#!/bin/zsh

CUR_WORKSPACE=$(swaymsg -t get_workspaces | jq -r '. | sort_by(.num) | map(.num) | .[]')

previous=0
while IFS= read -r n; do
    if (( n != previous + 1 )) ; then
        NEW_WORKSPACE=$(( previous + 1 ))
        break
    fi
    previous=$n
done <<< "$CUR_WORKSPACE"

swaymsg workspace number $NEW_WORKSPACE