fix: keep all digits when formatting 13-digit SP/MG voter ids

format_voter_id used hardcoded 12-digit forward slices, so a valid 13-digit
voter id (the SP/MG edge case with a 9-digit sequential number) lost its last
digit and showed the wrong federative union and verifying digits, even though
is_valid accepts it.

Slice length-aware: the federative union and verifying digits are always the
last four characters (via the existing backward-indexing helpers), and the
sequential number is everything before them. 12-digit output is unchanged;
13-digit ids now format losslessly.

Author: gaoflow

brutils/voter_id.py

@@ -285,11 +285,24 @@ def format_voter_id(voter_id: str) -> str | None:
         '6908 4709 28 28'
         >>> format_voter_id("163204010922")
         '1632 0401 09 22'
+        >>> format_voter_id("3244567800167")
+        '32445 6780 01 67'
     """
 
     if not is_valid(voter_id):
         return None
 
+    # The sequential number has 8 digits, except for the SP and MG edge case,
+    # where it can have 9 digits (making the voter id 13 digits long). The
+    # federative union and verifying digits are always the last 4 digits.
+    sequential_number = voter_id[:-4]
+    federative_union = _get_federative_union(voter_id)
+    verifying_digits = _get_verifying_digits(voter_id)
+
+    split = len(sequential_number) - 4
     return "{} {} {} {}".format(
-        voter_id[:4], voter_id[4:8], voter_id[8:10], voter_id[10:12]
+        sequential_number[:split],
+        sequential_number[split:],
+        federative_union,
+        verifying_digits,
     )

tests/test_voter_id.py

@@ -127,6 +127,16 @@ def test_format_voter_id(self):
         self.assertIsNone(format_voter_id("000000000000"))
         self.assertIsNone(format_voter_id("800911840197"))
 
+    def test_format_voter_id_special_case(self):
+        # SP & MG voter ids can have a 9-digit sequential number, making the
+        # voter id 13 digits long. Formatting must keep every digit and place
+        # the federative union and verifying digits correctly.
+        voter_id = "3244567800167"
+        self.assertIs(is_valid(voter_id), True)
+        formatted = format_voter_id(voter_id)
+        self.assertEqual(formatted, "32445 6780 01 67")
+        self.assertEqual(formatted.replace(" ", ""), voter_id)
+
 
 if __name__ == "__main__":
     main()