Task 1

CREATE OR REPLACE FUNCTION enclosure_available
    (f_id int, custom_date DATE)
RETURNS BOOLEAN
LANGUAGE plpgsql
AS $$
    DECLARE
        _booking_id int;
        _c BOOLEAN := FALSE;
    BEGIN

        BEGIN
            SELECT id
            INTO STRICT _booking_id
            FROM bookings WHERE id =  f_id;
        EXCEPTION
            WHEN NO_DATA_FOUND
            THEN
                RAISE NOTICE 'Не найден вольер с id %', f_id;
                RETURN;
        END;

    SELECT
        CASE
            WHEN custom_date BETWEEN date_begin AND date_end THEN _c
            ELSE _c = TRUE
        END
    FROM bookings WHERE id = f_id;

    END;
$$