perf: use digested font paths in CSS and preloads

Add path_resolver parameter to font generation functions so both
font preloads and CSS @font-face declarations use the same digested
paths in production. This prevents duplicate font downloads when
preloads were using digested paths but CSS used non-digested paths.

- Add path_resolver parameter to Fonts.generate_font_faces/2,
  Fonts.preload_links/2, and Fonts.generate_all_font_faces/1
- Update CSSGenerator.generate/2 to accept path_resolver
- Update CSSCache.warm/0 to use Endpoint.static_path/1
- Move CSSCache to start after Endpoint in supervision tree
- Add 1-year cache headers for static assets

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/simpleshop_theme/application.ex

@@ -18,10 +18,10 @@ defmodule SimpleshopTheme.Application do
       {Oban, Application.fetch_env!(:simpleshop_theme, Oban)},
       # Image variant cache - ensures all variants exist on startup
       SimpleshopTheme.Images.VariantCache,
-      # Theme CSS cache
-      SimpleshopTheme.Theme.CSSCache,
-      # Start to serve requests, typically the last entry
-      SimpleshopThemeWeb.Endpoint
+      # Start to serve requests
+      SimpleshopThemeWeb.Endpoint,
+      # Theme CSS cache - must start after Endpoint for static_path/1 to work
+      SimpleshopTheme.Theme.CSSCache
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/simpleshop_theme/theme/css_cache.ex

@@ -82,7 +82,11 @@ defmodule SimpleshopTheme.Theme.CSSCache do
     alias SimpleshopTheme.Theme.CSSGenerator
 
     settings = Settings.get_theme_settings()
-    css = CSSGenerator.generate(settings)
+
+    # Use endpoint's static_path for digested URLs in production
+    path_resolver = &SimpleshopThemeWeb.Endpoint.static_path/1
+
+    css = CSSGenerator.generate(settings, path_resolver)
     put(css)
     :ok
   end

lib/simpleshop_theme/theme/css_generator.ex

@@ -21,11 +21,14 @@ defmodule SimpleshopTheme.Theme.CSSGenerator do
   pages don't need the attribute-based CSS selectors.
 
   Also includes @font-face declarations for the fonts used by the typography preset.
+
+  Accepts an optional path_resolver function for digested font paths.
+  In production, pass `&SimpleshopThemeWeb.Endpoint.static_path/1`.
   """
-  def generate(%ThemeSettings{} = settings) do
+  def generate(%ThemeSettings{} = settings, path_resolver \\ fn path -> path end) do
     """
     /* Font faces for #{settings.typography} typography */
-    #{Fonts.generate_font_faces(settings.typography)}
+    #{Fonts.generate_font_faces(settings.typography, path_resolver)}
 
     /* Theme Tokens - Layer 2 (dynamically generated) */
     .themed {

lib/simpleshop_theme/theme/fonts.ex

@@ -114,8 +114,11 @@ defmodule SimpleshopTheme.Theme.Fonts do
   Generates @font-face CSS for a specific typography preset.
 
   Only includes the fonts needed for that preset.
+
+  Accepts an optional path_resolver function to transform font URLs.
+  In production, pass `&SimpleshopThemeWeb.Endpoint.static_path/1` for digested paths.
   """
-  def generate_font_faces(typography) do
+  def generate_font_faces(typography, path_resolver \\ &default_path_resolver/1) do
     %{heading: heading_key, body: body_key} = fonts_for_typography(typography)
 
     font_keys =
@@ -126,7 +129,7 @@ defmodule SimpleshopTheme.Theme.Fonts do
       end
 
     font_keys
-    |> Enum.map(&generate_font_face_for_font/1)
+    |> Enum.map(&generate_font_face_for_font(&1, path_resolver))
     |> Enum.join("\n")
   end
 
@@ -134,20 +137,22 @@ defmodule SimpleshopTheme.Theme.Fonts do
   Generates @font-face CSS for ALL fonts.
 
   Used in the theme editor where users can switch between typography presets.
+
+  Accepts an optional path_resolver function for digested paths.
   """
-  def generate_all_font_faces do
+  def generate_all_font_faces(path_resolver \\ &default_path_resolver/1) do
     @fonts
     |> Map.keys()
-    |> Enum.map(&generate_font_face_for_font/1)
+    |> Enum.map(&generate_font_face_for_font(&1, path_resolver))
     |> Enum.join("\n")
   end
 
   @doc """
-  Generates preload link tags for a specific typography preset.
+  Returns the font file paths (without /fonts prefix) for a typography preset.
 
