#!/usr/local/bin/perl

print "Content-type: text/html\n\n";

#####################  DISCLAIMER  #########################
##  I make no express guarantees...hey, it works for me.  ##
##  It should work for you.  It's quick, easy, and easily ##
##  portable to lots of pages, simply by renaming the cgi ##
##  script to another name and running another set of     ##
##  banners on another page, under that filename          ##
#####################  COPYRIGHT  ##########################
##  clicktrade.cgi Version 1.0, written by Eric Beck,     ##
##  Copyright, 1999    All rights reserved (Whoopee)      ##
##  Use this program as you see fit, per the GNU license. ##
#################### INSTRUCTIONS ##########################
##  Very simple script to do a banner rotation.  Used     ##
##  as a Server Side Include                              ##
##  Simply edit the location of the counter file, set     ##
##  the number of banners you want to use.                ##
#################### DEFINE VARIABLES ######################
##                                                        ##
##                                                        ##
## $cfile - The COUNTER file to increment the rotation.   ##
## Change this to the location of your count file. This   ##
## should be in a secure location out of the public html  ##
## path ideally, although it doesn't have to be.  HEY,    ##
## YOU'VE GOT TO MAKE THIS FILE, AND UPLOAD IT FIRST. Put ##
## it where you like and call it what you like; just def- ##
## ine it below here.  If you do change it's variable     ##
## name though to something other than $cfile, you'll     ##
## have to change all instances of '$cfile' in the lock   ##
## and unlock routines, and every other instance of $cfile##
############################################################

# Complete path to counter file.
$cfile = "/big/dom/xwebdesi/cgi-bin/clicktrade_count.txt"; 

############################################################
## Next:                                                  ##
## Change this to the number of banners in your rotation  ##
## Note: If you change this figure from '10', then you    ##
## will have to add IF statements onto the end of the     ##
## script.  See ###  NOTE  ###                            ##
############################################################

$number_of_banners = 10;

############################################################
## Define your banner code for each banner.               ##
## Format: $b[number] = "[exact banner code goes between  ##
## the quotes]";                                          ##
##                                                        ##
## See the EXAMPLE in Banner code for if ($unique == 1)   ##
## and you'll see how to modify this code if you wanted   ##
## to put all the gifs in one spot.  I started to do this ##
## and then thought, what the hell, I'm not going to get  ##
## that sophisticated as to start building a whole        ##
## complicated configurable program; I just wanted        ##
## something to rotate a bunch of banners using SSI.  If  ##
## I can't scroll down the page and paste the banner code ##
## in where it goes, then I need to get a life or stop    ##
## drinking coffee.  Maybe one day when I've got time,    ##
## work on suping it upt to something more sophisticated. ##
############################################################

########################### MAIN PROGRAM ###################
  ## Get the present count
  if (-w $cfile)  {
     &get_file_lock ("$cfile.lock"); ## We want to lock this of course.
     open (CFILE,"$cfile");
       while (<CFILE>)  {
     chomp;
     $unique = int($_);     
   }
 close CFILE;   
     
 ## Increase the count number by one.
     $unique ++;
     
 ## Reduce the count by 10
 ## We're using 10 banners in our rotation, so when the
 ## count gets to 11, we send it back to 1
 
 if ($unique == ($number_of_banners + 1)) {
  $unique = ($unique - $number_of_banners);
 }
 
 open (CFILE,">$cfile");
 print CFILE "$unique";
     close CFILE;
     &release_file_lock ("$cfile.lock");
  }

############################################################
##    Edit these next ten Banner Code URLs to your own.   ##
##    They rotate in order, 1 through 10.                 ##
##     The code just goes between the print <<end_html    ##
##     and the end_html.  The 'end_html's must remain to  ##
##     the left hand side.  Do not move them over at all  ##
##     The first one is just an example of how an actual  ##
##     banner code might look.  You just put it in just   ##
##     like you'd put it on your page.                    ##
############################################################

if ($unique == 1) {
  print <<end_html;
  
<a href="http://some_domain.com?extra&code=somevalue&and=so_on">
<img src="http://some_domain.com/path/to/image.gif"></a>

end_html
}

if ($unique == 2) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 3) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 4) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 5) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 6) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 7) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 8) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 9) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

if ($unique == 10) {
  print <<end_html;
<a href=""><img src=""></a>

end_html
}

############################################################
## Put more banner definitions below here, after the 10th ##
############################################################

######################### NOTE # ###########################
## Add more if statements here if going over 10 banners   ##
## in the rotation. Just change the ($unique == 10) to    ##
## ($unique == 11), ($unique == 12) and so on. The first  ##
## one is done below for you so you just UNCOMMENT        ##
## it to go for it, AND CHANGE THE NUMBER AT THE TOP TO   ##
## 11 BANNERS, INSTEAD OF 10.  Reapeat at will.           ##
############################################################

