// 修改WordPress用户名过滤机制，通过Email获取用户名
function ludou_allow_email_login($username, $raw_username, $strict) {
  if (filter_var($raw_username, FILTER_VALIDATE_EMAIL)) {
    $user_data = get_user_by('email', $raw_username);
    
    if (empty($user_data))
      wp_die(__('<strong>ERROR</strong>: There is no user registered with that email address.'), '用户名不正确');
    else
      return $user_data->user_login;
  }
  else {
    return $username;
  }
}

// 修改登录界面的文字，"用户名"改成"用户名或邮箱"
function ludou_change_text() {
  echo '<script type="text/javascript">
                var user_login_node = document.getElementById("user_login");
                var old_username_text = user_login_node.parentNode.innerHTML;
                user_login_node.parentNode.innerHTML = old_username_text.replace(/用户名/, "用户名或邮箱");
      </script>';
}

if (in_array($GLOBALS['pagenow'], array('wp-login.php')) && strpos($_SERVER['REQUEST_URI'], '?action=register') === FALSE && strpos($_SERVER['REQUEST_URI'], '?action=lostpassword') === FALSE && strpos($_SERVER['REQUEST_URI'], '?action=rp') === FALSE ) {
  add_filter('sanitize_user', 'ludou_allow_email_login', 10, 3);
  add_action('login_footer', 'ludou_change_text');
}