+sub filename {
+ my %a = @_;
+ my @discnumber = @{$a{discnumber} // []};
+ my $tracknumber = $a{tracknumber} // die('tracknumber required');
+ my $title = $a{title} // die('title required');
+ join('-',
+ (map { two_digits($_) } @discnumber),
+ two_digits($tracknumber),
+ mangle_for_file_name($title) . '.flac',
+ )
+}
+