#
# Graph::Reader::HTK - perl module for reading an HTK lattice into a Graph
#
# $Id: HTK.pm,v 1.3 2002/07/03 17:43:10 neilb Exp $
#
package Graph::Reader::HTK;

use Graph::Reader;
use Carp;
use vars qw(@ISA $VERSION);
@ISA = qw(Graph::Reader);
$VERSION = sprintf("%d.%02d", q$Revision: 1.3 $ =~ /(\d+)\.(\d+)/);

my %node_attributes =
(
  'WORD' => [ 'WORD', 'label' ],
  'W'    => [ 'WORD', 'label' ],
  'time' => [ 'time' ],
  't'    => [ 'time' ],
  'var'  => [ 'var' ],
  'v'    => [ 'var' ],
  'L'    => [ 'L' ],
);

my %edge_attributes =
(
  'WORD'     => [ 'WORD', 'label' ],
  'W'        => [ 'WORD', 'label' ],
  'START'    => [ 'START' ],
  'S'        => [ 'START' ],
  'END'      => [ 'END' ],
  'E'        => [ 'END' ],
  'var'      => [ 'var' ],
  'v'        => [ 'var' ],
  'div'      => [ 'div' ],
  'd'        => [ 'div' ],
  'acoustic' => [ 'acoustic' ],
  'a'        => [ 'acoustic' ],
  'ngram'    => [ 'ngram' ],
  'n'        => [ 'ngram' ],
  'language' => [ 'language', 'weight' ],
  'l'        => [ 'language', 'weight' ],
);

#=======================================================================
#
# _read_graph
#
# The private method which implements the actual reading of the file.
#
#=======================================================================
sub _read_graph
{
    my $self  = shift;
    my $graph = shift;
    my $FILE  = shift;

    my $nvertices;
    my $nedges;
    my $v;
    my $from;
    my $to;
    my $weight;
    my ($an, $av);


    while (<$FILE>)
    {
	chop;

	#---------------------------------------------------------------
	# ignore version line
	#---------------------------------------------------------------
	if (/^\s*(V|VERSION)\s*=\s*(\S+)/) {
	    $graph->set_attribute('HTK_VERSION', $2);
	    next;
	}

	if (/^\s*(base|lmname|lmscale|wdpenalty)\s*=\s*(\S+)/)
	{
	    # print STDERR "Setting graph attribute $1 to $2\n";
	    $graph->set_attribute($1, ''.$2);
	}

	#---------------------------------------------------------------
	# line which says how many nodes & links we have
	#---------------------------------------------------------------
	if (/N\s*=\s*(\d+)\s*L\s*=\s*(\d+)/)
	{
	    # $NUM_NODES = $1;
	    # $NUM_LINKS = $2;
	    next;
	}

	#---------------------------------------------------------------
	# node definition
	#---------------------------------------------------------------
	if (/^I\s*=\s*(\d+)/mg)
	{
	    #---------------------------------------------------------------
	    # strip off the fields from the rest of the line
	    # and set appropriate attributes
	    #---------------------------------------------------------------
	    $node_num = "n$1";
	    $graph->add_vertex($node_num);
	    # print STDERR "Node $node_num:\n";
	    while (/\s*(\S+)\s*=\s*(\S+)/mg)
	    {
		$an = $1;
		$av = $2;
		if (exists $node_attributes{$an})
		{
		    foreach my $a (@{ $node_attributes{$an} })
		    {
			# print STDERR "   attr $a = $av\n";
			$graph->set_attribute($a, $node_num, $av);
		    }
		} else {
		    carp "unknown node field \"$an\" - ignoring\n";
		}
	    }
	    next;
	}
	elsif (/I\s*=\s*/)
	{
	    carp "unexpected format for node line \"$_\" - ignoring\n";
	    next;
	}

	#---------------------------------------------------------------
	# edge definition
	#---------------------------------------------------------------
	if (/^J\s*=\s*(\d+)/mg)
	{
	    my %attr;

	    $link = $1;
	    # print STDERR "Edge $link:\n";
	    while (/\s*(\S+)\s*=\s*(\S+)/mg)
	    {
		$an = $1;
		$av = $2;
		# print STDERR "   field $an = $av\n";
		if (exists $edge_attributes{$an})
		{
		    foreach my $a (@{ $edge_attributes{$an} })
		    {
			$attr{$a} = $av;
		    }
		} else {
		    carp "unknown link field \"$an\" - ignoring\n";
		}
	    }

	    if (exists $attr{START} && exists $attr{END}) {
		$from = 'n'.$attr{START};
		$to   = 'n'.$attr{END};
		delete $attr{START};
		delete $attr{END};
	    } else {
		carp "link on line $. doesn't have START and END - ignoring\n";
		next;
	    }
	    $graph->add_edge($from, $to);
	    foreach $a (keys %attr)
	    {
		# print STDERR "     attr $a = ", $attr{$a}, "\n";
		$graph->set_attribute($a, $from, $to, $attr{$a});
	    }
	}
	elsif (/^J/)
	{
	    carp "unexpected format for link line \"$_\" - ignoring\n";
	    next;
	}
    }

    return 1;
}

1;

__END__

=head1 NAME

Graph::Reader::HTK - read an HTK lattice in as an instance of Graph

=head1 SYNOPSIS

    use Graph::Reader::HTK;
    
    $reader = Graph::Reader::HTK->new;
    $graph = $reader->read_graph('mylattice.lat');

=head1 DESCRIPTION

=head1 SEE ALSO

=over 4

=item Graph

Jarkko Hietaniemi's Graph class and others, used for representing
and manipulating directed graphs. Available from CPAN.
Also described / used in the chapter on directed graph algorithms
in the B<Algorithms in Perl> book from O'Reilly.

=item Graph::Reader

The base-class for this module, which defines the public methods,
and describes the ideas behind Graph reader and writer modules.

=item Graph::Writer::HTK

A class which will write a perl Graph out as an HTK lattice.

=back

=head1 AUTHOR

Neil Bowers E<lt>neil@bowers.comE<gt>

=head1 COPYRIGHT

Copyright (c) 2000, Neil Bowers. All rights reserved.
Copyright (c) 2000, Canon Research Centre Europe. All rights reserved.

This module is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=cut

