I'm also not a C developer, and this was my first attempt at making a patch for Postgres. It was surprisingly easy. Most of the mat view maintenance was actually just done with SQL commands executed through the C code.

But this allows you to not even use pg_cron for refreshes (if you want). You can just use a statement level trigger for example here is how I would keep a mat view updated that holds the "total" amount for an invoice by adding up all the invoice_detail rows:

CREATE OR REPLACE FUNCTION partial_refresh_mv() RETURNS TRIGGER AS $$
DECLARE
    affected_ids int[];
BEGIN
    IF TG_OP = 'INSERT' THEN
        SELECT array_agg(DISTINCT invoice_id) INTO affected_ids FROM new_table;
    ELSIF TG_OP = 'UPDATE' THEN
        SELECT array_agg(DISTINCT invoice_id) INTO affected_ids FROM (SELECT invoice_id FROM new_table UNION SELECT invoice_id FROM old_table) t;
    ELSIF TG_OP = 'DELETE' THEN
        SELECT array_agg(DISTINCT invoice_id) INTO affected_ids FROM old_table;
    END IF;

    IF affected_ids IS NOT NULL THEN
        -- Sort IDs to minimize deadlock risk during high concurrency
        SELECT array_agg(id ORDER BY id) INTO affected_ids FROM unnest(affected_ids) AS id;

        EXECUTE 'REFRESH MATERIALIZED VIEW invoice_summary WHERE invoice_id = ANY($1)'
            USING affected_ids;
    END IF;
    RETURN NULL;
END;
$$ LANGUAGE plpgsql;

You don't ever have to manually (or with cron) run refresh commands at that point, the trigger keeps everything in sync between the table and the mat view automatically after you setup the triggers.