#!/bin/sh

: ${TMPDIR:=/tmp}

cmd=`basename "$0"`
usage="Usage: $cmd [-v] [-i suf] [--] filter files...
	-v		Verbose.
	-i suf		Copy original to original.suf if changed.
	-i suf/		Copy original to suf/original if changed."

badopts=
verbose=
ibak=
while :
do
    case $1 in
	--)	shift ; break ;;
	-v)	verbose=1 ;;
	-i)	ibak=$2; shift ;;
	-i?*)	ibak=`expr "x$1" : 'x-i\(.*\)'` ;;
	-*)	echo "$cmd: $1: unknown option" >&2
		badopts=1
		;;
	*)	break ;;
    esac
    shift
done

if [ $# -gt 0 ]
then
    filter=$1; shift
else
    echo "$cmd: missing filter" >&2
    badopts=1
fi

[ $# -gt 0 ] || { echo "$cmd: missing filenames" >&2; badopts=1; }

[ $badopts ] && { echo "$usage" >&2; exit 2; }

tmp=$TMPDIR/$cmd.$$
trap 'rm -f "$tmp"; exit 1' 1 3 15

xit=0
while [ $# -gt 0 ]
do
    file=$1; shift
    if [ "x$file" = x- ]
    then
	[ $verbose ] && echo "reading filenames from stdin..."
	set x `cat` ${1+"$@"}; shift
    else
	[ $verbose ] && echo "$file ..."
	ok=
	if eval "$filter <\"\$file\" >\$tmp"
	then
	    if cmp -s "$file" "$tmp"
	    then
		ok=1		# no change
	    else
		[ $verbose ] && diff -c "$file" "$tmp"
		if [ -z "$ibak" ] || { case "$ibak" in
					*/)	filebak=$ibak/$file ;;
					*)	filebak=$file.$ibak ;;
				       esac
				       cat < "$file" > "$filebak"
				     }
		then
		    if cat "$tmp" > "$file"
		    then
			ok=1	# backup & update ok
		    else
			echo "$cmd: $file: can't update" >&2
			if [ -n "$ibak" ]
			then
			    if cat "$filebak" > "$file"
			    then
				echo "$cmd: $file: original restored" >&2
				rm "$filebak"
			    else
				echo "$cmd: $file: restore failed; original left in $filebak" >&2
			    fi
			else
			    echo "$cmd: $file: no backup, may be corrupt" >&2
			fi
		    fi
		else
		    echo "$cmd: $file: can't backup to $filebak; original unchanged" >&2
		fi
	    fi
	else
	    echo "$cmd: $file: edit fails; original unchanged" >&2
	fi
	[ $ok ] || xit=1
    fi
done