#!/bin/sh

usage() {
	_name="$(basename "$0")"
	cat << EOF
Utilizzo: ${_name} [nomePDF]

Esempi:

	${_name} MeccanicaRazionale.pdf

Per bug contattare f.minnocci@studenti.unipi.it
I ringraziamenti per l'idea originale vanno a http://poisson.phc.dm.unipi.it/~dilillo
EOF
exit $1
}

main() {
	# Initialize variables
	input="$(realpath "$1")"
	basename="$(basename "$1")"
	inputMul4="/tmp/${basename%.pdf}-Mul4.pdf"
	outputImpaginato="${basename%.pdf}-Impaginato.pdf"
	empty="/tmp/empty.pdf"
	echo "$input $basename $inputMul4 $outputImpaginato" > ~/log
	n="$(pdftk "$input" dump_data | grep NumberOfPages | cut -d' ' -f2)"

	# Add empty pages
	echo .bp | groff -T pdf > "$empty"

	pdftk F="$input" E="$empty" cat F1-$n $(for x in $(seq 1 $((4-n%4))); do printf 'E1 '; done) output "$inputMul4"

	# Generate alternating page ranges
	n=$((n+(4-n%4)))
	range=
	k=1
	while [ "$k" -lt $((n/2)) ]; do
		range="$range$k $((n/2+k)) $((n/2+k+1)) $((k+1)) "
		k=$((k+2))
	done

	# Output final pdf
	pdftk "$inputMul4" cat $range output "$outputImpaginato"

	rm "$empty" "$inputMul4"
}

if [ -z "$1" ] ; then
	printf "Non hai specificato nessun file...\n\n" && usage 1
else
	case "$1" in
	-h|--help)
		usage 0 ;;
	-*)
		error "Opzione invalida: $1" ;;
	*)
		main "$@" ;;
	esac
fi