add shipping costs with live exchange rates and country detection

Shipping rates fetched from Printify during product sync, converted to
GBP at sync time using frankfurter.app ECB exchange rates with 5%
buffer. Cached in shipping_rates table per blueprint/provider/country.

Cart page shows shipping estimate with country selector (detected from
Accept-Language header, persisted in cookie). Stripe Checkout includes
shipping_options for UK domestic and international delivery. Order
shipping_cost extracted from Stripe on payment.

ScheduledSyncWorker runs every 6 hours via Oban cron to keep rates
and exchange rates fresh. REST_OF_THE_WORLD fallback covers unlisted
countries. 780 tests, 0 failures.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/simpleshop_theme_web/controllers/checkout_controller.ex

@@ -3,6 +3,7 @@ defmodule SimpleshopThemeWeb.CheckoutController do
 
   alias SimpleshopTheme.Cart
   alias SimpleshopTheme.Orders
+  alias SimpleshopTheme.Shipping
 
   require Logger
 
@@ -54,16 +55,18 @@ defmodule SimpleshopThemeWeb.CheckoutController do
 
     base_url = SimpleshopThemeWeb.Endpoint.url()
 
-    params = %{
-      mode: "payment",
-      line_items: line_items,
-      success_url: "#{base_url}/checkout/success?session_id={CHECKOUT_SESSION_ID}",
-      cancel_url: "#{base_url}/cart",
-      metadata: %{"order_id" => order.id},
-      shipping_address_collection: %{
-        allowed_countries: ["GB", "US", "CA", "AU", "DE", "FR", "NL", "IE", "AT", "BE"]
+    params =
+      %{
+        mode: "payment",
+        line_items: line_items,
+        success_url: "#{base_url}/checkout/success?session_id={CHECKOUT_SESSION_ID}",
+        cancel_url: "#{base_url}/cart",
+        metadata: %{"order_id" => order.id},
+        shipping_address_collection: %{
+          allowed_countries: ["GB", "US", "CA", "AU", "DE", "FR", "NL", "IE", "AT", "BE"]
+        }
       }
-    }
+      |> maybe_add_shipping_options(hydrated_items)
 
     case Stripe.Checkout.Session.create(params) do
       {:ok, session} ->
@@ -89,4 +92,38 @@ defmodule SimpleshopThemeWeb.CheckoutController do
         |> redirect(to: ~p"/cart")
     end
   end
+
+  defp maybe_add_shipping_options(params, hydrated_items) do
+    gb_result = Shipping.calculate_for_cart(hydrated_items, "GB")
+    us_result = Shipping.calculate_for_cart(hydrated_items, "US")
+
+    options =
+      []
+      |> maybe_add_option(gb_result, "UK delivery", 5, 10)
+      |> maybe_add_option(us_result, "International delivery", 10, 20)
+
+    if options == [] do
+      params
+    else
+      Map.put(params, :shipping_options, options)
+    end
+  end
+
+  defp maybe_add_option(options, {:ok, cost}, name, min_days, max_days) when cost > 0 do
+    option = %{
+      shipping_rate_data: %{
+        type: "fixed_amount",
+        display_name: name,
+        fixed_amount: %{amount: cost, currency: "gbp"},
+        delivery_estimate: %{
+          minimum: %{unit: "business_day", value: min_days},
+          maximum: %{unit: "business_day", value: max_days}
+        }
+      }
+    }
+
+    options ++ [option]
+  end
+
+  defp maybe_add_option(options, _result, _name, _min, _max), do: options
 end

lib/simpleshop_theme_web/controllers/stripe_webhook_controller.ex

@@ -36,6 +36,9 @@ defmodule SimpleshopThemeWeb.StripeWebhookController do
         payment_intent_id = session.payment_intent
         {:ok, order} = Orders.mark_paid(order, payment_intent_id)
 
+        # Update shipping cost from Stripe (if shipping options were presented)
+        order = update_shipping_cost(order, session)
+
         # Update shipping address if collected by Stripe
         order =
           if session.shipping_details do
@@ -111,4 +114,19 @@ defmodule SimpleshopThemeWeb.StripeWebhookController do
 
     Orders.update_order(order, %{shipping_address: shipping_address})
   end
+
+  defp update_shipping_cost(order, session) do
+    shipping_amount = get_in(session, [Access.key(:shipping_cost), Access.key(:amount_total)])
+
+    if is_integer(shipping_amount) and shipping_amount > 0 do
+      new_total = order.subtotal + shipping_amount
+
+      case Orders.update_order(order, %{shipping_cost: shipping_amount, total: new_total}) do
+        {:ok, updated} -> updated
+        {:error, _} -> order
+      end
+    else
+      order
+    end
+  end
 end