#--------------------------------------------------
#
#   $Id: backdiff,v 1.2 2008/01/02 10:29:44 erwlem Exp $
#
#   description: see usage()
#
#   071128 ele Started
#   080102 ele Support crossing branches
#
#--------------------------------------------------

#--------------------------------------------------
#
#   get_prev_rev - take a cvs revision number and return the previous revision
#

PREVREV=

get_prev_rev() {
    REV=$1
    BRANCH=

    if [ `echo $REV | grep "\.1$" | wc -l` -eq "1" ]; then
	# truncate the last 2 digits to get the previous version
	PREVREV=`echo $REV | sed -e "s/\.[0-9]*\.1*$//"`
	# this works even if we REV=1.1

    else

        # split the current revision in a header part, specific to the current branch,
        # and a tailing number, specific to this file in the branch
	while [ `echo $REV | grep '\.' | wc -l` -ne "0" ]; do
	    BRANCH=$BRANCH`echo $REV | sed -e "s/\..*//"`"."
	    REV=`echo $REV | sed -e "s/^[0-9]*\.//"`
	done

	# then decrease REV...
	let BACKREV="$REV - 1"
	if [ $BACKREV -lt 1 ]; then
	    BACKREV=1
	fi

	PREVREV=$BRANCH$BACKREV
    fi
}

#--------------------------------------------------
#
#   usage blurb
#

usage() {
    cat <<EOF

 BACKDIFF - Show a file's last changes

Description:

 Backdiff makes a cvs diff between the current version of a file
 and the Nth former version of that file.
 Arguments must be declared before the file name.

Syntax:

    $ backdiff [-h] [-c N] <file>

    -h      help
    -c N    diff changes over the last N commits of file <file>

Example:

    # shows changes made during the last commit of essordgen.pl
    $ backdiff essordgen.pl

    # shows changes made since the 4th last commit of essordgen.pl
    $ backdiff -c 4 essordgen.pl

EOF
}

#--------------------------------------------------
#
#   main
#
#--------------------------------------------------

BACKCOMMIT=1

while getopts ":hc:" OPTION; do
    case $OPTION in
	h)  usage;
	    exit;;
	c)  BACKCOMMIT=$OPTARG;;
	*)  echo "ERROR: unexpected argument. type -h for usage."
	    exit;;
    esac
done

# get the file name
shift $(($OPTIND - 1))
FILE=$1

# is the file valid?
if [ -z $FILE ]; then
    echo "ERROR: your must provide a file name. type -h for usage."
    exit
fi

if [ ! -z $2 ]; then
    echo "ERROR: file name [$FILE] should not be followed by any argument. type -h for usage."
    exit
fi

if [ ! -f $FILE ]; then
    echo "ERROR: file [$FILE] does not exist or is not a file."
    exit
fi

# is the file up to date?
if [ `cvs status $FILE | grep "Up-to-date" | wc -l` -ne "1" ]; then
    echo "ERROR: [$FILE] is not in the cvs or is not up-to-date"
    exit
fi

# what is the file's current cvs version?
CURREV=`cvs status $FILE | grep "Working revision" | cut -d ':' -f 2 | sed -e "s/[ \t]//g"`

# now step back through revisions, one commit at a time
TMPREV=$CURREV
PREVREV=$CURREV

while [ $BACKCOMMIT -ne 0 ]; do
    get_prev_rev $TMPREV
    TMPREV=$PREVREV
    let BACKCOMMIT="$BACKCOMMIT - 1"
done

# show diff
cvs diff -r $PREVREV -r $CURREV $FILE