<?php
/*
Plugin Name: Sanitize Unique
Plugin URI: http://latrine.dgx.cz/wordpress-plugins/
Description: make permalink unique and not too long
Author: David Grudl
Author URI: http://www.davidgrudl.com
*/ 


function sanitize_unique($title)  {
    global $wpdb, $post_ID;
    
    // crop to length 30-40 chars
    // find word's edge
    $pos = max(30, min(40, @strpos($title, '-', 30)));
    $title = @substr($title, 0, $pos);
    
    // make unique by adding suffix     
    // now select all post
    $_title = addslashes($title);
    $posts = $wpdb->get_results("SELECT post_name, ID FROM $wpdb->posts WHERE post_name LIKE '$_title%'");
    if (!$posts) return $title;

    $suffix = ''; 
    do {
      $ok = true;  
      foreach ($posts as $post) {
        if ($post_ID == $post->ID) { continue; } // skip self
        if ($title.$suffix == $post->post_name) {  // is permalink unique?
          $suffix++;   // change suffix
          $ok = false; // and tray again
          break; 
        }
      }
    } while ($ok == false);

    return $title.$suffix;
}


add_action('sanitize_title', 'sanitize_unique', 20); // 20 - low priority!

?>