[i3] Lowest empty Workspace

[Heimo Stranner]

I want to switch to the lowest workspace that doesn't have any windows on it 
quite often. Because I use multiple monitors it is not always obvious and quick 
to see which workspaces are currently in use. So i wrote a little script that 
switches (or moves a window) to the lowest empty workspace.

#!/bin/bash
for i in {1..100}
do
        res=$(i3-save-tree --workspace $i | grep -v "^//")
        if [ -z "$res" ]; then
                if [ $1 = "m" ]; then
                        i3-msg move workspace $i
                fi
                if [ $1 = "n" ]; then
                        i3-msg workspace $i
                fi
                break
        fi
done

It works pretty well but is kinda hackish and could be faster. I am not aware 
of any native support for this use case. Does anyone know about a better way of 
addressing this use case?

Thanks.

Heimo