bp_settings_sanitize_notification_settings( array $settings = array() )

function bp_settings_sanitize_notification_settings( $settings = array() ) {
	$sanitized_settings = array();

	if ( empty( $settings ) ) {
		return $sanitized_settings;
	}

	// Get registered notification keys.
	$registered_notification_settings = bp_settings_get_registered_notification_keys();

	/*
	 * We sanitize values for core notification keys.
	 *
	 * @todo use register_meta()
	 */
	$core_notification_settings = array(
		'notification_messages_new_message',
		'notification_activity_new_mention',
		'notification_activity_new_reply',
		'notification_groups_invite',
		'notification_groups_group_updated',
		'notification_groups_admin_promotion',
		'notification_groups_membership_request',
		'notification_membership_request_completed',
		'notification_friends_friendship_request',
		'notification_friends_friendship_accepted',
	);

	foreach ( (array) $settings as $key => $value ) {
		// Skip if not a registered setting.
		if ( ! in_array( $key, $registered_notification_settings, true ) ) {
			continue;
		}

		// Force core keys to 'yes' or 'no' values.
		if ( in_array( $key, $core_notification_settings, true ) ) {
			$value = 'yes' === $value ? 'yes' : 'no';
		}

		$sanitized_settings[ $key ] = $value;
	}

	return $sanitized_settings;
}