Track last circ month

CREATE TABLE IF NOT EXISTS extend_reporter.last_circ_month (
id integer NOT NULL PRIMARY KEY, -- No FK intentionally because this isn't all that important to go away if the user does
circ_month date
);

INSERT INTO extend_reporter.last_circ_month(id, circ_month) SELECT usr, max(date_trunc('month', xact_start)) FROM action.circulation GROUP BY usr;

CREATE OR REPLACE FUNCTION extend_reporter.record_last_circ_month() RETURNS trigger AS $func$
BEGIN
    UPDATE extend_reporter.last_circ_month SET circ_month = GREATEST(circ_month, date_trunc('month', NEW.xact_start)) WHERE id = NEW.usr;
    IF NOT FOUND THEN
        INSERT INTO extend_reporter.last_circ_month(id, circ_month) VALUES (NEW.usr, date_trunc('month', NEW.xact_start));
    END IF;
    RETURN NEW;
END;
$func$
LANGUAGE plpgsql;

CREATE TRIGGER action_circulation_last_circ_month_trigger AFTER INSERT ON action.circulation FOR EACH ROW EXECUTE PROCEDURE extend_reporter.record_last_circ_month();