How to match and replace callback content tags using php regular rules

function my_wp_plugin_tag_action($content,$tag,$function,$args = FALSE) {
 // match all regular expressions
 preg_match_all($tag,$content,$matches);
 if (count($matches)>0) {
  // filter duplicates
  $matches = array_unique($matches);
  // loop through
  $tag_results = array();
  $found_tags = array();
  foreach ($matches as $idx => $match) {
   //build arg array
   $full_tag = array_shift($match);
   //call function, adding function output and full tag text to replacement array
   $tag_results[] = my_wp_plugin_buffer_func($function,$match);
   $found_tags[] = $full_tag;
  }
  // replace all tags with corresponding text
  $content = str_replace($found_tags,$tag_results,$content);
 }
 return $content;
}