#!/usr/bin/perl

use Socket;
use strict;
use FileHandle;

my $bit;
my @frame;
my $flag;
my @message;

&Server;

sub Server{
use Socket;
use Carp;

my ($port, $proto, $paddr, $iaddr, $name);

sub logmsg {
        print "$0 $$: @_ at ", scalar localtime, "\n";
}

$port = shift || 4000;
socket(Server, PF_INET, SOCK_STREAM, $proto)
        or die "socket: $!";
setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
        or die "setsockopt: $!";

bind(Server, sockaddr_in($port, INADDR_ANY))
        or die "bind: $!";
listen(Server, SOMAXCONN)
        or die "listen: $!";

logmsg "server started on port $port, type ^c to terminate";

for( ; $paddr = accept(Client, Server); close(Client)) {
   ($port, $iaddr) = sockaddr_in($paddr);
   $name = gethostbyaddr($iaddr, AF_INET);

   logmsg "connection from $name [", inet_ntoa($iaddr), "] at port $port";

   @frame=();
        
   autoflush Client;
   while ($bit=<Client>){
#       print $bit;
        if ($bit ne "!\n"){
                $bit =~ s/1(\d*)\n/1/;
                print "$bit";
                push(@frame,$bit);
        }

        else {
                $flag=&Check;
                if ($flag == 1){print Client "ACK\n";}
                else {print Client "NACK\n";}
        }

   ###Convert binary back to ASCII
   #&Convert_To_ASCII;
   }	
}

###Print to output file
open (OUT, "output.dat") 
                        || die "Can't open input.dat: $!\n";
print OUT "@message, \n";
close OUT;

}

###This is very similar to Generate_CRC in sender.pl
sub Check {
	my @pattern=(1,1,0,1,0,1,1,1,0,0,1,0,0,1,1,0,1);
	my $Q=0;
	my $P=0;
	my $FCS;

	$Q=&Convert_To_B10(@frame);
	$P=Convert_To_B10(@pattern);
	$FCS=$Q%$P;
	if ($FCS == 0) {
		return (1);
	} else {
		return (-1);
	}
}

sub Convert_To_B10 (@){
	my @string=@_;
	my $total;
	my $index;
	my $value;
	$total=@string;
	for ($index=0;$index<$total;$index++){
		$value+=$string[$index]*2**($total-$index-1);
	}
	return($value);
}

sub Convert_To_ASCII {
	my $index=0;
	my $index2;
	my @byte;
	my $numeric=0;
	my $character=0;

	while ($index ne 64) {
		@byte=();
		for ($index2=0, $index2<8, $index2++) {
			push(@byte, $frame[$index]);
			$index++;
		}
		$numeric=Convert_To_B10(@byte);
		print "Numeric is $numeric \n";

		$character=chr($numeric);
		print "Character is $character \n";

		push(@message, $character);
	}
}

sub Generate_CRC {

	my @pattern=(1,1,0,1,0,1,1,1,0,0,1,0,0,1,1,0,1);
	my $Q=0;
        my $P=0;
        my $FCS;

}