/**
  * Validates the user account and enrolment (ensures there is an avatar linked to a VLE account, and that the VLE account is enrolled in the current course).
  * Attempts auto-registration/enrolment if that is allowed and required, and logs-in the user.
  * Server access level is checked if it is specified in the request parameters.
  * If the request indicates that it relates to an object, then the validation fails.
  * Note: if you only require to ensure that an avatar is registered, then use {@link validate_avatar()}.
  * @param bool $require If true, the script will be terminated with an error message if validation fails
  * @param bool $suppress_autoreg If true, auto-registration will be completely suppressed for this function call
  * @param bool $suppress_autoenrol If true, auto-enrolment will be completely suppressed for this function call
  * @return bool Returns true if validation and/or autoregistration were successful. Returns false on failure (unless $require was true).
  * @see SloodleSession::validate_avatar()
  */
 function validate_user($require = true, $suppress_autoreg = false, $suppress_autoenrol = false)
 {
     // Is it an object request?
     if ($this->request->is_object_request()) {
         if ($require) {
             $this->response->quick_output(-301, 'USER_AUTH', 'Cannot validate object as user.', false);
             exit;
         }
         return false;
     }
     // Was a server access level specified in the request?
     $sal = $this->request->get_server_access_level(false);
     if ($sal != null) {
         // Check what level was specified
         $sal = (int) $sal;
         $allowed = false;
         $reason = 'Unknown.';
         switch ($sal) {
             case SLOODLE_SERVER_ACCESS_LEVEL_PUBLIC:
                 // Always allowed
                 $allowed = true;
                 break;
             case SLOODLE_SERVER_ACCESS_LEVEL_COURSE:
                 // Is a course already loaded?
                 if (!$this->course->is_loaded()) {
                     $reason = 'No course loaded.';
                     break;
                 }
                 // Was a user account already fully loaded?
                 if ($this->user->is_avatar_linked()) {
                     // Is the user enrolled on the current course?
                     if ($this->user->is_enrolled($this->course->get_course_id())) {
                         $allowed = true;
                     } else {
                         $reason = 'User not enrolled in course.';
                     }
                 } else {
                     $reason = 'User not registered on site.';
                 }
                 break;
             case SLOODLE_SERVER_ACCESS_LEVEL_SITE:
                 // Was a user account already fully loaded?
                 if ($this->user->is_avatar_linked()) {
                     $allowed = true;
                 } else {
                     $reason = 'User not registered on site.';
                 }
                 break;
             case SLOODLE_SERVER_ACCESS_LEVEL_STAFF:
                 // Is a course already loaded?
                 if (!$this->course->is_loaded()) {
                     $reason = 'No course loaded.';
                     break;
                 }
                 // Was a user account already fully loaded?
                 if ($this->user->is_avatar_linked()) {
                     // Is the user staff on the current course?
                     if ($this->user->is_staff($this->course->get_course_id())) {
                         $allowed = true;
                     } else {
                         $reason = 'User not staff in course.';
                     }
                 } else {
                     $reason = 'User not registered on site.';
                 }
                 break;
             default:
                 // Unknown access level
                 $reason = 'Access level not recognised';
                 break;
         }
         // Was the user blocked by access level?
         if (!$allowed) {
             if ($require) {
                 $this->response->quick_output(-331, 'USER_AUTH', $reason, false);
                 exit;
             }
             return false;
         }
     }
     // REGISTRATION //
     // Make sure a the course is loaded
     if (!$this->course->is_loaded()) {
         if ($require) {
             $this->response->quick_output(-511, 'COURSE', 'Cannot validate user - no course data loaded.', false);
             exit;
         }
         return false;
     }
     // Is the user already loaded?
     if (!$this->user->is_avatar_linked()) {
         // If an avatar is loaded, but the user isn't, then we probably have a deleted Moodle user
         if ($this->user->is_avatar_loaded() == true && $this->user->is_user_loaded() == false) {
             $this->response->quick_output(-301, 'USER_AUTH', 'Avatar linked to deleted user account', false);
             exit;
         }
         // Make sure avatar details were provided
         $uuid = $this->request->get_avatar_uuid(false);
         $avname = $this->request->get_avatar_name(false);
         // Is validation required?
         if ($require) {
             // Check the UUID
             if (empty($uuid)) {
                 $this->response->quick_output(-311, 'USER_AUTH', 'User UUID required', false);
                 exit;
             }
             // Check the name
             if (empty($avname)) {
                 $this->response->quick_output(-311, 'USER_AUTH', 'Avatar name required', false);
                 exit;
             }
         } else {
             if (empty($uuid) || empty($avname)) {
                 // If there was a problem, just stop
                 return false;
             }
         }
         // Ensure autoreg is not suppressed, and that it is permitted on that course and on the site
         if ($suppress_autoreg == true || $this->course->check_autoreg() == false) {
             if ($require) {
                 $this->response->quick_output(-321, 'USER_AUTH', 'User not registered, and auto-registration of users was not permitted', false);
                 exit;
             }
             return false;
         }
         // It is important that we also check auto-enrolment here.
         // If that is not enabled, but the call here requires it, then there is no point registering the user.
         if ($suppress_autoenrol == true || $this->course->check_autoenrol() == false) {
             if ($require) {
                 $this->response->quick_output(-421, 'USER_ENROL', 'User not enrolled, and auto-enrolment of users was not permitted', false);
                 exit;
             }
             return false;
         }
         // Is there an avatar loaded?
         if (!$this->user->is_avatar_loaded()) {
             // Add the avatar details, linked to imaginary user 0
             if (!$this->user->add_linked_avatar(0, $uuid, $avname)) {
                 if ($require) {
                     $this->response->quick_output(-322, 'USER_AUTH', 'Failed to add new avatar', false);
                     exit;
                 }
                 return false;
             }
         }
         // If we reached here then we definitely have an avatar
         // Create a matching Moodle user
         $password = $this->user->autoregister_avatar_user();
         if ($password === FALSE) {
             if ($require) {
                 $this->response->quick_output(-322, 'USER_AUTH', 'Failed to register new user account', false);
                 exit;
             }
             return false;
         }
         // Add a side effect code to our response data
         $this->response->add_side_effect(322);
         // The user needs to be notified of their new username/password
         if (isset($_SERVER['HTTP_X_SECONDLIFE_OBJECT_KEY'])) {
             sloodle_login_notification($_SERVER['HTTP_X_SECONDLIFE_OBJECT_KEY'], $uuid, $this->user->get_username(), $password);
         }
     }
     // ENROLMENT //
     // Is the user already enrolled on the course?
     if (!$this->user->is_enrolled($this->course->get_course_id())) {
         // Ensure auto-enrolment is not suppressed, and that it is permitted on that course and on the site
         if ($suppress_autoenrol == true || $this->course->check_autoenrol() == false) {
             if ($require) {
                 $this->response->quick_output(-421, 'USER_ENROL', 'Auto-enrolment of users was not permitted', false);
                 exit;
             }
             return false;
         }
         // Attempt to enrol the user
         if (!$this->user->enrol()) {
             if ($require) {
                 $this->response->quick_output(-422, 'USER_ENROL', 'Auto-enrolment failed', false);
                 exit;
             }
             return false;
         }
         // Add a side effect code to our response data
         $this->response->add_side_effect(422);
     }
     // Make sure the user is logged-in
     return $this->user->login();
 }