Check stock before completing order after Taler payment

app/controllers/payment_gateways/taler_controller.rb

@@ -2,15 +2,36 @@
 
 module PaymentGateways
   class TalerController < BaseController
+    include OrderStockCheck
     include OrderCompletion
 
+    class StockError < StandardError
+    end
+
     # The Taler merchant backend has taken the payment.
     # Now we just need to confirm that and update our local database
     # before finalising the order.
     def confirm
       payment = Spree::Payment.find(params[:payment_id])
+
+      # Process payment early because it's probably paid already.
+      # We want to capture that before any validations raise errors.
+      unless payment.process!
+        return redirect_to order_failed_route(step: "payment")
+      end
+
       @order = payment.order
-      process_payment_completion!
+      OrderLocker.lock_order_and_variants(@order) do
+        raise StockError unless sufficient_stock?
+
+        process_payment_completion!
+      end
+    rescue Spree::Core::GatewayError => e
+      flash[:notice] = e.message
+      redirect_to order_failed_route(step: "payment")
+    rescue StockError
+      flash[:notice] = t("checkout.payment_cancelled_due_to_stock")
+      redirect_to main_app.checkout_step_path(step: "details")
     end
   end
 end

spec/requests/payment_gateways/taler_spec.rb

@@ -3,16 +3,19 @@
 require 'spec_helper'
 
 RSpec.describe "/payment_gateways/taler/:id" do
-  it "completes the order", :vcr do
-    shop = create(:distributor_enterprise)
-    taler = Spree::PaymentMethod::Taler.create!(
+  let(:shop) { create(:distributor_enterprise) }
+  let(:taler) {
+    Spree::PaymentMethod::Taler.create!(
       name: "Taler",
       environment: "test",
       distributors: [shop],
       preferred_backend_url: "https://backend.demo.taler.net/instances/sandbox",
       preferred_api_key: "sandbox",
     )
-    order = create(:order_ready_for_confirmation, payment_method: taler)
+  }
+  let!(:order) { create(:order_ready_for_confirmation, payment_method: taler) }
+
+  it "completes the order", :vcr do
     payment = Spree::Payment.last
     payment.update!(
       source: taler,
@@ -30,4 +33,47 @@ RSpec.describe "/payment_gateways/taler/:id" do
     payment.reload
     expect(payment.state).to eq "completed"
   end
+
+  it "redirects when payment failed" do
+    payment = Spree::Payment.last
+    payment.update!(
+      source: taler,
+      payment_method: taler,
+      response_code: "2026.020-03R3ETNZZ0DVA",
+    )
+
+    allow_any_instance_of(Taler::Order)
+      .to receive(:fetch).with("order_status").and_return("claimed")
+
+    get payment_gateways_confirm_taler_path(payment_id: payment.id)
+    expect(response).to redirect_to "/checkout/payment"
+
+    payment.reload
+    expect(payment.state).to eq "failed"
+
+    order.reload
+    expect(order.state).to eq "confirmation"
+  end
+
+  it "handles all variants going out of stock" do
+    payment = Spree::Payment.last
+    payment.update!(
+      source: taler,
+      payment_method: taler,
+      response_code: "2026.020-03R3ETNZZ0DVA",
+    )
+
+    allow_any_instance_of(Taler::Order)
+      .to receive(:fetch).with("order_status").and_return("paid")
+    order.line_items[0].variant.on_hand = 0
+
+    get payment_gateways_confirm_taler_path(payment_id: payment.id)
+    expect(response).to redirect_to "/checkout/details"
+
+    payment.reload
+    expect(payment.state).to eq "completed"
+
+    order.reload
+    expect(order.state).to eq "confirmation"
+  end
 end