-- začátek aktuálního (+offset) 15min slotu v Europe/Prague jako timestamptz (UTC instants)

create or replace function ems.fn_planning_slot_boundary_prague(p_offset_slots int default 0)
returns timestamptz
language sql
stable
as $fn$
  select (
    (date_trunc('day', loc.ts)
     + make_interval(
         hours => extract(hour from loc.ts)::int,
         mins => (floor(extract(minute from loc.ts) / 15) * 15)::int
       )
    )::timestamp at time zone 'Europe/Prague'
  ) + make_interval(mins => coalesce(p_offset_slots, 0) * 15)
  from (select now() at time zone 'Europe/Prague' as ts) loc;
$fn$;

comment on function ems.fn_planning_slot_boundary_prague(int) is
  'Začátek 15min slotu v časové zóně site provozu (Europe/Prague floor); offset v násobcích 15 min.';