Función que permite recoger las categorías de Joomla! y mostrarlas en un select

categories_joomla.php

<?php
public function getCats()
{
    $db = JFactory::getDBO();
    $query = $db->getQuery(true);
 
    $query->select('a.id, a.title, a.level');
    $query->from('#__categories AS a');
    $query->join('LEFT', $db->quoteName('#__categories').' AS b ON a.lft > b.lft AND a.rgt where('a.extension = "com_content"');
    $query->where('a.published IN (0,1)');
    $query->group('a.id, a.title, a.level, a.lft, a.rgt, a.extension, a.parent_id');
    $query->order('a.lft ASC');
 
    $db->setQuery($query);
    return $db->loadObjectList();
}
?>
// HTML
<label for="categories">Seleccione categoría/s</label>
<select name="categories[]">
<?php foreach($this->cats as $cat):
$num = strlen($cat->title) + (int)$cat->level*3;
$category = str_pad(' '.$cat->title.' ', $num, "- - ", STR_PAD_LEFT);
$categories = explode(',',$this->term->category);
if(in_array($cat->id, $categories)){
  echo '<option selected="selected" value="'.$cat->id.'">'.$category.'</option>';
} else{
	echo '<option value="'.$cat->id.'">'.$category.'</option>';
}
endforeach; ?>
</select>