How to calculate distance between two rectangles? (Context: a game in Lua.)

Question

Given two rectangles with x, y, width, height in pixels and a rotation value in degrees -- how do I calculate the closest distance of their outlines toward each other?

Answer 1

Pseudo-code:

distance_between_rectangles = some_scary_big_number;
For each edge1 in Rectangle1:
    For each edge2 in Rectangle2:
        distance = calculate shortest distance between edge1 and edge2
        if (distance < distance_between_rectangles)
            distance_between_rectangles = distance