Add route, controller action and form

for promo codes csv import.

app/controllers/spree/admin/promotion_batches_controller.rb

@@ -14,6 +14,14 @@ def csv_export
                   disposition: :attachment,
                   type: "text/csv"
       end
+
+      def csv_import
+        content = params[:file]&.read.to_s
+        Spree::PromotionBatches::PromoCodesImporter.new(content: content, promotion_batch_id: params[:id]).call
+        redirect_back fallback_location: admin_promotions_path, notice: "Promo codes uploaded"
+      rescue Spree::PromotionBatches::PromoCodesImporter::Error => e
+        redirect_back fallback_location: admin_promotions_path, alert: e.message
+      end
     end
   end
 end

app/views/spree/admin/promotion_batches/show.html.erb

@@ -14,6 +14,11 @@
   <% end %>
 <% end %>
 
+<%= form_tag csv_import_admin_promotion_batch_path, method: :post, multipart: true do %>
+  <%= file_field_tag :file, accept: ".csv" %>
+  <%= submit_tag 'Import codes from CSV' %>
+<% end %>
+
 <table class="table">
   <thead class="text-muted">
     <tr>

config/routes.rb

@@ -14,6 +14,7 @@
     resources :promotion_batches do
       member do
         get :csv_export, to: 'promotion_batches#csv_export'
+        post :csv_import, to: 'promotion_batches#csv_import'
       end
     end