How do I convert this SQL query into Active Record statements, there are many answers those are not help me out?

Here's the query:

SELECT
  DISTINCT
  ((substring(r2.email FROM position('@' IN r2.email) + 1))) AS unknown_domain,
  count(DISTINCT (c2.id)) as contact_count,
  count(DISTINCT (dc.id)) as dc_count
FROM
  (SELECT
     unnest(emails) AS email,
     id
   FROM contacts c
   WHERE account_id = 612) AS r2
INNER JOIN domains d
    ON d.domain = ((substring(r2.email FROM position('@' IN r2.email) + 1)))
INNER JOIN contacts c2
    on c2.id = r2.id
INNER JOIN device_contacts dc
  on dc.contact_id = c2.id
where d.freebie = 'f'
      AND (NOT exists(SELECT 1
                      FROM (SELECT unnest(email_domains) :: CHARACTER VARYING AS domain
                            FROM companies) AS results
                      WHERE results.domain = ((substring(r2.email FROM position('@' IN r2.email) + 1)))))
      AND (defunct = FALSE OR defunct IS NULL)
      AND (dc.emails && ARRAY[r2.email]::character varying[])
GROUP BY unknown_domain
ORDER BY dc_count DESC, contact_count DESC;

I have no idea how to convert this into an active record query though. I've looked at numerous rails sites . I have no idea how to approach this at all though. I've tried a few different attempts, and all have failed.