#!/usr/local/bin/perl
# Program name: go-to-ad
# Installed in the CGI directory.

# Purpose:
#       This is a "click-through" CGI program that sends the browser to
# an advertiser's site.

# Optional Feature:
#       Before it does that, it can log certain information.
# The log file name is based on the url or image name passed to it.
# This avoids the overhead of dealing with a database. The data
# analysis and lookup can be done on a different machine later.

# Written by: Rajiv Pant (Betul)  betul@rajiv.com  http://rajiv.org

# Original Version: 1.0 1995/Dec
# Current Version: 1.1 1996/Jun

# Current status: Replaced by a more efficient Server API version.

use lib '/my/perl/lib/where/date/and/time/module/is/kept' ;

use Date_Time ; # Perl object package written by Betul.
# Freely available at http://rajiv.org


$AdLogFolder = '/inet/data/logs/advertisers' ;

$ImageExtensions = '(gif|jpg|jpeg)' ;

$Date = new Date_Time ;

($URL, $Image) = split '&image=', $ENV{'QUERY_STRING'} ;



$ToBeLogged = 0 ;


if ($ToBeLogged)
{

# The name of the log file is the Image name, if specified.
# If not, the URL is used. If the URL is used, then
# removing the initial http:// or https:// part of the URL
# for the log file name since over 99% of sites are http:// anyway.

($LogFile = ($Image or $URL)) =~ s{^\w+\://}{} ;


# Converting slashes to underscores because a unix file name can not
# contain any slashes.

$LogFile =~ tr[/][_] ;


# Removing the .GIF or .jpeg extension from the end of the file.
# We don't expect an advertiser's URL to end in an image.

$LogFile =~ s/\.$ImageExtensions$//i ;


# We start a new log file every month.

$LogFile = "$AdLogFolder/$LogFile." . $Date->year . $Date->month ;

open (LOGFILE, ">>$LogFile") ; # Disabled for now.

# Locking the log file so that another instance of this program
# or some other program wanting to open the same file has to wait
# until this instance unlocks it.

flock LOGFILE, 2 ; # 2 Means lock with exclusive rights on the file.

# Now we seek to the end of the file in case our previous lock
# request had to wait for another program to complete its work
# and unlock the file.

seek LOGFILE, 0, 2 ;


print LOGFILE

'DATE=',		$Date->year. $Date->month. $Date->day,	"\t",
'TIME=',		$Date->time_format_1,			"\t",
'HTTP_REFERER=',	$ENV{'HTTP_REFERER'},			"\t",
'HTTP_USER_AGENT=',	$ENV{'HTTP_USER_AGENT'},		"\t",
'REMOTE_ADDR=',		$ENV{'REMOTE_ADDR'} ;


# Unlocking the file.

flock LOGFILE, 8 ; # 8 Means unlock the file.

close (LOGFILE) ;

} # end if ToBeLogged


# Redirecting the browser to go to the advertiser's URL specified.

print "Location: $URL\n\n" ;