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use std::collections::BTreeMap;
use chrono::TimeDelta;
use futures::{
future,
stream::{self, StreamExt as _},
Stream,
};
use sqlx::sqlite::SqlitePool;
use super::{
broadcaster::Broadcaster,
repo::message::Provider as _,
types::{self, ChannelEvent, ResumePoint},
};
use crate::{
clock::DateTime,
repo::{
channel::{self, Provider as _},
error::NotFound as _,
login::Login,
},
};
pub struct Events<'a> {
db: &'a SqlitePool,
broadcaster: &'a Broadcaster,
}
impl<'a> Events<'a> {
pub const fn new(db: &'a SqlitePool, broadcaster: &'a Broadcaster) -> Self {
Self { db, broadcaster }
}
pub async fn send(
&self,
login: &Login,
channel: &channel::Id,
body: &str,
sent_at: &DateTime,
) -> Result<types::ChannelEvent, EventsError> {
let mut tx = self.db.begin().await?;
let channel = tx
.channels()
.by_id(channel)
.await
.not_found(|| EventsError::ChannelNotFound(channel.clone()))?;
let event = tx
.message_events()
.create(login, &channel, body, sent_at)
.await?;
tx.commit().await?;
self.broadcaster.broadcast(&event);
Ok(event)
}
pub async fn subscribe(
&self,
subscribed_at: &DateTime,
resume_at: ResumePoint,
) -> Result<impl Stream<Item = types::ResumableEvent> + std::fmt::Debug, sqlx::Error> {
// Somewhat arbitrarily, expire after 90 days.
let expire_at = subscribed_at.to_owned() - TimeDelta::days(90);
let mut tx = self.db.begin().await?;
let channels = tx.channels().all().await?;
let created_events = {
let resume_at = resume_at.clone();
let channels = channels.clone();
stream::iter(
channels
.into_iter()
.map(ChannelEvent::created)
.filter(move |event| resume_at.not_after(event)),
)
};
// Subscribe before retrieving, to catch messages broadcast while we're
// querying the DB. We'll prune out duplicates later.
let live_messages = self.broadcaster.subscribe();
tx.message_events().expire(&expire_at).await?;
let mut replays = BTreeMap::new();
let mut resume_live_at = resume_at.clone();
for channel in channels {
let replay = tx
.message_events()
.replay(&channel, resume_at.get(&channel.id))
.await?;
if let Some(last) = replay.last() {
resume_live_at.advance(&channel.id, last.sequence);
}
replays.insert(channel.id.clone(), replay);
}
let replay = stream::select_all(replays.into_values().map(stream::iter));
// no skip_expired or resume transforms for stored_messages, as it's
// constructed not to contain messages meeting either criterion.
//
// * skip_expired is redundant with the `tx.broadcasts().expire(…)` call;
// * resume is redundant with the resume_at argument to
// `tx.broadcasts().replay(…)`.
let live_messages = live_messages
// Sure, it's temporally improbable that we'll ever skip a message
// that's 90 days old, but there's no reason not to be thorough.
.filter(Self::skip_expired(&expire_at))
// Filtering on the broadcast resume point filters out messages
// before resume_at, and filters out messages duplicated from
// stored_messages.
.filter(Self::resume(resume_live_at));
Ok(created_events.chain(replay).chain(live_messages).scan(
resume_at,
|resume_point, event| {
let channel = &event.channel.id;
let sequence = event.sequence;
resume_point.advance(channel, sequence);
let event = types::ResumableEvent(resume_point.clone(), event);
future::ready(Some(event))
},
))
}
fn resume(
resume_at: ResumePoint,
) -> impl for<'m> FnMut(&'m types::ChannelEvent) -> future::Ready<bool> {
move |event| future::ready(resume_at.not_after(event))
}
fn skip_expired(
expire_at: &DateTime,
) -> impl for<'m> FnMut(&'m types::ChannelEvent) -> future::Ready<bool> {
let expire_at = expire_at.to_owned();
move |event| future::ready(expire_at < event.at)
}
}
#[derive(Debug, thiserror::Error)]
pub enum EventsError {
#[error("channel {0} not found")]
ChannelNotFound(channel::Id),
#[error(transparent)]
DatabaseError(#[from] sqlx::Error),
}
|
