Create radar to move around screen edge.

Hello,

I have a top down game where the player is in the centre of the view. I would like to create an arrow that "sticks" to the screen edges and points in the direction of an enemy whilst its off screen. My thinking is I need to "trace" some sort of straight line between the player and the enemy and place the radar arrow on that line at the point where the line intersects the screen edge.

Any code help with this would be appreciated. Thanks