admin_only_mode.module

<?php
// $Id$
/**
 * @file
 *
 * Adds an option to put the site in admin-only mode.
 */

/**
 * Implementation of hook_init().
 */
function admin_only_mode_init() {
  global $user;

  $in_admin_only = variable_get('admin_only_mode',FALSE);

  if ($in_admin_only && user_is_logged_in()) {
    $message = variable_get('admin_only_mode_message','');
    if ($user->uid != 1) {
      // Code taken from user_logout(), avoiding drupal_goto() to allow message display
      watchdog('user', 'Session closed for %name.', array('%name' => $user->name));

      // Destroy the current session:
      session_destroy();
      module_invoke_all('user', 'logout', NULL, $user);

      // Load the anonymous user
      $user = drupal_anonymous_user();
      drupal_get_messages(NULL, TRUE); // thow away error messages from complaining modules
      drupal_set_message(t('Sorry, you do not currently have permission to be logged in.'), 'warning');

    } else if (!empty($message)) {
      // Show a message to the admin reminding him that we're in admin-only mode
      drupal_set_message($message, 'status', FALSE /*repeat*/);
    }
  }
}

/**
 * Implementation of hook_form_FORM_ID_alter().
 * Alter the Site Login form.
 */
function admin_only_mode_form_user_login_alter(&$form, $form_state) {
  // If the site is in admin-only mode, show the message at the top of this form
  $in_admin_only = variable_get('admin_only_mode',FALSE);
  $message = variable_get('admin_only_mode_message', '');
  if ($in_admin_only) {
    if (!empty($message)) {
      $form['#prefix'] = $message;
    }
    $form['#validate'] = array_merge(
      array('admin_only_mode_user_login_validator'),
      $form['#validate']
    );
  }
}

/**
 * Implementation of hook_form_FORM_ID_alter().
 * Alter the Site Maintenance form.
 */
function admin_only_mode_form_system_site_maintenance_settings_alter(&$form, $form_state) {
  $form["admin_only_mode_fieldset"] = array(
    "#title" => "Admin Only Mode",
    "#type" => "fieldset",
    "#weight" => 0,
    "#collapsible" => FALSE,
  );
  
  $form["admin_only_mode_fieldset"]["admin_only_mode"] = array(
    "#type" => "checkbox",
    "#title" => t("Admin only mode"),
    "#description" => t("When set, only allow admins to be logged into the site. Other users will be logged out."),
    "#weight" => 0,
    "#default_value" => variable_get('admin_only_mode', FALSE),
  );

  $form["admin_only_mode_fieldset"]["admin_only_mode_message"] = array(
    "#type" => "textarea",
    "#title" => t("Site admin-only message"),
    "#description" => t("Message to show visitors when the site is in admin-only mode. Leave this area empty to disable the display of a message."),
    "#default_value" => variable_get('admin_only_mode_message', ''),
  );
}

/**
 * Validator for user_login form.
 *
 * @see admin_only_mode_form_user_login_alter()
 */
function admin_only_mode_user_login_validator($form, &$form_state) {
  $in_admin_only = variable_get('admin_only_mode',FALSE);

  if ($in_admin_only) {
    $myuser = user_load(array('name' => $form_state['values']['name']));

    if ($myuser->uid != 1) {
      form_set_error('name', t('Sorry, only the admin user may login currently'));
      watchdog('admin_only_mode', 'Login attempt failed for %user.', array('%user' => $form_state['values']['name']));
    }
  }
}

/**
 * Sets whether we are in admin-only mode.
 *
 * @param $mode 
 *   Integer setting the admin-only mode state -- 1 for on, 0 for off.
 * @param $clearcache
 *   Boolean whether to clear the cachse after setting the state.  Defaults to TRUE.
 */
function admin_only_mode_set($mode, $clearcache=TRUE) {
  $mode = $mode ? 1 : 0;
  variable_set('admin_only_mode',$mode);

  if ($clearcache) {
    cache_clear_all();
  }
}

/**
 * Sets the admin-only message, displayed on auto-logout and the login form.
 *
 * @param $message 
 *   A string containing the admin-only message.
 * @param $clearcache
 *   Boolean whether to clear the cachse after setting the state.  Defaults to TRUE.
 */
function admin_only_mode_set_message($message, $clearcache=TRUE) {
  variable_set('admin_only_mode_message',$message);

  if ($clearcache) {
    cache_clear_all();
  }
}