PostgreSQL 1 month calendar dates

kalender.sql

create or replace function kalender(p_tahun int, p_bulan int) returns text LANGUAGE plpgsql
AS $function$
declare
  y int;
  m int;
  d_start date;
  d_end date;
  nb int;
  c int;
  l text;
begin
  select
   tahun,
   bulan,
   case when hari_pertama > 0 then
      hari - interval '1 days' * hari_pertama
    else to_date(concat(tahun,'-',bulan,'-1'),'yyyy-mm-dd')
   end as tgl_pertama,
   tgl_terakhir
  from (
    select
      date_part('dow',
        to_date(concat(p_tahun,'-',p_bulan,'-01'),'yyyy-mm-dd')
      ) as hari_pertama,
      to_date(concat(p_tahun,'-',p_bulan,'-01'),'yyyy-mm-dd') + interval '1 months' - interval '1 days' as tgl_terakhir,
      to_date(concat(p_tahun,'-',p_bulan,'-01'),'yyyy-mm-dd') as hari,
      date_part('day',to_date(concat(p_tahun,'-',p_bulan,'-01'),'yyyy-mm-dd')) as hari_ini, 
      date_part('month',to_date(concat(p_tahun,'-',p_bulan,'-01'),'yyyy-mm-dd')) as bulan, 
      date_part('year',to_date(concat(p_tahun,'-',p_bulan,'-01'),'yyyy-mm-dd')) as tahun    
  ) a
  into y,m,d_start,d_end;
  
  c = 0;
  l = '';
  loop 
    if c = 35 then
      exit;
    end if;
    l = concat(l,'"',to_char(d_start + interval '1 days' * c,'yyyy-mm-dd'),'",');
    c = c + 1;
  end loop;
--  return l;
--  return concat('{"tahun":',y,',"bulan":',m,',"tanggal":{"awal":',to_char(d_start,'dd')::int,',"akhir":',to_char(d_end,'dd')::int,'}',l,'}');
  return concat('{"tahun":',y,',"bulan":',m,',"tanggal":[',substring(l,0,length(l)),']}');
 end;
 $function$