package Algorithm::CheckDigits::MXX_002;

use 5.006;
use strict;
use warnings;
use integer;

our @ISA = qw(Algorithm::CheckDigits);

sub new {
	my $proto = shift;
	my $type  = shift;
	my $class = ref($proto) || $proto;
	my $self  = bless({}, $class);
	$self->{type} = lc($type);
	return $self;
} # new()

sub is_valid {
	my ($self,$number) = @_;
	if ($number =~ /^(\d{1,6}-?\d{2}-?)(\d)$/) {
		return 1 if ($2 == $self->_compute_checkdigit($1));
	}
	return ''
} # is_valid()

sub complete {
	my ($self,$number) = @_;
	if ($number =~ /^\d{1,6}-?\d{2}-?$/) {
		return $number .  $self->_compute_checkdigit($number);
	}
	return '';
} # complete()

sub basenumber {
	my ($self,$number) = @_;
	if ($number =~ /^(\d{1,6}-?\d{2}-?)(\d)$/) {
		return $1 if ($2 == $self->_compute_checkdigit($1));
	}
	return '';
} # basenumber()

sub checkdigit {
	my ($self,$number) = @_;
	if ($number =~ /^(\d{1,6}-?\d{2}-?)(\d)$/) {
		return $2 if ($2 == $self->_compute_checkdigit($1));
	}
	return '';
} # checkdigit()

sub _compute_checkdigit {
	my $self   = shift;
	my $number = shift;

	$number =~ s/-//g;
	my @digits = split(//,$number);
	my $weight = 1;
	my $sum    = 0;

	for (my $i = $#digits; $i >= 0; $i--) {
		$sum += $digits[$i] * $weight++;
	}

	return $sum % 10;
} # _compute_checkdigit()

# Preloaded methods go here.

1;
__END__

=head1 NAME

CheckDigits::MXX_002 - compute check digits for CAS

=head1 SYNOPSIS

  use Algorithm::CheckDigits;

  $cas = CheckDigits('cas');

  if ($cas->is_valid('1333-74-0')) {
	# do something
  }

  $cn = $cas->complete('1333-74-');
  # $cn = '1333-74-0'

  $cd = $cas->checkdigit('1333-74-0');
  # $cd = '0'

  $bn = $cas->basenumber('1333-74-0');
  # $bn = '1333-74-'
  
=head1 DESCRIPTION

=head2 ALGORITHM

=over 4

=item 1

Beginning right with the second digit all digits are weighted
ascending starting with 1.

=item 2

The sum of those products is computed.

=item 3

The checksum is the last digit of the sum from step 2 (modulo 10).

=back

=head2 METHODS

=over 4

=item is_valid($number)

Returns true only if C<$number> consists solely of numbers and the last digit
is a valid check digit according to the algorithm given above.

Returns false otherwise,

=item complete($number)

The check digit for C<$number> is computed and concatenated to the end
of C<$number>.

Returns the complete number with check digit or '' if C<$number>
does not consist solely of digits and spaces.

=item basenumber($number)

Returns the basenumber of C<$number> if C<$number> has a valid check
digit.

Return '' otherwise.

=item checkdigit($number)

Returns the checkdigit of C<$number> if C<$number> has a valid check
digit.

Return '' otherwise.

=back

=head2 EXPORT

None by default.

=head1 AUTHOR

Mathias Weidner, E<lt>mathias@weidner.in-bad-schmiedeberg.deE<gt>

=head1 THANKS

Aaron W. West pointed me to a fault in the computing of the check
digit.

=head1 SEE ALSO

L<perl>,
L<CheckDigits>,
F<www.pruefziffernberechnung.de>,
F<www.cas.org>

=cut
