How to get database data file path

Recently I needed to create universal script which added new file group and file to database regardless of where the MSSQL server was installed. The reason for creating new file was to split data which were changing a lot (table with cached documents) and data which were more or less static.

There was necessary to find out where is located primary file for current database and then to get just directory where the file was located.

DECLARE @PATH nvarchar(max)

SELECT @PATH = LEFT(filename, LEN(filename) + 1 - CHARINDEX('\', REVERSE(filename)))
FROM  master.dbo.sysaltfiles WHERE db_name(dbid) = db_name() AND name = 'PrimaryFileName'