PHP Substring without breaking words and HTML tags

php_substring_html.php

<?php
/** 
 * Truncates text.
 *
 * Cuts a string to the length of $length and replaces the last characters
 * with the ending if the text is longer than length.
 *
 * @param string $text String to truncate.
 * @param integer $length Length of returned string, including ellipsis.
 * @param string $ending Ending to be appended to the trimmed string.
 * @param boolean $exact If false, $text will not be cut mid-word
 * @param boolean $considerHtml If true, HTML tags would be handled correctly
 * @return string Trimmed string.
 */
function truncate($text, $length = 100, $ending = '...', $exact = true, $considerHtml = false) {
 if ($considerHtml) {
  // if the plain text is shorter than the maximum length, return the whole text
  if (mb_strlen(preg_replace('/<.*?>/', '', $text)) <= $length) {
   return $text;
  }

  // splits all html-tags to scanable lines
  preg_match_all('/(<.+?>)?([^<>]*)/s', $text, $lines, PREG_SET_ORDER);

  $total_length = mb_strlen(($ending);
  $open_tags = array();
  $truncate = '';

  foreach ($lines as $line_matchings) {
   // if there is any html-tag in this line, handle it and add it (uncounted) to the output
   if (!empty($line_matchings[1])) {
    // if it’s an “empty element” with or without xhtml-conform closing slash (f.e.)
    if (preg_match('/^<(\s*.+?\/\s*|\s*(img|br|input|hr|area|base|basefont|col|frame|isindex|link|meta|param)(\s.+?)?)>$/is', $line_matchings[1])) {
    // do nothing
    // if tag is a closing tag (f.e.)
    } else if (preg_match('/^<\s*\/([^\s]+?)\s*>$/s', $line_matchings[1], $tag_matchings)) {
     // delete tag from $open_tags list
     $pos = array_search($tag_matchings[1], $open_tags);
     if ($pos !== false) {
      unset($open_tags[$pos]);
     }
     // if tag is an opening tag (f.e. )
    } else if (preg_match('/^<\s*([^\s>!]+).*?>$/s', $line_matchings[1], $tag_matchings)) {
     // add tag to the beginning of $open_tags list
     array_unshift($open_tags, mb_strtolower($tag_matchings[1]));
    }
    // add html-tag to $truncate’d text
    $truncate .= $line_matchings[1];
   }

   // calculate the length of the plain text part of the line; handle entities as one character
   $content_length = mb_strlen(preg_replace('/&[0-9a-z]{2,8};|&#[0-9]{1,7};|&#x[0-9a-f]{1,6};/i', ' ', $line_matchings[2]));
   if ($total_length+$content_length > $length) {
    // the number of characters which are left
    $left = $length - $total_length;
    $entities_length = 0;
    // search for html entities
    if (preg_match_all('/&[0-9a-z]{2,8};|&#[0-9]{1,7};|&#x[0-9a-f]{1,6};/i', $line_matchings[2], $entities, PREG_OFFSET_CAPTURE)) {
     // calculate the real length of all entities in the legal range
     foreach ($entities[0] as $entity) {
      if ($entity[1]+1-$entities_length <= $left) {
       $left--;
       $entities_length += mb_strlen($entity[0]);
      } else {
       // no more characters left
       break;
      }
     }
    }
    $truncate .= mb_substr($line_matchings[2], 0, $left+$entities_length);
    // maximum lenght is reached, so get off the loop
    break;
   } else {
    $truncate .= $line_matchings[2];
    $total_length += $content_length;
   }

   // if the maximum length is reached, get off the loop
   if($total_length >= $length) {
    break;
   }
  }
 } else {
  if (mb_strlen($text) <= $length) {
   return $text;
  } else {
   $truncate = mb_substr($text, 0, $length - mb_strlen($ending));
  }
 }

 // if the words shouldn't be cut in the middle...
 if (!$exact) {
  // ...search the last occurance of a space...
  $spacepos = mb_strrpos($truncate, ' ');
  if (isset($spacepos)) {
   // ...and cut the text in this position
   $truncate = mb_substr($truncate, 0, $spacepos);
  }
 }

 // add the defined ending to the text
 $truncate .= $ending;

 if($considerHtml) {
  // close all unclosed html-tags
  foreach ($open_tags as $tag) {
   $truncate .= '';
  }
 }

return $truncate;

}