The Golem-Brands of Ferrowick Foundry

The Ironwrights' Guild of Ferrowick casts clay-and-iron golems for the frontier: diggers, haulers and sentinels. Before a golem is woken, a brand is stamped into its brow, and the golem obeys whatever that brand says. A misstruck brand can wake a golem that tears its foundry apart. So the Guild pays a standing bounty to any inspector who checks every brand before the waking fires are lit.

Write inspectBrand(brand). It takes a string brand and returns a string verdict.

A well-formed brand has exactly three pieces joined by single dashes (-): a mark, a serial and a command. An example is FER-1236-DIG.

Apply these checks in this order. Return the verdict for the first check that fails:

1. If brand is the empty string, return "empty". 2. Split brand on every - character. Empty pieces count as pieces. If this does not give exactly 3 pieces, return "malformed". 3. The mark (first piece) must be 1 to 3 characters long, and every character must be an uppercase letter A-Z. Otherwise return "bad mark". 4. The serial (second piece) must be exactly 4 characters long, and every character must be a digit 0-9. Otherwise return "bad serial". 5. Add up the serial's first three digits. The last digit of that sum (the sum modulo 10) must equal the serial's fourth digit. Otherwise return "bad check". 6. The command (third piece) must be exactly one of DIG, HAUL, GUARD or HALT. Matching is case-sensitive. Otherwise return "unknown command".

If every check passes, return "ok".