create or replace function get_site(domain text) returns integer
	language sql immutable strict
	as $$
select get_site(tripdomain($1)) as result;
$$;

-- this function adds tag to domain
CREATE or replace FUNCTION mark(domain text, new_tag text) RETURNS integer
	LANGUAGE sql immutable STRICT
	AS $$
select mark(get_site($1), $2) as result;
$$;

-- this function adds tag to site by site id
CREATE or replace FUNCTION mark(my_id_site integer, new_tag text) RETURNS integer
	LANGUAGE plpgsql STRICT
	AS $$
declare
	-- maybe check should be added to make sure supplied site id really exists
	my_tag text[];
	my_tag_id integer;
begin
	-- selecting tags site already have and adding new tag to them
	-- note that tags should be sorted to eliminate permutations
	select coalesce(tag, '{}'::text[]) from urls natural left join tag where id_site = my_id_site into my_tag;
	if not found then
		-- no records found - creating new tag
		insert into urls (id_site, id_tag) values (my_id_site, get_tag(array[new_tag]));
	else
		-- joining tags
		select usort(my_tag || array[new_tag]) into my_tag;
		-- updating existing record
		update urls set id_tag = get_tag(my_tag || array[new_tag]) where id_site = my_id_site;
	end if;
	return my_id_site;
end;
$$;

-- this function returns id of tag array
create or replace function get_tag(my_tag text[]) returns integer
	language plpgsql strict
	as $$