pgSQL script to validate Iranian National ID format

validate.sql

-- AUTHOR: Mostafa

drop function if exists validate_national_id( text );
create or replace function validate_national_id(id text)
  returns boolean as $$
declare
  summation   integer := 0;
  arrayId     text[] ;
  rem         integer;
  lastElement integer;

begin
  -- prepend zeros if missing
  if length(id) = 8 then
     id := '00' || id;
     elseif length(id) = 9 then
     id :=  '0' || id;
     end if;
     
  --   validate size
  if length(id) != 10
  then
    return false;
  end if;
  
  --   cast code to array to iterate through
  arrayId := regexp_split_to_array(id, '');
  -- array index starts from 1 in postgres
  for i in 1..9
  loop
    summation := summation + arrayId [i] :: integer * (11 - i);
  end loop;

  rem := summation % 11;
  lastElement = arrayId [10] :: integer;

  if rem < 2
  then
    return rem = lastElement;
  end if;
  return rem = 11 - lastElement;
   exception when others then
   return false;
end;
$$
language plpgsql;


select *
from  validate_national_id('1111111111') valid2z,
      validate_national_id('01e518672') valid1z,
      validate_national_id('0018518672') valid,
      validate_national_id('7731689951') as invalid,
      validate_national_id('7731689956') as validAgain;