function headinganchors_filter in Table of Contents 5

Same name and namespace in other branches

1. 5.2 headinganchors.module \headinganchors_filter()
2. 6.2 headinganchors.module \headinganchors_filter()

Implementation of hook_filter().

The bulk of filtering work is done here.

File

./headinganchors.module, line 52

This is a module which takes <h2> and <h3> headings and adds id attributes to them to allow them to be linked to in a URL. The following rules are used to create an attribute:

Code

function headinganchors_filter($op, $delta = 0, $format = -1, $text = '') {
  if ($op == 'list') {
    return array(
      0 => t('Headings to Anchors'),
    );
  }

  // We currently only define one filter, so we don't need to switch on $delta
  switch ($op) {

    // Admin interface description
    case 'description':
      return t('Inserts named anchors for heading tags automatically.');

    // Ensure that the content is regenerated on every preview
    case 'no cache':
      return TRUE;

    // Need to find out if this is required
    case 'prepare':
      return $text;

    // Here, we pull out the required information and add the anchor
    case 'process':

      // matches[1] is the level of the heading
      // matches[2] is the text of the heading
      // matches[][$count] is the current heading being modified
      $matches = array();

      // In the future, there should probably be some way to define which headings are modified
      // We assume that the HTML is valid and that the tags match each other.
      preg_match_all("/<h([2-3])>(.*)<\\/h[2-3]>/i", $text, $matches, PREG_PATTERN_ORDER);
      $count = 0;
      $anchors = array();
      foreach ($matches[0] as $match) {

        // Pull out the level and the heading
        $level = $matches[1][$count];
        $heading = $matches[2][$count];

        // We do strip_tags to get rid of any extra HTML as we don't want that in the id.
        // Strip out amp; from entity as it's ugly
        $anchor = preg_replace("/&amp;/", "", strip_tags($matches[2][$count]));

        // Then, we punt that result and strip out anything which isn't alphanumeric
        $anchor = preg_replace("/[^A-Za-z0-9]/", "", $anchor);

        // Remove leading digits
        $anchor = preg_replace("/^[0-9]+/", "", $anchor);

        // Look for duplicate ID's, and add -number to make them unique
        if (array_key_exists($anchor, $anchors)) {
          $anchors[$anchor]++;
        }
        else {
          $anchors[$anchor] = 0;
        }
        if ($anchors[$anchor] > 0) {
          $anchor .= "-" . $anchors[$anchor];
        }
        $pattern = "/<h" . $level . ">" . preg_quote($heading, '/') . "<\\/h" . $level . ">/";

        // Now, append everything together to create the new heading
        $replacement = "<h" . $level . " id=\"" . $anchor . "\">" . $heading . "</h" . $level . ">";

        // Now, find the heading we were editing and replace it in the text.
        // Limit of one so that identical headers are only replaced one at a time
        $text = preg_replace($pattern, $replacement, $text, 1);
        $count++;
      }
      return $text;
  }
}