#!/usr/bin/bash

[ -z "$1" -o -z "$2" -o "$1" == "--help" ] && {
    echo "$0: flip even pages of a a PDF"
    echo "usage: $0 <infile.pdf> <outfile.pdf>"
    echo
    echo "This program requires pdfinfo from poppler-utils and pdf-stapler."
    exit 64
}

set -e
set -o pipefail
numpages=$(LANG=C LC_ALL=C pdfinfo "$1" | grep ^Pages: | awk ' { print $2 } ')
pagedirectives=
for page in `seq 1 $numpages`
do
    [ $((page%2)) -eq 0 ] && \
        pagedirectives="$pagedirectives ${page}D" || \
        pagedirectives="$pagedirectives ${page}"
done

rm -f "$2"
pdf-stapler cat "$1" $pagedirectives "$2"
