#! /bin/sh
#
# On the command line: a date (yyyymmdd) and a balance (in pennies), an
#  interest rate, and a payment amount (in pennies), in that order.  Note
#  that the interest rate is the half-yearly rate, which is half what's
#  usually quoted.  The payment amount is per payment, which is done twice
#  a month.
#
# Output: a series of lines,
#
#	jdate	yyyymmdd	balance
#
# starting with the supplied date and balance, printing on the 1st and 15th
#  of each month, stopping with the last line whose balance is positive.
#
case $# in
	4)	;;
	*)	echo Usage: $0 date balance rate payment 1>&2
		exit 1
		;;
esac
edate=`ndate -eo $1`
ddate=`ndate -ei $edate`
balance=$2
rate=$3
payment=$4
while case $balance in -*) false;; *) :;; esac
do
	echo $edate $ddate $balance
	case $ddate in
		*0?|*1[01234])	nxddate=${ddate%??}15 ;;
		*)		nxddate=`ndate $((${ddate%??}+1))01` ;;
	esac
	nxedate=`ndate -eo $nxddate`
	ndays=$(($nxedate - $edate))
	case `ndate ${ddate%????}0229` in
		*0229)	compden=183 ;;
		*0301)	compden=182.5 ;;
	esac
	interest=`interest $rate $compden $ndays $balance`
	balance=$(($balance + $interest - $payment))
	ddate=$nxddate
	edate=$nxedate
done