BEGIN;

-- PostgREST versions backed by hasql-transaction automatically retry SQLSTATE
-- 40001. A contended try-lock would therefore busy-loop until the lock holder
-- exited instead of reaching Edge as an immediate conflict. 55P03 expresses
-- the same lock-not-available condition without transaction auto-retry.
CREATE OR REPLACE FUNCTION public.enforce_system_push_claim_rate()
RETURNS trigger
LANGUAGE plpgsql
SECURITY DEFINER
SET search_path = ''
AS $$
BEGIN
  IF NEW.actor_kind <> 'system'
     OR NEW.status <> 'processing'
     OR NEW.dispatch_lease_token IS NULL THEN
    RETURN NEW;
  END IF;
  IF TG_OP = 'UPDATE'
     AND OLD.dispatch_lease_token IS NOT DISTINCT FROM NEW.dispatch_lease_token THEN
    RETURN NEW;
  END IF;

  IF NOT pg_try_advisory_xact_lock(
    hashtextextended('system-push-global', 73050)
  ) THEN
    RAISE EXCEPTION 'push_claim_busy' USING ERRCODE = '55P03';
  END IF;

  DELETE FROM public.push_dispatch_claim_events
  WHERE claimed_at < now() - interval '2 days';

  IF (
    SELECT count(*)
    FROM public.push_dispatch_claim_events
    WHERE claimed_at > now() - interval '1 minute'
  ) >= 500 OR (
    SELECT count(*)
    FROM public.push_dispatch_claim_events
    WHERE claimed_at > now() - interval '24 hours'
  ) >= 10000 THEN
    RAISE EXCEPTION 'push_rate_limited' USING ERRCODE = '54000';
  END IF;

  INSERT INTO public.push_dispatch_claim_events (
    attempt_id, dispatch_lease_token
  ) VALUES (
    NEW.id, NEW.dispatch_lease_token
  );
  RETURN NEW;
END;
$$;

REVOKE ALL ON FUNCTION public.enforce_system_push_claim_rate()
  FROM PUBLIC, anon, authenticated;

COMMIT;