fix: page variant flashing (#681)

dev.exs

@@ -77,6 +77,7 @@ defmodule DemoWeb.Router do
     plug :fetch_live_flash
     plug :protect_from_forgery
     plug :put_secure_browser_headers
+    plug Beacon.Plug
   end
 
   scope "/", DemoWeb do

lib/beacon/loader/page.ex

@@ -197,7 +197,7 @@ defmodule Beacon.Loader.Page do
           def render(var!(assigns)) when is_map(var!(assigns)) do
             var!(assigns)
             |> templates()
-            |> Beacon.Template.choose_template()
+            |> Beacon.Template.choose_template(var!(assigns).beacon.private[:variant_roll])
           end
 
           def templates(var!(assigns)) when is_map(var!(assigns)) do

lib/beacon/plug.ex

@@ -0,0 +1,25 @@
+defmodule Beacon.Plug do
+  @moduledoc """
+  Used to ensure consistency for Beacon Page rendering.
+
+  This is especially important when using Page Variants.
+
+  ## Usage
+
+  Add the plug to your Router's `:browser` pipeline:
+
+  ```
+  pipeline :browser do
+    ...
+    plug Beacon.Plug
+  end
+  ```
+  """
+  @behaviour Plug
+
+  @impl Plug
+  def init(_opts), do: []
+
+  @impl Plug
+  def call(conn, _opts), do: Plug.Conn.put_session(conn, :beacon_variant_roll, Enum.random(1..100))
+end

lib/beacon/template.ex

@@ -1,32 +1,3 @@
-defmodule Beacon.Template.LoadMetadata do
-  @moduledoc """
-  Metadata passed to page loading lifecycle.
-  """
-
-  defstruct [:site, :path]
-
-  @type t :: %__MODULE__{
-          site: Beacon.Types.Site.t(),
-          path: String.t()
-        }
-end
-
-defmodule Beacon.Template.RenderMetadata do
-  @moduledoc """
-  Metadata passed to page rendering lifecycle.
-  """
-
-  defstruct [:site, :path, :page_module, :assigns, :env]
-
-  @type t :: %__MODULE__{
-          site: Beacon.Types.Site.t(),
-          path: String.t(),
-          page_module: module(),
-          assigns: Phoenix.LiveView.Socket.assigns(),
-          env: Macro.Env.t()
-        }
-end
-
 defmodule Beacon.Template do
   @moduledoc """
   Template for layouts, pages, and any other resource that display HTML/HEEx.
@@ -36,16 +7,18 @@ defmodule Beacon.Template do
 
   Template engines that do not support dynamic content can make use of the `:static` field to store its contents.
   """
-
   alias Beacon.Web.BeaconAssigns
 
+  require Logger
+
   @typedoc """
   The AST representation of a `t:Phoenix.LiveView.Rendered.t/0` struct.
   """
   @type ast :: Macro.t()
 
   @type t :: Phoenix.LiveView.Rendered.t() | ast()
 
+  # Used for backwards-compatibility with Atom feeds
   @doc false
   def render_path(site, path_info, query_params \\ %{}) when is_atom(site) and is_list(path_info) and is_map(query_params) do
     case Beacon.RouterServer.lookup_page(site, path_info) do
@@ -55,7 +28,7 @@ defmodule Beacon.Template do
       page ->
         page_module = Beacon.Loader.fetch_page_module(page.site, page.id)
         live_data = Beacon.Web.DataSource.live_data(site, path_info)
-        beacon_assigns = BeaconAssigns.new(site, page, live_data, path_info, query_params)
+        beacon_assigns = BeaconAssigns.new(site, page, live_data, path_info, query_params, :beacon)
         assigns = Map.put(live_data, :beacon, beacon_assigns)
         env = Beacon.Web.PageLive.make_env(site)
 
@@ -69,11 +42,10 @@ defmodule Beacon.Template do
   end
 
   @doc false
-  def choose_template([primary]), do: primary
-  def choose_template([primary | variants]), do: choose_template(variants, Enum.random(1..100), primary)
+  def choose_template([primary | variants], roll), do: choose_template(variants, roll, primary)
 
-  @doc false
-  def choose_template([], _, primary), do: primary
-  def choose_template([{weight, template} | _], n, _) when weight >= n, do: template
-  def choose_template([{weight, _} | variants], n, primary), do: choose_template(variants, n - weight, primary)
+  defp choose_template([], _, primary), do: primary
+  defp choose_template(_, nil, primary), do: primary
+  defp choose_template([{weight, template} | _], n, _) when weight >= n, do: template
+  defp choose_template([{weight, _} | variants], n, primary), do: choose_template(variants, n - weight, primary)
 end

lib/beacon/template/load_metadata.ex

@@ -0,0 +1,12 @@
+defmodule Beacon.Template.LoadMetadata do
+  @moduledoc """
+  Metadata passed to page loading lifecycle.
+  """
+
+  defstruct [:site, :path]
+
+  @type t :: %__MODULE__{
+          site: Beacon.Types.Site.t(),
+          path: String.t()
+        }
+end

lib/beacon/template/render_metadata.ex

@@ -0,0 +1,15 @@
+defmodule Beacon.Template.RenderMetadata do
+  @moduledoc """
+  Metadata passed to page rendering lifecycle.
+  """
+
+  defstruct [:site, :path, :page_module, :assigns, :env]
+
+  @type t :: %__MODULE__{
+          site: Beacon.Types.Site.t(),
+          path: String.t(),
+          page_module: module(),
+          assigns: Phoenix.LiveView.Socket.assigns(),
+          env: Macro.Env.t()
+        }
+end

lib/beacon/web/beacon_assigns.ex

@@ -42,7 +42,8 @@ defmodule Beacon.Web.BeaconAssigns do
               info_handlers_module: nil,
               event_handlers_module: nil,
               live_data_keys: [],
-              live_path: []
+              live_path: [],
+              variant_roll: nil
             }
 
