package Algorithm::CheckDigits::M11_015;

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

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

my @weight = ( 2, 3, 4, 5, 6, 7 );

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 ($number =~ /^(\d\d)([\d ]+)$/) {
		return $1 == $self->_compute_checkdigits($2);
	}
	return ''
} # is_valid()

sub complete {
	my ($self,$number) = @_;
	if ($number =~ /^([\d ]+)$/) {
		return $self->_compute_checkdigits($1) . $1;
	}
	return '';
} # complete()

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

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

sub _compute_checkdigits {
	my ($self,$number) = @_;

	$number =~ s/\s//g;
	my @digits = split(//,$number);
	my $sum = 0;
	for (my $i = $#digits; $i >= 0; $i--) {
		$sum += $weight[($#digits - $i) % 6] * $digits[$i];
	}
	$sum %= 11;
	my $retval = (0 == $sum) ? '00' : sprintf("%02d",(11 - $sum));
	$retval;
} # _compute_checkdigit()

# Preloaded methods go here.

1;
__END__

=head1 NAME

CheckDigits::M11_015 - compute check digits for ESR5 (CH)

=head1 SYNOPSIS

  use Algorithm::CheckDigits;

  $ustid = CheckDigits('esr5_ch');

  if ($ustid->is_valid('050001000012000 241170032660178 10304')) {
	# do something
  }

  $cn = $ustid->complete('0001000012000 241170032660178 10304');
  # $cn = '050001000012000 241170032660178 10304'

  $cd = $ustid->checkdigit('0001000012000 241170032660178 10304');
  # $cd = '05'

  $bn = $ustid->basenumber('050001000012000 241170032660178 10304');
  # $bn = '0001000012000 241170032660178 10304';
  
=head1 DESCRIPTION

=head2 ALGORITHM

=over 4

=item 1

Beginning right all digits are weighted with the repeating
sequence 2, 3, 4, 5, 6, 7.

=item 2

The weighted digits are added.

=item 3

The sum from step 2 is taken modulo 11.

=item 4

The checkdigit is 11 minus the sum from step 3.
If the difference is 11, the checkdigit is 00.

=back

=head2 METHODS

=over 4

=item is_valid($number)

Returns true only if C<$number> consists solely of numbers and hyphens
and the two digits in the middle
are valid check digits according to the algorithm given above.

Returns false otherwise,

=item complete($number)

The check digit for C<$number> is computed and inserted before the
C<$number>.

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

Return '' otherwise.

=back

=head2 EXPORT

None by default.

=head1 AUTHOR

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

=head1 SEE ALSO

L<perl>,
L<CheckDigits>,
F<http://www.pruefziffernberechnung.de/E/Einzahlungsschein-CH.shtml> (german),
F<http://www.sic.ch/de/dl_tkicch_dta.pdf>, page 52 (german)

=cut