package LUHN;

use warnings;
use strict;

use List::Util qw(sum);

use Data::Dump qw(dd);

sub cd_kschwab {  # pm#1226545
  use integer;
  my $total = 0;
  my $flip = 1;
  foreach my $c (reverse split //, shift) {
    $c *= 2 unless $flip = !$flip;
    while ($c) {
      $total += $c % 10;
      $c = $c / 10;
    }
  }
  return (10 - $total % 10) % 10;
}

my @x2_cast_out_9 = (
  # 0  1  2  3  4  5  6  7  8  9  # input number n
    0, 2, 4, 6, 8, 1, 3, 5, 7, 9  # output: n * 2, cast out 9
    );

my @check_digit = map { (10 - $_ % 10) % 10 } 0 .. 9 * 15;

sub cd_AnomalousMonk {

    my $ccn = shift;

    my $total = 0;

    for (1, 3, 5, 7, 9, 11, 13) {
        $total += substr($ccn, $_, 1);
        }

    for (0, 2, 4, 6, 8, 10, 12, 14) {
        $total += $x2_cast_out_9[ substr($ccn, $_, 1) ];
        }

    return $check_digit[ $total ];

    }

sub cd_BrowserUk {  # pm#1226582
    use integer;
    my $s = $_[ 0 ];
    my $total = 0;
    for my $i ( 0 .. 14 ) {
        my $d = substr( $s, $i, 1 );
        unless( $i & 1 ) {
            $d *= 2;
            $d -= 9 if $d > 9;
        }
        $total += $d;
    }
    $total *= 9;
    return chop $total;
}

1;

##</code><code>##

# test_LUHN_1.pl                                            01dec18waw

use warnings;
use strict;

use Benchmark qw(cmpthese);

use LUHN;

for ('000' .. '999') {
    my $ccn = '401135000000' . $_;
    my $kschwab_cd       = LUHN::cd_kschwab       ($ccn);
    my $AnomalousMonk_cd = LUHN::cd_AnomalousMonk ($ccn);
    die "$ccn: kschwab $kschwab_cd != $AnomalousMonk_cd"
        if $kschwab_cd != $AnomalousMonk_cd;
    }
print "tested cc number range kschwab vs. AnomalousMonk ok \n";

for ('000' .. '999') {
    my $ccn = '401135000000' . $_;
    my $kschwab_cd   = LUHN::cd_kschwab   ($ccn);
    my $BrowserUk_cd = LUHN::cd_BrowserUk ($ccn);
    die "$ccn: kschwab $kschwab_cd != $BrowserUk_cd"
        if $kschwab_cd != $BrowserUk_cd;
    }
print "tested cc number range kschwab vs. BrowserUk ok \n";

cmpthese (-1, {
  cd_kschwab   => sub { LUHN::cd_kschwab       ('401135000000000') },
  cd_AM        => sub { LUHN::cd_AnomalousMonk ('401135000000000') },
  cd_BrowserUk => sub { LUHN::cd_BrowserUk     ('401135000000000') },
  });

##</code><code>##

c:\@Work\Perl\monks\kschwab>perl test_LUHN_1.pl
tested cc number range kschwab vs. AnomalousMonk ok
tested cc number range kschwab vs. BrowserUk ok
                 Rate   cd_kschwab cd_BrowserUk        cd_AM
cd_kschwab    52764/s           --         -40%         -62%
cd_BrowserUk  88033/s          67%           --         -37%
cd_AM        139999/s         165%          59%           --

##</code><code>##

sub cd_AM_HOP {  # iterator solution

    my ($n_digits,  # n of digits for which to generate luhn checksum
        ) = @_;

    my $order = $n_digits & 1;
    my @straight = grep +($_ & $order), 0 .. $n_digits-1;  # dd '---', \@straight;
    my @adjusted = grep !($_ & $order), 0 .. $n_digits-1;  # dd '===', \@adjusted;

    my @check_digit = map { (10 - $_ % 10) % 10 } 0 .. 9 * $n_digits;

    return sub {

        my $ccn = shift;  # digits for which to generate checksum

        my $total = 0;

        for (@straight) {
            $total += substr($ccn, $_, 1);
            }

        for (@adjusted) {
            $total += $x2_cast_out_9[ substr($ccn, $_, 1) ];
            }

      # return $check_digit[ $total ];  # return check digit
        $total *= 9;
        return chop $total;  # return check digit

        };  # end sub iterator

    }