use strict;
sub prepareFormat {
    my $format = shift;

    # TODO: check that only valid characters appear in the format
    # The logic should be: for any character A-Z in the format string,
    #   die if it's not one of: Y M D h m s p

    my ($i, @order) = 0;
    my $num_chars  = 'YMDhms';
    $format =~ s{([$num_chars]+|pp)(\?)?}{
		$order[$i++] = substr($1,0,1);
		if ($1 eq 'pp') {
			"(AM|PM|am|pm)"
		} else {
			'('.('\d' x length($1))."$2)"
		}
	}ge;

    $format = qr/^(?:$format)$/;
    return [$format, \@order];
}

sub parseDate {
    my ($format, $date) = @_;
    my @data = ($date =~ $format->[0])
        or return;
    my %result;
    for(my $i = 0; $i <= $#data; $i++) {
        $result{$format->[1]->[$i]} ||= $data[$i];
    }

    $result{h} += 12 if (uc($result{p}) eq 'PM' and $result{h} != 12);
    $result{h} = 0   if (uc($result{p}) eq 'AM' and $result{h} == 12);


    return map $result{$_}, qw(Y M D h m s);
}
...