Cursor movement controlling size of mc

Hi all. I’ve been searching the forum and google for a while but I can’t seem to figure this out:

I want to have a circle (that’s a movie clip serving as a mask, but I don’t think that matters). If the cursor stays still or is off the frame, the circle slowly smoothly grows until it gets really big (fills the frame) and then stops and stays that way unless the cursor starts moving again. If the user moves the cursor around, it slowly shrinks until it disappears. The circle should start in a disappeared (too small to see, i guess) state. I need this to work even if, say, the cursor is still for a while and the circle grows halfway, but then the cursor moves - it should then start to shrink from where it is until the movement stops, then it should start to grow again.

I went through trying to just have an animation of a growing circle, and messing around with it reversing when the mouse came in the frame, but I couldn’t get that to work, and furthermore, I’d like it to be based on cursor movement, not if it’s simply there. I’m open to any kind of solution here…

I’m an artist with more ideas than programming skills. But I’m trying! I’m studying a book on actionscript, but I JUST started, so if you have a solution for me, please keep in mind that I’m a beginner.

Thank you sooo much!