#!/usr/bin/perl --

use strict;
use warnings;

use Time::Piece;
use DateTime::Format::Strptime;

Main(@ARGV);
exit(0);

sub Main {

#~     yyddd (or yyyyddd) to yyyymmdd (e.g, convert 11004 to 20110104).

    Yo( 11004   => 20110104 );
    Yo( 2011004 => 20110104 );
    Yo( 11005   => 20110105 );

} ## end sub Main

BEGIN {

#~ http://www.unix.com/man-page/FreeBSD/3/strftime/
    my @Y = (
        [
            yyddd => sub {
                my ($in) = @_;
                if ( $in =~ /^\d{5}$/ ) {

#~                     $in = Time::Piece->strptime( $in, '%y%j' );
                    $in =
                      DateTime::Format::Strptime->new( pattern => '%y%j' )
                      ->parse_datetime($in)->epoch;
                    $in = gmtime($in)->strftime('%Y-%m-%d');
                    return $in;
                } ## end if ( $in =~ /^\d{5}$/ )
              }
        ], [
            yyyyddd => sub {
                my ($in) = @_;
                if ( $in =~ /^\d{7}$/ ) {

#~                     $in = Time::Piece->strptime( $in, '%Y%j' );
                    $in =
                      DateTime::Format::Strptime->new( pattern => '%Y%j' )
                      ->parse_datetime($in)->epoch;
                    $in = gmtime($in)->strftime('%Y-%m-%d');
                    return $in;
                } ## end if ( $in =~ /^\d{7}$/ )
              }
        ],
    );

    sub Y {
        for my $Y (@Y) {
            if ( my $p = $Y->[1]->(@_) ) {
                return $p;
            }
        }
    } ## end sub Y
} ## end BEGIN

sub Yo {
    my ( $in, $ou ) = @_;
    print "$in\n->$ou\n->";
    print Y($in), "\n\n";
}

__END__
11004
->20110104
->2011-01-04

2011004
->20110104
->2011-01-04

11005
->20110105
->2011-01-05