#!/usr/bin/env bash

set -eu -o pipefail

pages="$1"
infile="$2"
outdir="$3"

if [ ! -f "$infile" ]; then
	echo "$infile does not exist" 2>&1
	exit 1
fi

if [ -e "$outdir" -a ! -d "$outdir" ]; then
	echo "$outdir must be a directory or not exist at all" 2>&1
	exit 1
fi
mkdir -p "$outdir"

if [ "$((${pages}%2))" -ne 0 ]; then
	echo "The number of pages ($pages) must be even" 2>&1
	exit 1
fi

i=0
while [ "$i" -lt "$pages" ]; do
	paperjam "select { $((${i}+1)) $((${i}+2)) }" "$infile" "$outdir/$(printf '%0*d' ${#pages} $i).pdf"
	i="$((${i}+2))"
done