South Africa ID Number Checksum Validation

create or replace 
	function validate_sa_id_number(id_number text)
		returns boolean 
		language plpgsql 
as
$$
declare
  char_val char;
 	i int := 1;
  
	digit int := 0;
  weight int := 0;
  sub_total int := 0;
  total int := 0;
 
  check_digit int;
  calculated_digit int;
begin
	-- Check if the id number is 13 digits long
	if length(id_number) != 13 then
		return false;
	end if;
 
	foreach char_val in array regexp_split_to_array(id_number, '') loop
		exit when i > 12;
		 
		digit := char_val::int;
		weight := (case when (i % 2) = 0 then 2 else 1 end);
		sub_total := digit * weight;
		
		-- If sub_total is two digits, sum the digits
		if sub_total > 9 then
			sub_total := (sub_total / 10) + (sub_total % 10);
		end if;
		
		total := total + sub_total;
		i := i + 1;
	end loop;
 
	-- Calculate the check digit
	check_digit := 10 - (total % 10);
	if check_digit = 10 then
	    check_digit := 0;
	end if;

  raise notice 'total: %', total;
  raise notice 'calculated check digit: %', check_digit;
	 
	-- Compare the calculated check digit with the last digit of the ID number
	calculated_digit := substring(id_number from 13 for 1)::int;
 
	return check_digit = calculated_digit;
end;
$$;