Firestore's newId function implemented in PostgreSQL. Converted using ChatGPT.

firestore-new-id.sql

create or replace function public.gen_id()
returns text as $$
declare
  chars text := 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  max_multiple integer := floor(256 / char_length(chars)) * char_length(chars);
  i integer;
  auto_id text := '';
  target_length integer := 20;
  bytes bytea;
begin
  while char_length(auto_id) < target_length loop
    bytes := gen_random_bytes(40);
    for i in 1..40 loop
      if char_length(auto_id) < target_length and ascii(substring(encode(bytes, 'escape'), i, 1)) < max_multiple then
        auto_id := auto_id || substring(chars, (ascii(substring(encode(bytes, 'escape'), i, 1)) % char_length(chars)) + 1, 1);
      end if;
    end loop;
  end loop;

  return auto_id;
end;
$$ language plpgsql;