From cb4698bec851c826aaa86d47c4ca003a92f735cc Mon Sep 17 00:00:00 2001
From: jamey <jamey@server.jamey.stream>
Date: Sun, 8 Feb 2026 12:24:39 +0000
Subject: [PATCH] refactor: extract Cart.build_state/1 as single source of
 truth for cart state

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 lib/simpleshop_theme/cart.ex          | 17 +++++++++++++++++
 lib/simpleshop_theme_web/cart_hook.ex | 14 +++++---------
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/lib/simpleshop_theme/cart.ex b/lib/simpleshop_theme/cart.ex
index 19b5f86..a288520 100644
--- a/lib/simpleshop_theme/cart.ex
+++ b/lib/simpleshop_theme/cart.ex
@@ -166,6 +166,23 @@ defmodule SimpleshopTheme.Cart do
   # Helpers
   # =============================================================================
 
+  @doc """
+  Builds the full display state for a cart.
+
+  Takes raw cart items (list of {variant_id, quantity} tuples) and returns
+  a map with hydrated items, count, and formatted subtotal. Single source
+  of truth for cart state computation — used by CartHook.
+  """
+  def build_state(raw_cart) do
+    hydrated = hydrate(raw_cart)
+
+    %{
+      items: hydrated,
+      count: item_count(raw_cart),
+      subtotal: format_subtotal(hydrated)
+    }
+  end
+
   @doc """
   Returns the total item count in the cart.
   """
diff --git a/lib/simpleshop_theme_web/cart_hook.ex b/lib/simpleshop_theme_web/cart_hook.ex
index a17ac10..895a8b9 100644
--- a/lib/simpleshop_theme_web/cart_hook.ex
+++ b/lib/simpleshop_theme_web/cart_hook.ex
@@ -21,14 +21,10 @@ defmodule SimpleshopThemeWeb.CartHook do
 
   def on_mount(:mount_cart, _params, session, socket) do
     cart_items = Cart.get_from_session(session)
-    hydrated = Cart.hydrate(cart_items)
 
     socket =
       socket
-      |> assign(:raw_cart, cart_items)
-      |> assign(:cart_items, hydrated)
-      |> assign(:cart_count, Cart.item_count(cart_items))
-      |> assign(:cart_subtotal, Cart.format_subtotal(hydrated))
+      |> update_cart_assigns(cart_items)
       |> assign(:cart_drawer_open, false)
       |> assign(:cart_status, nil)
       |> attach_hook(:cart_events, :handle_event, &handle_cart_event/3)
@@ -84,13 +80,13 @@ defmodule SimpleshopThemeWeb.CartHook do
   Updates all cart-related assigns from raw cart data.
   """
   def update_cart_assigns(socket, cart) do
-    hydrated = Cart.hydrate(cart)
+    %{items: items, count: count, subtotal: subtotal} = Cart.build_state(cart)
 
     socket
     |> assign(:raw_cart, cart)
-    |> assign(:cart_items, hydrated)
-    |> assign(:cart_count, Cart.item_count(cart))
-    |> assign(:cart_subtotal, Cart.format_subtotal(hydrated))
+    |> assign(:cart_items, items)
+    |> assign(:cart_count, count)
+    |> assign(:cart_subtotal, subtotal)
   end
 
   @doc """