Evaluate next french working day from a date and a frequency string

postgresql evaluate next working day.sql

-- -----------------------------------
-- FUNCTION: easter_date
-- -----------------------------------
CREATE OR REPLACE FUNCTION easter_date(year integer)
RETURNS timestamp as $$
DECLARE
  g integer := year % 19;
  c integer := (year/100)::int;
  h integer := ((c - (c/4)::int - ((8*c+13)/25)::int + 19*g + 15) % 30)::int;
  i integer := h - (h/28)::int * (1 - (h/28)::int * (29/(h + 1))::int * ((21 - g)/11)::int);
  j integer := (year + (year/4)::int + i + 2 - c + (c/4)::int) % 7;
  l integer := i - j;
  m integer := 3 + ((l + 40)/44)::int;
  d integer := l + 28 - 31 * (m/4)::int;
  easter varchar(10) := year::text || '-' || m::text || '-' || d::text;
BEGIN
  return easter::timestamp;
END;
$$ language plpgsql;


-- -----------------------------------
-- FUNCTION: get_holidays
-- -----------------------------------
CREATE OR REPLACE FUNCTION get_holidays() 
RETURNS table(holiday date) AS $$
DECLARE
  year text := extract(year from current_date);
  next text := (year::int+1)::text;
  easter1 timestamp := easter_date(year::int);
  easter2 timestamp := easter_date(next::int);
BEGIN
  return query
  select t.*
  from unnest(array[
  -- current year
    (year||'-01-01')::date, (year||'-05-01')::date,
    (year||'-05-08')::date, (year||'-07-14')::date,
    (year||'-08-15')::date, (year||'-11-01')::date,
    (year||'-11-11')::date, (year||'-12-25')::date,
    easter1::date + 1, easter1::date + 39, easter1::date + 50,
  -- next year
    (next||'-01-01')::date, (next||'-05-01')::date,
    (next||'-05-08')::date, (next||'-07-14')::date,
    (next||'-08-15')::date, (next||'-11-01')::date,
    (next||'-11-11')::date, (next||'-12-25')::date,
    easter2::date + 1, easter2::date + 39, easter2::date + 50
  ]) t;
END;
$$ language plpgsql;


-- -----------------------------------
-- FUNCTION: evaluate_next_run
-- -----------------------------------
CREATE OR REPLACE FUNCTION evaluate_next_run(last_run timestamp with time zone, rule text)
RETURNS timestamp with time zone AS $$
DECLARE
  options text;
  nextday text;
  daily interval := '1 day'::interval;
  monthly interval := '1 mon'::interval;
  next_run timestamp;
BEGIN
  CASE substring($2 from 'freq=(\w+)')
    WHEN 'daily' THEN
      options := substring($2 from 'days=([\w,]+)');

      select min(l.next_runs) into next_run from (
        select s::timestamp as next_runs
          from generate_series($1 + daily, $1 + daily * 7, daily) s
         where options like '%' || extract(dow from s) || '%'
        except select holiday + ($1)::time from get_holidays()
       ) l;

    WHEN 'monthly' THEN
      options := substring($2 from 'days=-([\d]+)');
      
      IF options IS NOT NULL THEN
        select min(next_runs) into next_run from (
          select row_number() over (
                   partition by extract(mon from next_runs)
                   order by extract(day from next_runs) desc
                 ) as rownum, next_runs
          from (
            select s::timestamp as next_runs
              from generate_series($1 + daily, $1 + monthly * 2 - daily, daily) s 
             where extract(dow from s) in (1,2,3,4,5)
            except select holiday + ($1)::time from get_holidays()
          ) l1
        ) l2 where rownum = options::int;
      ELSE
        options := substring($2 from 'days=([\d,]+)');

        select min(t.day) into nextday
          from unnest(string_to_array(options, ',')) as t(day)
          where t.day::int > extract(day from $1);

        IF nextday IS NULL THEN
          nextday := split_part(options, ',', 1);
        END IF;

        select min(next_runs) into next_run from (
          select
            row_number() over (order by extract(mon from s) desc, extract(day from s)) as rownum,
            s::timestamp as next_runs
          from generate_series($1, $1 + monthly - daily, daily) s
        ) l where l.rownum = nextday::int;

        next_run := evaluate_next_run(next_run - daily, 'freq=daily; days=1,2,3,4,5');
      END IF;
  END CASE;

  return next_run;
END;
$$ language plpgsql;