From normal DB query to Eloquent

Hi all,

I would like to know which steps would you use to convert this into an Eloquent query please, do you know of any convertor? I have 2 problems in keeping this query this way: 1)I need pagination 2)I need to use ->where() as

                ->when($variable, function ($query) use ($variable) {
                   $query->where('C1.sent', '=', $variable);
                })

DB::select("SELECT
  C1.chat_title,
  C1.chat_object,
  C1.created_at,
  C1.id,
  MAX(C1.message) AS messages,
  C2.unread,
  C1.group_id
FROM chats C1
  INNER JOIN (SELECT
      C2.created_at,
      C2.chat_object,
      SUM(IF(C2.admin_read = 0, 1, 0)) AS unread
    FROM chats C2
    GROUP BY C2.chat_object) C2
    ON C1.chat_object = C2.chat_object
WHERE C1.group_id = 82
GROUP BY C1.chat_object,
         C1.group_id
ORDER BY C1.id DESC")

Any ideas please? I tried to manually convert this query to Eloquent but failed to get anything working. I have CHAT model already.

Thanks all.