#!/bin/ksh

ME=${0##*/}

set -A DAYS 31 28 31 30 31 30 31 31 30 31 30 31

typeset -Z2 MM
typeset -Z2 DD
typeset -Z4 YY
typeset -Z2 YR
typeset -Z3 DayOfYear
typeset -i LeapCount
typeset -i JUL

LEAP=0
JUSTDAY=0
YEARDAY=0
NOCENTURY=0
NOYEAR=0
VERIFY=0
SORTORDER=0

ExitUsage()
{
	print "usage: $ME [-D [-c]|-d|-v] mmdd[[cc]yy]"
	print ""
	print "       generates julian value"
	print "       if yy is omitted, defaults to current year"
	print "       if cc is omitted, year assumed to fall"
	print "           between 1915 and 2014 inclusive"
	print "       use = to specify today's date"
	print ""
	print "   or: $ME [-s ] [-d|-c|-y] -j julianVal"
	print "       $ME [-s ] [-c|-y] -J [[cc]yy]ddd"
	print ""
	print "       generates gregorian date"
	print "       default output format is mmddccyy"
	print ""
	print "OPTIONS:  -d   day of year only"
	print "          -D   year & day of year (ccyyddd)"
	print "          -c   omit century"
	print "          -y   omit year"
	print "          -v   validate only"
	print "          -s   output in sort order (year first)"
	print
	exit 0
}

ExitErr()
{
	(( VERIFY )) || print "${ME}: [00$1] invalid date"
	exit 1
}

CheckLeapYear()
{
    (( (YY%4 == 0 && YY%100 != 0) || YY%400 == 0 )) && LEAP=1
}

##########################################################################
## begin main entry
##

while (( $# > 0 )); do
	case $1 in
		-j )	break ;;
		-J )	break ;;

		-v )	VERIFY=1
				shift ;;

		-d )	JUSTDAY=1
				shift ;;

		-D )	YEARDAY=1
				shift ;;

		-c )	NOCENTURY=1
				shift ;;

		-y )	NOYEAR=1
				shift ;;

		-s )	SORTORDER=1
				shift ;;

		-* )	ExitUsage ;;

		* )		break ;;
	esac
done

(( $# < 1 )) && ExitUsage

if [[ $1 = -J ]]; then
	(( $# < 2 )) && ExitUsage
	shift
	arg=$1
	JUL=arg
	(( JUL < 1 )) && ExitErr 0

	if (( ${#arg} == 3 )); then
		YY=$(date '+%Y')
	else
		(( YY=JUL/1000 ))
		if (( YY < 20 )); then
			(( YY+=2000 ))
		else
			(( YY+=1900 ))
		fi
		(( JUL%=1000 ))
	fi

	CheckLeapYear
	(( YR=YY%100 ))

	(( JUL > 365+LEAP )) && ExitErr 6

	(( LEAP )) && (( DAYS[1]=29 ))
	(( MM=1 ))
	while (( JUL > DAYS[MM-1] )); do
		(( JUL-=DAYS[MM-1] ))
		(( MM+=1 ))
	done
	(( DD=JUL ))

	if (( NOYEAR )); then
		print "$MM$DD"

	elif (( SORTORDER )); then
		if (( NOCENTURY )); then
			print "$YR$MM$DD"
		else
			print "$YY$MM$DD"
		fi

	else
		if (( NOCENTURY )); then
			print "$MM$DD$YR"
		else
			print "$MM$DD$YY"
		fi
	fi

elif [[ $1 = -j ]]; then
	(( $# < 2 )) && ExitUsage
	shift
	YY=1
	JUL=$1
	(( JUL < 1 )) && ExitErr 0

	while (( JUL > 146097 )); do
		(( YY+=400 ))
		(( JUL-=146097 ))
	done
	while (( JUL > 36524 )); do
		(( YY+=100 ))
		(( JUL-=36524 ))
	done
	while (( JUL > 1461 )); do
		(( YY+=4 ))
		(( JUL-=1461 ))
	done
	while (( JUL > 365 )); do
		(( YY+=1 ))
		(( JUL-=365 ))
	done
	CheckLeapYear
	(( YR=YY%100 ))
	DayOfYear=$JUL

	(( LEAP )) && (( DAYS[1]=29 ))
	(( MM=1 ))
	while (( JUL > DAYS[MM-1] )); do
		(( JUL-=DAYS[MM-1] ))
		(( MM+=1 ))
	done
	(( DD=JUL ))

	if (( JUSTDAY )); then
		print $DayOfYear

	elif (( NOYEAR )); then
		print "$MM$DD"

	elif (( SORTORDER )); then
		if (( NOCENTURY )); then
			print "$YR$MM$DD"
		else
			print "$YY$MM$DD"
		fi

	else
		if (( NOCENTURY )); then
			print "$MM$DD$YR"
		else
			print "$MM$DD$YY"
		fi
	fi

else
	if [[ $1 = '=' ]]; then
		DATE=$(date +%m%d)
	else
		DATE=$(print $1 | sed s/[^0-9]//g)
	fi

	VerLEN=${#DATE}
	if (( ${#DATE} == 8 )); then
		(( YY=DATE % 10000 ))
		(( DATE/=10000 ))

	elif (( ${#DATE} == 6 )); then
		(( YY=DATE % 100 ))
		if (( YY < 20 )); then
			(( YY+=2000 ))
		else
			(( YY+=1900 ))
		fi
		(( DATE/=100 ))

	elif (( ${#DATE} == 4 )); then
		YY=$(date +%Y)
	else
		ExitErr 1
	fi
	CheckLeapYear

	(( MM=DATE / 100 ))
	(( DD=DATE % 100 ))

	(( MM < 1 || MM > 12 )) && ExitErr 2
	(( DD < 1 )) && ExitErr 3
	if (( LEAP == 1 && MM == 2 )); then
		(( DD > 29 )) && ExitErr 4
	else
		(( DD > DAYS[MM-1] )) && ExitErr 5
	fi

	if (( VERIFY )); then
		(( VerLEN > 4 )) && exit 0
		(( NOCENTURY )) && exit 0
		exit 1
	fi

	(( X=YY - 1 ))
	(( LeapCount=(X / 400) * 97 ))
	(( X%=400 ))
	(( LeapCount+=(X / 100) * 24 ))
	(( X%=100 ))
	(( LeapCount+=(X / 4) ))

	(( JUL=(YY-1) * 365 ))
	(( JUL+=LeapCount ))

	DayOfYear=0
	X=1
	while (( X < MM )); do
		(( DayOfYear+=DAYS[X-1] ))
		(( X+=1 ))
	done
	(( LEAP == 1 && MM > 2 )) && (( DayOfYear+=1 ))
	(( DayOfYear+=DD ))

	(( JUL+=DayOfYear ))

	if (( JUSTDAY )); then
		print $DayOfYear
	elif (( YEARDAY )); then
		if (( NOCENTURY )); then
			(( YR=YY % 100 ))
			print "$YR$DayOfYear"
		else
			print "$YY$DayOfYear"
		fi
	else
		print $JUL
	fi
fi

##
## end of file ################################################################