From 61fec653cfd753cf5b1f4955ae81992189de780e Mon Sep 17 00:00:00 2001
From: Maikel Linke <maikel@email.org.au>
Date: Wed, 25 Sep 2024 14:07:55 +1000
Subject: [PATCH] Abstract OrderLocker for re-use

---
 app/services/current_order_locker.rb | 29 +-----------------------
 app/services/order_locker.rb         | 33 ++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 28 deletions(-)
 create mode 100644 app/services/order_locker.rb

diff --git a/app/services/current_order_locker.rb b/app/services/current_order_locker.rb
index 1584701d1a..602ee1f15d 100644
--- a/app/services/current_order_locker.rb
+++ b/app/services/current_order_locker.rb
@@ -10,33 +10,6 @@ class CurrentOrderLocker
   #   https://guides.rubyonrails.org/action_controller_overview.html#filters
   #
   def self.around(controller, &)
-    lock_order_and_variants(controller.current_order, &)
+    OrderLocker.lock_order_and_variants(controller.current_order, &)
   end
-
-  # Locking will not prevent all access to these rows. Other processes are
-  # only waiting if they try to lock one of these rows as well.
-  #
-  #   https://api.rubyonrails.org/classes/ActiveRecord/Locking/Pessimistic.html
-  #
-  def self.lock_order_and_variants(order)
-    return yield if order.nil?
-
-    order.with_lock do
-      lock_variants_of(order)
-      yield
-    end
-  end
-  private_class_method :lock_order_and_variants
-
-  # There are many places in which stock is stored in the database. Row locking
-  # on variant level ensures that there are no conflicts even when an item is
-  # sold through multiple shops.
-  def self.lock_variants_of(order)
-    variant_ids = order.line_items.select(:variant_id)
-
-    # Ordering the variants by id prevents deadlocks. Plucking the ids sends
-    # the locking query without building Spree::Variant objects.
-    Spree::Variant.where(id: variant_ids).order(:id).lock.pluck(:id)
-  end
-  private_class_method :lock_variants_of
 end
diff --git a/app/services/order_locker.rb b/app/services/order_locker.rb
new file mode 100644
index 0000000000..4f864ca769
--- /dev/null
+++ b/app/services/order_locker.rb
@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+# Locks an order including its variants.
+#
+# It should be used when making major changes like checking out the order.
+# It can keep stock checking in sync and prevent overselling of an item.
+class OrderLocker
+  # Locking will not prevent all access to these rows. Other processes are
+  # only waiting if they try to lock one of these rows as well.
+  #
+  #   https://api.rubyonrails.org/classes/ActiveRecord/Locking/Pessimistic.html
+  #
+  def self.lock_order_and_variants(order)
+    return yield if order.nil?
+
+    order.with_lock do
+      lock_variants_of(order)
+      yield
+    end
+  end
+
+  # There are many places in which stock is stored in the database. Row locking
+  # on variant level ensures that there are no conflicts even when an item is
+  # sold through multiple shops.
+  def self.lock_variants_of(order)
+    variant_ids = order.line_items.select(:variant_id)
+
+    # Ordering the variants by id prevents deadlocks. Plucking the ids sends
+    # the locking query without building Spree::Variant objects.
+    Spree::Variant.where(id: variant_ids).order(:id).lock.pluck(:id)
+  end
+  private_class_method :lock_variants_of
+end