You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: indicators.rs
    path of file: ./repos/paper-plane/src/ui/session/content/message_row
    
    the code of the file until where you have to start completion: use std::cell::OnceCell;

use gettextrs::gettext;
use glib::clone;
use glib::once_cell::sync::Lazy;
use gtk::glib;
use gtk::prelude::*;
use gtk::subclass::prelude::*;
use gtk::CompositeTemplate;

use crate::model;

mod imp {
    use super::*;

    #[derive(Debug, Default, CompositeTemplate)]
    #[template(resource = "/app/drey/paper-plane/ui/session/content/message_row/indicators.ui")]
    pub(crate) struct MessageIndicators {
        pub(super) message: glib::WeakRef<glib::Object>,
        pub(supe
    
    fn update_sending_state(&self) {
        let icon_name = self
            .message()
            .and_downcast::<model::Message>()
            .filter(|message| message.is_outgoing())
            .map(|message| match message.sending_state() {
                Some(state) => match state.0 {
                    tdlib::enums::MessageSendingState::Failed(_) => "message-failed-symbolic",
                    tdlib::enums::MessageSendingState::Pending(_) => "message-pending-symbolic",
                },
                None => {
                    let chat = message.chat_();

                    if chat.is_own_chat() || message.id() <= chat.last_read_outbox_message_id() {
                        "message-read-symbolic"
                    } else {
                        "message-unread-left-symbolic"
                    }
                }
            });

        let imp = self.imp();

        if let Some(icon_name) = icon_name {
            imp.sending_state_icon.set_icon_name(Some(icon_name));
            imp.sending_state_icon.set_visible(true);
        } else {
            imp.sending_state_icon.set_icon_name(None);
            imp.sending_state_icon.set_visible(false);
        }
    }