#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';

sub validate_serial_number {
    my $v = shift;
    $v =~ s/\s//g;  # remove whitespace
    $v = uc $v;     # convert to uppercase

    # 1) Try regex:
    
    return 0 if !length $v;
    return 1 if $v =~ /^JM-\d+-\S{4}[1-9Zz]{6}$/;


    # 2) Initialize the %map hash with (A=>0, B=>1, C=>2, ...):

    my $dv = 0;
    my %map = map { $_ => $dv++ }
        qw(A B C D E F G H J K L M N P Q R T U V W Y 3 4 6 7 8 9);


    # 3) Extract significant character data, for example:
    #     'FOOBAR123ABCDE' -> chars: qw(D C B A 3 R A B F)
    #                         check: 'E'

    my @chars = reverse split '', $v;
    my $check = shift @chars;
    @chars = grep { exists $map{$_} } @chars;


    # 4) Sanity check:
    
    return 0 if @chars != 9;


    # 5) Perform check digit algorithm:
    
    my $totalVal = 0;
    
    # Loop over the reversed array of input characters:
    for my $i (0..$#chars) {
    
        # Map the character to a unique numeric value:
        my $posVal = $map{$chars[$i]};
        
        # Double the value, but only for every second character:
        $posVal *= 2 if !($i % 2);
        
        # Add the sum of the digits of $posVal to $totalVal:
        while($posVal){
            $totalVal += $posVal % 10;
            $posVal = int($posVal / 10);
        }
    }

    # Substract the last digit of $totalVal from 10, and take the
    # last digit of *that* to get the check digit:
    return ( $check eq ( 10 - $totalVal % 10 ) % 10 );
}

for ('Foo abr 123 ABCD6',
     'Foo bar 123 ABCD6') {
  say "'$_' is " . (validate_serial_number($_) ? "valid" : "invalid");
}

##</code><code>##

'Foo abr 123 ABCD6' is invalid
'Foo bar 123 ABCD6' is valid