is this trigger safe and efective? - locking (caching via triiggers)

Hello

I write sample about triggers and i have question. is my solution
correct and exists better solution?

Regards
Pavel Stehule

DROP SCHEMA safecache CASCADE;

CREATE SCHEMA safecache;

CREATE TABLE safecache.source_tbl(category int, int_value int);

CREATE TABLE safecache.cache(category int, sum_val int);

CREATE OR REPLACE FUNCTION safecache.source_tbl_trg_fce()
RETURNS trigger AS
$$
BEGIN IF TG_OP = 'INSERT' THEN   -- row cannot exists in cache -- complication   -- I would to finish these transaction
withoutconflict   IF NOT EXISTS(SELECT category                    FROM safecache.cache                   WHERE
category= NEW.category) THEN     LOCK TABLE safecache.cache IN SHARE ROW EXCLUSIVE MODE;     -- I have to repeat test
 IF NOT EXISTS(SELECT category                      FROM safecache.cache                     WHERE category =
NEW.category)THEN       INSERT INTO safecache.cache          VALUES(NEW.category, NEW.int_value);     END IF;   ELSE
-- simple     UPDATE safecache.cache        SET sum_val = sum_val + NEW.int_value       WHERE category = NEW.category;
END IF; ELSEIF TG_OP = 'UPDATE' THEN   -- if category is without change simple   IF NEW.category = OLD.category THEN
UPDATE safecache.cache        SET sum_val = sum_val + (NEW.int_value - OLD.int_value)       WHERE category =
OLD.category;  ELSE     -- old category has to exists     UPDATE safecache.cache        SET sum_val = sum_val -
OLD.int_value      WHERE category = OLD.category;     -- new category is maybe problem     IF NOT EXISTS(SELECT
category                     FROM safecache.cache                     WHERE category = NEW.category) THEN       LOCK
TABLEsafecache.cache IN SHARE ROW EXCLUSIVE MODE;       -- I have to repeat test       IF NOT EXISTS(SELECT category
                   FROM safecache.cache                       WHERE category = NEW.category) THEN         INSERT INTO
safecache.cache           VALUES(NEW.category, NEW.int_value);       END IF;     ELSE       -- simple, new category
exists      UPDATE safecache.cache          SET sum_val = sum_val + OLD.int_value         WHERE category =
NEW.category;    END IF;   END IF; ELSE -- DELETE   -- value have to exist in cache, simple   UPDATE safecache.cache
 SET sum_val = sum_val - OLD.int_value     WHERE category = OLD.category; END IF; RETURN NEW;
 
END
$$ LANGUAGE plpgsql;

CREATE TRIGGER actualise_cache  AFTER INSERT OR UPDATE OR DELETE  ON safecache.source_tbl  FOR EACH ROW EXECUTE
PROCEDUREsafecache.source_tbl_trg_fce();