#!/bin/ksh

# brute force method using constant number and table of orders
#
# make ntr randomizations of 4 items such that no
# item occurs twice in a row, and all M items
# occur before any item is repeated

# this script generates a script that will populate
# the folder "dest" with links to the image files

# number of trials -- change as needed
ntr=100

# list of four image files -- change as needed
set -A imgs foo.jpg bar.jpg xxx.jpg yyy.jpg

set -A ord4 \
	"0 1 2 3" "0 1 3 2" "0 2 1 3" "0 2 3 1" "0 3 1 2" "0 3 2 1" \
	"1 0 2 3" "1 0 3 2" "1 2 0 3" "1 2 3 0" "1 3 0 2" "1 3 2 0" \
	"2 0 1 3" "2 0 3 1" "2 1 0 3" "2 1 3 0" "2 3 0 1" "2 3 1 0" \
	"3 0 1 2" "3 0 2 1" "3 1 0 2" "3 1 2 0" "3 2 0 1" "3 2 1 0"

# destination folder -- change as needed
dest="randset1"

T=/tmp/rand4.$$
trap "rm -f $T" EXIT
trap "rm -f $T;exit" INT

last=-1

((tr=0))
while [[ tr -lt ntr ]] ; do
	eval "set -A this ${ord4[$RANDOM%24]}"
	if [[ ${this[0]} -eq last ]] ; then
		continue
	fi

	((ev=0))
	while [[ ev -lt 4 ]] ; do
		img=${imgs[${this[ev]}]}
		printf "ln -s %s %s/%03d-%d-%s\n" $img $dest $tr $ev $img
		((ev++))
	done
	((tr++))
	last=${this[3]}
done

exit 0