#if ($unique == 11) {
#  print <<end_html;
#  <a href="THE LINK URL HERE"><img src="IMAGE SOURCE HERE"></a>
#end_html
#}

##################### END MAIN PROGRAM ####################

##################### SUB ROUTINES ########################
## THIS PARSE FORM SUB GOES IN ALL CGI SCRIPTS IN        ##
## CASE WE'RE MAKING A SCRIPT THAT IS TAKING FORM VARs   ##
## PARSE THE FORM FOR DATA                               ##
###########################################################
sub parse_form {       

  read(STDIN, $buffer, $ENV{'CONTENT_LENGTH'});
  if (length($buffer) < 5) {
     $buffer = $ENV{QUERY_STRING};
  }
  @pairs=split(/&/,$buffer);
  foreach $pair(@pairs) {
     ($name, $value)=split(/=/,$pair);
     $value =~ tr/+/ /;
     $value =~ s/%([a-fA-F0-9][A-F0-9])/pack("C",hex($1))/eg;
     if($input{$name} eq "") {
$FORM{$name} = $value;
        push (@FIELDS,$name);
     }
     else {
  $FORM{$name} = $FORM{$name}." ".$value;
     }
  }
}

#######################################################################
#                            get_file_lock                            #
#######################################################################

                # get_file_lock is a subroutine used to create a lockfile.
                # Lockfiles are used to make sure that no more than one
                # instance of the script can modify a file at one time.  A
                # lock file is vital to the integrity of your data.
                # Imagine what would happen if two or three people
                # were using the same script to modify a shared file (like
                # the error log) and each accessed the file at the same
                # time.  At best, the data entered by some of the users
                # would be lost.  Worse, the conflicting demands could
                # possibly result in the corruption of the file.
                #
                # Thus, it is crucial to provide a way to monitor and
                # control access to the file.  This is the goal of the
                # lock file routines.  When an instance of this script
                # tries to  access a shared file, it must first check for
                # the existence of a lock file by using the file lock
                # checks in get_file_lock.
                #
                # If get_file_lock determines that there is an existing
                # lock file, it instructs the instance that called it to
                # wait until the lock file disappears.  The script then
                # waits and checks back after some time interval.  If the
                # lock file still remains, it continues to wait until some
                # point at which the admin has given it permissios to just
                # overwrite the file because some other error must have
                # occurred.
                #
                # If, on the other hand, the lock file has dissappeared,
                # the script asks get_file_lock to create a new lock file
                # and then goes ahead and edits the file.
                #
                # The subroutine takes one argumnet, the name to use for
                # the lock file and is called with the following syntax:
                #
                # &get_file_lock("file.name");    

sub get_file_lock
  {
  local ($lock_file) = @_;
  local ($endtime);
  $endtime = 20;
  $endtime = time + $endtime;

                # We set endtime to wait 20 seconds.  If the lockfile has
                # not been removed by then, there must be some other
                # problem with the file system.  Perhaps an instance of
                # the script crashed and never could delete the lock file.

  while (-e $lock_file && time < $endtime)
    {
    sleep(1);
    }           

#  open(LOCK_FILE, ">$lock_file") || &file_open_error ("$lock_file", "Lock File Routine",  __FILE__, __LINE__);

                # Note: If flock is available on your system, feel free to
                # use it.  flock is an even safer method of locking your
                # file because it locks it at the system level.  The above
                # routine is "pretty good" and it will server for most
                # systems.  But if youare lucky enough to have a server
                # with flock routines built in, go ahead and uncomment
                # the next line and comment the one above.

 flock(LOCK_FILE, 2); # 2 exclusively locks the file

  }

#######################################################################
#                            release_file_lock                        #     
#######################################################################

                # release_file_lock is the partner of get_file_lock.  When
                # an instance of this script is done using the file it
                # needs to manipulate, it calls release_file_lock to
                # delete the lock file that it put in place so that other
                # instances of the script can get to the shared file.  It
                # takes one argument, the name of the lock file, and is
                # called with the following syntax:
                #
                # &release_file_lock("file.name");

sub release_file_lock
  {
  local ($lock_file) = @_;

  flock(LOCK_FILE, 8); # 8 unlocks the file

                # As we mentioned in the discussion of get_file_lock,
                # flock is a superior file locking system.  If your system
                # has it, go ahead and use it instead of the hand rolled
                # version here.  Uncomment the above line and comment the
                # two that follow.

#  close(LOCK_FILE);
#  unlink($lock_file);
  }