Splitting Out Names From One Field Delimted By Comma And A Space

have a field in a table that has combined lastname,firstname and middle name like

combs,albert mike
woods-athere,jane alice

The last and first name are separated by a comma, and the middle name by a space
I need in tsql to split them to last name,first name and middle name
I used below

select substring (longname, 1, patindex( '%,%' , longname) -1 ) 'firstname',
substring (longname, patindex( '%,%', longname) + 1, len(longname)) 'lastname',
substring (longname, patindex( '% %', longname) + 1, len(longname)) 'middlename'
FROM Demographic_staging

I get the names all split, but I get the middle name with the first name. How can I limit the first name to recoginze the comma, but stop at the space