#!/bin/ksh

# returns 1 if leap year, Gregorian
# usage: isleapyr <year>

isleapyr()
{
	year=$1
	if [[ $(( $year % 4 )) -eq  0 && $(( $year % 100 )) -ne 0  \
			  || $(( $year % 400 )) -eq 0 ]] ; then
	   echo 1
	else
	   echo 0
	fi
}

# days_in_year number of days in full years 
#   since Dec 31 1970 midnight
#          
# usage: days_in_years <year>

days_in_years()
{

	start=1970
	total=0
	year=$1
	while [[ $start -lt $year ]]
	do
		days=365
		if [[ $(( $start % 4 )) -eq 0 ]] ; then
			if [[ $( isleapyr $start ) -eq 1 ]] ; then
				days=366
			fi
		fi
		start=$(( $start + 1 ))
		total=$(( $total + $days ))
	done

	echo $total
}


# days_in_months: return days in months
# usage: <month_number> <year>

days_in_months()
{
	month=$(( $1 - 1 ))
	start=0
	result=0

	if [[ $( isleapyr $2 ) -eq 1 ]] ; then
		set -A arr 31 29 31 30 31 30 31 31 30 31 30 31
	else
		set -A arr 31 28 31 30 31 30 31 31 30 31 30 31
	fi
	while [[ $start -lt $month ]]
	do
		result=$(( $result + ${arr[start]} ))
		start=$(( $start + 1 ))
	done
	echo $result
}

# y_total total days after epoch start midnight Dec 31 1969
# usage <day of month> <month> <year>

y_total()
{
	totaly=$( days_in_years $3 )
	totalm=$( days_in_months $2 $3 )
	echo $(( $totaly  + $totalm + $1 ))
}

# date_diff
#
# usage: date_diff <dd/mm/yyyy> <dd/mm/yyyy>
#   difference in days: date range from 01/01/1970 -> on
#   return +/- value or zero

date_diff()
{
	if [[ "$1"  = "$2" ]] ; then
		echo 0
		return
	fi
	echo "$1" | awk -F'/' '{print $1 +0, $2 +0, $3} ' | read d1 m1 y1
	days1=$( y_total $d1 $m1 $y1 )
	echo "$2" | awk -F'/' '{print $1 +0, $2 +0, $3} ' | read d1 m1 y1
	days2=$( y_total $d1 $m1 $y1 )
	echo "$(( $days2 - $days1))"
}

# example

date_diff 31/12/2007 03/03/2008

csadev:/home/jmcnama> ddiff.shl
63