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use std::collections::{hash_map::Entry, HashMap};
use std::sync::{Arc, Mutex};
use futures::{
stream::{self, StreamExt as _, TryStreamExt as _},
Stream,
};
use sqlx::sqlite::SqlitePool;
use tokio::sync::broadcast::{channel, Sender};
use tokio_stream::wrappers::BroadcastStream;
use super::repo::{
channels::{Id as ChannelId, Provider as _},
messages::{Message, Provider as _},
};
use crate::{clock::DateTime, error::BoxedError, login::repo::logins::Login};
pub struct Channels<'a> {
db: &'a SqlitePool,
broadcaster: &'a Broadcaster,
}
impl<'a> Channels<'a> {
pub fn new(db: &'a SqlitePool, broadcaster: &'a Broadcaster) -> Self {
Self { db, broadcaster }
}
pub async fn create(&self, name: &str) -> Result<(), BoxedError> {
let mut tx = self.db.begin().await?;
let channel = tx.channels().create(name).await?;
tx.commit().await?;
self.broadcaster.register_channel(&channel)?;
Ok(())
}
pub async fn send(
&self,
login: &Login,
channel: &ChannelId,
body: &str,
sent_at: &DateTime,
) -> Result<(), BoxedError> {
let mut tx = self.db.begin().await?;
let message = tx
.messages()
.create(&login.id, channel, body, sent_at)
.await?;
tx.commit().await?;
self.broadcaster.broadcast(channel, message)?;
Ok(())
}
pub async fn events(
&self,
channel: &ChannelId,
) -> Result<impl Stream<Item = Result<Message, BoxedError>>, BoxedError> {
let live_messages = self.broadcaster.listen(channel)?.map_err(BoxedError::from);
let mut tx = self.db.begin().await?;
let stored_messages = tx.messages().all(channel).await?;
tx.commit().await?;
let stored_messages = stream::iter(stored_messages.into_iter().map(Ok));
Ok(stored_messages.chain(live_messages))
}
}
// Clones will share the same senders collection.
#[derive(Clone)]
pub struct Broadcaster {
// The use of std::sync::Mutex, and not tokio::sync::Mutex, follows Tokio's
// own advice: <https://tokio.rs/tokio/tutorial/shared-state>. Methods that
// lock it must be sync.
senders: Arc<Mutex<HashMap<ChannelId, Sender<Message>>>>,
}
impl Broadcaster {
pub async fn from_database(db: &SqlitePool) -> Result<Broadcaster, BoxedError> {
let mut tx = db.begin().await?;
let channels = tx.channels().all().await?;
tx.commit().await?;
let channels = channels.iter().map(|c| &c.id);
let broadcaster = Broadcaster::new(channels);
Ok(broadcaster)
}
fn new<'i>(channels: impl IntoIterator<Item = &'i ChannelId>) -> Self {
let senders: HashMap<_, _> = channels
.into_iter()
.cloned()
.map(|id| (id, Self::make_sender()))
.collect();
Self {
senders: Arc::new(Mutex::new(senders)),
}
}
pub fn register_channel(&self, channel: &ChannelId) -> Result<(), RegisterError> {
match self.senders.lock().unwrap().entry(channel.clone()) {
Entry::Occupied(_) => Err(RegisterError::Duplicate),
vacant => {
vacant.or_insert_with(Self::make_sender);
Ok(())
}
}
}
pub fn broadcast(&self, channel: &ChannelId, message: Message) -> Result<(), BroadcastError> {
let lock = self.senders.lock().unwrap();
let tx = lock.get(channel).ok_or(BroadcastError::Unregistered)?;
// Per the Tokio docs, the returned error is only used to indicate that
// there are no receivers. In this use case, that's fine; a lack of
// listening consumers (chat clients) when a message is sent isn't an
// error.
let _ = tx.send(message);
Ok(())
}
pub fn listen(&self, channel: &ChannelId) -> Result<BroadcastStream<Message>, BroadcastError> {
let lock = self.senders.lock().unwrap();
let tx = lock.get(channel).ok_or(BroadcastError::Unregistered)?;
let rx = tx.subscribe();
let stream = BroadcastStream::from(rx);
Ok(stream)
}
fn make_sender() -> Sender<Message> {
// Queue depth of 16 chosen entirely arbitrarily. Don't read too much
// into it.
let (tx, _) = channel(16);
tx
}
}
#[derive(Debug, thiserror::Error)]
pub enum RegisterError {
#[error("duplicate channel registered")]
Duplicate,
}
#[derive(Debug, thiserror::Error)]
pub enum BroadcastError {
#[error("requested channel not registered")]
Unregistered,
}
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