/**
 * Automatically generate a teaser for a node body in a given format.
 */
function node_teaser($body, $format = NULL) {

  $size = variable_get('teaser_length', 600);

  // find where the delimiter is in the body
  $delimiter = strpos($body, '<!--break-->');

  // If the size is zero, and there is no delimiter, the entire body is the teaser.
  if ($size == 0 && $delimiter == 0) {
    return $body;
  }

  // We check for the presence of the PHP evaluator filter in the current
  // format. If the body contains PHP code, we do not split it up to prevent
  // parse errors.
  if (isset($format)) {
    $filters = filter_list_format($format);
    if (isset($filters['filter/1']) && strpos($body, '<?') !== false) {
      return $body;
    }
  }

  // If a valid delimiter has been specified, use it to chop of the teaser.
  if ($delimiter > 0) {
    return substr($body, 0, $delimiter);
  }

  // If we have a short body, the entire body is the teaser.
  if (strlen($body) < $size) {
    return $body;
  }

  // In some cases, no delimiter has been specified (e.g. when posting using
  // the Blogger API). In this case, we try to split at paragraph boundaries.
  // When even the first paragraph is too long, we try to split at the end of
  // the next sentence.
  $breakpoints = array('</p>' => 4, '<br />' => 0, '<br>' => 0, "\n" => 0, '. ' => 1, '! ' => 1, '? ' => 1, '。' => 1, '؟ ' => 1);
  foreach ($breakpoints as $point => $charnum) {
    if ($length = strpos($body, $point, $size)) {
      return substr($body, 0, $length + $charnum);
    }
  }

  // If all else fails, we simply truncate the string.
  return truncate_utf8($body, $size);
}