feat: set users locale

lib/mv_web/router.ex

@@ -139,8 +139,47 @@ defmodule MvWeb.Router do
   end
 
   defp set_locale(conn, _opts) do
-    locale = get_session(conn, :locale) || "de"
+    locale =
+      get_session(conn, :locale) ||
+        extract_locale_from_headers(conn.req_headers)
+
     Gettext.put_locale(MvWeb.Gettext, locale)
+
     conn
+    |> put_session(:locale, locale)
+    |> assign(:locale, locale)
   end
+
+  # Get locale from user
+  defp extract_locale_from_headers(headers) do
+    headers
+    |> Enum.find_value(fn
+      {"accept-language", value} -> value
+      _ -> nil
+    end)
+    |> parse_accept_language()
+    |> Enum.find(&supported_locale?/1)
+    |> fallback_locale()
+  end
+
+  defp parse_accept_language(nil), do: []
+
+  defp parse_accept_language(header) do
+    header
+    |> String.split(",")
+    |> Enum.map(&String.trim/1)
+    |> Enum.map(fn lang ->
+      lang
+      # we only want the first part
+      |> String.split(";")
+      |> hd()
+      |> String.split("-")
+      |> hd()
+    end)
+  end
+
+  # Our supported languages for now are german and english, english as fallback language
+  defp supported_locale?(locale), do: locale in ["en", "de"]
+  defp fallback_locale(nil), do: "en"
+  defp fallback_locale(locale), do: locale
 end