1 files changed, 52 insertions, 0 deletions
diff --git a/app/serializers/environment_serializer.rb b/app/serializers/environment_serializer.rb
index 91955542f25..d0a60f134da 100644
--- a/app/serializers/environment_serializer.rb
+++ b/app/serializers/environment_serializer.rb
@@ -1,3 +1,55 @@
 class EnvironmentSerializer < BaseSerializer
+  Item = Struct.new(:name, :size, :latest)
+
   entity EnvironmentEntity
+
+  def within_folders
+    tap { @itemize = true }
+  end
+
+  def with_pagination(request, response)
+    tap { @paginator = Gitlab::Serializer::Pagination.new(request, response) }
+  end
+
+  def itemized?
+    @itemize
+  end
+
+  def paginated?
+    @paginator.present?
+  end
+
+  def represent(resource, opts = {})
+    if itemized?
+      itemize(resource).map do |item|
+        { name: item.name,
+          size: item.size,
+          latest: super(item.latest, opts) }
+      end
+    else
+      resource = @paginator.paginate(resource) if paginated?
+
+      super(resource, opts)
+    end
+  end
+
+  private
+
+  def itemize(resource)
+    items = resource.order('folder_name ASC')
+      .group('COALESCE(environment_type, name)')
+      .select('COALESCE(environment_type, name) AS folder_name',
+              'COUNT(*) AS size', 'MAX(id) AS last_id')
+
+    # It makes a difference when you call `paginate` method, because
+    # although `page` is effective at the end, it calls counting methods
+    # immediately.
+    items = @paginator.paginate(items) if paginated?
+
+    environments = resource.where(id: items.map(&:last_id)).index_by(&:id)
+
+    items.map do |item|
+      Item.new(item.folder_name, item.size, environments[item.last_id])
+    end
+  end
 end