#!/usr/bin/perl

#
### this module
package GPS::NMEAserial;

use strict;
use warnings;

# serial port communication
use Device::SerialPort qw( :PARAM :STAT 0.07 );

# flush output of filehandle
use IO::Handle;

# create filehandles
use Symbol qw( gensym );

sub new_nmea_port {
	my $class = shift;

	# open the serial port attached to control unit
	# $quiet parameter just for compatability
	my ( $port, $config_file, $quiet ) = @_;

	# this tests for an existing config file,
	# and creates one if necessary...
	if ( !-e $config_file ) {
		my $PortObj = new Device::SerialPort( $port, $quiet )
		  or die("Can't open $port: $!");
		$PortObj->baudrate(4800);
		$PortObj->parity('none');
		$PortObj->databits(8);
		$PortObj->handshake('none');

		# when nmea data is available every second
		$PortObj->read_const_time(1100);
		$PortObj->read_char_time(700);
		$PortObj->stopbits(1);
		$PortObj->write_settings or undef $PortObj;
		$PortObj->save($config_file)
		  or die("Can't save $config_file: $!");

		# close serial port
		$PortObj->close
		  or warn("Close $PortObj at $port failed: $!");

		# destroy serial object
		# frees memory back to perl
		undef $PortObj;
	} else {
		print("$config_file already exists!");
	}

	# tie filehandle to read/write from serial port (nmea device)
	my $fh = gensym();
	tie( *$fh, 'Device::SerialPort', $config_file )
	  or die("Can't tie $port: $!");
	my $self = bless {
					   PortName              => $port,
					   FileHandle            => $fh,
					   ConfigurationFileName => $config_file
	}, $class;
	$self->{'FileHandle'}->autoflush(1);
	return $self;
}

# this shouldn't be necessary
sub destroy_create_fh {
	my $self    = shift;
	my $fh_self = $self->{'FileHandle'};
	tie( *$fh_self, 'Device::SerialPort', 
$self->{'ConfigurationFileName'} )
	  or die("Can't tie $self->{'PortName'}: $!");
	$self->{'FileHandle'} = $fh_self;
}


sub get_heading {
	my $self = shift;
	if ( !-e $self->{'PortName'} ) {
		warn("Device $self->{'PortName'} doesn't exist");
	}
	$self->destroy_create_fh();
	while ( my $line = readline( $self->{'FileHandle'} ) ) {
		print "Do something with $line";
		return $line;
	}
}

1;

##</code><code>##

use strict;
use warnings;

use lib '/usr/local/lib';
use GPS::NMEAserial;

my $nmea_unit =
  GPS::NMEAserial->new_nmea_port( '/dev/nmea', 
			 	  "/var/run/.nmea_unit.conf" );

my $heading_string = $nmea_unit->get_heading();
print "$heading_string\n";
sleep(10);
my $heading_string2 = $nmea_unit->get_heading();
print "$heading_string2 is not most recent value\n";

##</code><code>##

	# tie filehandle to read/write from serial port (nmea device)
	my $fh = gensym();
	tie( *$fh, 'Device::SerialPort', $config_file )
	  or die("Can't tie $port: $!");
	my $self = bless {
					   PortName              => $port,
					   FileHandle            => $fh,
					   ConfigurationFileName => $config_file
	}, $class;
	$self->{'FileHandle'}->autoflush(1);
	return $self;