pm_role.admin.inc

<?php
// $Id$

function pm_role_admin_settings() {
  $form = array();
  $roles = user_roles(TRUE);
  foreach ($roles as $rid1 => $role1) {
    foreach ($roles as $rid2 => $role2) {
      $form['foo_messages_role_sent_from'. $rid1 .'_to_'. $rid2] = array(
        '#type' => 'checkbox',
        '#title' => t('@role1 cannot sent to @role2'),
        '#description' => t('@role1 is not allowed to sent messages to @role2'),
      );
    }
  }
  return system_settings_form($form);
}

pm_role.info

; $Id$
name = Privatemsg Role permissions
description = Adds permissions between roles, wether they can sent mesages to each other.
core = 6.x

pm_role.module

<?php
// $Id$

/**
 * Implementation of hook_form_privatemsg_new_alter().
 */
function pm_role_form_privatemsg_new_alter(&$form, &$form_state) {
  $form['#validate'][] = 'pm_role_form_privatemsg_new_validate';
}

function pm_role_form_privatemsg_new_validate(&$form, &$form_state) {
  // @TODO
  //   set a form_set_error if the user has entered a not allowed user.
}

/**
 * Implementation of hook_menu().
 */
function pm_role_menu() {
  $items['admin/settings/pm_role_settings'] = array(
    'title' => 'Pm Role settings',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('pm_role_admin_settings'),
    'access arguments' => array('administer site configuration'),
    'file' => 'pm_role.admin.inc',
  );

  return $items;
}

/**
 * Implementation of hook_menu_alter().
 */
function pm_role_menu_alter() {
  $callbacks['messages/user-name-autocomplete']['page callback'] = 'foo_messages_autocomplete_callback';
}

/**
 * This function does the same as the normal privatemsg autocomplete but only returns valid users.
 * @see privatemsg_user_name_autocomplete
 *
 * @TODO
 *   Don't use the default one :)
 */
function pm_role_messages_autocomplete_callback($string) {
  $names = array();
  // 1: Parse $string and build list of valid user names.
  $fragments = explode(',', $string);
  foreach ($fragments as $index => $name) {
    $name = trim($name);
    if ($error = module_invoke('user', 'validate_name', $name)) {
      // Do nothing if this name does not validate.
    }
    else {
      $names[$name] = $name;
    }
  }

  // By using user_validate_user we can ensure that names included in $names are at least logisticaly possible.
  // 2: Find the next user name suggestion.
  $fragment = array_pop($names);
  if (!empty($fragment)) {
    $query = "SELECT name FROM {users} u WHERE name like '%s%%'";
    $query .= " AND name NOT IN ('". implode("', '", $names) ."')"; // This will prevent suggesting a name that is already in our list.
    $query .= " AND status <> 0 ORDER BY name ASC";
    $result = db_query_range($query, $fragment, 0, 10);
    $prefix = count($names) ? implode(", ", $names) .", " : '';
    // 3: Build proper suggestions and print.
    $matches = array();
    while ($user = db_fetch_object($result)) {
      $matches[$prefix . $user->name .", "] = $user->name;
    }
    print drupal_to_js($matches);
    exit();
  }
}

pm_role.test

<?php
// $Id$

class pmRoleTestCase extends DrupalWebTestCase {
  static function getInfo() {
    return array(
      'name' => t('Privatemsg Role Permission.'),
      'group' => t('Privatemsg'),
    );
  }

  function setUp() {
    parent::setUp('privatemsg', 'pm_role');
  }
}