   @doc false
@@ -52,15 +53,23 @@ defmodule Beacon.Web.BeaconAssigns do
   end
 
   @doc false
-  def new(site, %Beacon.Content.Page{} = page) do
+  def new(site, %Beacon.Content.Page{} = page, variant_roll) do
     components_module = Beacon.Loader.Components.module_name(site)
     page_module = Beacon.Loader.Page.module_name(site, page.id)
-    %__MODULE__{site: site, private: %{components_module: components_module, page_module: page_module}}
+
+    %__MODULE__{
+      site: site,
+      private: %{
+        components_module: components_module,
+        page_module: page_module,
+        variant_roll: variant_roll
+      }
+    }
   end
 
   @doc false
-  def new(site, %Beacon.Content.Page{} = page, live_data, path_info, query_params, source \\ :beacon)
-      when is_atom(site) and is_map(live_data) and is_list(path_info) and is_map(query_params) do
+  def new(site, %Beacon.Content.Page{} = page, live_data, path_info, query_params, source, variant_roll \\ nil)
+      when is_atom(site) and is_map(live_data) and is_list(path_info) and is_map(query_params) and source in [:beacon, :admin] do
     %{site: ^site} = page
     page_module = Beacon.Loader.Page.module_name(site, page.id)
     live_data = Beacon.Web.DataSource.live_data(site, path_info, Map.drop(query_params, ["path"]))
@@ -81,7 +90,8 @@ defmodule Beacon.Web.BeaconAssigns do
         info_handlers_module: info_handlers_module,
         event_handlers_module: event_handlers_module,
         live_data_keys: Map.keys(live_data),
-        live_path: path_info
+        live_path: path_info,
+        variant_roll: variant_roll
       }
     }
   end

lib/beacon/web/live/page_live.ex

@@ -23,8 +23,23 @@ defmodule Beacon.Web.PageLive do
       :ok = Beacon.PubSub.subscribe_to_page(site, path)
     end
 
+    variant_roll =
+      case session["beacon_variant_roll"] do
+        nil ->
+          Logger.warning("""
+          Beacon.Plug is missing from the Router pipeline.
+
+          Page Variants will not be used.
+          """)
+
+          nil
+
+        roll ->
+          roll
+      end
+
     page = RouterServer.lookup_page!(site, path)
-    socket = Component.assign(socket, beacon: BeaconAssigns.new(site, page))
+    socket = Component.assign(socket, beacon: BeaconAssigns.new(site, page, variant_roll))
 
     {:ok, socket, layout: {Beacon.Web.Layouts, :dynamic}}
   end
@@ -124,7 +139,7 @@ defmodule Beacon.Web.PageLive do
 
         page = RouterServer.lookup_page!(site, path_info)
         live_data = Beacon.Web.DataSource.live_data(site, path_info, Map.drop(params, ["path"]))
-        beacon_assigns = BeaconAssigns.new(site, page, live_data, path_info, params)
+        beacon_assigns = BeaconAssigns.new(site, page, live_data, path_info, params, :beacon, socket.assigns.beacon.private.variant_roll)
 
         socket =
           socket

test/beacon_web/beacon_assigns_test.exs

@@ -32,7 +32,7 @@ defmodule Beacon.Web.BeaconAssignsTest do
   test "build with published page resolves page title", %{site: site} do
     page = beacon_published_page_fixture(path: "/blog", title: "blog index")
 
-    assigns = BeaconAssigns.new(site, page, %{}, ["blog"], %{})
+    assigns = BeaconAssigns.new(site, page, %{}, ["blog"], %{}, :beacon)
 
     assert %BeaconAssigns{
              site: @site,
@@ -46,7 +46,7 @@ defmodule Beacon.Web.BeaconAssignsTest do
   test "build with path info and query params", %{site: site} do
     page = beacon_published_page_fixture(path: "/blog")
 
-    assigns = BeaconAssigns.new(site, page, %{}, ["blog"], %{source: "search"})
+    assigns = BeaconAssigns.new(site, page, %{}, ["blog"], %{source: "search"}, :beacon)
 
     assert %BeaconAssigns{
              site: @site,
@@ -60,7 +60,7 @@ defmodule Beacon.Web.BeaconAssignsTest do
   test "build with path params", %{site: site} do
     page = beacon_published_page_fixture(path: "/blog/:post")
 
-    assigns = BeaconAssigns.new(site, page, %{}, ["blog", "hello"], %{})
+    assigns = BeaconAssigns.new(site, page, %{}, ["blog", "hello"], %{}, :beacon)
 
     assert %BeaconAssigns{
              site: @site,
@@ -74,7 +74,7 @@ defmodule Beacon.Web.BeaconAssignsTest do
     live_data = beacon_live_data_fixture(path: "/blog")
     beacon_live_data_assign_fixture(live_data: live_data, format: :text, key: "customer_id", value: "123")
 
-    assigns = BeaconAssigns.new(site, page, live_data, ["blog"], %{})
+    assigns = BeaconAssigns.new(site, page, live_data, ["blog"], %{}, :beacon)
 
     assert %BeaconAssigns{
              site: @site,