Use OrderPaymentFinder methods instead of payments.last and payments.pending.last

app/controllers/checkout_controller.rb

@@ -153,10 +153,12 @@ class CheckoutController < Spree::StoreController
   end
 
   def valid_payment_intent_provided?
-    params["payment_intent"]&.starts_with?("pi_") &&
-      @order.state == "payment" &&
-      @order.payments.last.state == "pending" &&
-      @order.payments.last.response_code == params["payment_intent"]
+    return false unless params["payment_intent"]&.starts_with?("pi_")
+
+    last_payment = OrderPaymentFinder.new(@order).last_payment
+    @order.state == "payment" &&
+      last_payment&.state == "pending" &&
+      last_payment&.response_code == params["payment_intent"]
   end
 
   def handle_redirect_from_stripe

app/services/order_payment_finder.rb

@@ -6,13 +6,23 @@ class OrderPaymentFinder
   end
 
   def last_payment
-    # `max_by` avoids additional database queries when payments are loaded
-    # already. There is usually only one payment and this shouldn't cause
-    # any overhead compared to `order(:created_at).last`. Using `last`
-    # without order is not deterministic.
-    #
-    # We are not using `updated_at` because all payments are touched when the
-    # order is updated and then all payments have the same `updated_at` value.
-    @order.payments.max_by(&:created_at)
+    last(@order.payments)
+  end
+
+  def last_pending_payment
+    last(@order.pending_payments)
+  end
+
+  private
+
+  # `max_by` avoids additional database queries when payments are loaded
+  # already. There is usually only one payment and this shouldn't cause
+  # any overhead compared to `order(:created_at).last`. Using `last`
+  # without order is not deterministic.
+  #
+  # We are not using `updated_at` because all payments are touched when the
+  # order is updated and then all payments have the same `updated_at` value.
+  def last(payments)
+    payments.max_by(&:created_at)
   end
 end