Montly report SQL from existing tables by worker

Question

Need to repair this code to monthly report
Radnik is worker
Vrijemeprijave is datetime come to work,

Vrijemeodjave is work end

 

SELECT  [radnik] as Radnik,SUM(cast((CASE WHEN DATEPART(WEEKDAY, vrijemeprijave) in (1, 7) then 0 else (CASE WHEN(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) > 8 THEN 8 ELSE(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) END) end)as float))   AS radni_sati,"
                     + "SUM(cast((CASE WHEN DATEPART(WEEKDAY, vrijemeodjave) in (1, 7) then(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) else(case when(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) > 8  then((DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) - 8) ELSE NULL END) end)as float))   AS 'Prekovremeni'"
                     + "from[prijava_radnika]"
                     + "group by[radnik]";