How can I update the calculated value for the status of linked issues?

[jun lee]

I made a number type custom field named PlanPercent. I I would like to update the percentage value by counting the issues whose status of the linked issue type is Hierarchy link (WBSGantt) and whose status is Completed.  If issue A has 5 Hierarchy link (WBSGantt) linked issues, and 3 linked issues are Completed, percentage value must be 60 (3/5* 100).

Can you tell me groovy script or Automation rule setting?

Thanks in advance.