#!/bin/sh
# unpatch [-g] [-pN] FILES... - re-generate patch from files and their .orig copy

STRIP=0
PREFIX_A=
PREFIX_B=
ORIG=.orig
while getopts gp: opt; do
	case "$opt" in
	g) PREFIX_A=a/ PREFIX_B=b/ ORIG=;;
	p) STRIP=$OPTARG;;
	?) sed -n -e '2s/^# //p' "$0" 1>&2; exit 1;;
	esac
done
shift $((OPTIND-1))

pstrip() {
	i=0 p=$1
	while [ "$i" -lt "$STRIP" ]; do
	      i=$((i+1)) p=${p#*/}
	done
	printf %s "$p"
}

match() {
	case "$1" in
	     $2) true;;
	     *) false;;
	esac
}

if [ "$#" -eq 0 ]; then
	set -- .
	STRIP=$((STRIP+1))
fi
for f; do
	if [ -f "$f" ] && [ -f "$f.orig" ]; then
		diff -u --label "$PREFIX_A$(pstrip "$f$ORIG")" "$f.orig" \
			--label "$PREFIX_B$(pstrip "$f")" "$f"
	elif match "$f" "*.orig" && [ -f "$f" ] && [ -f "${f%.orig}" ]; then
		diff -u --label "$PREFIX_A$(pstrip "${f%.orig}$ORIG")" "$f" \
			--label "$PREFIX_B$(pstrip "${f%.orig}")" "${f%.orig}"
	elif [ -d "$f" ]; then
		find "$f" -type f -name '*.orig' -exec "$0" ${PREFIX_A:+-g} "-p$STRIP" {} ';'
	else
		printf "Can't unpatch '%s'.\n" "$f" 1>&2
	fi
done