1 files changed, 79 insertions, 0 deletions
diff --git a/app/models/work_item.rb b/app/models/work_item.rb
index a7cd522f023..10476339ca9 100644
--- a/app/models/work_item.rb
+++ b/app/models/work_item.rb
@@ -67,6 +67,16 @@ class WorkItem < Issue
     end
   end
 
+  # Returns widget object if available
+  # type parameter can be a symbol, for example, `:description`.
+  def get_widget(type)
+    widgets.find do |widget|
+      widget.instance_of?(WorkItems::Widgets.const_get(type.to_s.camelize, false))
+    end
+  rescue NameError
+    nil
+  end
+
   def ancestors
     hierarchy.ancestors(hierarchy_order: :asc)
   end
@@ -130,6 +140,75 @@ class WorkItem < Issue
 
     ::Gitlab::WorkItems::WorkItemHierarchy.new(base, options: options)
   end
+
+  override :allowed_work_item_type_change
+  def allowed_work_item_type_change
+    return unless work_item_type_id_changed?
+
+    child_links = WorkItems::ParentLink.for_parents(id)
+    parent_link = ::WorkItems::ParentLink.find_by(work_item: self)
+
+    validate_parent_restrictions(parent_link)
+    validate_child_restrictions(child_links)
+    validate_depth(parent_link, child_links)
+  end
+
+  def validate_parent_restrictions(parent_link)
+    return unless parent_link
+
+    parent_link.work_item.work_item_type_id = work_item_type_id
+
+    unless parent_link.valid?
+      errors.add(
+        :work_item_type_id,
+        format(
+          _('cannot be changed to %{new_type} with %{parent_type} as parent type.'),
+          new_type: work_item_type.name, parent_type: parent_link.work_item_parent.work_item_type.name
+        )
+      )
+    end
+  end
+
+  def validate_child_restrictions(child_links)
+    return if child_links.empty?
+
+    child_type_ids = child_links.joins(:work_item).select(self.class.arel_table[:work_item_type_id]).distinct
+    restrictions = ::WorkItems::HierarchyRestriction.where(
+      parent_type_id: work_item_type_id,
+      child_type_id: child_type_ids
+    )
+
+    # We expect a restriction for every child type
+    if restrictions.size < child_type_ids.size
+      errors.add(
+        :work_item_type_id,
+        format(_('cannot be changed to %{new_type} with these child item types.'), new_type: work_item_type.name)
+      )
+    end
+  end
+
+  def validate_depth(parent_link, child_links)
+    restriction = ::WorkItems::HierarchyRestriction.find_by_parent_type_id_and_child_type_id(
+      work_item_type_id,
+      work_item_type_id
+    )
+    return unless restriction&.maximum_depth
+
+    children_with_new_type = self.class.where(id: child_links.select(:work_item_id))
+      .where(work_item_type_id: work_item_type_id)
+    max_child_depth = ::Gitlab::WorkItems::WorkItemHierarchy.new(children_with_new_type).max_descendants_depth.to_i
+
+    ancestor_depth =
+      if parent_link&.work_item_parent && parent_link.work_item_parent.work_item_type_id == work_item_type_id
+        parent_link.work_item_parent.same_type_base_and_ancestors.count
+      else
+        0
+      end
+
+    if max_child_depth + ancestor_depth > restriction.maximum_depth - 1
+      errors.add(:work_item_type_id, _('reached maximum depth'))
+    end
+  end
 end
 
 WorkItem.prepend_mod