How do I write a locale-aware DateTime sensibly into Spreadsheet::WriteExcel? - excel

Question

I have got a DateTime object that is in a specific locale (with a DateTime::Locale object attached to it). I want to write a date string to an XLS file using Spreadsheet::WriteExcel, but I want the output that's visible to user of the Excel file to be of the same locale as the one attached to my DateTime object.
There is some documentation on this matter within Spreadsheet::WriteExcel. It's possible to set formats using a combination of a string, $wb->add_format() and $ws->write_date_time().
I can get locale information from DateTime via DateTime::Locale by looking at the CLDR patterns. There are also the named formats, which are easier to use. Something like $locale->date_format_short is actually quite nice.
use DateTime::Locale;
say DateTime::Locale->load('en_GB')->date_format_short; # dd/MM/y
say DateTime::Locale->load('en_US')->date_format_short; # M/d/yy
Now the problem with this is, that Excel does not know what a single y means. So my workaround has been to just replace a single y with yy, as that seems to roughly be the same.
Excel also doesn't like upper case letters in the format. I have no idea how it distinguishes between minutes and months, but it works.
This example seems to work, but I am sure it's not perfect.
use strict;
use warnings;
use Spreadsheet::WriteExcel;
use DateTime;
use DateTime::Locale;
my $workbook = Spreadsheet::WriteExcel->new("date_time.xls");
my $worksheet = $workbook->add_worksheet();
# Write the column headers
$worksheet->write('A1', 'Formatted date');
$worksheet->write('B1', 'Format');
$worksheet->write('C1', 'Locale');
my $row = 0;
for my $locale (qw/en_GB en_US de_DE ko_KR/) {
$row++;
my $format_string =
lc(DateTime::Locale->load($locale)->date_format_short)
=~ s{
(?<!y) # 2. not preceded by a y
y # 1. a single y
(?!y) # 3. not followed by a y
}{yy}xr; # 4. replaced with two y
my $format = $workbook->add_format(num_format => $format_string);
$worksheet->write_date_time($row, 0, DateTime->now->datetime, $format);
$worksheet->write($row, 1, $format_string);
$worksheet->write($row, 2, $locale);
}
This produces the following Excel file.
They all work, but the code is smelly. Is there something I've overlooked? Maybe someone has written a more correct converter for these format strings that I've not seen yet.
Please note that DateTime::Format::Excel is not helpful as it only works the other way around, turning Excel dates into DateTime objects.