I would like to use healing spells only if my tank is under 70% HP, otherwise DPS. This is mainly because on most trash pulls my tanks keeps himself at almost 100% HP getting passive healing from totems and seal of light + judgement of light.

At the end of the day this is a huge mana and DPS waste if I run around with a dedicated healer... and when I run with no dedicated healer boss fights become a bit tricky, specially some bosses that require constant and steady healing.

Is such kind of macro possible? Perhaps there is an addon that does it.