-- Validation of the Austrian Sozialversicherungsnummer (SVNR).
--
-- `sv_nummer` has been free text since the initial schema. For employees at
-- an Austrian location it follows a fixed standard — three-digit serial,
-- check digit, then TTMMJJ — and the check digit is verifiable, so typos
-- that would otherwise surface at the payroll interface can be caught on
-- entry. Employees at the German/Czech/Slovenian locations keep the field
-- free-form; their national equivalents have different formats.
--
-- Enforced by a trigger rather than inside hire_employee/change_employee_data
-- for the same reason as the assignment history: both functions have been
-- redefined by half a dozen migrations, and a check in the table catches
-- every write path including ones added later.

create or replace function is_valid_svnr(p_svnr text, p_birth_date date default null)
returns boolean
language plpgsql
immutable
as $$
declare
  v text := regexp_replace(coalesce(p_svnr, ''), '[\s./-]', '', 'g');
  v_weights int[] := array[3, 7, 9, 0, 5, 8, 4, 2, 1, 6];
  v_days_in_month int[] := array[31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
  v_sum int := 0;
  v_day int;
  v_month int;
  v_check int;
begin
  if v !~ '^\d{10}$' then return false; end if;
  -- 000 is never issued as a serial.
  if substr(v, 1, 3) = '000' then return false; end if;

  v_day := substr(v, 5, 2)::int;
  v_month := substr(v, 7, 2)::int;
  if v_month < 1 or v_month > 12 or v_day < 1 then return false; end if;
  -- February is allowed 29 days: a two-digit year cannot tell us whether the
  -- year was a leap year, so the generous bound is the correct one here.
  if v_day > v_days_in_month[v_month] then return false; end if;

  for i in 1..10 loop
    if i <> 4 then
      v_sum := v_sum + substr(v, i, 1)::int * v_weights[i];
    end if;
  end loop;

  v_check := v_sum % 11;
  -- A serial whose weighted sum lands on 11 leaves no single digit to use,
  -- so that serial is skipped rather than wrapped around.
  if v_check = 10 then return false; end if;
  if v_check <> substr(v, 4, 1)::int then return false; end if;

  if p_birth_date is not null and to_char(p_birth_date, 'DDMMYY') <> substr(v, 5, 6) then
    return false;
  end if;

  return true;
end;
$$;

comment on function is_valid_svnr(text, date) is
  'Prüft eine österreichische SV-Nummer (10 Ziffern, Prüfziffer mod 11). Mit p_birth_date wird zusätzlich der TTMMJJ-Teil gegen das Geburtsdatum geprüft.';

create or replace function fn_validate_employee_svnr()
returns trigger
language plpgsql
as $$
declare
  v_country text;
begin
  if new.sv_nummer is null or btrim(new.sv_nummer) = '' then
    return new;
  end if;

  -- Only a *newly written* value is checked. Rows that predate this
  -- migration keep whatever they hold, so an unrelated edit — a transfer, a
  -- promotion, an address change — is never blocked by a legacy value the
  -- user is not touching.
  if tg_op = 'UPDATE' and new.sv_nummer is not distinct from old.sv_nummer then
    return new;
  end if;

  select country into v_country from locations where id = new.location_id;
  if v_country is distinct from 'Österreich' then
    return new;
  end if;

  if not is_valid_svnr(new.sv_nummer, new.birth_date) then
    raise exception 'Ungültige SV-Nummer: %. Erwartet werden 10 Ziffern (laufende Nummer, Prüfziffer, TTMMJJ) mit gültiger Prüfziffer und dem Geburtsdatum des/der Mitarbeiter:in.', new.sv_nummer
      using errcode = '23514';
  end if;

  return new;
end;
$$;

drop trigger if exists trg_validate_employee_svnr on employees;
create trigger trg_validate_employee_svnr
before insert or update on employees
for each row execute function fn_validate_employee_svnr();