Using Case Statement To Determine Order By Field And Direction (asc Or Desc) When Using Row_number

I am trying to order by the field and direction as provided by input parameters @COLTOSORTBY and @DIR while using a CTE and assigning Row_Number, but am running into syntax errors.

Say I have a table called myTable with columns col1,col2,col3,

Here's what I'm trying to do

with myCTE AS
(
Select
col1
,col2
,col3
,row_number() over (order by
case when(@DIR = 'ASC') then


case when @COLTOSORTBY='col1' then col1 asc
when @COLTOSORTBY='col2' then col2 asc
else col3 asc
end
else

case when @COLTOSORTBY='col1' then col1 desc
when @COLTOSORTBY='col2' then col2 desc
else col3 desc
end
end
from myTable
)



Please let me know what i can do with minimal code repetition and achive my goal of dynamically sorting column and direction. I do not want to use dynamic SQL under any circumstance.

Thanks.