Finding the direction/rotation of a vector2 from a mouse in a pie chart?

This is a bit a more complicated situation.

First of all.

In the center of the screen is a perfect circle, this circle is divided into pieces like a pie. Whenever the mouse moves, I want the direction vector2 value returned.

For example

When I place the mouse on screen position {0,10}, assuming that the center position of the screen is {10,10}, my script will return the value "180".

Or if you place the mouse at position {10,0} then the script will return "90".

Or at {5,5}, the script returns "135".

The returned rotation value will then be used to determine on what piece of the pie chart that the mouse is touching. This way, I can have gui collision in a shape of an arc of a circle.

Now what I essentially want is this

function((X,Y) position of Mouse) 

return direction value of the vector from 0-360 from the center of the screen.

If this question is too confusing feel free to ask.