File Coverage

blib/lib/Data/Decrement.pm

Criterion	Covered	Total	%
statement	35	39	89.7
branch	15	18	83.3
condition			n/a
subroutine	5	5	100.0
pod	1	1	100.0
total	56	63	88.8

package Data::Decrement;

our $DATE = '2019-01-26'; # DATE
our $VERSION = '0.002'; # VERSION

use strict;
use warnings;
use Carp;

use Exporter qw(import);
our @EXPORT_OK = qw(decr);

sub decr {
    my $val = shift;

    return -1 unless defined $val;
    return $val-1 unless $val =~ /^[a-zA-Z]*[0-9]*\z/;

    my @digits = split //, $val;
    my $carry = 0;
    for (my $i = $#digits; $i >= 0; $i--) {
        my $digit = $digits[$i];
        if ($digit eq 'a') {
            do { carp "Cannot decrement '$val'"; return $val } unless $i;
            $digit = 'z'; $carry++;
        } elsif ($digit eq 'A') {
            do { carp "Cannot decrement '$val'"; return $val } unless $i;
            $digit = 'Z'; $carry++;
        } elsif ($digit eq '0') {
            do { carp "Cannot decrement '$val'"; return $val } unless $i;
            $digit = '9'; $carry++;
        } else {
            $digit = chr(ord($digit)-1);
        }
        $digits[$i] = $digit;
        last unless $carry--;
    }

    join '', @digits;
}

1;
# ABSTRACT: Provide extra magic logic for auto-decrement

__END__