#!/bin/sh
# vim: ft=sh ts=4 sw=4 et
#
# The scripts cur_param and next_param allow their callers to cycle through
# circular lists of parameters. Both scripts take two parameters, a directory
# name and a counter name.
#
# The idea is that the user sets up the file $dir/list.$counter to contain
# a list of parameters, one per line. Each time the user calls cur_param,
# they get back as the output of the script the current parameter (initially
# the first). Each time the user calls next_param, the scripts' notion of
# the current parameter is set to the parameter on the next line of the file,
# or, if there are none left, back to the parameter on the first line.
# next_param has only this side-effect; it does not output anything.
#
# Both scripts exit with a non-zero status in case of internal error.

usage="next_param dir counter"

if test $# != 2
then
    echo $usage
    exit 1
fi

dir=$1
counter=$2

if test ! -f $dir/next.$counter
then
    echo 0 > $dir/next.$counter
fi

if test -s $dir/list.$counter
then
    prev=`cat $dir/next.$counter`
    next=`expr $prev + 1`
    length=`wc -l $dir/list.$counter`
    if test "$next" -gt "$length"
    then
        next=1
    fi
    echo "$next" > $dir/next.$counter
else
    echo "$dir/list.$counter doesn't exist or is empty"
    exit 1
fi

exit 0