
            // scope of this article, I will leave that out.
            if ($exception) {
              \Drupal::messenger()->addMessage('Error charging you!!: '.$exception->getMessage());
              return;
            }
          }
          /**
           * if no exception go ahead and save something(s) to the database,
           * clear temporary values in the url, and thank the user.
           * you can dump($payment) below and choose what to post to database
           *
           */
          $paymentState = $payment->getState();
 
          if ($paymentState === 'approved') {
            $amount = $payment->transactions[0]->amount->total;
 
 
            // clear the temporary values in the Url by redirect the user
 
            $response = new RedirectResponse($urlString);#same page but cleared url vals
            $response->send();
 
            \Drupal::messenger()->addMessage('Thank you!, Payment received for amount: '.$amount . ' AUD.');
 
            return;
          }
        }
      }
    }
  }
 
  public static function getSubscribedEvents() {
    return [
      KernelEvents::REQUEST => 'paypalResponseEvent', // implement paypalResponseEvent method above
    ];
  }
}