Get list item permission along with role defination using REST Api

Hello All,

I am trying to find the sharepoint groups having 'Approve' permission on a list item which is having unique permission.

I tried following approach:

1) http://SharePoint/sites/abc/_api/Web/Lists(guid'a5fffbd8-d36b-4165-9fc3-fe59afb84edd')/Items(12)?$expand=RoleAssignments/Member

but this gives me all groups and users but I don't get the role defination so that I can filter for Approver.

2) http://SharePoint/sites/abc/_api/Web/Lists(guid'a5fffbd8-d36b-4165-9fc3-fe59afb84edd')/Items(12)?$expand=RoleAssignments/RoleDefinitionBindings

but this give me only role defination and not the groups and users.

What I need is all the sharepoint group having 'Approver' role.

Please suggest.

Thanks!

Ashish H