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|
use chrono::TimeDelta;
use futures::{
future,
stream::{self, StreamExt as _},
Stream,
};
use sqlx::sqlite::SqlitePool;
use super::Broadcaster;
use crate::{
clock::DateTime,
events::repo::broadcast::{self, Provider as _},
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<broadcast::Message, EventsError> {
let mut tx = self.db.begin().await?;
let channel = tx
.channels()
.by_id(channel)
.await
.not_found(|| EventsError::ChannelNotFound(channel.clone()))?;
let message = tx
.broadcast()
.create(login, &channel, body, sent_at)
.await?;
tx.commit().await?;
self.broadcaster.broadcast(&channel.id, &message);
Ok(message)
}
pub async fn subscribe(
&self,
channel: &channel::Id,
subscribed_at: &DateTime,
resume_at: Option<broadcast::Sequence>,
) -> Result<impl Stream<Item = broadcast::Message> + std::fmt::Debug, EventsError> {
// Somewhat arbitrarily, expire after 90 days.
let expire_at = subscribed_at.to_owned() - TimeDelta::days(90);
let mut tx = self.db.begin().await?;
let channel = tx
.channels()
.by_id(channel)
.await
.not_found(|| EventsError::ChannelNotFound(channel.clone()))?;
// 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(&channel.id);
tx.broadcast().expire(&expire_at).await?;
let stored_messages = tx.broadcast().replay(&channel, resume_at).await?;
tx.commit().await?;
let resume_broadcast_at = stored_messages
.last()
.map(|message| message.sequence)
.or(resume_at);
// This should always be the case, up to integer rollover, primarily
// because every message in stored_messages has a sequence not less
// than `resume_at`, or `resume_at` is None. We use the last message
// (if any) to decide when to resume the `live_messages` stream.
//
// It probably simplifies to assert!(resume_at <= resume_broadcast_at), but
// this form captures more of the reasoning.
assert!(
(resume_at.is_none() && resume_broadcast_at.is_none())
|| (stored_messages.is_empty() && resume_at == resume_broadcast_at)
|| resume_at < resume_broadcast_at
);
// 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 stored_messages = stream::iter(stored_messages);
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_broadcast_at));
Ok(stored_messages.chain(live_messages))
}
fn resume(
resume_at: Option<broadcast::Sequence>,
) -> impl for<'m> FnMut(&'m broadcast::Message) -> future::Ready<bool> {
move |msg| {
future::ready(match resume_at {
None => true,
Some(resume_at) => msg.sequence > resume_at,
})
}
}
fn skip_expired(
expire_at: &DateTime,
) -> impl for<'m> FnMut(&'m broadcast::Message) -> future::Ready<bool> {
let expire_at = expire_at.to_owned();
move |msg| future::ready(msg.sent_at > expire_at)
}
}
#[derive(Debug, thiserror::Error)]
pub enum EventsError {
#[error("channel {0} not found")]
ChannelNotFound(channel::Id),
#[error(transparent)]
DatabaseError(#[from] sqlx::Error),
}
|
