Minor refactor of doPayment, extracting to separate functions. NFC.

The primary aim of this refactor was to remove the http redirect(),
since this means the doPayment function could not be used for embedded
checkout in InlayPay. I also tried to split functions so that each did a
specific thing, and in particular, to separate out the munging of the
payment_params array from the doing-things-with-stripe code. I hope this
will make things clearer going forward and more easily integrated in
other APIs, like InlayPay.

CRM/Core/Payment/StripeCheckout.php

@@ -9,13 +9,9 @@
  +--------------------------------------------------------------------+
  */
 
-use Civi\Api4\PaymentprocessorWebhook;
 use CRM_Stripe_ExtensionUtil as E;
 use Civi\Payment\PropertyBag;
-use Stripe\Stripe;
 use Civi\Payment\Exception\PaymentProcessorException;
-use Stripe\StripeObject;
-use Stripe\Webhook;
 
 /**
  * Class CRM_Core_Payment_Stripe
@@ -132,9 +128,6 @@ class CRM_Core_Payment_StripeCheckout extends CRM_Core_Payment_Stripe {
    *   Assoc array of input parameters for this transaction.
    * @param string $component
    *
-   * @return array
-   *   Result array
-   *
    * @throws \CRM_Core_Exception
    * @throws \Civi\Payment\Exception\PaymentProcessorException
    */
@@ -150,23 +143,22 @@ class CRM_Core_Payment_StripeCheckout extends CRM_Core_Payment_Stripe {
 
     // Not sure what the point of this next line is.
     $this->_component = $component;
+
     $successUrl = $this->getReturnSuccessUrl($paymentParams['qfKey']);
     $failUrl = $this->getCancelUrl($paymentParams['qfKey'], NULL);
+    $lineItems = $this->calculateLineItems($paymentParams);
+    $checkoutSession = $this->createCheckoutSession($successUrl, $failUrl, $propertyBag, $lineItems);
 
-    // Get existing/saved Stripe customer or create a new one
-    $existingStripeCustomer = \Civi\Api4\StripeCustomer::get(FALSE)
-      ->addWhere('contact_id', '=', $propertyBag->getContactID())
-      ->addWhere('processor_id', '=', $this->getPaymentProcessor()['id'])
-      ->execute()
-      ->first();
-    if (empty($existingStripeCustomer)) {
-      $stripeCustomer = $this->getStripeCustomer($propertyBag);
-      $stripeCustomerID = $stripeCustomer->id;
-    }
-    else {
-      $stripeCustomerID = $existingStripeCustomer['customer_id'];
-    }
+    // Allow each CMS to do a pre-flight check before redirecting to Stripe.
+    CRM_Core_Config::singleton()->userSystem->prePostRedirect();
+    CRM_Utils_System::setHttpHeader("HTTP/1.1 303 See Other", '');
+    CRM_Utils_System::redirect($checkoutSession->url);
+  }
 
+  /**
+   * This gathers the line items which are then used in buildCheckoutLineItems()
+   */
+  public function calculateLineItems(array|PropertyBag $paymentParams): array {
     $lineItems = [];
     if (!empty($paymentParams['skipLineItem']) || empty($paymentParams['line_item'])) {
       if (!empty($paymentParams['participants_info'])) {
@@ -185,14 +177,38 @@ class CRM_Core_Payment_StripeCheckout extends CRM_Core_Payment_Stripe {
               'field_title' => $paymentParams['source'] ?? $paymentParams['description'],
               'label' => $paymentParams['source'] ?? $paymentParams['description'],
               'qty' => 1,
-            ]
-          ]
+            ],
+          ],
         ];
       }
     }
     else {
-      $lineItems = $paymentParams['line_item'];
+      $lineItems = $paymentParams['line_item'] ?? [];
     }
+    return $lineItems;
+  }
+
+  /**
+   * Create a Stripe Checkout Session
+   *
+   * @return \Stripe\Checkout\Session
+   */
+  public function createCheckoutSession(string $successUrl, string $failUrl, PropertyBag $propertyBag, array $lineItems) {
+
+    // Get existing/saved Stripe customer or create a new one
+    $existingStripeCustomer = \Civi\Api4\StripeCustomer::get(FALSE)
+      ->addWhere('contact_id', '=', $propertyBag->getContactID())
+      ->addWhere('processor_id', '=', $this->getPaymentProcessor()['id'])
+      ->execute()
+      ->first();
+    if (empty($existingStripeCustomer)) {
+      $stripeCustomer = $this->getStripeCustomer($propertyBag);
+      $stripeCustomerID = $stripeCustomer->id;
+    }
+    else {
+      $stripeCustomerID = $existingStripeCustomer['customer_id'];
+    }
+
     // Build the checkout session parameters
     $checkoutSessionParams = [
       'line_items' => $this->buildCheckoutLineItems($lineItems, $propertyBag),
@@ -233,10 +249,7 @@ class CRM_Core_Payment_StripeCheckout extends CRM_Core_Payment_Stripe {
 
     CRM_Stripe_BAO_StripeCustomer::updateMetadata(['contact_id' => $propertyBag->getContactID()], $this, $checkoutSession['customer']);
 
-    // Allow each CMS to do a pre-flight check before redirecting to PayPal.
-    CRM_Core_Config::singleton()->userSystem->prePostRedirect();
-    CRM_Utils_System::setHttpHeader("HTTP/1.1 303 See Other", '');
-    CRM_Utils_System::redirect($checkoutSession->url);
+    return $checkoutSession;
   }
 
   /**
@@ -277,7 +290,6 @@ class CRM_Core_Payment_StripeCheckout extends CRM_Core_Payment_Stripe {
     return $result;
   }
 
-
   /**
    * Takes the lineitems passed into doPayment and converts them into an array suitable for passing to Stripe Checkout
    *