BBP_Converter_Base::clean( $start )

	public function clean( $start ) {

		$start      = 0;
		$has_delete = false;

		/** Delete bbconverter topics/forums/posts ****************************/

		if ( true === $this->sync_table ) {
			$query = 'SELECT value_id FROM ' . $this->sync_table_name . ' INNER JOIN ' . $this->wpdb->posts . ' ON(value_id = ID) WHERE meta_key LIKE "_bbp_%" AND value_type = "post" GROUP BY value_id ORDER BY value_id DESC LIMIT ' . $this->max_rows;
		} else {
			$query = 'SELECT post_id AS value_id FROM ' . $this->wpdb->postmeta . ' WHERE meta_key LIKE "_bbp_%" GROUP BY post_id ORDER BY post_id DESC LIMIT ' . $this->max_rows;
		}

		update_option( '_bbp_converter_query', $query );

		$posts = $this->wpdb->get_results( $query, ARRAY_A );

		if ( isset( $posts[0] ) && ! empty( $posts[0]['value_id'] ) ) {
			foreach ( (array) $posts as $value ) {
				wp_delete_post( $value['value_id'], true );
			}
			$has_delete = true;
		}

		/** Delete bbconverter users ******************************************/

		if ( true === $this->sync_table ) {
			$query = 'SELECT value_id FROM ' . $this->sync_table_name . ' INNER JOIN ' . $this->wpdb->users . ' ON(value_id = ID) WHERE meta_key = "_bbp_user_id" AND value_type = "user" LIMIT ' . $this->max_rows;
		} else {
			$query = 'SELECT user_id AS value_id FROM ' . $this->wpdb->usermeta . ' WHERE meta_key = "_bbp_user_id" LIMIT ' . $this->max_rows;
		}

		update_option( '_bbp_converter_query', $query );

		$users = $this->wpdb->get_results( $query, ARRAY_A );

		if ( !empty( $users ) ) {
			foreach ( $users as $value ) {
				wp_delete_user( $value['value_id'] );
			}
			$has_delete = true;
		}

		unset( $posts );
		unset( $users );

		return ! $has_delete;
	}