#!/usr/bin/perl
#
# Convert day-of-year to month and day-of-month
# Convert month and day-of-month to day-of-year

use strict;

if ( $#ARGV != 1 && $#ARGV != 2 ) {
    print "Usage: doy year ([yday] | [month] [mday])\n";
    exit;
}

if ( $#ARGV == 1 ) {
    my ($month, $mday) = &doy2md ($ARGV[0], $ARGV[1]);
    
    print "$ARGV[0] : $month : $mday\n";
}
elsif ( $#ARGV == 2 ) {
    my ($yday) = &md2doy ($ARGV[0], $ARGV[1], $ARGV[2]); 

    print "$ARGV[0] : $yday\n";
}

############################################################################
# doy2md:
#
# Compute the month and day-of-month (mday) from a year and
# day-of-year (yday).
#
# Year is expected to be in the range 1900-2100, jday is expected to
# be in the range 1-366, month will be in the range 1-12 and mday
# will be in the range 1-31
#
# Returns the month and day-of-month (mday)
############################################################################
sub doy2md {  # doy2md (year, yday)
    my $year = shift;
    my $yday = shift;
    
    my @days = (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
    my $month = -1;
    my $mday = -1;
    
    # Sanity check for the supplied year
    if ( $year < 1900 || $year > 2100 ) {
	print "doy2md(): year ($year) is out of range\n";
	return;
    }
    
    # Test for leap year
    my $leap = ( (($year%4 == 0) && ($year%100 != 0)) || ($year%400 == 0) ) ? 1 : 0;
    
    # Add a day to February if leap year
    if ( $leap ) {
	$days[1]++;
    }
    
    if ( $yday > 365+$leap || $yday <= 0 ) {
	print "doy2md(): day-of-year ($yday) is out of range\n";
	return;
    }
    
    for ( my $idx=0; $idx < 12; $idx++ ) {
	$yday -= $days[$idx];

	if ( $yday <= 0 ) {
	    $month = $idx + 1;
	    $mday = $days[$idx] + $yday;
	    last;
	}
    }
    
    return ($month, $mday);
}  # End of doy2md()


############################################################################
# md2doy:
#
# Compute the day-of-year from a year, month and day-of-month.
#
# Year is expected to be in the range 1900-2100, month is expected to
# be in the range 1-12, mday is expected to be in the range 1-31 and
# jday will be in the range 1-366
#
# Returns 0 on success and -1 on error.
############################################################################
sub md2doy { # md2doy (year, month, mday)
    my $year = shift;
    my $month = shift;
    my $mday = shift;
    
    my @days = (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
    
    # Sanity check for the supplied parameters */
    if ( $year < 1900 || $year > 2100 ) {
	print "md2doy(): year ($year) is out of range\n";
	return;
    }
    if ( $month < 1 || $month > 12 ) {
	print "md2doy(): month ($month) is out of range\n";
	return;
    }
    if ( $mday < 1 || $mday > 31 ) {
	print "md2doy(): day-of-month ($mday) is out of range\n";
	return;
    }
  
    # Test for leap year
    my $leap = ( (($year%4 == 0) && ($year%100 != 0)) || ($year%400 == 0) ) ? 1 : 0;
    
    # Add a day to February if leap year
    if ( $leap ) {
	$days[1]++;
    }
  
    # Check that the day-of-month jives with specified month
    if ( $mday > $days[$month-1] ) {
	print "md2doy(): day-of-month ($mday) is out of range for month $month\n";
	return;
    }

    $month--;

    my $yday = 0;
    
    for ( my $idx=0; $idx < 12; $idx++ ) {
	if ( $idx == $month ) {
	    $yday += $mday;
	    last;
	}
      
	$yday += $days[$idx];
    }
    
  return $yday;
}  # End of md2doy()