# RDF::Query::Plan::Distinct
# -----------------------------------------------------------------------------

=head1 NAME

RDF::Query::Plan::Distinct - Executable query plan for Distincts.

=head1 VERSION

This document describes RDF::Query::Plan::Distinct version 2.916.

=head1 METHODS

Beyond the methods documented below, this class inherits methods from the
L<RDF::Query::Plan> class.

=over 4

=cut

package RDF::Query::Plan::Distinct;

use strict;
use warnings;
use base qw(RDF::Query::Plan);

######################################################################

our ($VERSION);
BEGIN {
	$VERSION	= '2.916';
}

######################################################################

=item C<< new ( $plan ) >>

=cut

sub new {
	my $class	= shift;
	my $plan	= shift;
	my $self	= $class->SUPER::new( $plan );
	$self->[0]{referenced_variables}	= [ $plan->referenced_variables ];
	return $self;
}

=item C<< execute ( $execution_context ) >>

=cut

sub execute ($) {
	my $self	= shift;
	my $context	= shift;
	$self->[0]{delegate}	= $context->delegate;
	if ($self->state == $self->OPEN) {
		throw RDF::Query::Error::ExecutionError -text => "DISTINCT plan can't be executed while already open";
	}
	my $plan	= $self->[1];
	$plan->execute( $context );

	if ($plan->state == $self->OPEN) {
		$self->[0]{seen}	= {};
		$self->state( $self->OPEN );
	} else {
		warn "could not execute plan in distinct";
	}
	$self;
}

=item C<< next >>

=cut

sub next {
	my $self	= shift;
	unless ($self->state == $self->OPEN) {
		throw RDF::Query::Error::ExecutionError -text => "next() cannot be called on an un-open DISTINCT";
	}
	my $plan	= $self->[1];
	while (1) {
		my $row	= $plan->next;
		return undef unless ($row);
		if (not $self->[0]{seen}{ $row->as_string }++) {
			if (my $d = $self->delegate) {
				$d->log_result( $self, $row );
			}
			return $row;
		}
	}
}

=item C<< close >>

=cut

sub close {
	my $self	= shift;
	unless ($self->state == $self->OPEN) {
		throw RDF::Query::Error::ExecutionError -text => "close() cannot be called on an un-open DISTINCT";
	}
	delete $self->[0]{seen};
	$self->[1]->close();
	$self->SUPER::close();
}

=item C<< pattern >>

Returns the query plan that will be used to produce the data to be made distinct.

=cut

sub pattern {
	my $self	= shift;
	return $self->[1];
}

=item C<< distinct >>

Returns true if the pattern is guaranteed to return distinct results.

=cut

sub distinct {
	return 1;
}

=item C<< ordered >>

Returns true if the pattern is guaranteed to return ordered results.

=cut

sub ordered {
	my $self	= shift;
	return $self->pattern->ordered;
}

=item C<< plan_node_name >>

Returns the string name of this plan node, suitable for use in serialization.

=cut

sub plan_node_name {
	return 'distinct';
}

=item C<< plan_prototype >>

Returns a list of scalar identifiers for the type of the content (children)
nodes of this plan node. See L<RDF::Query::Plan> for a list of the allowable
identifiers.

=cut

sub plan_prototype {
	my $self	= shift;
	return qw(P);
}

=item C<< plan_node_data >>

Returns the data for this plan node that corresponds to the values described by
the signature returned by C<< plan_prototype >>.

=cut

sub plan_node_data {
	my $self	= shift;
	return ($self->pattern);
}

=item C<< graph ( $g ) >>

=cut

sub graph {
	my $self	= shift;
	my $g		= shift;
	my $c		= $self->pattern->graph( $g );
	$g->add_node( "$self", label => "Distinct" . $self->graph_labels );
	$g->add_edge( "$self", $c );
	return "$self";
}


1;

__END__

=back

=head1 AUTHOR

 Gregory Todd Williams <gwilliams@cpan.org>

=cut
