Extract logic from controller to renderer service

Re-using the filter_visible method for both products and variants

app/controllers/api/exchange_products_controller.rb

@@ -28,24 +28,22 @@ module Api
     private
 
     def render_variant_count
-      variants_relation = Spree::Variant.
-          not_master.
-          where(product_id: products.select(&:id))
-
-      if @order_cycle.present? &&
-         @order_cycle.prefers_product_selection_from_coordinator_inventory_only?
-        variants_relation = variants_relation.visible_for(@order_cycle.coordinator)
-      end
-
       render text: {
-        count: variants_relation.count
+        count: variants.count
       }.to_json
     end
 
+    def variants
+      renderer.exchange_variants(@incoming, @enterprise)
+    end
+
     def products
-      ExchangeProductsRenderer.
-        new(@order_cycle, spree_current_user).
-        exchange_products(@incoming, @enterprise)
+      renderer.exchange_products(@incoming, @enterprise)
+    end
+
+    def renderer
+      @renderer ||= ExchangeProductsRenderer.
+        new(@order_cycle, spree_current_user)
     end
 
     def paginated_products

app/services/exchange_products_renderer.rb

@@ -12,6 +12,14 @@ class ExchangeProductsRenderer
     end
   end
 
+  def exchange_variants(incoming, enterprise)
+    variants_relation = Spree::Variant.
+      not_master.
+      where(product_id: exchange_products(incoming, enterprise).select(&:id))
+
+    filter_visible(variants_relation)
+  end
+
   private
 
   def products_for_incoming_exchange(enterprise)
@@ -21,12 +29,16 @@ class ExchangeProductsRenderer
   def supplied_products(enterprises_query_matcher)
     products_relation = Spree::Product.where(supplier_id: enterprises_query_matcher)
 
+    filter_visible(products_relation)
+  end
+
+  def filter_visible(relation)
     if @order_cycle.present? &&
        @order_cycle.prefers_product_selection_from_coordinator_inventory_only?
-      products_relation = products_relation.visible_for(@order_cycle.coordinator)
+      relation = relation.visible_for(@order_cycle.coordinator)
     end
 
-    products_relation
+    relation
   end
 
   def products_for_outgoing_exchange