created item availability checking tool

back-office/app/controllers/items_controller.rb

@@ -3,4 +3,16 @@ class ItemsController < ApplicationController
     conf.columns[:unit].form_ui = :select
     conf.columns[:sub_category].form_ui = :select
   end
+
+  def check_availability
+    @suppliers = Supplier.order(:name).all
+    @selected_supplier = Supplier.find_by_id(params[:supplier_id])
+    @items = @selected_supplier.try(:items) || []
+    @codes_to_check = params[:codes] || ""
+    @codes_to_check_array = @codes_to_check.split("\n").reject { |code| code.strip.blank? }.map(&:strip)
+    items_to_check = @items.map { |i| i.code.strip }
+
+    @missing_from_database =  (@codes_to_check_array - items_to_check) || []
+    @missing_from_codes = (items_to_check - @codes_to_check_array) || []
+  end
 end