1 files changed, 90 insertions, 0 deletions
diff --git a/lib/gitlab/import_export/group_project_object_builder.rb b/lib/gitlab/import_export/group_project_object_builder.rb
new file mode 100644
index 00000000000..6c2af770119
--- /dev/null
+++ b/lib/gitlab/import_export/group_project_object_builder.rb
@@ -0,0 +1,90 @@
+module Gitlab
+  module ImportExport
+    # Given a class, it finds or creates a new object
+    # (initializes in the case of Label) at group or project level.
+    # If it does not exist in the group, it creates it at project level.
+    #
+    # Example:
+    #   `GroupProjectObjectBuilder.build(Label, label_attributes)`
+    #    finds or initializes a label with the given attributes.
+    #
+    # It also adds some logic around Group Labels/Milestones for edge cases.
+    class GroupProjectObjectBuilder
+      def self.build(*args)
+        Project.transaction do
+          new(*args).find
+        end
+      end
+
+      def initialize(klass, attributes)
+        @klass = klass < Label ? Label : klass
+        @attributes = attributes
+        @group = @attributes['group']
+        @project = @attributes['project']
+      end
+
+      def find
+        find_object || @klass.create(project_attributes)
+      end
+
+      private
+
+      def find_object
+        @klass.where(where_clause).first
+      end
+
+      def where_clause
+        @attributes.slice('title').map do |key, value|
+          scope_clause = table[:project_id].eq(@project.id)
+          scope_clause = scope_clause.or(table[:group_id].eq(@group.id)) if @group
+
+          table[key].eq(value).and(scope_clause)
+        end.reduce(:or)
+      end
+
+      def table
+        @table ||= @klass.arel_table
+      end
+
+      def project_attributes
+        @attributes.except('group').tap do |atts|
+          if label?
+            atts['type'] = 'ProjectLabel' # Always create project labels
+          elsif milestone?
+            if atts['group_id'] # Transform new group milestones into project ones
+              atts['iid'] = nil
+              atts.delete('group_id')
+            else
+              claim_iid
+            end
+          end
+        end
+      end
+
+      def label?
+        @klass == Label
+      end
+
+      def milestone?
+        @klass == Milestone
+      end
+
+      # If an existing group milestone used the IID
+      # claim the IID back and set the group milestone to use one available
+      # This is necessary to fix situations like the following:
+      #  - Importing into a user namespace project with exported group milestones
+      #    where the IID of the Group milestone could conflict with a project one.
+      def claim_iid
+        # The milestone has to be a group milestone, as it's the only case where
+        # we set the IID as the maximum. The rest of them are fixed.
+        milestone = @project.milestones.find_by(iid: @attributes['iid'])
+
+        return unless milestone
+
+        milestone.iid = nil
+        milestone.ensure_project_iid!
+        milestone.save!
+      end
+    end
+  end
+end