# A single relation, useful for initial testing and debugging.
1-1        1-2

##</code><code>##

use diagnostics;
use strict;
use Vertex;
use Edge;

sub make_vertex($);
sub make_edge($$$);
if (1) {}; # Emacs Perl-mode does not like prototypes; indentation destroyed.

my ( @data,  $i, $comment, $nr_edges, $nr_verteces );
my ( $v1, $v2 );
my ( @verteces, %verteces, @edges, %edges );

$comment = '#.*$';
while (<>) {
    my ( $vertex_1, $vertex_2, $edge, $key);

    $i++;
    s/$comment//;
    next if /^\s*$/;
    /^\s*(\S+)\s+(\S+)/;

    if (!$1 || !$2) {
	print STDERR "Non-valid data on line $i.\n";
	next;
    }
    ($v1, $v2) = ($1, $2);
    
    $vertex_1 = $verteces{$v1};
    if (!$vertex_1) {
	$vertex_1 = make_vertex($v1);
	$verteces{$v1} = $vertex_1;
	push @verteces, $vertex_1;
    }
    $vertex_2 = $verteces{$v2};
    if (!$vertex_2) {
	$vertex_2 = make_vertex($v2);
	$verteces{$v2} = $vertex_2;
	push @verteces, $vertex_2;
    }
    $key = $v1 . '_' . $v2;
    $edge = $edges{$key};
    if (!$edge) {
	$edge = make_edge($vertex_1, $vertex_2, $key);
	$edges{$key} = $edge;
	push @edges, $edge;
    }
    $vertex_1 -> add_edge_reference($edge);
    $vertex_2 -> add_edge_reference($edge);
}

$verteces[0] -> print_vertex(2);

#--------------------------------------
# Subroutines and functions.
sub make_vertex ($) {
    my ( $label ) = @_;

    return Vertex->new('x' => int(rand(100)),
		       'y' => int(rand(100)),
		       'label' => $label);
} # make_vertex

sub make_edge ($$$) {
    my ( $vertex_1, $vertex_2, $label ) = @_;

    return Edge->new('vertex_1' => $vertex_1,
		     'vertex_2' => $vertex_2,
		     'label'    => $label
		     );
} # make_vertex

##</code><code>##

package Vertex;
use strict;

sub new {
    my ($class, %params) = @_;
    bless {
	'_x'        => $params{'x'} || 0,
	'_y'        => $params{'y'} || 0,
	'_label'    => $params{'label'} || '',
	'_edges'    => {}, # Neighbouring verteces connected through an edge.
	'_verteces' => {}, # Neighbouring verteces not connected through an edge.
	'_fx'       => 0,
	'_fy'       => 0,
	'_dx'       => 0,
	'_dy'       => 0,
    }, $class;
} # new

sub print_vertex {
    my ($class, $i) = @_;
    my $is;
    
    if (!defined($i)) {
	$is = '';
    }
    else {
	$is = sprintf('%' . $i . 's', '');
    }
    print $is, 'label=', $_[0]->{'_label'}, "\n";
    print $is, 'x='    , $_[0]->{'_x'},     "\n";
    print $is, 'y='    , $_[0]->{'_y'},     "\n";
    print $is, 'fx='   , $_[0]->{'_fx'},    "\n";
    print $is, 'fy='   , $_[0]->{'_fy'},    "\n";

    my @tmp = keys %{$_[0]->{'_edges'}};
    my $tmp;
    
    if ($#tmp >= 0) {
	print $is, 'Edges: (', 1+$#tmp, ") \n";
	for $tmp ( @tmp ) {
	    print "  ", $tmp->query_label(), "\n"; ### ERROR OCCURS HERE.
	}
    }
    else {
	print $is, "No edges.\n";
    }
    
    @tmp = keys %{$_[0]->{'_verteces'}};
    if ($#tmp >= 0) {
	print $is, 'Verteces:', "\n";
	for ( @tmp ) {
	    print $is, "  ", $_->query_label(), "\n";
	}
    }
    else {
	print $is, "No verteces.\n";
    }
} # print_vertex

# Only neighbours not connected through an edge should be added here.
sub add_neighbour_reference {
    my ($self, @params) = @_;
    my $key;
    for $key ( @params ) {
	$self->{_neighbours}[$key] = 1;
    }
} # add_neighbour

sub add_edge_reference {
    my ($self, @params) = @_;
    my $key;
    for $key ( @params ) {
	$self->{_edges}{$key} = 1;
    }
} # add_edge_references

sub query_x {
    $_[0]->{_x};
} # query_x

sub set_x {
    $_[0]->{_x} = $_[1] if defined($_[1]);
} # set_x

sub query_y {
    $_[0]->{_y};
} # query_y

sub set_y {
    $_[0]->{_y} = $_[1] if defined($_[1]);
} # set_y

sub query_label {
    $_[0]->{_label};
} # query_label

sub set_label {
    $_[0]->{_label} = $_[1] if defined($_[1]);
} # set_label

1;

##</code><code>##

package Edge;
use strict;

sub new {
    my ($class, %params) = @_;
    bless {
 	'_strength' => $params{'strength'} || 1,
	'_length'   => $params{'length'}   || 1,
	'_vertex_1' => $params{'vertex_1'} || 0,
	'_vertex_2' => $params{'vertex_2'} || 0,
	'_label'    => $params{'label'}    || '',
    }, $class;
} # new

sub print_edge {
    print 'label='   , $_[0]->{'_label'}   , "\n";
    print 'strength=', $_[0]->{'_strength'}, "\n";
    print 'length='  , $_[0]->{'_length'}  , "\n";
    print 'vertex_1=', $_[0]->{'_vertex_1'}->query_label(), "\n";
    print 'vertex_2=', $_[0]->{'_vertex_2'}->query_label(), "\n";

} # print_edge

# ------------------------------------------------------------------
# Set functions.

sub set_strength {
    $_[0]->{_strength} = $_[1] if defined($_[1]);
} # set_strength

sub set_length {
    $_[0]->{_length} = $_[1] if defined($_[1]);
} # set_length

sub set_label {
    $_[0]->{_label} = $_[1] if defined($_[1]);
} # set_label

sub set_vertex_1 {
    $_[0]->{_vertex_1} = $_[1] if defined($_[1]);
} # set_vertex_1

sub set_vertex_2 {
    $_[0]->{_vertex_2} = $_[1] if defined($_[1]);
} # set_vertex_2

sub set_verteces {
    $_[0]->{_vertex_1} = $_[1] if defined($_[1]);
    $_[0]->{_vertex_2} = $_[2] if defined($_[2]);
} # set_verteces

# ------------------------------------------------------------------
# Query functions.

sub query_strength {
    $_[0]->{_strength};
} # query_strength

sub query_length {
    $_[0]->{_length};
} # query_length

sub query_label {
    $_[0]->{_label};
} # query_label

sub query_vertex_1 {
    $_[0]->{_vertex_1};
} # query_vertex_1

sub query_vertex_2 {
    $_[0]->{_vertex_2};
} # query_vertex_2

sub query_verteces {
    ( $_[0]->{_vertex_1}, $_[0]->{_vertex_2} );
} # query_verteces

1;