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/providers/printify.ex

@@ -10,6 +10,8 @@ defmodule SimpleshopTheme.Providers.Printify do
   alias SimpleshopTheme.Clients.Printify, as: Client
   alias SimpleshopTheme.Products.ProviderConnection
 
+  require Logger
+
   @impl true
   def provider_type, do: "printify"
 
@@ -114,6 +116,101 @@ defmodule SimpleshopTheme.Providers.Printify do
     end
   end
 
+  # =============================================================================
+  # Shipping Rates
+  # =============================================================================
+
+  @impl true
+  def fetch_shipping_rates(%ProviderConnection{} = conn, products) when is_list(products) do
+    with api_key when is_binary(api_key) <- ProviderConnection.get_api_key(conn),
+         :ok <- set_api_key(api_key) do
+      pairs = extract_blueprint_provider_pairs(products)
+      Logger.info("Fetching shipping rates for #{length(pairs)} blueprint/provider pairs")
+
+      rates =
+        pairs
+        |> Enum.with_index()
+        |> Enum.flat_map(fn {pair, index} ->
+          # Rate limit: 100ms between requests
+          if index > 0, do: Process.sleep(100)
+          fetch_shipping_for_pair(pair)
+        end)
+
+      {:ok, rates}
+    else
+      nil -> {:error, :no_api_key}
+    end
+  end
+
+  defp extract_blueprint_provider_pairs(products) do
+    products
+    |> Enum.flat_map(fn product ->
+      provider_data = product[:provider_data] || %{}
+      blueprint_id = provider_data[:blueprint_id] || provider_data["blueprint_id"]
+      print_provider_id = provider_data[:print_provider_id] || provider_data["print_provider_id"]
+
+      if blueprint_id && print_provider_id do
+        [{blueprint_id, print_provider_id}]
+      else
+        []
+      end
+    end)
+    |> Enum.uniq()
+  end
+
+  defp fetch_shipping_for_pair({blueprint_id, print_provider_id}) do
+    case Client.get_shipping(blueprint_id, print_provider_id) do
+      {:ok, response} ->
+        normalize_shipping_response(blueprint_id, print_provider_id, response)
+
+      {:error, reason} ->
+        Logger.warning(
+          "Failed to fetch shipping for blueprint #{blueprint_id}, " <>
+            "provider #{print_provider_id}: #{inspect(reason)}"
+        )
+
+        []
+    end
+  end
+
+  defp normalize_shipping_response(blueprint_id, print_provider_id, response) do
+    handling_time_days =
+      case response["handling_time"] do
+        %{"value" => value, "unit" => "day"} -> value
+        _ -> nil
+      end
+
+    profiles = response["profiles"] || []
+
+    # For each profile, expand countries into individual rate maps.
+    # Then group by country and take the max first_item_cost across profiles
+    # (conservative estimate across variant groups).
+    profiles
+    |> Enum.flat_map(fn profile ->
+      countries = profile["countries"] || []
+      first_cost = get_in(profile, ["first_item", "cost"]) || 0
+      additional_cost = get_in(profile, ["additional_items", "cost"]) || 0
+      currency = get_in(profile, ["first_item", "currency"]) || "USD"
+
+      Enum.map(countries, fn country ->
+        %{
+          blueprint_id: blueprint_id,
+          print_provider_id: print_provider_id,
+          country_code: country,
+          first_item_cost: first_cost,
+          additional_item_cost: additional_cost,
+          currency: currency,
+          handling_time_days: handling_time_days
+        }
+      end)
+    end)
+    |> Enum.group_by(& &1.country_code)
+    |> Enum.map(fn {_country, country_rates} ->
+      # Take the max first_item_cost across variant groups for this country
+      Enum.max_by(country_rates, & &1.first_item_cost)
+    end)
+  end
+
   # =============================================================================
   # Webhook Registration
   # =============================================================================

lib/simpleshop_theme/providers/provider.ex

@@ -57,6 +57,21 @@ defmodule SimpleshopTheme.Providers.Provider do
   @callback get_order_status(ProviderConnection.t(), provider_order_id :: String.t()) ::
               {:ok, map()} | {:error, term()}
 
+  @doc """
+  Fetches shipping rates from the provider for the given products.
+
+  Takes the connection and the already-fetched product list (from fetch_products).
+  Returns normalized rate maps with keys: blueprint_id, print_provider_id,
+  country_code, first_item_cost, additional_item_cost, currency, handling_time_days.
+
+  Optional — providers that don't support shipping rate lookup can skip this.
+  The sync worker checks `function_exported?/3` before calling.
+  """
+  @callback fetch_shipping_rates(ProviderConnection.t(), products :: [map()]) ::
+              {:ok, [map()]} | {:error, term()}
+
+  @optional_callbacks [fetch_shipping_rates: 2]
+
   @doc """
   Returns the provider module for a given provider type.