Write a case statemt SSIS

Hello All,

I am writing a derived column and i need to write a case statement for the following :

case when FINDSTRING(substring((right((DT_WSTR,255)@[User::CurrentFile],len((DT_WSTR,255)@[User::CurrentFile])- FINDSTRING(@[User::CurrentFile],"v1",1)-1)),1,8),"_",1)>0 
then substring((right((DT_WSTR,255)@[User::CurrentFile],len((DT_WSTR,255)@[User::CurrentFile])- FINDSTRING(@[User::CurrentFile],"v1",1)-1)),2,8)
end

else substring((right((DT_WSTR,255)@[User::CurrentFile],len((DT_WSTR,255)@[User::CurrentFile])- FINDSTRING(@[User::CurrentFile],"v1",1)-1)),1,8)
end

some one please help me?

Thanks