create function array_uniq (a anyarray) returns anyarray
immutable
language sql
as $$
  select array_agg(distinct x) from unnest(a) x;
$$;
comment on function array_uniq is
  'Sorts and deduplicates elements of an array.';

create function trg_person_roles_normalize () returns trigger
language plpgsql
as $$
  begin
    NEW.roles = array_uniq(NEW.roles);
    return NEW;
  end;
$$;
comment on function trg_person_roles_normalize is
  'A trigger function for table person that sorts and deduplicates elements of '
  'the roles array.';

create trigger roles_normalize
  before insert or update of roles on person
  for each row
  when (cardinality(NEW.roles) > 0)
  execute function trg_person_roles_normalize();