convert query to CI 3 query builder

Code:

Hello team i hope you're doing well i have a query which i want to convert to CI 3 query builder

with t as  (
            select    regexp_substr(TAG_ID,'\d',1,level) as ID
                      ,count(*)                          as NUB_of_POSTS
            from      post 
            connect by ID = prior ID and level <= regexp_count(TAG_ID,'\d') and sys_guid() <> prior sys_guid()
            group by  regexp_substr(TAG_ID,'\d',1,level)
          )
select    NAME
          ,NUB_of_POSTS
from      t join tag using(ID)