-- Make reorg undo respect employee_history's append-only contract
-- (spec §6.1: "append-only, keine normale
-- Update-/Delete-Funktion").
--
-- The previous undo_reorg deleted the employee_history rows a reorg had
-- created (functions.sql:549), which required a narrow RLS carve-out
-- (functions_3.sql's "history_delete_admin_reorg_undo" policy) allowing
-- hr_admin to delete reorg-tagged history rows. That is the one place in
-- the whole schema where history was not actually immutable. Fixed by
-- appending a compensating "Reorganisation rückgängig" history entry per
-- affected employee instead of deleting anything — the original
-- Reorganisation rows stay in the record, exactly like every other history
-- event type. The now-unused delete policy is dropped.

drop policy if exists "history_delete_admin_reorg_undo" on employee_history;

create or replace function undo_reorg(payload jsonb)
returns void language plpgsql as $$
declare
  v_scenario record;
  v_key text;
  v_val jsonb;
  v_name text;
  v_count int := 0;
begin
  perform require_hr_admin();
  select * into v_scenario from reorg_scenarios where id = (payload->>'scenario_id')::uuid and applied = true;
  if not found or v_scenario.undo_snapshot is null then
    raise exception 'Reorganisation kann nicht rückgängig gemacht werden (kein Snapshot vorhanden).';
  end if;

  -- Any pending (not-yet-applied) deferred moves belonging to this scenario
  -- are cancelled rather than left to fire later against a since-reverted
  -- state.
  update pending_org_changes set status = 'cancelled'
    where reorg_scenario_id = v_scenario.id and status = 'pending';

  for v_key, v_val in select * from jsonb_each(v_scenario.undo_snapshot)
  loop
    update employees set
      team_id = nullif(v_val->>'team_id','')::uuid,
      division_id = (v_val->>'division_id')::uuid,
      manager_id = nullif(v_val->>'manager_id','')::uuid
    where id = v_key::uuid;

    select first_name || ' ' || last_name into v_name from employees where id = v_key::uuid;
    insert into employee_history (employee_id, event_date, event_type, description, reorg_scenario_id)
      values (v_key::uuid, current_date, 'Reorganisation',
        'Reorganisation "' || v_scenario.name || '" rückgängig gemacht — vorheriges Team wiederhergestellt', v_scenario.id);

    v_count := v_count + 1;
  end loop;

  update reorg_scenarios set applied = false where id = v_scenario.id;

  insert into audit_log (actor_user_id, actor_name, action, target_label, details)
    values (auth.uid(), current_actor_name(), 'Reorganisation rückgängig', v_scenario.name, v_count || ' Mitarbeiter:innen zurückgesetzt');
end;
$$;