#! /bin/sh

# configure these
LOCKDIR=/usr/spool/uucp
NOHUP_START_TIME=5
DYING_TIME=60

linestat()
{
    LOCK=$1

    [ ! -f $LOCK ] && return 0
    [ ! -r $LOCK ] && return 1
    PID=`cat $LOCK`
    PID=`expr $PID + 0`

    # this line tests if process $PID exists
    [ ! -d /proc/$PID ] && return 3

    # lock exists isn't ll
    [ ! -f $LOCK.$PROGNAME ] && return 2
    # lock exists is ll
    return 4
}

report_line()
{
    LOCK=$1

    linestat $LOCK
    STAT=$?

    case $STAT in
       0) echo "not locked" ;;
       1) echo "$PROGNAME: ERROR: can't read $LOCK" ;;
       2) echo "locked by another process" ;;
       4) echo "locked by $PROGNAME" ;;
       3) echo "stale lock" ;;
    esac
    exit 0
}

unlock_line()
{
    LOCK=$1

    linestat $LOCK
    STAT=$?

    case $STAT in
	0)   echo "$PROGNAME: WARNING: already unlocked"
	     [ -f $LOCK.$PROGNAME ] && { echo "$PROGNAME: WARNING: removing stale $PROGNAME lock"; rm -f $LOCK.$PROGNAME; }
	     exit 0 ;;
	1)   echo "$PROGNAME: ERROR: can't read $LOCK"
	     [ -f $LOCK.$PROGNAME ] && { echo "$PROGNAME: WARNING: removing $PROGNAME lock, hope $PROGNAME was running"; rm -f $LOCK.$PROGNAME; }
	     exit 1 ;;
	2)   [ $FORCE = false ] && { echo "$PROGNAME: WARNING: lock is not an $PROGNAME lock, not removing"; exit 1; }
             echo "$PROGNAME: WARNING: killing locking process"
             PID=`cat $LOCK`
	     PID=`expr $PID + 0`
             kill -9 $PID ;;
	4)   rm -f $LOCK.$PROGNAME
	     exit 0 ;;
	3)   echo "$PROGNAME: WARNING: removing stale lock"
	     rm -f $LOCK
	     [ -f $LOCK.$PROGNAME ] && { echo "$PROGNAME: WARNING: removing stale $PROGNAME lock"; rm -f $LOCK.$PROGNAME; }
	     exit ;;
    esac
}

lock_line()
{
    LOCK=$1

    linestat $LOCK
    STAT=$?
    case $STAT in
	0|3) lock_it $LOCK 
	     exit $? ;;
	1)   echo "$PROGNAME: ERROR: can't read $LOCK"
	     exit 1 ;;
	2)   [ $FORCE = false ] && { echo "$PROGNAME: ERROR: line already locked by another process"; exit 0; }
             PID=`cat $LOCK`
	     PID=`expr $PID + 0`
             kill -9 $PID
             lock_it $LOCK
	     exit $? ;;
	4)   echo "$PROGNAME: ERROR: line is already locked by $PROGNAME"
             exit 1 ;;
    esac
}

lock_it()
{
    LOCK=$1

    [ -f $LOCK ] && rm -f $LOCK
    [ -f $LOCK ] && { echo "$PROGNAME: ERROR: can't remove old lock"; exit 1; }

    nohup sh -c "
	umask 033
	# This is a mess. It should be possible to store the return 
	# value in a variable and then just echo that variable on the
	# second file ... but it doesn't work
	echo \$\$ | awk '{ printf \"%09d\", \$1 }' > $LOCK
	cp $LOCK $LOCK.ll
	while [ -f $LOCK.$PROGNAME ]; do
	    sleep $DYING_TIME
	done
	rm -f $LOCK" > /dev/null 2>&1 &

    # This bit gives the nohup process time to create its locks and then reports
    sleep $NOHUP_START_TIME
    [ ! -f $LOCK ] && { echo "$PROGNAME: ERROR: can't create $LOCK"; return 1; }
    [ ! -f $LOCK.$PROGNAME ] && { rm -f $LOCK; echo "$PROGNAME: ERROR: can't create $LOCK.$PROGNAME"; return 1; }
    return 0
}

main()
{
    # global constants
    PROGNAME=`basename $0`
    USAGE="Usage: $PROGNAME [ -f ] [ -d timout ] line [ on | off ]"

    # default values for options, others may be at the top of this file
    FORCE=false

    while :; do
	case "$1" in
	    -f) FORCE=true ;;
	    -d) [ ! "$2" ] && { echo $USAGE; exit 1; }
		DYING_TIME=$2
		shift ;;
	    *)  break ;;
	esac
	shift
    done

    [ $# -eq 1 -o $# -eq 2 ] || { echo $USAGE; exit 1; }

    # get lock file name
    case "$1" in
        /dev/*) LOCK=$LOCKDIR/LCK..`basename $1` ;;
        *)      LOCK=$LOCKDIR/LCK..$1 ;;
    esac

    # process required arguments
    case "$2" in
        "")     report_line $LOCK ;;
        on)     lock_line $LOCK ;;
        off)    unlock_line $LOCK ;;
        *)      echo $USAGE; exit 1 ;;
    esac

    exit 0
}

main "$@"