From f6dc90fb287a1536b82d208208ec19a9e7ca578e Mon Sep 17 00:00:00 2001
From: Raphael Michel <mail@raphaelmichel.de>
Date: Fri, 30 Oct 2020 22:33:44 +0100
Subject: [PATCH] Show message and cart after tax rate has changed

---
 src/pretix/base/services/cart.py                           | 1 +
 src/pretix/presale/checkoutflow.py                         | 7 ++++++-
 .../templates/pretixpresale/event/checkout_base.html       | 2 +-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/pretix/base/services/cart.py b/src/pretix/base/services/cart.py
index 9485526058..65ebe23d63 100644
--- a/src/pretix/base/services/cart.py
+++ b/src/pretix/base/services/cart.py
@@ -1063,6 +1063,7 @@ def update_tax_rates(event: Event, cart_id: str, invoice_address: InvoiceAddress
         if pos.tax_rate != rate:
             current_net = pos.price - pos.tax_value
             new_gross = pos.item.tax(current_net, base_price_is='net', invoice_address=invoice_address).gross
+            totaldiff += new_gross - pos.price
             pos.price = new_gross
             pos.includes_tax = rate != Decimal('0.00')
             pos.override_tax_rate = rate
diff --git a/src/pretix/presale/checkoutflow.py b/src/pretix/presale/checkoutflow.py
index 8336e8d65e..a561bb7b56 100644
--- a/src/pretix/presale/checkoutflow.py
+++ b/src/pretix/presale/checkoutflow.py
@@ -554,11 +554,16 @@ class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
             addr = self.invoice_form.save()
             self.cart_session['invoice_address'] = addr.pk
 
-            update_tax_rates(
+            diff = update_tax_rates(
                 event=request.event,
                 cart_id=get_or_create_cart_id(request),
                 invoice_address=self.invoice_form.instance
             )
+            if abs(diff) > Decimal('0.001'):
+                messages.info(request, _('Due to thec invoice address you entered, we need to apply a different tax '
+                                         'rate to your purchase and the price of the products in your cart has '
+                                         'changed accordingly.'))
+                return redirect(self.get_next_url(request) + '?open_cart=true')
 
         return redirect(self.get_next_url(request))
 
diff --git a/src/pretix/presale/templates/pretixpresale/event/checkout_base.html b/src/pretix/presale/templates/pretixpresale/event/checkout_base.html
index 90b4742796..4b785a9acd 100644
--- a/src/pretix/presale/templates/pretixpresale/event/checkout_base.html
+++ b/src/pretix/presale/templates/pretixpresale/event/checkout_base.html
@@ -3,7 +3,7 @@
 {% load bootstrap3 %}
 {% block title %}{% trans "Checkout" %}{% endblock %}
 {% block content %}
-    <details class="panel panel-default cart">
+    <details class="panel panel-default cart" {% if "open_cart" in request.GET %}open{% endif %}>
         <summary class="panel-heading">
             <h3 class="panel-title">
                 <span>