Add support for SO numbers

Adds the possibility of using SO numbers when registering in GREG.

greg/utils.py

@@ -14,10 +14,36 @@ def camel_to_snake(s: str) -> str:
 
 def is_valid_id_number(input_digits: str) -> bool:
     """
-    Checks whether the input represents a valid national ID number (fødselsnummer) or a valid D-number.
+    Checks whether the input represents a valid national ID number (fødselsnummer), a valid D-number
+    or a valid SO-number.
     """
     is_dnumber = int(input_digits[0:1]) >= 4
-    return is_valid_norwegian_national_id_number(input_digits, is_dnumber)
+    return is_valid_norwegian_national_id_number(
+        input_digits, is_dnumber
+    ) or is_valid_so_number(input_digits)
+
+
+def is_valid_so_number(input_digits: str) -> bool:
+    """
+    Checks if SO numbers are allowed and if so, check that it is valid.
+    """
+    if not settings.ALLOW_SO_NUMBERS:
+        return False
+    SO_NUMBER = False
+    day, month, year, pnr = (
+        input_digits[0:2],
+        int(input_digits[2:4]),
+        input_digits[4:6],
+        input_digits[6:],
+    )
+    if pnr[0] != "1":
+        return False
+    if month > 50:
+        SO_NUMBER = True
+        month -= 50
+        input_digits = day + str(month) + year + pnr
+
+    return SO_NUMBER and _check_birthdate(input_digits, is_dnumber=False)
 
 
 def is_valid_norwegian_national_id_number(input_digits: str, is_dnumber: bool) -> bool: