#!/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";