suggest_login.info

name = Suggest Login
description = Suggests an account to login with that has a similar name to an invalid attempt.
core="6.x"
version="6.x-1.0"

suggest_login.module

<?php

/**
 * Implementation of hook_form_alter
 **/
function suggest_login_form_alter(&$form, $form_state, $form_id) {
  if($form['#id'] === 'user-login-form') {
    $form['#validate'][0] = 'suggest_login_validate';
  }
}

function suggest_login_validate(&$form, $form_state) {
  user_login_name_validate($form, $form_state);
  $res = db_query("SELECT name FROM {users}");
  while($row = db_fetch_array($res)) {
    if(strlen($row['name']) > 0) {
      $accounts[] = $row['name'];
    }
  }

  $input = $form_state['values']['name'];

  if(!in_array($input, $accounts)) {  
    $shortest = -1;
  
    foreach($accounts as $account) {
      $lev = levenshtein($input, $account);
      if($lev == 0) {
        $closest = $account;
        $shortest = 0;
        break;
      }
      if($lev <= $shortest || $shortest < 0) {
        $closest = $account;
        $shortest = $lev;
      }
    }
  
    form_set_error('name', t("No user by that name! Did you mean <a href='#' id='suggest-login'>@user</a>?", array('@user' => $closest)));
    drupal_add_js(
      "$(document).ready(function() {
        $('div.messages a').click(function(e) {
          $('#edit-name').val('$closest');
        });
      });",
      'inline'
    );
  }
}

?>