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use std::collections::{hash_map::Entry, HashMap};
use std::sync::{Arc, Mutex, MutexGuard};
use futures::{
future,
stream::{self, StreamExt as _, TryStreamExt as _},
TryStream,
};
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::{BroadcastMessage, 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 const 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?;
self.broadcaster.register_channel(&channel);
tx.commit().await?;
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,
resume_at: Option<&DateTime>,
) -> Result<impl TryStream<Ok = BroadcastMessage, Error = BoxedError>, BoxedError> {
fn skip_stale<E>(
resume_at: Option<&DateTime>,
) -> impl for<'m> FnMut(&'m BroadcastMessage) -> future::Ready<Result<bool, E>> {
let resume_at = resume_at.cloned();
move |msg| {
future::ready(Ok(match resume_at {
None => false,
Some(resume_at) => msg.sent_at <= resume_at,
}))
}
}
let live_messages = self
.broadcaster
.listen(channel)
.map_err(BoxedError::from)
.try_skip_while(skip_stale(resume_at));
let mut tx = self.db.begin().await?;
let stored_messages = tx.messages().for_replay(channel, resume_at).await?;
tx.commit().await?;
let stored_messages = stream::iter(stored_messages).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<BroadcastMessage>>>>,
}
impl Broadcaster {
pub async fn from_database(db: &SqlitePool) -> Result<Self, 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 = Self::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)),
}
}
// panic: if ``channel`` is already registered.
pub fn register_channel(&self, channel: &ChannelId) {
match self.senders().entry(channel.clone()) {
// This ever happening indicates a serious logic error.
Entry::Occupied(_) => panic!("duplicate channel registration for channel {channel}"),
Entry::Vacant(entry) => {
entry.insert(Self::make_sender());
}
}
}
// panic: if ``channel`` has not been previously registered, and was not
// part of the initial set of channels.
pub fn broadcast(&self, channel: &ChannelId, message: BroadcastMessage) {
let tx = self.sender(channel);
// 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);
}
// panic: if ``channel`` has not been previously registered, and was not
// part of the initial set of channels.
pub fn listen(&self, channel: &ChannelId) -> BroadcastStream<BroadcastMessage> {
let rx = self.sender(channel).subscribe();
BroadcastStream::from(rx)
}
// panic: if ``channel`` has not been previously registered, and was not
// part of the initial set of channels.
fn sender(&self, channel: &ChannelId) -> Sender<BroadcastMessage> {
self.senders()[channel].clone()
}
fn senders(&self) -> MutexGuard<HashMap<ChannelId, Sender<BroadcastMessage>>> {
self.senders.lock().unwrap() // propagate panics when mutex is poisoned
}
fn make_sender() -> Sender<BroadcastMessage> {
// Queue depth of 16 chosen entirely arbitrarily. Don't read too much
// into it.
let (tx, _) = channel(16);
tx
}
}
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