package URI::urn;    # RFC 2141

use strict;
use warnings;

our $VERSION = '5.37';

use parent 'URI';

use Carp qw(carp);

my %implementor;

sub _init {
    my $class = shift;
    my $self  = $class->SUPER::_init(@_);
    my $nid   = $self->nid;

    my $impclass = $implementor{$nid};
    return $impclass->_urn_init($self, $nid) if $impclass;

    $impclass = "URI::urn";
    if ($nid =~ /^[A-Za-z\d][A-Za-z\d\-]*\z/) {
        my $id = $nid;

        # make it a legal perl identifier
        $id =~ s/-/_/g;
        $id = "_$id" if $id =~ /^\d/;

        $impclass = "URI::urn::$id";
        no strict 'refs';
        unless (@{"${impclass}::ISA"}) {

            # Try to load it
            my $_old_error = $@;
            eval "require $impclass";
            die $@ if $@ && $@ !~ /Can\'t locate.*in \@INC/;
            $@        = $_old_error;
            $impclass = "URI::urn" unless @{"${impclass}::ISA"};
        }
    }
    else {
        carp("Illegal namespace identifier '$nid' for URN '$self'") if $^W;
    }
    $implementor{$nid} = $impclass;
    return $impclass->_urn_init($self, $nid);
}

sub _urn_init {
    my ($class, $self) = @_;
    bless $self, $class;
}

sub _nid {
    my $self   = shift;
    my $opaque = $self->opaque;
    if (@_) {
        my $v   = $opaque;
        my $new = shift;
        $v =~ s/[^:]*/$new/;
        $self->opaque($v);

        # XXX possible rebless
    }
    $opaque =~ s/:.*//s;
    return $opaque;
}

sub nid {    # namespace identifier
    my $self = shift;
    my $nid  = $self->_nid(@_);
    $nid = lc($nid) if defined($nid);
    return $nid;
}

sub nss {    # namespace specific string
    my $self   = shift;
    my $opaque = $self->opaque;
    if (@_) {
        my $v   = $opaque;
        my $new = shift;
        if (defined $new) {
            $v =~ s/(:|\z).*/:$new/;
        }
        else {
            $v =~ s/:.*//s;
        }
        $self->opaque($v);
    }
    return undef unless $opaque =~ s/^[^:]*://;
    return $opaque;
}

sub canonical {
    my $self = shift;
    my $nid  = $self->_nid;
    my $new  = $self->SUPER::canonical;
    return $new        if $nid !~ /[A-Z]/ || $nid =~ /%/;
    $new = $new->clone if $new == $self;
    $new->nid(lc($nid));
    return $new;
}

1;
