SQL & PL/SQL

Hi Sir, I am facing an issue in deriving week_number which needs to be derived in the below format The correct format is shown as below

MON-WEEK_NUMBER-YEAR(YY)

MON-WEEK_NUMBER-YEAR

declare
v_cost_pa_period VARCHAR2(10);
v_last_date  VARCHAR2(10);
v_sun_date VARCHAR2(10);
v_max_dim_number INTEGER;
v_tues_date VARCHAR2(10);
v_sat_date VARCHAR2(10);
v_last_day NUMBER;
v_sun_number NUMBER;
V_cost_pa_partial VARCHAR2(10);
v_last_date_partial VARCHAR2(10);
v_cost_pa_period1 VARCHAR2(10);
BEGIN


select Initcap(to_char(next_day ( trunc (sysdate, 'iw') , 'Tuesday'  ) ,'DD-MON-YY')) into v_tues_date from dual;
    dbms_output.put_line('The TUESDAY DATE  is '||v_tues_date);
    select Initcap(to_char(next_day ( trunc (sysdate-5, 'iw') , 'Saturday'  ) ,'DD-MON-YY')) into v_sat_date from dual;
    dbms_output.put_line('The SATURDAY DATE  is '||v_sat_date);
    select to_date(to_char(next_day ( trunc (sysdate-5, 'iw') , 'Sunday'  ) ,'DD-MON-YY'),'DD/MM/RRRR') into v_sun_date from dual;
    dbms_output.put_line('The SUNDAY DATE  is '||v_sun_date);
    select last_day(sysdate) into v_last_date from dual;
    select TO_NUMBER(Initcap(to_char(next_day ( trunc (sysdate-5, 'iw') , 'Sunday'  ) ,'DD'))) into v_sun_number from dual;
    dbms_output.put_line('The sunday number is '||v_sun_number);
       
 select case to_char (last_day(sysdate), 'FmDay', 'nls_date_language=english')
          when 'Monday' then 1
          when 'Tuesday' then 2
          when 'Wednesday' then 3
          when 'Thursday' then 4
          when 'Friday' then 5
          when 'Saturday' then 6
          when 'sunday' then 7
       end d
     INTO v_last_day
  from dual;




 dbms_output.put_line('The v_last_day is '||v_last_day);

select TO_CHAR(SYSDATE,'MON')||'-'||decode(to_char(to_date(sysdate,'MM/DD/YYYY'),'iw')-1,'0','00','1','01','2','02','3','03','4','04','5','05','6','06','7','07','8','08','9','09',to_char(to_date(sysdate,'MM/DD/YYYY'),'iw')-1)||'-'||TO_CHAR(SYSDATE,'YY') into 
v_cost_pa_period from dual;


dbms_output.put_line('The cost pa period is '||v_cost_pa_period);


  IF v_sun_number < 7 THEN
    select NVL(MAX(dim_number),0) into v_max_dim_number from dim_date_20151123;
    select to_char (add_months (last_day(sysdate), -1),'MON')||'-'||decode(to_char(to_date(add_months (last_day(sysdate), -1),'MM/DD/YYYY'),'WW'),'0','00','1','01','2','02','3','03','4','04','5','05','6','06','7','07','8','08','9','09',to_char(to_date(add_months (last_day(sysdate), -1),'MM/DD/YYYY'),'WW'))||'-'||TO_CHAR(add_months (last_day(sysdate), -1),'YY') 
    INTO v_cost_pa_partial from dual;
    select TO_CHAR(SYSDATE,'MON')||'-'||decode(to_char(to_date(sysdate,'MM/DD/YYYY'),'WW'),'0','00','1','01','2','02','3','03','4','04','5','05','6','06','7','07','8','08','9','09',to_char(to_date(sysdate,'MM/DD/YYYY'),'WW'))||'-'||TO_CHAR(SYSDATE,'YY') into 
    v_cost_pa_period1 from dual;
    SELECT to_date (add_months (last_day(sysdate), -1),'MM/DD/YYYY') into v_last_date_partial from dual;
   
    insert into dim_date_20151123 values (v_max_dim_number+1,v_cost_pa_partial , v_last_date_partial   , NULL, NULL, 'I'  );
    COMMIT;
    select NVL(MAX(dim_number),0) into v_max_dim_number from dim_date_20151123;
    insert into dim_date_20151123  values (v_max_dim_number+1,V_cost_pa_partial , v_sun_date   , NULL, NULL, NULL  );
    COMMIT;
    select NVL(MAX(dim_number),0) into v_max_dim_number from dim_date_20151123;
    insert into dim_date_20151123  values (v_max_dim_number+1,v_cost_pa_period1 , v_sun_date   , NULL, NULL, NULL  );
    COMMIT;
  ELSIF V_LAST_DAY = 7 THEN 
    select NVL(MAX(dim_number),0) into v_max_dim_number from dim_date_20151123;
     insert into dim_date_20151123 values (v_max_dim_number+1,v_cost_pa_period , v_last_date   , NULL, NULL, 'I'  );
     commit;
     select NVL(MAX(dim_number),0) into v_max_dim_number from dim_date_20151123;
     insert into dim_date_20151123 values (v_max_dim_number+1,v_cost_pa_period , v_last_date   , NULL, NULL,NULL );
     Commit;
  ELSE
     select NVL(MAX(dim_number),0) into v_max_dim_number from dim_date_20151123;
     insert into dim_date_20151123  values (v_max_dim_number+1,v_cost_pa_period , v_sun_date   , NULL, NULL, NULL  );
     Commit;
 END IF;
 EXCEPTION
  WHEN OTHERS THEN
   RETURN;
END;
/

The problem is I am facing is deriving of week_number

From Oracle documentation:

WW: Week of year (1-53) where week 1 starts on the first day of the year and continues to the seventh day of the year.

IW : Week of year (1-52 or 1-53) based on the ISO standard.

The issue I am facing is deriving of week_number which  is coming as wrong.Now this code runs on every Wednesday and Thursday

This code has given me output as shown below

Actually DEC-53-15 is coming as wrong. It should be coming as DEC-52-15 whereas JAN-01-16 is also coming as wrong.It should be coming as JAN-00-16.

Appreciate your help sir on this.

Regards,