Calculating a primary key

[Colt Brunton]

Hi folks
 
I need a MySQL statement that will calculate a new unique identifier for
each record in a table.
 
The identifier format is "AAAA-888" where the letters are the first four
letters of the company's name and the 3 digit number is accounts for
each occurrence of the letters.
 
E.G. MadMax Ltd should produce the key, "MADM001".
 
Any ideas?