[SCRIPT]Change to specific random map

[FlawlessHappiness]

Hey guys!

So in my custom story i want to change to different maps with one script, posted in the end of all the maps.

It will work like this:

You start in the default map (Which is NOT random).
You get to a point where the script calls and you change map:
There are 3 different maps to change to, and the first change should be completely random.
After getting to the "end-point" in map 1, the script calls again, but now it can only choose between the 2 maps which haven't been played yet.
At last when finishing that map, you will change to the last map, not played.

I cannot figure out how to script this.

Yes it's something with SetGlobalVarInt("Map_1", 1) and GetGlobalVarInt and that... but when it also has to choose randomly between them. It cannot seem to form correctly in my head.
Could anybody help me?
Lets just call the maps:

Path_1
Path_2
Path_3