#!/bin/sh
#######################################################################
# Program Name:  adddays.sh
# Purpose:  calculate date ahead or behind by X days
# Written by: J. David Schronce 
# Creation Date: 03/03/2000
#######################################################################
# 3/29/2007 - JDS - replace complex leapyear and DOM calculations 
#             with call to 'cal'
#
#set -xv
USAGE="
$0 USAGE:[-]number_of_days (where number_of_days between 365 and -365)\n\n
Example: \n
$0 -7 will return the date one week ago\n
$0 90 will return the date in 90 days"

if test $# = "0"
then
	echo $USAGE
      exit
elif test $1 -gt 365
then
	echo "parameter too large - max 365"
	exit
elif test $1 -lt -365
then
	echo "parameter too large - max -365"
	exit
else
	diffdays=`echo $1 | sed 's/+//g'`
fi
dom=`date '+%d'`
dow=`date '+%w'`
doy=`date '+%j'`
year=`date '+%Y'`	# 4 digit

if test $diffdays -lt 0
then
    sign="-"
    diffdays=`echo "$diffdays * -1" | bc`
    if test $diffdays -ge $doy
    then
        year=`echo "$year - 1" | bc`
# Test for leapyear
        if test `cal 2 $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'` -eq "29"
        then
	    yeardays=366
        else
    	    yeardays=365
        fi
        doy=`echo "$yeardays + $doy" | bc`
    fi
    targetday=`echo "$doy $sign $diffdays" | bc`
else
    sign="+"
# Test for leapyear
    if test `cal 2 $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'` -eq "29"
    then
	    yeardays=366
    else
    	    yeardays=365
    fi
    if test `echo "$diffdays + $doy" | bc` -gt $yeardays
    then
        year=`echo "$year + 1" | bc`
    	echo "$sign doy=$doy"
        targetday=`echo "($diffdays + $doy) - $yeardays" | bc`
    else
        targetday=`echo "($diffdays + $doy)" | bc`
    fi
fi

# calculate current month
# Test for leapyear
#if test `cal 2 $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'` -eq "29"
#if test `/usr/local/bin/leapyear $year` = "Yes"
#then
#	FEB=29
#else
#	FEB=28
#fi
month=1
continue="yes"
while test $continue = "yes"
do
    subdays=`cal $month $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'`
#    case $month in
#	1|3|5|7|8|10|12) subdays=31;;
#	2) subdays=$FEB;;
#	4|6|9|11) subdays=30;;
#    esac

    if test $targetday -le $subdays
    then
	continue="no"
	case $month in
		?) month="0$month";;
	esac
	case $targetday in
		?) targetday="0$targetday";;
	esac
	echo "$month-$targetday-$year"
	exit
    else
	#((month=month+1))
        month=`echo "$month + 1" | bc`
	targetday=`echo "$targetday - $subdays" | bc`
	continue="yes"
    fi
done
# Test for leapyear - see if Feb has 29 days
    if test `cal 2 $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'` -eq "29"
        then
	    yeardays=366
        else
    	    yeardays=365
        fi
        doy=`echo "$yeardays + $doy" | bc`
    fi
    targetday=`echo "$doy $sign $diffdays" | bc`
else
    sign="+"
# Test for leapyear - see if Feb has 29 days
    if test `cal 2 $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'` -eq "29"
    then
	    yeardays=366
    else
    	    yeardays=365
    fi
    if test `echo "$diffdays + $doy" | bc` -gt $yeardays
    then
        year=`echo "$year + 1" | bc`
    	echo "$sign doy=$doy"
        targetday=`echo "($diffdays + $doy) - $yeardays" | bc`
    else
        targetday=`echo "($diffdays + $doy)" | bc`
    fi
fi

# calculate current month
# Test for leapyear - see if Feb has 29 days
#    if test `cal 2 $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'` -eq "29"
#then
#	FEB=29
#else
#	FEB=28
#fi
month=1
continue="yes"
while test $continue = "yes"
do
    subdays=`cal $month $year | grep -v  \^\$ | tail -1 | awk '{print $NF}'`
#    case $month in
#	1|3|5|7|8|10|12) subdays=31;;
#	2) subdays=$FEB;;
#	4|6|9|11) subdays=30;;
#    esac

    if test $targetday -le $subdays
    then
	continue="no"
	case $month in
		?) month="0$month";;
	esac
	case $targetday in
		?) targetday="0$targetday";;
	esac
	echo "$month-$targetday-$year"
	exit
    else
	((month=month+1))
	targetday=`echo "$targetday - $subdays" | bc`
	continue="yes"
    fi
done