<?
  $p_id  = floor($_GET['p_id']);
  $file  = "photos/$p_id.jpg";
  $thumb = "cache/thumbs/$p_id.jpg";

  if(!file_exists($thumb)) {
    if(file_exists($file)) {
      $im    = imagecreatetruecolor(150,120);
      $white = imagecolorallocate($im, 255, 255, 255);
      imagefill($im, 0, 0, $white);

      $info = getimagesize($file);
      switch($info[2]) {
        case 1:  $src = imagecreatefromgif($file);  break;
        case 2:  $src = imagecreatefromjpeg($file); break;
        case 3:  $src = imagecreatefrompng($file);  break;
      }

      if($src) {
        $width  = $info[0];
        $height = $info[1];

        while($width > 150 || $height > 120) {
          $scale = ($width > 150 ? 150 / $width : 120 / $height);
          $width  *= $scale;
          $height *= $scale;
        }
        imagecopyresampled($im, $src, (150-$width)/2, (120-$height)/2, 0, 0, $width, $height, $info[0], $info[1]);
      }

      header('Content-type: image/jpeg');
      imagejpeg($im, $thumb, 85);
    }
  }

  $last_modified     = gmdate('D, d M Y H:i:s', filemtime($thumb)) . ' GMT';
  $etag              = sprintf('"thumb-%08X-%08X"', $p_id, filemtime($thumb));
  if(isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
    $if_none_match = stripslashes($_SERVER['HTTP_IF_NONE_MATCH']);
    if($if_none_match == $etag) {
      header($_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified');
      exit;
    }
  }
  if(isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
    $if_modified_since = preg_replace('/;.*$/', '', $_SERVER['HTTP_IF_MODIFIED_SINCE']);
    if($if_modified_since == $gmdate_mod) {
      header($_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified');
      exit;
    }
  }

  header("Last-Modified: $last_modified");
  header("ETag: $etag");
  header('Content-Length: ' . filesize($thumb));
  header('Content-type: image/jpeg');
  readfile($thumb);
  exit;
?>