[FIX] website_sale_stock: check cart before payment

Have a Storable Product configured to 'Show inventory below a threshold
and prevent sales if not enough stock' (availability settings). Have a
quantity available of such product, i.e 100
From the shop create 2 sessions with 2 different users A and B.

With both follow the steps in parallel:
- put 100 of product in cart
- go to checkout up to payment screen

Press 'Pay Now' with A (and confirm the order in backend if auto
confirm is not enabled so available quantity is updated)
Press 'Pay Now' with B

200 of product are requested because all cart checks for availability
are done before payment but not on the final step.

Adding a final step of check for availability

opw-2261598

closes odoo/odoo#51898

Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>

addons/website_sale_stock/controllers/__init__.py

@@ -2,3 +2,4 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from . import variant
+from . import main

addons/website_sale_stock/controllers/main.py

+# -*- coding: utf-8 -*-
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+from odoo.addons.website_sale.controllers.main import WebsiteSale
+
+from odoo import http,_
+from odoo.http import request
+from odoo.exceptions import ValidationError
+
+
+class WebsiteSaleStock(WebsiteSale):
+    @http.route()
+    def payment_transaction(self, **kwargs):
+        """ Payment transaction override to double check cart quantities before
+        placing the order
+        """
+        order = request.website.sale_get_order()
+        values = []
+        for line in order.order_line:
+            if line.product_id.type == 'product' and line.product_id.inventory_availability in ['always', 'threshold']:
+                cart_qty = sum(order.order_line.filtered(lambda p: p.product_id.id == line.product_id.id).mapped('product_uom_qty'))
+                avl_qty = line.product_id.with_context(warehouse=order.warehouse_id.id).virtual_available
+                if cart_qty > avl_qty:
+                    values.append(_('You ask for %s products but only %s is available') % (cart_qty, avl_qty if avl_qty > 0 else 0))
+        if values:
+            raise ValidationError('. '.join(values) + '.')
+        return super(WebsiteSaleStock, self).payment_transaction(**kwargs)