#!/usr/bin/perl

use strict;
use URI;

my $dirc = 'none';
my $HtmlBase = "/usr/lib/apache/htdocs";
my ($rq, $rf, $prevDir, $nextDir, $newLocation);
my ($basedir, $subdir, $file, $TheDir, $host);
my (@dirs, @pathsegs);

$rq = URI->new($ENV{"REQUEST_URI"});
$dirc = $rq->query;

$rf = URI->new($ENV{"HTTP_REFERER"});

$host = $rf->host;
$subdir = $rf->path;
@pathsegs = $rf->path_segments;

$file = $pathsegs[-1];
$subdir = $pathsegs[-2];
$basedir = join('/', @pathsegs[0..$#pathsegs-2]);

opendir(DIRHNDL, "$HtmlBase/$basedir");

while($TheDir = readdir(DIRHNDL)) {
  if($TheDir =~ /^\w/ && -d "$HtmlBase/$basedir/$TheDir") {
    push @dirs, $TheDir;
  }
}

@dirs = sort @dirs;

for(my $i = 0; $i <= $#dirs; $i++) {
  if ($dirs[$i] eq $subdir) {
    if($i > 0) { $prevDir = $dirs[$i - 1] }
    else       { $prevDir = $subdir }

    if($i < $#dirs) { $nextDir = $dirs[$i + 1] }
    else            { $nextDir = $subdir }

    last;
  }
}

if($dirc eq 'prev') {
  if(-f "$HtmlBase/$basedir/$prevDir/$file") {
    $newLocation = "http://$host$basedir/$prevDir/$file";
  } else {
    $newLocation = "http://$host$basedir/$subdir/$file";
  }
} elsif ($dirc eq 'next') {
  if(-f "$HtmlBase/$basedir/$nextDir/$file") {
    $newLocation = "http://$host$basedir/$nextDir/$file";
  } else {
    $newLocation = "http://$host$basedir/$subdir/$file";
  }
} elsif ($dirc eq 'index') {
  if($file eq 'index.html') { 
    $newLocation = "http://$host$basedir/index.html";
  } else {
    $newLocation = "http://$host$basedir/$subdir/index.html";
  }
} else {
  $newLocation = $ENV{"HTTP_REFERER"};
}

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