How to get ID of line closest to the given node using tcl?

Guys, how to get ID of line closest to the given node? Actually, I need to get IDs of 4 closest lines like in the situation shown in the figure below. I thought that I could create centroids of all possible lines, then find centroids that are closest to the given node, and then identify line IDs. But there is no function to get centroid of line. Thank you!