#!/usr/bin/perl -w
# gus_atom_xsl.pl
# Sort-order switch for Atom feeds.

use CGI::Carp qw{fatalsToBrowser};
print "Content-Type: text/xml; charset=utf-8\n\n";

# Split on '!' versus '&' for GET because source doc is XML.
# Uses only GET never POST.
if ($ENV{'REQUEST_METHOD'} eq "GET") {
  @pairs = split /!|%21/, $ENV{'QUERY_STRING'};
} else {
  print "<p> Use GET method only! </p>";
}

foreach $pair (@pairs) {
  ($key, $value) = split (/=/, $pair);
  $key   =~ tr/+/ /;
  $key   =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack ("C", hex($1))/eg;
  $value =~ tr/+/ /;
  $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack ("C", hex($1))/eg;
  $value =~ s/<!--(.|\n)*-->//g;
  if ($form_data{$key}) {
    $form_data{$key} .= ", $value";
  } else {
    $form_data{$key} = $value;
  }
}

my $http_base = '/home/your_own_account/';
my $http_url  = 'your_own_domain.us';
my $flag = 1;

if (open $ATOM, "<$http_base" . $form_data{atom}) {
  while (<$ATOM>) {
  
    # Edit the stylesheet link to escape the cgi-bin.
    if ($flag && $_ =~ /gus_atom.xsl/) {
      $_ =~ s{href="\.\/gus_atom.xsl}{href="../gus_atom.xsl};
    }
  
    # Edit the self-link to fix the url for cgi-bin.
    if ($flag && $_ =~ /rel="self"/) {
      $_ =~ s{http://$http_url/}{http://$http_url/cgi-bin/gus_atom_xsl.pl?atom=};
      $_ =~ s{\.xml}{.xml!sort_order=$form_data{sort_order}};
      if ($ENV{'QUERY_STRING'} =~ /%21/) { $_ =~ s/!/%21/g }
      $flag = 0;    
    }
    
    print $_;
  }
} else { print "OOPS! Cannot open $http_base" . "$form_data{atom}" }

# How Perl/CGI gets a URL and the regular way...
# href="http://69.51.152.43/cgi-bin/gus_atom_xsl.pl?atom=starling_us_atom.xml%21sort_order=Title"
# href="http://69.51.152.43/starling_us_atom.xml"