-- Проверка: выписка должна быть позже поступления
CREATE OR REPLACE FUNCTION check_discharge_after_admission ()
    RETURNS TRIGGER
    AS $$
DECLARE
    admission_time timestamp;
BEGIN
    SELECT
        admission_datetime INTO admission_time
    FROM
        hospital_admission
    WHERE
        hospital_admission_id = NEW.hospital_admission_id;
    IF NEW.discharge_datetime <= admission_time THEN
        RAISE EXCEPTION
            USING ERRCODE = 'P0001', MESSAGE = '10003: DISCHARGE_BEFORE_ADMISSION';
        END IF;
        RETURN NEW;
END;
$$
LANGUAGE plpgsql;

CREATE TRIGGER trg_check_discharge_after_admission
    BEFORE INSERT OR UPDATE ON hospital_discharge
    FOR EACH ROW
    EXECUTE FUNCTION check_discharge_after_admission ();

-- Триггер: нельзя создать выписку, если уже есть выписка по этой госпитализации
CREATE OR REPLACE FUNCTION check_unique_discharge ()
    RETURNS TRIGGER
    AS $$
DECLARE
    discharge_count integer;
BEGIN
    SELECT
        COUNT(*) INTO discharge_count
    FROM
        hospital_discharge
    WHERE
        hospital_admission_id = NEW.hospital_admission_id
        AND hospital_discharge_id <> COALESCE(NEW.hospital_discharge_id, -1);
    IF discharge_count > 0 THEN
        RAISE EXCEPTION
            USING ERRCODE = 'P0001', MESSAGE = '10004: DISCHARGE_ALREADY_EXISTS';
        END IF;
        RETURN NEW;
END;
$$
LANGUAGE plpgsql;

CREATE TRIGGER trg_check_unique_discharge
    BEFORE INSERT OR UPDATE ON hospital_discharge
    FOR EACH ROW
    EXECUTE FUNCTION check_unique_discharge ();