-  Returns a list of maps with href, as, type, and crossorigin attributes.
+  Used by templates to generate preload links with digested paths via ~p sigil.
   """
-  def preload_links(typography) do
+  def preload_font_paths(typography) do
     %{heading: heading_key, body: body_key} = fonts_for_typography(typography)
 
     # Preload the most commonly used weights
@@ -158,21 +163,60 @@ defmodule SimpleshopTheme.Theme.Fonts do
       body: [400, 600]
     }
 
-    heading_links = generate_preload_links_for_font(heading_key, preload_weights.heading)
-    body_links = generate_preload_links_for_font(body_key, preload_weights.body)
+    heading_paths = font_paths_for_weights(heading_key, preload_weights.heading)
+    body_paths = font_paths_for_weights(body_key, preload_weights.body)
 
     # Deduplicate in case heading and body use the same font
-    (heading_links ++ body_links) |> Enum.uniq_by(& &1.href)
+    (heading_paths ++ body_paths) |> Enum.uniq()
+  end
+
+  defp font_paths_for_weights(key, weights) do
+    case get_font(key) do
+      %{file_prefix: prefix, weights: available_weights} ->
+        weights
+        |> Enum.filter(&(&1 in available_weights))
+        |> Enum.map(fn weight ->
+          weight_suffix = if weight == 400, do: "regular", else: to_string(weight)
+          "#{prefix}-#{weight_suffix}.woff2"
+        end)
+
+      nil ->
+        []
+    end
+  end
+
+  @doc """
+  Generates preload link tags for a specific typography preset.
+
+  Returns a list of maps with href, as, type, and crossorigin attributes.
+
+  Accepts an optional path_resolver function for digested paths.
+  In production, pass `&SimpleshopThemeWeb.Endpoint.static_path/1`.
+  """
+  def preload_links(typography, path_resolver \\ &default_path_resolver/1) do
+    typography
+    |> preload_font_paths()
+    |> Enum.map(fn filename ->
+      %{
+        href: path_resolver.("/fonts/#{filename}"),
+        as: "font",
+        type: "font/woff2",
+        crossorigin: true
+      }
+    end)
   end
 
   # Private functions
 
-  defp generate_font_face_for_font(key) do
+  defp default_path_resolver(path), do: path
+
+  defp generate_font_face_for_font(key, path_resolver) do
     case get_font(key) do
       %{family: family, file_prefix: prefix, weights: weights} ->
         weights
         |> Enum.map(fn weight ->
           weight_suffix = if weight == 400, do: "regular", else: to_string(weight)
+          font_path = path_resolver.("/fonts/#{prefix}-#{weight_suffix}.woff2")
 
           """
           @font-face {
@@ -180,7 +224,7 @@ defmodule SimpleshopTheme.Theme.Fonts do
             font-style: normal;
             font-weight: #{weight};
             font-display: swap;
-            src: url('/fonts/#{prefix}-#{weight_suffix}.woff2') format('woff2');
+            src: url('#{font_path}') format('woff2');
           }
           """
         end)
@@ -191,24 +235,4 @@ defmodule SimpleshopTheme.Theme.Fonts do
     end
   end
 
-  defp generate_preload_links_for_font(key, weights) do
-    case get_font(key) do
-      %{file_prefix: prefix, weights: available_weights} ->
-        weights
-        |> Enum.filter(&(&1 in available_weights))
-        |> Enum.map(fn weight ->
-          weight_suffix = if weight == 400, do: "regular", else: to_string(weight)
-
-          %{
-            href: "/fonts/#{prefix}-#{weight_suffix}.woff2",
-            as: "font",
-            type: "font/woff2",
-            crossorigin: true
-          }
-        end)
-
-      nil ->
-        []
-    end
-  end
 end

lib/simpleshop_theme_web/components/layouts/shop_root.html.heex

@@ -7,8 +7,11 @@
     <meta name="description" content={assigns[:page_description] || @theme_settings.site_description || "Welcome to #{@theme_settings.site_name}"} />
     <.live_title><%= assigns[:page_title] || @theme_settings.site_name %></.live_title>
     <!-- Preload critical fonts for the current typography preset -->
-    <%= for preload <- SimpleshopTheme.Theme.Fonts.preload_links(@theme_settings.typography) do %>
-      <link rel="preload" href={preload.href} as={preload.as} type={preload.type} crossorigin />
+    <%= for preload <- SimpleshopTheme.Theme.Fonts.preload_links(
+          @theme_settings.typography,
+          &SimpleshopThemeWeb.Endpoint.static_path/1
+        ) do %>
+      <link rel="preload" href={preload.href} as="font" type="font/woff2" crossorigin />
     <% end %>
     <link phx-track-static rel="stylesheet" href={~p"/assets/css/app.css"} />
     <script defer phx-track-static src={~p"/assets/js/app.js"}>

lib/simpleshop_theme_web/endpoint.ex

@@ -20,11 +20,16 @@ defmodule SimpleshopThemeWeb.Endpoint do
   # When code reloading is disabled (e.g., in production),
   # the `gzip` option is enabled to serve compressed
   # static files generated by running `phx.digest`.
+  #
+  # Cache headers: 1 year for all static assets. Digested assets (with hash
+  # in filename) use `immutable`. Fonts/mockups/images rarely change and
+  # benefit from aggressive caching.
   plug Plug.Static,
     at: "/",
     from: :simpleshop_theme,
     gzip: not code_reloading?,
-    only: SimpleshopThemeWeb.static_paths()
+    only: SimpleshopThemeWeb.static_paths(),
+    cache_control_for_etags: "public, max-age=31536000, immutable"
 
   if Code.ensure_loaded?(Tidewave) do
     plug Tidewave