AD Item Idea, Bow of Diligence (Name not final)

So I thought of an interesting item idea that I just wanted to get out there. I don't know how much gold it would be worth, but I know how to make it cool. Bow of Diligence (Name isn't very catchy, but I didn't want to waste time coming up with a good name. Just the idea behind it.) 30 attack damage 10% lifesteal Unique Passive: You build up 2 bonus attack damage each second you don't cast a spell, stacking up to 28. If you cast a spell, the bonus attack damage is lost. However, if the spell scales with the bonus attack damage, the scaling will not be lowered by losing the stacks on that instance. Unique Active: Your next spell cast that deals damage to enemy champions will reveal a magic red field around them, it closes in on them over four seconds. After four seconds, they will take damage, plus damage X your champions level. This is a burst item, that benefits marksman with longer cooldowns, and bruisers too. Its meant to become gold efficient after a while of using its passive properly, and using the active once. How does it sound, I didn't add too many details because I'm not the best for balancing stuff obviously.